Programs & Examples On #Types

Types, and type systems, are used to enforce levels of abstraction in programs.

How to declare a Fixed length Array in TypeScript

The Tuple approach :

This solution provides a strict FixedLengthArray (ak.a. SealedArray) type signature based in Tuples.

Syntax example :

// Array containing 3 strings
let foo : FixedLengthArray<[string, string, string]> 

This is the safest approach, considering it prevents accessing indexes out of the boundaries.

Implementation :

type ArrayLengthMutationKeys = 'splice' | 'push' | 'pop' | 'shift' | 'unshift' | number
type ArrayItems<T extends Array<any>> = T extends Array<infer TItems> ? TItems : never
type FixedLengthArray<T extends any[]> =
  Pick<T, Exclude<keyof T, ArrayLengthMutationKeys>>
  & { [Symbol.iterator]: () => IterableIterator< ArrayItems<T> > }

Tests :

var myFixedLengthArray: FixedLengthArray< [string, string, string]>

// Array declaration tests
myFixedLengthArray = [ 'a', 'b', 'c' ]  // ? OK
myFixedLengthArray = [ 'a', 'b', 123 ]  // ? TYPE ERROR
myFixedLengthArray = [ 'a' ]            // ? LENGTH ERROR
myFixedLengthArray = [ 'a', 'b' ]       // ? LENGTH ERROR

// Index assignment tests 
myFixedLengthArray[1] = 'foo'           // ? OK
myFixedLengthArray[1000] = 'foo'        // ? INVALID INDEX ERROR

// Methods that mutate array length
myFixedLengthArray.push('foo')          // ? MISSING METHOD ERROR
myFixedLengthArray.pop()                // ? MISSING METHOD ERROR

// Direct length manipulation
myFixedLengthArray.length = 123         // ? READ-ONLY ERROR

// Destructuring
var [ a ] = myFixedLengthArray          // ? OK
var [ a, b ] = myFixedLengthArray       // ? OK
var [ a, b, c ] = myFixedLengthArray    // ? OK
var [ a, b, c, d ] = myFixedLengthArray // ? INVALID INDEX ERROR

(*) This solution requires the noImplicitAny typescript configuration directive to be enabled in order to work (commonly recommended practice)


The Array(ish) approach :

This solution behaves as an augmentation of the Array type, accepting an additional second parameter(Array length). Is not as strict and safe as the Tuple based solution.

Syntax example :

let foo: FixedLengthArray<string, 3> 

Keep in mind that this approach will not prevent you from accessing an index out of the declared boundaries and set a value on it.

Implementation :

type ArrayLengthMutationKeys = 'splice' | 'push' | 'pop' | 'shift' |  'unshift'
type FixedLengthArray<T, L extends number, TObj = [T, ...Array<T>]> =
  Pick<TObj, Exclude<keyof TObj, ArrayLengthMutationKeys>>
  & {
    readonly length: L 
    [ I : number ] : T
    [Symbol.iterator]: () => IterableIterator<T>   
  }

Tests :

var myFixedLengthArray: FixedLengthArray<string,3>

// Array declaration tests
myFixedLengthArray = [ 'a', 'b', 'c' ]  // ? OK
myFixedLengthArray = [ 'a', 'b', 123 ]  // ? TYPE ERROR
myFixedLengthArray = [ 'a' ]            // ? LENGTH ERROR
myFixedLengthArray = [ 'a', 'b' ]       // ? LENGTH ERROR

// Index assignment tests 
myFixedLengthArray[1] = 'foo'           // ? OK
myFixedLengthArray[1000] = 'foo'        // ? SHOULD FAIL

// Methods that mutate array length
myFixedLengthArray.push('foo')          // ? MISSING METHOD ERROR
myFixedLengthArray.pop()                // ? MISSING METHOD ERROR

// Direct length manipulation
myFixedLengthArray.length = 123         // ? READ-ONLY ERROR

// Destructuring
var [ a ] = myFixedLengthArray          // ? OK
var [ a, b ] = myFixedLengthArray       // ? OK
var [ a, b, c ] = myFixedLengthArray    // ? OK
var [ a, b, c, d ] = myFixedLengthArray // ? SHOULD FAIL

Datatype for storing ip address in SQL Server

sys.dm_exec_connections uses varchar(48) after SQL Server 2005 SP1. Sounds good enough for me especially if you want to use it compare to your value.

Realistically, you won't see IPv6 as mainstream for a while yet, so I'd prefer the 4 tinyint route. Saying that, I'm using varchar(48) because I have to use sys.dm_exec_connections...

Otherwise. Mark Redman's answer mentions a previous SO debate question.

Typescript input onchange event.target.value

as HTMLInputElement works for me

Return multiple fields as a record in PostgreSQL with PL/pgSQL

To return a single row

Simpler with OUT parameters:

CREATE OR REPLACE FUNCTION get_object_fields(_school_id int
                                       , OUT user1_id   int
                                       , OUT user1_name varchar(32)
                                       , OUT user2_id   int
                                       , OUT user2_name varchar(32)) AS 
$func$
BEGIN
   SELECT INTO user1_id, user1_name
          u.id, u.name
   FROM   users u
   WHERE  u.school_id = _school_id
   LIMIT  1;  -- make sure query returns 1 row - better in a more deterministic way?

   user2_id := user1_id + 1; -- some calculation

   SELECT INTO user2_name
          u.name       
   FROM   users u
   WHERE  u.id = user2_id;
END
$func$  LANGUAGE plpgsql;

Call:

SELECT * FROM get_object_fields(1);
  • You don't need to create a type just for the sake of this plpgsql function. It may be useful if you want to bind multiple functions to the same composite type. Else, OUT parameters do the job.

  • There is no RETURN statement. OUT parameters are returned automatically with this form that returns a single row. RETURN is optional.

  • Since OUT parameters are visible everywhere inside the function body (and can be used just like any other variable), make sure to table-qualify columns of the same name to avoid naming conflicts! (Better yet, use distinct names to begin with.)

Simpler yet - also to return 0-n rows

Typically, this can be simpler and faster if queries in the function body can be combined. And you can use RETURNS TABLE() (since Postgres 8.4, long before the question was asked) to return 0-n rows.

The example from above can be written as:

CREATE OR REPLACE FUNCTION get_object_fields2(_school_id int)
  RETURNS TABLE (user1_id   int
               , user1_name varchar(32)
               , user2_id   int
               , user2_name varchar(32)) AS 
$func$
BEGIN
   RETURN QUERY
   SELECT u1.id, u1.name, u2.id, u2.name
   FROM   users u1
   JOIN   users u2 ON u2.id = u1.id + 1
   WHERE  u1.school_id = _school_id
   LIMIT  1;  -- may be optional
END
$func$  LANGUAGE plpgsql;

Call:

SELECT * FROM get_object_fields2(1);
  • RETURNS TABLE is effectively the same as having a bunch of OUT parameters combined with RETURNS SETOF record, just shorter.

  • The major difference: this function can return 0, 1 or many rows, while the first version always returns 1 row.
    Add LIMIT 1 like demonstrated to only allow 0 or 1 row.

  • RETURN QUERY is simple way to return results from a query directly.
    You can use multiple instances in a single function to add more rows to the output.

db<>fiddle here (demonstrating both)

Varying row-type

If your function is supposed to dynamically return results with a different row-type depending on the input, read more here:

Error: Cannot invoke an expression whose type lacks a call signature

Let's break this down:

  1. The error says

    Cannot invoke an expression whose type lacks a call signature.

  2. The code:

The problem is in this line public toggleBody: string; &

it's relation to these lines:

...
return this.toggleBody(true);
...
return this.toggleBody(false);
  1. The result:

Your saying toggleBody is a string but then your treating it like something that has a call signature (i.e. the structure of something that can be called: lambdas, proc, functions, methods, etc. In JS just function tho.). You need to change the declaration to be public toggleBody: (arg: boolean) => boolean;.

Extra Details:

"invoke" means your calling or applying a function.

"an expression" in Javascript is basically something that produces a value, so this.toggleBody() counts as an expression.

"type" is declared on this line public toggleBody: string

"lacks a call signature" this is because your trying to call something this.toggleBody() that doesn't have signature(i.e. the structure of something that can be called: lambdas, proc, functions, methods, etc.) that can be called. You said this.toggleBody is something that acts like a string.

In other words the error is saying

Cannot call an expression (this.toggleBody) because it's type (:string) lacks a call signature (bc it has a string signature.)

Generics in C#, using type of a variable as parameter

The point about generics is to give compile-time type safety - which means that types need to be known at compile-time.

You can call generic methods with types only known at execution time, but you have to use reflection:

// For non-public methods, you'll need to specify binding flags too
MethodInfo method = GetType().GetMethod("DoesEntityExist")
                             .MakeGenericMethod(new Type[] { t });
method.Invoke(this, new object[] { entityGuid, transaction });

Ick.

Can you make your calling method generic instead, and pass in your type parameter as the type argument, pushing the decision one level higher up the stack?

If you could give us more information about what you're doing, that would help. Sometimes you may need to use reflection as above, but if you pick the right point to do it, you can make sure you only need to do it once, and let everything below that point use the type parameter in a normal way.

When to use NSInteger vs. int

You usually want to use NSInteger when you don't know what kind of processor architecture your code might run on, so you may for some reason want the largest possible integer type, which on 32 bit systems is just an int, while on a 64-bit system it's a long.

I'd stick with using NSInteger instead of int/long unless you specifically require them.

NSInteger/NSUInteger are defined as *dynamic typedef*s to one of these types, and they are defined like this:

#if __LP64__ || TARGET_OS_EMBEDDED || TARGET_OS_IPHONE || TARGET_OS_WIN32 || NS_BUILD_32_LIKE_64
typedef long NSInteger;
typedef unsigned long NSUInteger;
#else
typedef int NSInteger;
typedef unsigned int NSUInteger;
#endif

With regard to the correct format specifier you should use for each of these types, see the String Programming Guide's section on Platform Dependencies

Type Checking: typeof, GetType, or is?

Performance test typeof() vs GetType():

using System;
namespace ConsoleApplication1
    {
    class Program
    {
        enum TestEnum { E1, E2, E3 }
        static void Main(string[] args)
        {
            {
                var start = DateTime.UtcNow;
                for (var i = 0; i < 1000000000; i++)
                    Test1(TestEnum.E2);
                Console.WriteLine(DateTime.UtcNow - start);
            }
            {
                var start = DateTime.UtcNow;
                for (var i = 0; i < 1000000000; i++)
                    Test2(TestEnum.E2);
                Console.WriteLine(DateTime.UtcNow - start);
            }
            Console.ReadLine();
        }
        static Type Test1<T>(T value) => typeof(T);
        static Type Test2(object value) => value.GetType();
    }
}

Results in debug mode:

00:00:08.4096636
00:00:10.8570657

Results in release mode:

00:00:02.3799048
00:00:07.1797128

Is there a good reason I see VARCHAR(255) used so often (as opposed to another length)?

Historically, 255 characters has often been the maximum length of a VARCHAR in some DBMSes, and it sometimes still winds up being the effective maximum if you want to use UTF-8 and have the column indexed (because of index length limitations).

How do I check if a type is a subtype OR the type of an object?

Apparently, no.

Here's the options:

Type.IsSubclassOf

As you've already found out, this will not work if the two types are the same, here's a sample LINQPad program that demonstrates:

void Main()
{
    typeof(Derived).IsSubclassOf(typeof(Base)).Dump();
    typeof(Base).IsSubclassOf(typeof(Base)).Dump();
}

public class Base { }
public class Derived : Base { }

Output:

True
False

Which indicates that Derived is a subclass of Base, but that Baseis (obviously) not a subclass of itself.

Type.IsAssignableFrom

Now, this will answer your particular question, but it will also give you false positives. As Eric Lippert has pointed out in the comments, while the method will indeed return True for the two above questions, it will also return True for these, which you probably don't want:

void Main()
{
    typeof(Base).IsAssignableFrom(typeof(Derived)).Dump();
    typeof(Base).IsAssignableFrom(typeof(Base)).Dump();
    typeof(int[]).IsAssignableFrom(typeof(uint[])).Dump();
}

public class Base { }
public class Derived : Base { }

Here you get the following output:

True
True
True

The last True there would indicate, if the method only answered the question asked, that uint[] inherits from int[] or that they're the same type, which clearly is not the case.

So IsAssignableFrom is not entirely correct either.

is and as

The "problem" with is and as in the context of your question is that they will require you to operate on the objects and write one of the types directly in code, and not work with Type objects.

In other words, this won't compile:

SubClass is BaseClass
^--+---^
   |
   +-- need object reference here

nor will this:

typeof(SubClass) is typeof(BaseClass)
                    ^-------+-------^
                            |
                            +-- need type name here, not Type object

nor will this:

typeof(SubClass) is BaseClass
^------+-------^
       |
       +-- this returns a Type object, And "System.Type" does not
           inherit from BaseClass

Conclusion

While the above methods might fit your needs, the only correct answer to your question (as I see it) is that you will need an extra check:

typeof(Derived).IsSubclassOf(typeof(Base)) || typeof(Derived) == typeof(Base);

which of course makes more sense in a method:

public bool IsSameOrSubclass(Type potentialBase, Type potentialDescendant)
{
    return potentialDescendant.IsSubclassOf(potentialBase)
           || potentialDescendant == potentialBase;
}

Difference between string and char[] types in C++

One of the difference is Null termination (\0).

In C and C++, char* or char[] will take a pointer to a single char as a parameter and will track along the memory until a 0 memory value is reached (often called the null terminator).

C++ strings can contain embedded \0 characters, know their length without counting.

#include<stdio.h>
#include<string.h>
#include<iostream>

using namespace std;

void NullTerminatedString(string str){
   int NUll_term = 3;
   str[NUll_term] = '\0';       // specific character is kept as NULL in string
   cout << str << endl <<endl <<endl;
}

void NullTerminatedChar(char *str){
   int NUll_term = 3;
   str[NUll_term] = 0;     // from specific, all the character are removed 
   cout << str << endl;
}

int main(){
  string str = "Feels Happy";
  printf("string = %s\n", str.c_str());
  printf("strlen = %d\n", strlen(str.c_str()));  
  printf("size = %d\n", str.size());  
  printf("sizeof = %d\n", sizeof(str)); // sizeof std::string class  and compiler dependent
  NullTerminatedString(str);


  char str1[12] = "Feels Happy";
  printf("char[] = %s\n", str1);
  printf("strlen = %d\n", strlen(str1));
  printf("sizeof = %d\n", sizeof(str1));    // sizeof char array
  NullTerminatedChar(str1);
  return 0;
}

Output:

strlen = 11
size = 11
sizeof = 32  
Fee s Happy


strlen = 11
sizeof = 12
Fee

Finding the type of an object in C++

Your description is a little confusing.

Generally speaking, though some C++ implementations have mechanisms for it, you're not supposed to ask about the type. Instead, you are supposed to do a dynamic_cast on the pointer to A. What this will do is that at runtime, the actual contents of the pointer to A will be checked. If you have a B, you'll get your pointer to B. Otherwise, you'll get an exception or null.

How to cast or convert an unsigned int to int in C?

Unsigned int can be converted to signed (or vice-versa) by simple expression as shown below :

unsigned int z;
int y=5;
z= (unsigned int)y;   

Though not targeted to the question, you would like to read following links :

Difference between <input type='button' /> and <input type='submit' />

Button won't submit form on its own.It is a simple button which is used to perform some operation by using javascript whereas Submit is a kind of button which by default submit the form whenever user clicks on submit button.

Difference between timestamps with/without time zone in PostgreSQL

The differences are covered at the PostgreSQL documentation for date/time types. Yes, the treatment of TIME or TIMESTAMP differs between one WITH TIME ZONE or WITHOUT TIME ZONE. It doesn't affect how the values are stored; it affects how they are interpreted.

The effects of time zones on these data types is covered specifically in the docs. The difference arises from what the system can reasonably know about the value:

  • With a time zone as part of the value, the value can be rendered as a local time in the client.

  • Without a time zone as part of the value, the obvious default time zone is UTC, so it is rendered for that time zone.

The behaviour differs depending on at least three factors:

  • The timezone setting in the client.
  • The data type (i.e. WITH TIME ZONE or WITHOUT TIME ZONE) of the value.
  • Whether the value is specified with a particular time zone.

Here are examples covering the combinations of those factors:

foo=> SET TIMEZONE TO 'Japan';
SET
foo=> SELECT '2011-01-01 00:00:00'::TIMESTAMP;
      timestamp      
---------------------
 2011-01-01 00:00:00
(1 row)

foo=> SELECT '2011-01-01 00:00:00'::TIMESTAMP WITH TIME ZONE;
      timestamptz       
------------------------
 2011-01-01 00:00:00+09
(1 row)

foo=> SELECT '2011-01-01 00:00:00+03'::TIMESTAMP;
      timestamp      
---------------------
 2011-01-01 00:00:00
(1 row)

foo=> SELECT '2011-01-01 00:00:00+03'::TIMESTAMP WITH TIME ZONE;
      timestamptz       
------------------------
 2011-01-01 06:00:00+09
(1 row)

foo=> SET TIMEZONE TO 'Australia/Melbourne';
SET
foo=> SELECT '2011-01-01 00:00:00'::TIMESTAMP;
      timestamp      
---------------------
 2011-01-01 00:00:00
(1 row)

foo=> SELECT '2011-01-01 00:00:00'::TIMESTAMP WITH TIME ZONE;
      timestamptz       
------------------------
 2011-01-01 00:00:00+11
(1 row)

foo=> SELECT '2011-01-01 00:00:00+03'::TIMESTAMP;
      timestamp      
---------------------
 2011-01-01 00:00:00
(1 row)

foo=> SELECT '2011-01-01 00:00:00+03'::TIMESTAMP WITH TIME ZONE;
      timestamptz       
------------------------
 2011-01-01 08:00:00+11
(1 row)

What's the difference between size_t and int in C++?

From the friendly Wikipedia:

The stdlib.h and stddef.h header files define a datatype called size_t which is used to represent the size of an object. Library functions that take sizes expect them to be of type size_t, and the sizeof operator evaluates to size_t.

The actual type of size_t is platform-dependent; a common mistake is to assume size_t is the same as unsigned int, which can lead to programming errors, particularly as 64-bit architectures become more prevalent.

Also, check Why size_t matters

Class constructor type in typescript?

Like that:

class Zoo {
    AnimalClass: typeof Animal;

    constructor(AnimalClass: typeof Animal ) {
        this.AnimalClass = AnimalClass
        let Hector = new AnimalClass();
    }
}

Or just:

class Zoo {
    constructor(public AnimalClass: typeof Animal ) {
        let Hector = new AnimalClass();
    }
}

typeof Class is the type of the class constructor. It's preferable to the custom constructor type declaration because it processes static class members properly.

Here's the relevant part of TypeScript docs. Search for the typeof. As a part of a TypeScript type annotation, it means "give me the type of the symbol called Animal" which is the type of the class constructor function in our case.

What primitive data type is time_t?

You could always use something like mktime to create a known time (midnight, last night) and use difftime to get a double-precision time difference between the two. For a platform-independant solution, unless you go digging into the details of your libraries, you're not going to do much better than that. According to the C spec, the definition of time_t is implementation-defined (meaning that each implementation of the library can define it however they like, as long as library functions with use it behave according to the spec.)

That being said, the size of time_t on my linux machine is 8 bytes, which suggests a long int or a double. So I did:

int main()
{
    for(;;)
    {
        printf ("%ld\n", time(NULL));
        printf ("%f\n", time(NULL));
        sleep(1);
    }
    return 0;
}

The time given by the %ld increased by one each step and the float printed 0.000 each time. If you're hell-bent on using printf to display time_ts, your best bet is to try your own such experiment and see how it work out on your platform and with your compiler.

How can I round a number in JavaScript? .toFixed() returns a string?

Number.prototype.toFixed is a function designed to format a number before printing it out. It's from the family of toString, toExponential and toPrecision.

To round a number, you would do this:

someNumber = 42.008;
someNumber = Math.round( someNumber * 1e2 ) / 1e2;
someNumber === 42.01;

// if you need 3 digits, replace 1e2 with 1e3 etc.
// or just copypaste this function to your code:

function toFixedNumber(num, digits, base){
  var pow = Math.pow(base||10, digits);
  return Math.round(num*pow) / pow;
}

.

Or if you want a “native-like” function, you can extend the prototype:

Number.prototype.toFixedNumber = function(digits, base){
  var pow = Math.pow(base||10, digits);
  return Math.round(this*pow) / pow;
}
someNumber = 42.008;
someNumber = someNumber.toFixedNumber(2);
someNumber === 42.01;


//or even hexadecimal

someNumber = 0xAF309/256  //which is af3.09
someNumber = someNumber.toFixedNumber(1, 16);
someNumber.toString(16) === "af3.1";

However, bear in mind that polluting the prototype is considered bad when you're writing a module, as modules shouldn't have any side effects. So, for a module, use the first function.

C# Generics and Type Checking

The typeof operator...

typeof(T)

... won't work with the c# switch statement. But how about this? The following post contains a static class...

Is there a better alternative than this to 'switch on type'?

...that will let you write code like this:

TypeSwitch.Do(
    sender,
    TypeSwitch.Case<Button>(() => textBox1.Text = "Hit a Button"),
    TypeSwitch.Case<CheckBox>(x => textBox1.Text = "Checkbox is " + x.Checked),
    TypeSwitch.Default(() => textBox1.Text = "Not sure what is hovered over"));

How to resolve "must be an instance of string, string given" prior to PHP 7?

Maybe not safe and pretty but if you must:

class string
{
    private $Text;
    public function __construct($value)
    {
        $this->Text = $value;
    }

    public function __toString()
    {
        return $this->Text;
    }
}

function Test123(string $s)
{
    echo $s;
}

Test123(new string("Testing"));

How to check if string input is a number?

try this! it worked for me even if I input negative numbers.

  def length(s):
    return len(s)

   s = input("Enter the String: ")
    try:
        if (type(int(s)))==int :
            print("You input an integer")

    except ValueError:      
        print("it is a string with length " + str(length(s)))   

Groovy / grails how to determine a data type?

To determine the class of an object simply call:

someObject.getClass()

You can abbreviate this to someObject.class in most cases. However, if you use this on a Map it will try to retrieve the value with key 'class'. Because of this, I always use getClass() even though it's a little longer.

If you want to check if an object implements a particular interface or extends a particular class (e.g. Date) use:

(somObject instanceof Date)

or to check if the class of an object is exactly a particular class (not a subclass of it), use:

(somObject.getClass() == Date)

Difference between text and varchar (character varying)

There is no difference, under the hood it's all varlena (variable length array).

Check this article from Depesz: http://www.depesz.com/index.php/2010/03/02/charx-vs-varcharx-vs-varchar-vs-text/

A couple of highlights:

To sum it all up:

  • char(n) – takes too much space when dealing with values shorter than n (pads them to n), and can lead to subtle errors because of adding trailing spaces, plus it is problematic to change the limit
  • varchar(n) – it's problematic to change the limit in live environment (requires exclusive lock while altering table)
  • varchar – just like text
  • text – for me a winner – over (n) data types because it lacks their problems, and over varchar – because it has distinct name

The article does detailed testing to show that the performance of inserts and selects for all 4 data types are similar. It also takes a detailed look at alternate ways on constraining the length when needed. Function based constraints or domains provide the advantage of instant increase of the length constraint, and on the basis that decreasing a string length constraint is rare, depesz concludes that one of them is usually the best choice for a length limit.

How to check if an object is a list or tuple (but not string)?

I do this in my testcases.

def assertIsIterable(self, item):
    #add types here you don't want to mistake as iterables
    if isinstance(item, basestring): 
        raise AssertionError("type %s is not iterable" % type(item))

    #Fake an iteration.
    try:
        for x in item:
            break;
    except TypeError:
        raise AssertionError("type %s is not iterable" % type(item))

Untested on generators, I think you are left at the next 'yield' if passed in a generator, which may screw things up downstream. But then again, this is a 'unittest'

What is the difference between “int” and “uint” / “long” and “ulong”?

The difference is that the uint and ulong are unsigned data types, meaning the range is different: They do not accept negative values:

int range: -2,147,483,648 to 2,147,483,647
uint range: 0 to 4,294,967,295

long range: –9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
ulong range: 0 to 18,446,744,073,709,551,615

What's the difference between 'int?' and 'int' in C#?

the symbol ? after the int means that it can be nullable.

The ? symbol is usually used in situations whereby the variable can accept a null or an integer or alternatively, return an integer or null.

Hope the context of usage helps. In this way you are not restricted to solely dealing with integers.

What data type to use for hashed password field and what length?

Update: Simply using a hash function is not strong enough for storing passwords. You should read the answer from Gilles on this thread for a more detailed explanation.

For passwords, use a key-strengthening hash algorithm like Bcrypt or Argon2i. For example, in PHP, use the password_hash() function, which uses Bcrypt by default.

$hash = password_hash("rasmuslerdorf", PASSWORD_DEFAULT);

The result is a 60-character string similar to the following (but the digits will vary, because it generates a unique salt).

$2y$10$.vGA1O9wmRjrwAVXD98HNOgsNpDczlqm3Jq7KnEd1rVAGv3Fykk1a

Use the SQL data type CHAR(60) to store this encoding of a Bcrypt hash. Note this function doesn't encode as a string of hexadecimal digits, so we can't as easily unhex it to store in binary.

Other hash functions still have uses, but not for storing passwords, so I'll keep the original answer below, written in 2008.


It depends on the hashing algorithm you use. Hashing always produces a result of the same length, regardless of the input. It is typical to represent the binary hash result in text, as a series of hexadecimal digits. Or you can use the UNHEX() function to reduce a string of hex digits by half.

  • MD5 generates a 128-bit hash value. You can use CHAR(32) or BINARY(16)
  • SHA-1 generates a 160-bit hash value. You can use CHAR(40) or BINARY(20)
  • SHA-224 generates a 224-bit hash value. You can use CHAR(56) or BINARY(28)
  • SHA-256 generates a 256-bit hash value. You can use CHAR(64) or BINARY(32)
  • SHA-384 generates a 384-bit hash value. You can use CHAR(96) or BINARY(48)
  • SHA-512 generates a 512-bit hash value. You can use CHAR(128) or BINARY(64)
  • BCrypt generates an implementation-dependent 448-bit hash value. You might need CHAR(56), CHAR(60), CHAR(76), BINARY(56) or BINARY(60)

As of 2015, NIST recommends using SHA-256 or higher for any applications of hash functions requiring interoperability. But NIST does not recommend using these simple hash functions for storing passwords securely.

Lesser hashing algorithms have their uses (like internal to an application, not for interchange), but they are known to be crackable.

Which MySQL datatype to use for an IP address?

Since IPv4 addresses are 4 byte long, you could use an INT (UNSIGNED) that has exactly 4 bytes:

`ipv4` INT UNSIGNED

And INET_ATON and INET_NTOA to convert them:

INSERT INTO `table` (`ipv4`) VALUES (INET_ATON("127.0.0.1"));
SELECT INET_NTOA(`ipv4`) FROM `table`;

For IPv6 addresses you could use a BINARY instead:

`ipv6` BINARY(16)

And use PHP’s inet_pton and inet_ntop for conversion:

'INSERT INTO `table` (`ipv6`) VALUES ("'.mysqli_real_escape_string(inet_pton('2001:4860:a005::68')).'")'
'SELECT `ipv6` FROM `table`'
$ipv6 = inet_pton($row['ipv6']);

Test if a variable is a list or tuple

Has to be more complex test if you really want to handle just about anything as function argument.

type(a) != type('') and hasattr(a, "__iter__")

Although, usually it's enough to just spell out that a function expects iterable and then check only type(a) != type('').

Also it may happen that for a string you have a simple processing path or you are going to be nice and do a split etc., so you don't want to yell at strings and if someone sends you something weird, just let him have an exception.

No function matches the given name and argument types

Your function has a couple of smallint parameters.
But in the call, you are using numeric literals that are presumed to be type integer.

A string literal or string constant ('123') is not typed immediately. It remains type "unknown" until assigned or cast explicitly.

However, a numeric literal or numeric constant is typed immediately. Per documentation:

A numeric constant that contains neither a decimal point nor an exponent is initially presumed to be type integer if its value fits in type integer (32 bits); otherwise it is presumed to be type bigint if its value fits in type bigint (64 bits); otherwise it is taken to be type numeric. Constants that contain decimal points and/or exponents are always initially presumed to be type numeric.

More explanation and links in this related answer:

Solution

Add explicit casts for the smallint parameters or quote them.

Demo

CREATE OR REPLACE FUNCTION f_typetest(smallint)
  RETURNS bool AS 'SELECT TRUE' LANGUAGE sql;

Incorrect call:

SELECT * FROM f_typetest(1);

Correct calls:

SELECT * FROM f_typetest('1');
SELECT * FROM f_typetest(smallint '1');
SELECT * FROM f_typetest(1::int2);
SELECT * FROM f_typetest('1'::int2);

db<>fiddle here
Old sqlfiddle.

How to find out if a Python object is a string?

Python 2

Use isinstance(obj, basestring) for an object-to-test obj.

Docs.

How can I get the data type of a variable in C#?

check out one of the simple way to do this

// Read string from console
        string line = Console.ReadLine(); 
        int valueInt;
        float valueFloat;
        if (int.TryParse(line, out valueInt)) // Try to parse the string as an integer
        {
            Console.Write("This input is of type Integer.");
        }
        else if (float.TryParse(line, out valueFloat)) 
        {
            Console.Write("This input is of type Float.");
        }
        else
        {
            Console.WriteLine("This input is of type string.");
        }

What is the difference between String and string in C#?

New answer after 6 years and 5 months (procrastination).

While string is a reserved C# keyword that always has a fixed meaning, String is just an ordinary identifier which could refer to anything. Depending on members of the current type, the current namespace and the applied using directives and their placement, String could be a value or a type distinct from global::System.String.

I shall provide two examples where using directives will not help.


First, when String is a value of the current type (or a local variable):

class MySequence<TElement>
{
  public IEnumerable<TElement> String { get; set; }

  void Example()
  {
    var test = String.Format("Hello {0}.", DateTime.Today.DayOfWeek);
  }
}

The above will not compile because IEnumerable<> does not have a non-static member called Format, and no extension methods apply. In the above case, it may still be possible to use String in other contexts where a type is the only possibility syntactically. For example String local = "Hi mum!"; could be OK (depending on namespace and using directives).

Worse: Saying String.Concat(someSequence) will likely (depending on usings) go to the Linq extension method Enumerable.Concat. It will not go to the static method string.Concat.


Secondly, when String is another type, nested inside the current type:

class MyPiano
{
  protected class String
  {
  }

  void Example()
  {
    var test1 = String.Format("Hello {0}.", DateTime.Today.DayOfWeek);
    String test2 = "Goodbye";
  }
}

Neither statement in the Example method compiles. Here String is always a piano string, MyPiano.String. No member (static or not) Format exists on it (or is inherited from its base class). And the value "Goodbye" cannot be converted into it.

C++ auto keyword. Why is it magic?

The auto keyword is an important and frequently used keyword for C ++.When initializing a variable, auto keyword is used for type inference(also called type deduction).

There are 3 different rules regarding the auto keyword.

First Rule

auto x = expr; ----> No pointer or reference, only variable name. In this case, const and reference are ignored.

int  y = 10;
int& r = y;
auto x = r; // The type of variable x is int. (Reference Ignored)

const int y = 10;
auto x = y; // The type of variable x is int. (Const Ignored)

int y = 10;
const int& r = y;
auto x = r; // The type of variable x is int. (Both const and reference Ignored)

const int a[10] = {};
auto x = a; //  x is const int *. (Array to pointer conversion)

Note : When the name defined by auto is given a value with the name of a function,
       the type inference will be done as a function pointer.

Second Rule

auto& y = expr; or auto* y = expr; ----> Reference or pointer after auto keyword.

Warning : const is not ignored in this rule !!! .

int y = 10;
auto& x = y; // The type of variable x is int&.

Warning : In this rule, array to pointer conversion (array decay) does not occur !!!.

auto& x = "hello"; // The type of variable x is  const char [6].

static int x = 10;
auto y = x; // The variable y is not static.Because the static keyword is not a type. specifier 
            // The type of variable x is int.

Third Rule

auto&& z = expr; ----> This is not a Rvalue reference.

Warning : If the type inference is in question and the && token is used, the names introduced like this are called "Forwarding Reference" (also called Universal Reference).

auto&& r1 = x; // The type of variable r1 is int&.Because x is Lvalue expression. 

auto&& r2 = x+y; // The type of variable r2 is int&&.Because x+y is PRvalue expression. 

BOOLEAN or TINYINT confusion

MySQL does not have internal boolean data type. It uses the smallest integer data type - TINYINT.

The BOOLEAN and BOOL are equivalents of TINYINT(1), because they are synonyms.

Try to create this table -

CREATE TABLE table1 (
  column1 BOOLEAN DEFAULT NULL
);

Then run SHOW CREATE TABLE, you will get this output -

CREATE TABLE `table1` (
  `column1` tinyint(1) DEFAULT NULL
)

Why isn't textarea an input[type="textarea"]?

Maybe this is going a bit too far back but…

Also, I’d like to suggest that multiline text fields have a different type (e.g. “textarea") than single-line fields ("text"), as they really are different types of things, and imply different issues (semantics) for client-side handling.

Marc Andreessen, 11 October 1993

How to pass a type as a method parameter in Java

I had a similar question, so I worked up a complete runnable answer below. What I needed to do is pass a class (C) to an object (O) of an unrelated class and have that object (O) emit new objects of class (C) back to me when I asked for them.

The example below shows how this is done. There is a MagicGun class that you load with any subtype of the Projectile class (Pebble, Bullet or NuclearMissle). The interesting is you load it with subtypes of Projectile, but not actual objects of that type. The MagicGun creates the actual object when it's time to shoot.

The Output

You've annoyed the target!
You've holed the target!
You've obliterated the target!
click
click

The Code

import java.util.ArrayList;
import java.util.List;

public class PassAClass {
    public static void main(String[] args) {
        MagicGun gun = new MagicGun();
        gun.loadWith(Pebble.class);
        gun.loadWith(Bullet.class);
        gun.loadWith(NuclearMissle.class);
        //gun.loadWith(Object.class);   // Won't compile -- Object is not a Projectile
        for(int i=0; i<5; i++){
            try {
                String effect = gun.shoot().effectOnTarget();
                System.out.printf("You've %s the target!\n", effect);
            } catch (GunIsEmptyException e) {
                System.err.printf("click\n");
            }
        }
    }
}

class MagicGun {
    /**
     * projectiles holds a list of classes that extend Projectile. Because of erasure, it
     * can't hold be a List<? extends Projectile> so we need the SuppressWarning. However
     * the only way to add to it is the "loadWith" method which makes it typesafe. 
     */
    private @SuppressWarnings("rawtypes") List<Class> projectiles = new ArrayList<Class>();
    /**
     * Load the MagicGun with a new Projectile class.
     * @param projectileClass The class of the Projectile to create when it's time to shoot.
     */
    public void loadWith(Class<? extends Projectile> projectileClass){
        projectiles.add(projectileClass);
    }
    /**
     * Shoot the MagicGun with the next Projectile. Projectiles are shot First In First Out.
     * @return A newly created Projectile object.
     * @throws GunIsEmptyException
     */
    public Projectile shoot() throws GunIsEmptyException{
        if (projectiles.isEmpty())
            throw new GunIsEmptyException();
        Projectile projectile = null;
        // We know it must be a Projectile, so the SuppressWarnings is OK
        @SuppressWarnings("unchecked") Class<? extends Projectile> projectileClass = projectiles.get(0);
        projectiles.remove(0);
        try{
            // http://www.java2s.com/Code/Java/Language-Basics/ObjectReflectioncreatenewinstance.htm
            projectile = projectileClass.newInstance();
        } catch (InstantiationException e) {
            System.err.println(e);
        } catch (IllegalAccessException e) {
            System.err.println(e);
        }
        return projectile;
    }
}

abstract class Projectile {
    public abstract String effectOnTarget();
}

class Pebble extends Projectile {
    @Override public String effectOnTarget() {
        return "annoyed";
    }
}

class Bullet extends Projectile {
    @Override public String effectOnTarget() {
        return "holed";
    }
}

class NuclearMissle extends Projectile {
    @Override public String effectOnTarget() {
        return "obliterated";
    }
}

class GunIsEmptyException extends Exception {
    private static final long serialVersionUID = 4574971294051632635L;
}

Fastest way to convert a dict's keys & values from `unicode` to `str`?

Just use print(*(dict.keys()))

The * can be used for unpacking containers e.g. lists. For more info on * check this SO answer.

Determine the data types of a data frame's columns

For small data frames:

library(tidyverse)

as_tibble(mtcars)

gives you a print out of the df with data types

# A tibble: 32 x 11
     mpg   cyl  disp    hp  drat    wt  qsec    vs    am  gear  carb
 * <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl>
 1  21       6  160    110  3.9   2.62  16.5     0     1     4     4
 2  21       6  160    110  3.9   2.88  17.0     0     1     4     4
 3  22.8     4  108     93  3.85  2.32  18.6     1     1     4     1

For large data frames:

glimpse(mtcars)

gives you a structured view of data types:

Observations: 32
Variables: 11
$ mpg  <dbl> 21.0, 21.0, 22.8, 21.4, 18.7, 18.1, 14.3, 24.4, 22.8, 19.2, 17.8, 16.4, 17....
$ cyl  <dbl> 6, 6, 4, 6, 8, 6, 8, 4, 4, 6, 6, 8, 8, 8, 8, 8, 8, 4, 4, 4, 4, 8, 8, 8, 8, ...
$ disp <dbl> 160.0, 160.0, 108.0, 258.0, 360.0, 225.0, 360.0, 146.7, 140.8, 167.6, 167.6...
$ hp   <dbl> 110, 110, 93, 110, 175, 105, 245, 62, 95, 123, 123, 180, 180, 180, 205, 215...
$ drat <dbl> 3.90, 3.90, 3.85, 3.08, 3.15, 2.76, 3.21, 3.69, 3.92, 3.92, 3.92, 3.07, 3.0...
$ wt   <dbl> 2.620, 2.875, 2.320, 3.215, 3.440, 3.460, 3.570, 3.190, 3.150, 3.440, 3.440...
$ qsec <dbl> 16.46, 17.02, 18.61, 19.44, 17.02, 20.22, 15.84, 20.00, 22.90, 18.30, 18.90...
$ vs   <dbl> 0, 0, 1, 1, 0, 1, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, ...
$ am   <dbl> 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, ...
$ gear <dbl> 4, 4, 4, 3, 3, 3, 3, 4, 4, 4, 4, 3, 3, 3, 3, 3, 3, 4, 4, 4, 3, 3, 3, 3, 3, ...
$ carb <dbl> 4, 4, 1, 1, 2, 1, 4, 2, 2, 4, 4, 3, 3, 3, 4, 4, 4, 1, 2, 1, 1, 2, 2, 4, 2, ...

To get a list of the columns' data type (as said by @Alexandre above):

map(mtcars, class)

gives a list of data types:

$mpg
[1] "numeric"

$cyl
[1] "numeric"

$disp
[1] "numeric"

$hp
[1] "numeric"

To change data type of a column:

library(hablar)

mtcars %>% 
  convert(chr(mpg, am),
          int(carb))

converts columns mpg and am to character and the column carb to integer:

# A tibble: 32 x 11
   mpg     cyl  disp    hp  drat    wt  qsec    vs am     gear  carb
   <chr> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <chr> <dbl> <int>
 1 21        6  160    110  3.9   2.62  16.5     0 1         4     4
 2 21        6  160    110  3.9   2.88  17.0     0 1         4     4
 3 22.8      4  108     93  3.85  2.32  18.6     1 1         4     1
 4 21.4      6  258    110  3.08  3.22  19.4     1 0         3     1

Check whether variable is number or string in JavaScript

XOR operation can be used to detect number or string. number ^ 0 will always give the number as output and string ^ 0 will give 0 as output.

Example: 
   1)  2 ^ 0 = 2
   2)  '2' ^ 0  = 2
   3)  'Str' ^ 0 = 0

min and max value of data type in C

Look at the these pages on limits.h and float.h, which are included as part of the standard c library.

How to concatenate columns in a Postgres SELECT?

it is better to use CONCAT function in PostgreSQL for concatenation

eg : select CONCAT(first_name,last_name) from person where pid = 136

if you are using column_a || ' ' || column_b for concatenation for 2 column , if any of the value in column_a or column_b is null query will return null value. which may not be preferred in all cases.. so instead of this

||

use

CONCAT

it will return relevant value if either of them have value

What is the inclusive range of float and double in Java?

Of course you can use floats or doubles for "critical" things ... Many applications do nothing but crunch numbers using these datatypes.

You might have misunderstood some of the various caveats regarding floating-point numbers, such as the recommendation to never compare for exact equality, and so on.

What are the differences between type() and isinstance()?

To summarize the contents of other (already good!) answers, isinstance caters for inheritance (an instance of a derived class is an instance of a base class, too), while checking for equality of type does not (it demands identity of types and rejects instances of subtypes, AKA subclasses).

Normally, in Python, you want your code to support inheritance, of course (since inheritance is so handy, it would be bad to stop code using yours from using it!), so isinstance is less bad than checking identity of types because it seamlessly supports inheritance.

It's not that isinstance is good, mind you—it's just less bad than checking equality of types. The normal, Pythonic, preferred solution is almost invariably "duck typing": try using the argument as if it was of a certain desired type, do it in a try/except statement catching all exceptions that could arise if the argument was not in fact of that type (or any other type nicely duck-mimicking it;-), and in the except clause, try something else (using the argument "as if" it was of some other type).

basestring is, however, quite a special case—a builtin type that exists only to let you use isinstance (both str and unicode subclass basestring). Strings are sequences (you could loop over them, index them, slice them, ...), but you generally want to treat them as "scalar" types—it's somewhat incovenient (but a reasonably frequent use case) to treat all kinds of strings (and maybe other scalar types, i.e., ones you can't loop on) one way, all containers (lists, sets, dicts, ...) in another way, and basestring plus isinstance helps you do that—the overall structure of this idiom is something like:

if isinstance(x, basestring)
  return treatasscalar(x)
try:
  return treatasiter(iter(x))
except TypeError:
  return treatasscalar(x)

You could say that basestring is an Abstract Base Class ("ABC")—it offers no concrete functionality to subclasses, but rather exists as a "marker", mainly for use with isinstance. The concept is obviously a growing one in Python, since PEP 3119, which introduces a generalization of it, was accepted and has been implemented starting with Python 2.6 and 3.0.

The PEP makes it clear that, while ABCs can often substitute for duck typing, there is generally no big pressure to do that (see here). ABCs as implemented in recent Python versions do however offer extra goodies: isinstance (and issubclass) can now mean more than just "[an instance of] a derived class" (in particular, any class can be "registered" with an ABC so that it will show as a subclass, and its instances as instances of the ABC); and ABCs can also offer extra convenience to actual subclasses in a very natural way via Template Method design pattern applications (see here and here [[part II]] for more on the TM DP, in general and specifically in Python, independent of ABCs).

For the underlying mechanics of ABC support as offered in Python 2.6, see here; for their 3.1 version, very similar, see here. In both versions, standard library module collections (that's the 3.1 version—for the very similar 2.6 version, see here) offers several useful ABCs.

For the purpose of this answer, the key thing to retain about ABCs (beyond an arguably more natural placement for TM DP functionality, compared to the classic Python alternative of mixin classes such as UserDict.DictMixin) is that they make isinstance (and issubclass) much more attractive and pervasive (in Python 2.6 and going forward) than they used to be (in 2.5 and before), and therefore, by contrast, make checking type equality an even worse practice in recent Python versions than it already used to be.

SSIS Excel Import Forcing Incorrect Column Type

  1. Click File on the ribbon menu, and then click on Options.
  2. Click Advanced, and then under When calculating this workbook, select the Set precision as displayed check box, and then click OK.

  3. Click OK.

  4. In the worksheet, select the cells that you want to format.

  5. On the Home tab, click the Dialog Box Launcher Button image next to Number.

  6. In the Category box, click Number.

  7. In the Decimal places box, enter the number of decimal places that you want to display.

Appropriate datatype for holding percent values?

  • Hold as a decimal.
  • Add check constraints if you want to limit the range (e.g. between 0 to 100%; in some cases there may be valid reasons to go beyond 100% or potentially even into the negatives).
  • Treat value 1 as 100%, 0.5 as 50%, etc. This will allow any math operations to function as expected (i.e. as opposed to using value 100 as 100%).
  • Amend precision and scale as required (these are the two values in brackets columnName decimal(precision, scale). Precision says the total number of digits that can be held in the number, scale says how many of those are after the decimal place, so decimal(3,2) is a number which can be represented as #.##; decimal(5,3) would be ##.###.
  • decimal and numeric are essentially the same thing. However decimal is ANSI compliant, so always use that unless told otherwise (e.g. by your company's coding standards).

Example Scenarios

  • For your case (0.00% to 100.00%) you'd want decimal(5,4).
  • For the most common case (0% to 100%) you'd want decimal(3,2).
  • In both of the above, the check constraints would be the same

Example:

if object_id('Demo') is null
create table Demo
    (
        Id bigint not null identity(1,1) constraint pk_Demo primary key
        , Name nvarchar(256) not null constraint uk_Demo unique 
        , SomePercentValue decimal(3,2) constraint chk_Demo_SomePercentValue check (SomePercentValue between 0 and 1)
        , SomePrecisionPercentValue decimal(5,2) constraint chk_Demo_SomePrecisionPercentValue check (SomePrecisionPercentValue between 0 and 1)
    )

Further Reading:

How to get input type using jquery?

You could do the following:

var inputType = $('#inputid').attr('type');

What MySQL data type should be used for Latitude/Longitude with 8 decimal places?

Additionally, you will see that float values are rounded.

// e.g: given values 41.0473112,29.0077011

float(11,7) | decimal(11,7)
---------------------------
41.0473099  | 41.0473112
29.0077019  | 29.0077011

How to compare type of an object in Python?

You can always use the type(x) == type(y) trick, where y is something with known type.

# check if x is a regular string
type(x) == type('')
# check if x is an integer
type(x) == type(1)
# check if x is a NoneType
type(x) == type(None)

Often there are better ways of doing that, particularly with any recent python. But if you only want to remember one thing, you can remember that.

In this case, the better ways would be:

# check if x is a regular string
type(x) == str
# check if x is either a regular string or a unicode string
type(x) in [str, unicode]
# alternatively:
isinstance(x, basestring)
# check if x is an integer
type(x) == int
# check if x is a NoneType
x is None

Note the last case: there is only one instance of NoneType in python, and that is None. You'll see NoneType a lot in exceptions (TypeError: 'NoneType' object is unsubscriptable -- happens to me all the time..) but you'll hardly ever need to refer to it in code.

Finally, as fengshaun points out, type checking in python is not always a good idea. It's more pythonic to just use the value as though it is the type you expect, and catch (or allow to propagate) exceptions that result from it.

MySQL integer field is returned as string in PHP

In my project I usually use an external function that "filters" data retrieved with mysql_fetch_assoc.

You can rename fields in your table so that is intuitive to understand which data type is stored.

For example, you can add a special suffix to each numeric field: if userid is an INT(11) you can rename it userid_i or if it is an UNSIGNED INT(11) you can rename userid_u. At this point, you can write a simple PHP function that receive as input the associative array (retrieved with mysql_fetch_assoc), and apply casting to the "value" stored with those special "keys".

How do I check if a variable is of a certain type (compare two types) in C?

C does not support this form of type introspection. What you are asking is not possible in C (at least without compiler-specific extensions; it would be possible in C++, however).

In general, with C you're expected to know the types of your variable. Since every function has concrete types for its parameters (except for varargs, I suppose), you don't need to check in the function body. The only remaining case I can see is in a macro body, and, well, C macros aren't really all that powerful.

Further, note that C does not retain any type information into runtime. This means that, even if, hypothetically, there was a type comparison extension, it would only work properly when the types are known at compile time (ie, it wouldn't work to test whether two void * point to the same type of data).

As for typeof: First, typeof is a GCC extension. It is not a standard part of C. It's typically used to write macros that only evaluate their arguments once, eg (from the GCC manual):

 #define max(a,b) \
   ({ typeof (a) _a = (a); \
      typeof (b) _b = (b); \
     _a > _b ? _a : _b; })

The typeof keyword lets the macro define a local temporary to save the values of its arguments, allowing them to be evaluated only once.

In short, C does not support overloading; you'll just have to make a func_a(struct a *) and func_b(struct b *), and call the correct one. Alternately, you could make your own introspection system:

struct my_header {
  int type;
};

#define TYPE_A 0
#define TYPE_B 1

struct a {
  struct my_header header;
  /* ... */
};

struct b {
  struct my_header header;
  /* ... */
};

void func_a(struct a *p);
void func_b(struct b *p);

void func_switch(struct my_header *head);
#define func(p) func_switch( &(p)->header )

void func_switch(struct my_header *head) {
  switch (head->type) {
    case TYPE_A: func_a((struct a *)head); break;
    case TYPE_B: func_b((struct b *)head); break;
    default: assert( ("UNREACHABLE", 0) );
  }
}

You must, of course, remember to initialize the header properly when creating these objects.

What's the difference between primitive and reference types?

These are the primitive types in Java:

  • boolean
  • byte
  • short
  • char
  • int
  • long
  • float
  • double

All the other types are reference types: they reference objects.

This is the first part of the Java tutorial about the basics of the language.

Where to find the complete definition of off_t type?

As the "GNU C Library Reference Manual" says

off_t
    This is a signed integer type used to represent file sizes. 
    In the GNU C Library, this type is no narrower than int.
    If the source is compiled with _FILE_OFFSET_BITS == 64 this 
    type is transparently replaced by off64_t.

and

off64_t
    This type is used similar to off_t. The difference is that 
    even on 32 bit machines, where the off_t type would have 32 bits,
    off64_t has 64 bits and so is able to address files up to 2^63 bytes
    in length. When compiling with _FILE_OFFSET_BITS == 64 this type 
    is available under the name off_t.

Thus if you want reliable way of representing file size between client and server, you can:

  1. Use off64_t type and stat64() function accordingly (as it fills structure stat64, which contains off64_t type itself). Type off64_t guaranties the same size on 32 and 64 bit machines.
  2. As was mentioned before compile your code with -D_FILE_OFFSET_BITS == 64 and use usual off_t and stat().
  3. Convert off_t to type int64_t with fixed size (C99 standard). Note: (my book 'C in a Nutshell' says that it is C99 standard, but optional in implementation). The newest C11 standard says:
7.20.1.1 Exact-width integer types

    1 The typedef name intN_t designates a signed integer type with width N ,
    no padding bits, and a two’s complement representation. Thus, int8_t 
    denotes such a signed integer type with a width of exactly 8 bits.
    without mentioning.

And about implementation:

7.20 Integer types <stdint.h>

    ... An implementation shall provide those types described as ‘‘required’’,
    but need not provide any of the others (described as ‘‘optional’’).
    ...
    The following types are required:
    int_least8_t  uint_least8_t
    int_least16_t uint_least16_t
    int_least32_t uint_least32_t
    int_least64_t uint_least64_t
    All other types of this form are optional.

Thus, in general, C standard can't guarantee types with fixed sizes. But most compilers (including gcc) support this feature.

What is time_t ultimately a typedef to?

Under Visual Studio 2008, it defaults to an __int64 unless you define _USE_32BIT_TIME_T. You're better off just pretending that you don't know what it's defined as, since it can (and will) change from platform to platform.

Get data type of field in select statement in ORACLE

I came into the same situation. As a workaround, I just created a view (If you have privileges) and described it and dropped it later. :)

How to determine a Python variable's type?

Just do not do it. Asking for something's type is wrong in itself. Instead use polymorphism. Find or if necessary define by yourself the method that does what you want for any possible type of input and just call it without asking about anything. If you need to work with built-in types or types defined by a third-party library, you can always inherit from them and use your own derivatives instead. Or you can wrap them inside your own class. This is the object-oriented way to resolve such problems.

If you insist on checking exact type and placing some dirty ifs here and there, you can use __class__ property or type function to do it, but soon you will find yourself updating all these ifs with additional cases every two or three commits. Doing it the OO way prevents that and lets you only define a new class for a new type of input instead.

List vs tuple, when to use each?

The first thing you need to decide is whether the data structure needs to be mutable or not. As has been mentioned, lists are mutable, tuples are not. This also means that tuples can be used for dictionary keys, wheres lists cannot.

In my experience, tuples are generally used where order and position is meaningful and consistant. For example, in creating a data structure for a choose your own adventure game, I chose to use tuples instead of lists because the position in the tuple was meaningful. Here is one example from that data structure:

pages = {'foyer': {'text' : "some text", 
          'choices' : [('open the door', 'rainbow'),
                     ('go left into the kitchen', 'bottomless pit'),
                     ('stay put','foyer2')]},}

The first position in the tuple is the choice displayed to the user when they play the game and the second position is the key of the page that choice goes to and this is consistent for all pages.

Tuples are also more memory efficient than lists, though I'm not sure when that benefit becomes apparent.

Also check out the chapters on lists and tuples in Think Python.

Import Package Error - Cannot Convert between Unicode and Non Unicode String Data Type

At some point, you're trying to convert an nvarchar column to a varchar column (or vice-versa).

Moreover, why is everything (supposedly) nvarchar(max)? That's a code smell if I ever saw one. Are you aware of how SQL Server stores those columns? They use pointers to where the column is stored from the actual rows, since they don't fit within the 8k pages.

"X does not name a type" error in C++

  1. Forward declare User
  2. Put the declaration of MyMessageBox before User

How To Change DataType of a DataColumn in a DataTable?

Dim tblReady1 As DataTable = tblReady.Clone()

'' convert all the columns type to String 
For Each col As DataColumn In tblReady1.Columns
  col.DataType = GetType(String)
Next

tblReady1.Load(tblReady.CreateDataReader)

Comparing Class Types in Java

Comparing an object with a class using instanceOf or ... is already answered.

If you have two objects and you want to compare their types with each other, you can use:

if (obj1.getClass() == obj2.getClass()) {
   // Both have the same type
}

Converting stream of int's to char's in java

Simple casting:

int a = 99;
char c = (char) a;

Is there any reason this is not working for you?

Objective-C : BOOL vs bool

Another difference between bool and BOOL is that they do not convert exactly to the same kind of objects, when you do key-value observing, or when you use methods like -[NSObject valueForKey:].

As everybody has said here, BOOL is char. As such, it is converted to an NSNumber holding a char. This object is indistinguishable from an NSNumber created from a regular char like 'A' or '\0'. You have totally lost the information that you originally had a BOOL.

However, bool is converted to an CFBoolean, which behaves the same as NSNumber, but which retains the boolean origin of the object.

I do not think that this is an argument in a BOOL vs. bool debate, but this may bite you one day.

Generally speaking, you should go with BOOL, since this is the type used everywhere in the Cocoa/iOS APIs (designed before C99 and its native bool type).

Hashmap holding different data types as values for instance Integer, String and Object

You have some variables that are different types in Java language like that:

 message of type string
 timestamp of type time
 count of type integer
 version of type integer

If you use a HashMap like:

HashMap<String,Object> yourHash = new HashMap<String,Object>();
yourHash.put("message","message");
yourHash.put("timestamp",timestamp);
yourHash.put("count ",count);
yourHash.put("version ",version);

If you want to use the yourHash:

for(String key : yourHash.keySet()){
  String message = (String) yourHash.get(key);
  Datetime timestamp= (Datetime) yourHash.get(key);
  int timestamp= (int) yourHash.get(key);
}

mysql datatype for telephone number and address

Well, personally I do not use numeric datatype to store phone numbers or related info.

How do you store a number say 001234567? It'll end up as 1234567, losing the leading zeros.

Of course you can always left-pad it up, but that's provided you know exactly how many digits the number should be.

This doesn't answer your entire post,
Just my 2 cents

Float vs Decimal in ActiveRecord

In Rails 3.2.18, :decimal turns into :integer when using SQLServer, but it works fine in SQLite. Switching to :float solved this issue for us.

The lesson learned is "always use homogeneous development and deployment databases!"

What is dtype('O'), in pandas?

It means "a python object", i.e. not one of the builtin scalar types supported by numpy.

np.array([object()]).dtype
=> dtype('O')

type checking in javascript

Quite a few utility libraries such as YourJS offer functions for determining if something is an array or if something is an integer or a lot of other types as well. YourJS defines isInt by checking if the value is a number and then if it is divisible by 1:

function isInt(x) {
  return typeOf(x, 'Number') && x % 1 == 0;
}

The above snippet was taken from this YourJS snippet and thusly only works because typeOf is defined by the library. You can download a minimalistic version of YourJS which mainly only has type checking functions such as typeOf(), isInt() and isArray(): http://yourjs.com/snippets/build/34,2

Common MySQL fields and their appropriate data types

Since you're going to be dealing with data of a variable length (names, email addresses), then you'd be wanting to use VARCHAR. The amount of space taken up by a VARCHAR field is [field length] + 1 bytes, up to max length 255, so I wouldn't worry too much about trying to find a perfect size. Take a look at what you'd imagine might be the longest length might be, then double it and set that as your VARCHAR limit. That said...:

I generally set email fields to be VARCHAR(100) - i haven't come up with a problem from that yet. Names I set to VARCHAR(50).

As the others have said, phone numbers and zip/postal codes are not actually numeric values, they're strings containing the digits 0-9 (and sometimes more!), and therefore you should treat them as a string. VARCHAR(20) should be well sufficient.

Note that if you were to store phone numbers as integers, many systems will assume that a number starting with 0 is an octal (base 8) number! Therefore, the perfectly valid phone number "0731602412" would get put into your database as the decimal number "124192010"!!

Check if a value is an object in JavaScript

you can just use JSON.stringify to test your Object, like this:

_x000D_
_x000D_
var test = {}_x000D_
if(JSON.stringify(test)[0] === '{') {_x000D_
  console.log('this is a Object')_x000D_
}
_x000D_
_x000D_
_x000D_

How to cast Object to its actual type?

If multiple types are possible, the method itself does not know the type to cast, but the caller does, you might use something like this:

void TheObliviousHelperMethod<T>(object obj) {
    (T)obj.ThatClassMethodYouWantedToInvoke();
}

// Meanwhile, where the method is called:
TheObliviousHelperMethod<ActualType>(obj);

Restrictions on the type could be added using the where keyword after the parentheses.

Passing just a type as a parameter in C#

You can do this, just wrap it in typeof()

foo.GetColumnValues(typeof(int))

public void GetColumnValues(Type type)
{
    //logic
}

Casting a variable using a Type variable

After not finding anything to get around "Object must implement IConvertible" exception when using Zyphrax's answer (except for implementing the interface).. I tried something a little bit unconventional and worked for my situation.

Using the Newtonsoft.Json nuget package...

var castedObject = JsonConvert.DeserializeObject(JsonConvert.SerializeObject(myObject), myType);

What is the purpose of a question mark after a type (for example: int? myVariable)?

practical usage:

public string someFunctionThatMayBeCalledWithNullAndReturnsString(int? value)
{
  if (value == null)
  {
    return "bad value";
  }

  return someFunctionThatHandlesIntAndReturnsString(value);
}

What is uintptr_t data type

There are already many good answers to the part "what is uintptr_t data type". I will try to address the "what it can be used for?" part in this post.

Primarily for bitwise operations on pointers. Remember that in C++ one cannot perform bitwise operations on pointers. For reasons see Why can't you do bitwise operations on pointer in C, and is there a way around this?

Thus in order to do bitwise operations on pointers one would need to cast pointers to type unitpr_t and then perform bitwise operations.

Here is an example of a function that I just wrote to do bitwise exclusive or of 2 pointers to store in a XOR linked list so that we can traverse in both directions like a doubly linked list but without the penalty of storing 2 pointers in each node.

 template <typename T>
 T* xor_ptrs(T* t1, T* t2)
 {
     return reinterpret_cast<T*>(reinterpret_cast<uintptr_t>(t1)^reinterpret_cast<uintptr_t>(t2));
  }

How to round up integer division and have int result in Java?

Use Math.ceil() and cast the result to int:

  • This is still faster than to avoid doubles by using abs().
  • The result is correct when working with negatives, because -0.999 will be rounded UP to 0

Example:

(int) Math.ceil((double)divident / divisor);

C# string reference type?

If we have to answer the question: String is a reference type and it behaves as a reference. We pass a parameter that holds a reference to, not the actual string. The problem is in the function:

public static void TestI(string test)
{
    test = "after passing";
}

The parameter test holds a reference to the string but it is a copy. We have two variables pointing to the string. And because any operations with strings actually create a new object, we make our local copy to point to the new string. But the original test variable is not changed.

The suggested solutions to put ref in the function declaration and in the invocation work because we will not pass the value of the test variable but will pass just a reference to it. Thus any changes inside the function will reflect the original variable.

I want to repeat at the end: String is a reference type but since its immutable the line test = "after passing"; actually creates a new object and our copy of the variable test is changed to point to the new string.

Append a tuple to a list - what's the difference between two ways?

It has nothing to do with append. tuple(3, 4) all by itself raises that error.

The reason is that, as the error message says, tuple expects an iterable argument. You can make a tuple of the contents of a single object by passing that single object to tuple. You can't make a tuple of two things by passing them as separate arguments.

Just do (3, 4) to make a tuple, as in your first example. There's no reason not to use that simple syntax for writing a tuple.

What are POD types in C++?

The concept of POD and the type trait std::is_pod will be deprecated in C++20. See this question for further information.

Change column type in pandas

Starting pandas 1.0.0, we have pandas.DataFrame.convert_dtypes. You can even control what types to convert!

In [40]: df = pd.DataFrame(
    ...:     {
    ...:         "a": pd.Series([1, 2, 3], dtype=np.dtype("int32")),
    ...:         "b": pd.Series(["x", "y", "z"], dtype=np.dtype("O")),
    ...:         "c": pd.Series([True, False, np.nan], dtype=np.dtype("O")),
    ...:         "d": pd.Series(["h", "i", np.nan], dtype=np.dtype("O")),
    ...:         "e": pd.Series([10, np.nan, 20], dtype=np.dtype("float")),
    ...:         "f": pd.Series([np.nan, 100.5, 200], dtype=np.dtype("float")),
    ...:     }
    ...: )

In [41]: dff = df.copy()

In [42]: df 
Out[42]: 
   a  b      c    d     e      f
0  1  x   True    h  10.0    NaN
1  2  y  False    i   NaN  100.5
2  3  z    NaN  NaN  20.0  200.0

In [43]: df.dtypes
Out[43]: 
a      int32
b     object
c     object
d     object
e    float64
f    float64
dtype: object

In [44]: df = df.convert_dtypes()

In [45]: df.dtypes
Out[45]: 
a      Int32
b     string
c    boolean
d     string
e      Int64
f    float64
dtype: object

In [46]: dff = dff.convert_dtypes(convert_boolean = False)

In [47]: dff.dtypes
Out[47]: 
a      Int32
b     string
c     object
d     string
e      Int64
f    float64
dtype: object

TypeError: 'str' object cannot be interpreted as an integer

A simplest fix would be:

x = input("Give starting number: ")
y = input("Give ending number: ")

x = int(x)  # parse string into an integer
y = int(y)  # parse string into an integer

for i in range(x,y):
    print(i)

input returns you a string (raw_input in Python 2). int tries to parse it into an integer. This code will throw an exception if the string doesn't contain a valid integer string, so you'd probably want to refine it a bit using try/except statements.

How to create a new object instance from a Type

Its pretty simple. Assume that your classname is Car and the namespace is Vehicles, then pass the parameter as Vehicles.Car which returns object of type Car. Like this you can create any instance of any class dynamically.

public object GetInstance(string strNamesapace)
{         
     Type t = Type.GetType(strNamesapace); 
     return  Activator.CreateInstance(t);         
}

If your Fully Qualified Name(ie, Vehicles.Car in this case) is in another assembly, the Type.GetType will be null. In such cases, you have loop through all assemblies and find the Type. For that you can use the below code

public object GetInstance(string strFullyQualifiedName)
{
     Type type = Type.GetType(strFullyQualifiedName);
     if (type != null)
         return Activator.CreateInstance(type);
     foreach (var asm in AppDomain.CurrentDomain.GetAssemblies())
     {
         type = asm.GetType(strFullyQualifiedName);
         if (type != null)
             return Activator.CreateInstance(type);
     }
     return null;
 }

And you can get the instance by calling the above method.

object objClassInstance = GetInstance("Vehicles.Car");

what is the unsigned datatype?

In C and C++

unsigned = unsigned int (Integer type)
signed   = signed int (Integer type)

An unsigned integer containing n bits can have a value between 0 and (2^n-1) , which is 2^n different values.

An unsigned integer is either positive or zero.

Signed integers are stored in a computer using 2's complement.

Why SQL Server throws Arithmetic overflow error converting int to data type numeric?

Numeric defines the TOTAL number of digits, and then the number after the decimal.

A numeric(3,2) can only hold up to 9.99.

What is the difference between old style and new style classes in Python?

Old style classes are still marginally faster for attribute lookup. This is not usually important, but it may be useful in performance-sensitive Python 2.x code:

In [3]: class A:
   ...:     def __init__(self):
   ...:         self.a = 'hi there'
   ...:

In [4]: class B(object):
   ...:     def __init__(self):
   ...:         self.a = 'hi there'
   ...:

In [6]: aobj = A()
In [7]: bobj = B()

In [8]: %timeit aobj.a
10000000 loops, best of 3: 78.7 ns per loop

In [10]: %timeit bobj.a
10000000 loops, best of 3: 86.9 ns per loop

What data type to use for money in Java?

For simple case (one currency) it'is enough int/long. Keep money in cents (...) or hundredth / thousandth of cents (any precision you need with fixed divider)

Why in C++ do we use DWORD rather than unsigned int?

For myself, I would assume unsigned int is platform specific. Integer could be 8 bits, 16 bits, 32 bits or even 64 bits.

DWORD in the other hand, specifies its own size, which is Double Word. Word are 16 bits so DWORD will be known as 32 bit across all platform

long long in C/C++

Try:

num3 = 100000000000LL;

And BTW, in C++ this is a compiler extension, the standard does not define long long, thats part of C99.

Where in memory are my variables stored in C?

For those future visitors who may be interested in knowing about those memory segments, I am writing important points about 5 memory segments in C:

Some heads up:

  1. Whenever a C program is executed some memory is allocated in the RAM for the program execution. This memory is used for storing the frequently executed code (binary data), program variables, etc. The below memory segments talks about the same:
  2. Typically there are three types of variables:
    • Local variables (also called as automatic variables in C)
    • Global variables
    • Static variables
    • You can have global static or local static variables, but the above three are the parent types.

5 Memory Segments in C:

1. Code Segment

  • The code segment, also referred as the text segment, is the area of memory which contains the frequently executed code.
  • The code segment is often read-only to avoid risk of getting overridden by programming bugs like buffer-overflow, etc.
  • The code segment does not contain program variables like local variable (also called as automatic variables in C), global variables, etc.
  • Based on the C implementation, the code segment can also contain read-only string literals. For example, when you do printf("Hello, world") then string "Hello, world" gets created in the code/text segment. You can verify this using size command in Linux OS.
  • Further reading

Data Segment

The data segment is divided in the below two parts and typically lies below the heap area or in some implementations above the stack, but the data segment never lies between the heap and stack area.

2. Uninitialized data segment

  • This segment is also known as bss.
  • This is the portion of memory which contains:
    1. Uninitialized global variables (including pointer variables)
    2. Uninitialized constant global variables.
    3. Uninitialized local static variables.
  • Any global or static local variable which is not initialized will be stored in the uninitialized data segment
  • For example: global variable int globalVar; or static local variable static int localStatic; will be stored in the uninitialized data segment.
  • If you declare a global variable and initialize it as 0 or NULL then still it would go to uninitialized data segment or bss.
  • Further reading

3. Initialized data segment

  • This segment stores:
    1. Initialized global variables (including pointer variables)
    2. Initialized constant global variables.
    3. Initialized local static variables.
  • For example: global variable int globalVar = 1; or static local variable static int localStatic = 1; will be stored in initialized data segment.
  • This segment can be further classified into initialized read-only area and initialized read-write area. Initialized constant global variables will go in the initialized read-only area while variables whose values can be modified at runtime will go in the initialized read-write area.
  • The size of this segment is determined by the size of the values in the program's source code, and does not change at run time.
  • Further reading

4. Stack Segment

  • Stack segment is used to store variables which are created inside functions (function could be main function or user-defined function), variable like
    1. Local variables of the function (including pointer variables)
    2. Arguments passed to function
    3. Return address
  • Variables stored in the stack will be removed as soon as the function execution finishes.
  • Further reading

5. Heap Segment

  • This segment is to support dynamic memory allocation. If the programmer wants to allocate some memory dynamically then in C it is done using the malloc, calloc, or realloc methods.
  • For example, when int* prt = malloc(sizeof(int) * 2) then eight bytes will be allocated in heap and memory address of that location will be returned and stored in ptr variable. The ptr variable will be on either the stack or data segment depending on the way it is declared/used.
  • Further reading

Converting std::__cxx11::string to std::string

I had a similar issue recently while trying to link with the pre-built binaries of hdf5 version 1.10.5 on Ubuntu 16.04. None of the solutions suggested here worked for me, and I was using g++ version 9.1. I found that the best solution is to build the hdf5 library from source. Do not use the pre-built binaries since these were built using gcc 4.9! Instead, download the source code archives from the hdf website for your particular distribution and build the library. It is very easy.

You will also need the compression libraries zlib and szip from here and here, respectively, if you do not already have them on your system.

When to use std::size_t?

size_t is an unsigned type that can hold maximum integer value for your architecture, so it is protected from integer overflows due to sign (signed int 0x7FFFFFFF incremented by 1 will give you -1) or short size (unsigned short int 0xFFFF incremented by 1 will give you 0).

It is mainly used in array indexing/loops/address arithmetic and so on. Functions like memset() and alike accept size_t only, because theoretically you may have a block of memory of size 2^32-1 (on 32bit platform).

For such simple loops don't bother and use just int.

What is SYSNAME data type in SQL Server?

Let me list a use case below. Hope it helps. Here I'm trying to find the Table Owner of the Table 'Stud_dtls' from the DB 'Students'. As Mikael mentioned, sysname could be used when there is a need for creating some dynamic sql which needs variables holding table names, column names and server names. Just thought of providing a simple example to supplement his point.

USE Students

DECLARE @TABLE_NAME sysname

SELECT @TABLE_NAME = 'Stud_dtls'

SELECT TABLE_SCHEMA 
  FROM INFORMATION_SCHEMA.Tables
 WHERE TABLE_NAME = @TABLE_NAME

What is the size of column of int(11) in mysql in bytes?

4294967295 is the answer, because int(11) shows maximum of 11 digits IMO

Size of character ('a') in C/C++

As Paul stated, it's because 'a' is an int in C but a char in C++.

I cover that specific difference between C and C++ in something I wrote a few years ago, at: http://david.tribble.com/text/cdiffs.htm

Defining TypeScript callback type

I just found something in the TypeScript language specification, it's fairly easy. I was pretty close.

the syntax is the following:

public myCallback: (name: type) => returntype;

In my example, it would be

class CallbackTest
{
    public myCallback: () => void;

    public doWork(): void
    {
        //doing some work...
        this.myCallback(); //calling callback
    }
}

What's the canonical way to check for type in Python?

For more complex type validations I like typeguard's approach of validating based on python type hint annotations:

from typeguard import check_type
from typing import List

try:
    check_type('mylist', [1, 2], List[int])
except TypeError as e:
    print(e)

You can perform very complex validations in very clean and readable fashion.

check_type('foo', [1, 3.14], List[Union[int, float]])
# vs
isinstance(foo, list) and all(isinstance(a, (int, float)) for a in foo) 

What is the benefit of zerofill in MySQL?

When you select a column with type ZEROFILL it pads the displayed value of the field with zeros up to the display width specified in the column definition. Values longer than the display width are not truncated. Note that usage of ZEROFILL also implies UNSIGNED.

Using ZEROFILL and a display width has no effect on how the data is stored. It affects only how it is displayed.

Here is some example SQL that demonstrates the use of ZEROFILL:

CREATE TABLE yourtable (x INT(8) ZEROFILL NOT NULL, y INT(8) NOT NULL);
INSERT INTO yourtable (x,y) VALUES
(1, 1),
(12, 12),
(123, 123),
(123456789, 123456789);
SELECT x, y FROM yourtable;

Result:

        x          y
 00000001          1
 00000012         12
 00000123        123
123456789  123456789

How can I check if my python object is a number?

Use Number from the numbers module to test isinstance(n, Number) (available since 2.6).

isinstance(n, numbers.Number)

Here it is in action with various kinds of numbers and one non-number:

>>> from numbers import Number
... from decimal import Decimal
... from fractions import Fraction
... for n in [2, 2.0, Decimal('2.0'), complex(2,0), Fraction(2,1), '2']:
...     print '%15s %s' % (n.__repr__(), isinstance(n, Number))
              2 True
            2.0 True
 Decimal('2.0') True
         (2+0j) True
 Fraction(2, 1) True
            '2' False

This is, of course, contrary to duck typing. If you are more concerned about how an object acts rather than what it is, perform your operations as if you have a number and use exceptions to tell you otherwise.

Git ignore local file changes

git pull wants you to either remove or save your current work so that the merge it triggers doesn't cause conflicts with your uncommitted work. Note that you should only need to remove/save untracked files if the changes you're pulling create files in the same locations as your local uncommitted files.

Remove your uncommitted changes

Tracked files

git checkout -f

Untracked files

git clean -fd

Save your changes for later

Tracked files

git stash

Tracked files and untracked files

git stash -u

Reapply your latest stash after git pull:

git stash pop

Run a single test method with maven

What I do with my TestNG, (sorry, JUnit doesn't support this) test cases is I can assign a group to the test I want to run

@Test(groups="broken")

And then simply run 'mvn -Dgroups=broken'.

How to delete last item in list?

you should use this

del record[-1]

The problem with

record = record[:-1]

Is that it makes a copy of the list every time you remove an item, so isn't very efficient

Do I need to close() both FileReader and BufferedReader?

The source code for BufferedReader shows that the underlying is closed when you close the BufferedReader.

Calculate RSA key fingerprint

This is the shell function I use to get my SSH key finger print for creating DigitalOcean droplets:

fingerprint() {
    pubkeypath="$1"
    ssh-keygen -E md5 -lf "$pubkeypath" | awk '{ print $2 }' | cut -c 5-
}

Put it in your ~/.bashrc, source it, and then you can get the finger print as so:

$ fingerprint ~/.ssh/id_rsa.pub
d2:47:0a:87:30:a0:c0:df:6b:42:19:55:b4:f3:09:b9

Java Singleton and Synchronization

What is the best way to implement Singleton in Java, in a multithreaded environment?

Refer to this post for best way to implement Singleton.

What is an efficient way to implement a singleton pattern in Java?

What happens when multiple threads try to access getInstance() method at the same time?

It depends on the way you have implemented the method.If you use double locking without volatile variable, you may get partially constructed Singleton object.

Refer to this question for more details:

Why is volatile used in this example of double checked locking

Can we make singleton's getInstance() synchronized?

Is synchronization really needed, when using Singleton classes?

Not required if you implement the Singleton in below ways

  1. static intitalization
  2. enum
  3. LazyInitalaization with Initialization-on-demand_holder_idiom

Refer to this question fore more details

Java Singleton Design Pattern : Questions

No Exception while type casting with a null in java

Println(Object) uses String.valueOf()

public static String valueOf(Object obj) {
    return (obj == null) ? "null" : obj.toString();
}

Print(String) does null check.

public void print(String s) {
    if (s == null) {
        s = "null";
    }
    write(s);
}

Custom HTTP headers : naming conventions

Modifying, or more correctly, adding additional HTTP headers is a great code debugging tool if nothing else.

When a URL request returns a redirect or an image there is no html "page" to temporarily write the results of debug code to - at least not one that is visible in a browser.

One approach is to write the data to a local log file and view that file later. Another is to temporarily add HTTP headers reflecting the data and variables being debugged.

I regularly add extra HTTP headers like X-fubar-somevar: or X-testing-someresult: to test things out - and have found a lot of bugs that would have otherwise been very difficult to trace.

What evaluates to True/False in R?

T and TRUE are True, F and FALSE are False. T and F can be redefined, however, so you should only rely upon TRUE and FALSE. If you compare 0 to FALSE and 1 to TRUE, you will find that they are equal as well, so you might consider them to be True and False as well.

Spark Kill Running Application

It may be time consuming to get all the application Ids from YARN and kill them one by one. You can use a Bash for loop to accomplish this repetitive task quickly and more efficiently as shown below:

Kill all applications on YARN which are in ACCEPTED state:

for x in $(yarn application -list -appStates ACCEPTED | awk 'NR > 2 { print $1 }'); do yarn application -kill $x; done

Kill all applications on YARN which are in RUNNING state:

for x in $(yarn application -list -appStates RUNNING | awk 'NR > 2 { print $1 }'); do yarn application -kill $x; done

SQL query with avg and group by

As I understand, you want the average value for each id at each pass. The solution is

SELECT id, pass, avg(value) FROM data_r1
GROUP BY id, pass;

Java converting int to hex and back again

Using Integer.toHexString(...) is a good answer. But personally prefer to use String.format(...).

Try this sample as a test.

byte[] values = new byte[64];
Arrays.fill(values, (byte)8);  //Fills array with 8 just for test
String valuesStr = "";
for(int i = 0; i < values.length; i++)
    valuesStr += String.format("0x%02x", values[i] & 0xff) + " ";
valuesStr.trim();

Export to csv/excel from kibana

I totally missed the export button at the bottom of each visualization. As for read only access...Shield from Elasticsearch might be worth exploring.

Automatically plot different colored lines

You could use a colormap such as HSV to generate a set of colors. For example:

cc=hsv(12);
figure; 
hold on;
for i=1:12
    plot([0 1],[0 i],'color',cc(i,:));
end

MATLAB has 13 different named colormaps ('doc colormap' lists them all).

Another option for plotting lines in different colors is to use the LineStyleOrder property; see Defining the Color of Lines for Plotting in the MATLAB documentation for more information.

error LNK2038: mismatch detected for '_ITERATOR_DEBUG_LEVEL': value '0' doesn't match value '2' in main.obj

If you would like to purposely link your project A in Release against another project B in Debug, say to keep the overall performance benefits of your application while debugging, then you will likely hit this error. You can fix this by temporarily modifying the preprocessor flags of project B to disable iterator debugging (and make it match project A):

In Project B's "Debug" properties, Configuration Properties -> C/C++ -> Preprocessor, add the following to Preprocessor Definitions:

_HAS_ITERATOR_DEBUGGING=0;_ITERATOR_DEBUG_LEVEL=0;

Rebuild project B in Debug, then build project A in Release and it should link correctly.

CORS with spring-boot and angularjs not working

I had been into the similar situation. After doing research and testing, here is my findings:

  1. With Spring Boot, the recommended way to enable global CORS is to declare within Spring MVC and combined with fine-grained @CrossOrigin configuration as:

    @Configuration
    public class CorsConfig {
    
        @Bean
        public WebMvcConfigurer corsConfigurer() {
            return new WebMvcConfigurerAdapter() {
                @Override
                public void addCorsMappings(CorsRegistry registry) {
                    registry.addMapping("/**").allowedMethods("GET", "POST", "PUT", "DELETE").allowedOrigins("*")
                            .allowedHeaders("*");
                }
            };
        }
    }
    
  2. Now, since you are using Spring Security, you have to enable CORS at Spring Security level as well to allow it to leverage the configuration defined at Spring MVC level as:

    @EnableWebSecurity
    public class WebSecurityConfig extends WebSecurityConfigurerAdapter {
    
        @Override
        protected void configure(HttpSecurity http) throws Exception {
            http.cors().and()...
        }
    }
    

    Here is very excellent tutorial explaining CORS support in Spring MVC framework.

AngularJS - Create a directive that uses ng-model

I wouldn't set the ngmodel via an attribute, you can specify it right in the template:

template: '<div class="some"><label>{{label}}</label><input data-ng-model="ngModel"></div>',

plunker: http://plnkr.co/edit/9vtmnw?p=preview

When to use pthread_exit() and when to use pthread_join() in Linux?

As explained in the openpub documentations,

pthread_exit() will exit the thread that calls it.

In your case since the main calls it, main thread will terminate whereas your spawned threads will continue to execute. This is mostly used in cases where the main thread is only required to spawn threads and leave the threads to do their job

pthread_join will suspend execution of the thread that has called it unless the target thread terminates

This is useful in cases when you want to wait for thread/s to terminate before further processing in main thread.

git push vs git push origin <branchname>

First, you need to create your branch locally

git checkout -b your_branch

After that, you can work locally in your branch, when you are ready to share the branch, push it. The next command push the branch to the remote repository origin and tracks it

git push -u origin your_branch

Your Teammates/colleagues can push to your branch by doing commits and then push explicitly

... work ...
git commit
... work ...
git commit
git push origin HEAD:refs/heads/your_branch 

go to link on button click - jquery

$('.button1').click(function() {
   window.location = "www.example.com/index.php?id=" + this.id;
});

First of all using window.location is better as according to specification document.location value was read-only and might cause you headaches in older/different browsers. Check notes @MDC DOM document.location page

And for the second - using attr jQuery method to get id is a bad practice - you should use direct native DOM accessor this.id as the value assigned to this is normal DOM element.

Log all queries in mysql

Top answer doesn't work in mysql 5.6+. Use this instead:

[mysqld]
general_log = on
general_log_file=/usr/log/general.log

in your my.cnf / my.ini file

Ubuntu/Debian: /etc/mysql/my.cnf
Windows: c:\ProgramData\MySQL\MySQL Server 5.x
wamp: c:\wamp\bin\mysql\mysqlx.y.z\my.ini
xampp: c:\xampp\mysql\bin\my.ini.

How to check if an object is defined?

You check if it's null in C# like this:

if(MyObject != null) {
  //do something
}

If you want to check against default (tough to understand the question on the info given) check:

if(MyObject != default(MyObject)) {
 //do something
}

Where is Ubuntu storing installed programs?

Simply, type the command:

~$ whereis "program name"

How can I reverse the order of lines in a file?

Best solution:

tail -n20 file.txt | tac

How to set background image in Java?

The Path is the only thing you really have to worry about if you are really new to Java. You need to drag your image into the main project file, and it will show up at the very bottom of the list.

Then the file path is pretty straight forward. This code goes into the constructor for the class.

    img = Toolkit.getDefaultToolkit().createImage("/home/ben/workspace/CS2/Background.jpg");

CS2 is the name of my project, and everything before that is leading to the workspace.

Perform curl request in javascript?

You can use JavaScripts Fetch API (available in your browser) to make network requests.

If using node, you will need to install the node-fetch package.

const url = "https://api.wit.ai/message?v=20140826&q=";

const options = {
  headers: {
    Authorization: "Bearer 6Q************"
  }
};

fetch(url, options)
  .then( res => res.json() )
  .then( data => console.log(data) );

ffmpeg - Converting MOV files to MP4

The command to just stream it to a new container (mp4) needed by some applications like Adobe Premiere Pro without encoding (fast) is:

ffmpeg -i input.mov -qscale 0 output.mp4

Alternative as mentioned in the comments, which re-encodes with best quaility (-qscale 0):

ffmpeg -i input.mov -q:v 0 output.mp4

refresh div with jquery

I want to just refresh the div, without refreshing the page ... Is this possible?

Yes, though it isn't going to be obvious that it does anything unless you change the contents of the div.

If you just want the graphical fade-in effect, simply remove the .html(data) call:

$("#panel").hide().fadeIn('fast');

Here is a demo you can mess around with: http://jsfiddle.net/ZPYUS/

It changes the contents of the div without making an ajax call to the server, and without refreshing the page. The content is hard coded, though. You can't do anything about that fact without contacting the server somehow: ajax, some sort of sub-page request, or some sort of page refresh.

html:

<div id="panel">test data</div>
<input id="changePanel" value="Change Panel" type="button">?

javascript:

$("#changePanel").click(function() {
    var data = "foobar";
    $("#panel").hide().html(data).fadeIn('fast');
});?

css:

div {
    padding: 1em;
    background-color: #00c000;
}

input {
    padding: .25em 1em;
}?

how to set ulimit / file descriptor on docker container the image tag is phusion/baseimage-docker

For boot2docker, we can set it on /var/lib/boot2docker/profile, for instance:

ulimit -n 2018

Be warned not to set this limit too high as it will slow down apt-get! See bug #1332440. I had it with debian jessie.

What is the difference between a symbolic link and a hard link?

Some nice intuition that might help, using any Linux(ish) console.

Create two files:

$ touch foo; touch bar

Enter some Data into them:

$ echo "Cat" > foo
$ echo "Dog" > bar

(Actually, I could have used echo in the first place, as it creates the files if they don't exist... but never mind that.)

And as expected:

$cat foo; cat bar
Cat
Dog

Let's create hard and soft links:

$ ln foo foo-hard
$ ln -s bar bar-soft

Let's see what just happened:

$ ls -l

foo
foo-hard
bar
bar-soft -> bar

Changing the name of foo does not matter:

$ mv foo foo-new
$ cat foo-hard
Cat

foo-hard points to the inode, the contents, of the file - that wasn't changed.

$ mv bar bar-new
$ ls bar-soft
bar-soft
$ cat bar-soft  
cat: bar-soft: No such file or directory

The contents of the file could not be found because the soft link points to the name, that was changed, and not to the contents.

Likewise, If foo is deleted, foo-hard still holds the contents; if bar is deleted, bar-soft is just a link to a non-existing file.

Why should you use strncpy instead of strcpy?

The strncpy() function was designed with a very particular problem in mind: manipulating strings stored in the manner of original UNIX directory entries. These used a fixed sized array, and a nul-terminator was only used if the filename was shorter than the array.

That's what's behind the two oddities of strncpy():

  • It doesn't put a nul-terminator on the destination if it is completely filled; and
  • It always completely fills the destination, with nuls if necessary.

For a "safer strcpy()", you are better off using strncat() like so:

if (dest_size > 0)
{
    dest[0] = '\0';
    strncat(dest, source, dest_size - 1);
}

That will always nul-terminate the result, and won't copy more than necessary.

Qt c++ aggregate 'std::stringstream ss' has incomplete type and cannot be defined

Like it's written up there, you forget to type #include <sstream>

#include <sstream>
using namespace std;

QString Stats_Manager::convertInt(int num)
{
   stringstream ss;
   ss << num;
   return ss.str();
}

You can also use some other ways to convert int to string, like

char numstr[21]; // enough to hold all numbers up to 64-bits
sprintf(numstr, "%d", age);
result = name + numstr;

check this!

How to scroll table's "tbody" independent of "thead"?

thead {
  position: fixed;
  height: 10px; /* This is whatever height you want */
}
  tbody {
  position: fixed;
  margin-top: 10px; /* This has to match the height of thead */
  height: 300px; /* This is whatever height you want */
}

React Native Change Default iOS Simulator Device

I had an issue with XCode 10.2 specifying the correct iOS simulator version number, so used:

react-native run-ios --simulator='iPhone X (com.apple.CoreSimulator.SimRuntime.iOS-12-1)'

Scraping: SSL: CERTIFICATE_VERIFY_FAILED error for http://en.wikipedia.org

Two steps worked for me : - going Macintosh HD > Applications > Python3.7 folder - click on "Install Certificates.command"

Loop through all the files with a specific extension

Recursively add subfolders,

for i in `find . -name "*.java" -type f`; do
    echo "$i"
done

linq query to return distinct field values from a list of objects

If just want to user pure Linq, you can use groupby:

List<obj> distinct =
  objs.GroupBy(car => car.typeID).Select(g => g.First()).ToList();

If you want a method to be used all across the app, similar to what MoreLinq does:

public static IEnumerable<TSource> DistinctBy<TSource, TKey>
    (this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
{
    HashSet<TKey> seenKeys = new HashSet<TKey>();
    foreach (TSource element in source)
    {
        if (!seenKeys.Contains(keySelector(element)))
        {
            seenKeys.Add(keySelector(element));
            yield return element;
        }
    }
}

Using this method to find the distinct values using just the Id property, you could use:

var query = objs.DistinctBy(p => p.TypeId);

you can use multiple properties:

var query = objs.DistinctBy(p => new { p.TypeId, p.Name });

How do you allow spaces to be entered using scanf?

/*reading string which contains spaces*/
#include<stdio.h>
int main()
{
   char *c,*p;
   scanf("%[^\n]s",c);
   p=c;                /*since after reading then pointer points to another 
                       location iam using a second pointer to store the base 
                       address*/ 
   printf("%s",p);
   return 0;
 }

How can I switch views programmatically in a view controller? (Xcode, iPhone)

I think the OP is asking how to swap a VIEW without changing viewCONTROLLERs. Am I misunderstanding his question?

In pseudocode, he wants to do:

let myController = instantiate(someParentController)

let view1 = Bundle.main.loadNib(....) as... blah
myController.setThisViewTo( view1 )

let view2 = Bundle.main.loadNib(....) as... blah
myController.setThisViewTo( view2 )

Am I getting his question wrong?

ERROR: Cannot open source file " "

This was the top result when googling "cannot open source file" so I figured I would share what my issue was since I had already included the correct path.

I'm not sure about other IDEs or compilers, but least for Visual Studio, make sure there isn't a space in your list of include directories. I had put a space between the ; of the last entry and the beginning of my new entry which then caused Visual Studio to disregard my inclusion.

What is the difference between gravity and layout_gravity in Android?

Their names should help you:

  • android:gravity sets the gravity of the contents (i.e. its subviews) of the View it's used on.
  • android:layout_gravity sets the gravity of the View or Layout relative to its parent.

And an example is here.

Monad in plain English? (For the OOP programmer with no FP background)

A monad is an array of functions

(Pst: an array of functions is just a computation).

Actually, instead of a true array (one function in one cell array) you have those functions chained by another function >>=. The >>= allows to adapt the results from function i to feed function i+1, perform calculations between them or, even, not to call function i+1.

The types used here are "types with context". This is, a value with a "tag". The functions being chained must take a "naked value" and return a tagged result. One of the duties of >>= is to extract a naked value out of its context. There is also the function "return", that takes a naked value and puts it with a tag.

An example with Maybe. Let's use it to store a simple integer on which make calculations.

-- a * b
multiply :: Int -> Int -> Maybe Int
multiply a b = return  (a*b)

-- divideBy 5 100 = 100 / 5
divideBy :: Int -> Int -> Maybe Int
divideBy 0 _ = Nothing -- dividing by 0 gives NOTHING
divideBy denom num = return (quot num denom) -- quotient of num / denom

-- tagged value
val1 = Just 160 

-- array of functions feeded with val1
array1 = val1 >>= divideBy 2  >>= multiply 3 >>= divideBy  4 >>= multiply 3

-- array of funcionts created with the do notation
-- equals array1 but for the feeded val1
array2 :: Int -> Maybe Int
array2 n = do
       v <- divideBy 2  n
       v <- multiply 3 v
       v <- divideBy 4 v
       v <- multiply 3 v
       return v

-- array of functions, 
-- the first >>= performs 160 / 0, returning Nothing
-- the second >>= has to perform Nothing >>= multiply 3 ....
-- and simply returns Nothing without calling multiply 3 ....
array3 = val1 >>= divideBy 0  >>= multiply 3 >>= divideBy  4 >>= multiply 3

main = do
     print array1
     print (array2 160)
     print array3

Just to show that monads are array of functions with helper operations, consider the equivalent to the above example, just using a real array of functions

type MyMonad = [Int -> Maybe Int] -- my monad as a real array of functions

myArray1 = [divideBy 2, multiply 3, divideBy 4, multiply 3]

-- function for the machinery of executing each function i with the result provided by function i-1
runMyMonad :: Maybe Int -> MyMonad -> Maybe Int
runMyMonad val [] = val
runMyMonad Nothing _ = Nothing
runMyMonad (Just val) (f:fs) = runMyMonad (f val) fs

And it would be used like this:

print (runMyMonad (Just 160) myArray1)

Catching exceptions from Guzzle

Depending on your project, disabling exceptions for guzzle might be necessary. Sometimes coding rules disallow exceptions for flow control. You can disable exceptions for Guzzle 3 like this:

$client = new \Guzzle\Http\Client($httpBase, array(
  'request.options' => array(
     'exceptions' => false,
   )
));

This does not disable curl exceptions for something like timeouts, but now you can get every status code easily:

$request = $client->get($uri);
$response = $request->send();
$statuscode = $response->getStatusCode();

To check, if you got a valid code, you can use something like this:

if ($statuscode > 300) {
  // Do some error handling
}

... or better handle all expected codes:

if (200 === $statuscode) {
  // Do something
}
elseif (304 === $statuscode) {
  // Nothing to do
}
elseif (404 === $statuscode) {
  // Clean up DB or something like this
}
else {
  throw new MyException("Invalid response from api...");
}

For Guzzle 5.3

$client = new \GuzzleHttp\Client(['defaults' => [ 'exceptions' => false ]] );

Thanks to @mika

For Guzzle 6

$client = new \GuzzleHttp\Client(['http_errors' => false]);

What is the difference between a deep copy and a shallow copy?

I would like to give example rather than the formal definition.

var originalObject = { 
    a : 1, 
    b : 2, 
    c : 3,
};

This code shows a shallow copy:

var copyObject1 = originalObject;

console.log(copyObject1.a);         // it will print 1 
console.log(originalObject.a);       // it will also print 1 
copyObject1.a = 4; 
console.log(copyObject1.a);           //now it will print 4 
console.log(originalObject.a);       // now it will also print 4

var copyObject2 = Object.assign({}, originalObject);

console.log(copyObject2.a);        // it will print 1 
console.log(originalObject.a);      // it will also print 1 
copyObject2.a = 4; 
console.log(copyObject2.a);        // now it will print 4 
console.log(originalObject.a);      // now it will print 1

This code shows a deep copy:

var copyObject2 = Object.assign({}, originalObject);

console.log(copyObject2.a);        // it will print 1 
console.log(originalObject.a);      // it will also print 1 
copyObject2.a = 4; 
console.log(copyObject2.a);        // now it will print 4 
console.log(originalObject.a);      // !! now it will print 1 !!

regular expression to match exactly 5 digits

No need to care of whether before/after this digit having other type of words

To just match the pattern of 5 digits number anywhere in the string, no matter it is separated by space or not, use this regular expression (?<!\d)\d{5}(?!\d).

Sample JavaScript codes:

var regexp = new RegExp(/(?<!\d)\d{5}(?!\d)/g); 
    var matches = yourstring.match(regexp);
    if (matches && matches.length > 0) {
        for (var i = 0, len = matches.length; i < len; i++) {
            // ... ydo something with matches[i] ...
        } 
    }

Here's some quick results.

  • abc12345xyz (?)

  • 12345abcd (?)

  • abcd12345 (?)

  • 0000aaaa2 (?)

  • a1234a5 (?)

  • 12345 (?)

  • <space>12345<space>12345 (??)

What happens to C# Dictionary<int, int> lookup if the key does not exist?

Assuming you want to get the value if the key does exist, use Dictionary<TKey, TValue>.TryGetValue:

int value;
if (dictionary.TryGetValue(key, out value))
{
    // Key was in dictionary; "value" contains corresponding value
} 
else 
{
    // Key wasn't in dictionary; "value" is now 0
}

(Using ContainsKey and then the the indexer makes it look the key up twice, which is pretty pointless.)

Note that even if you were using reference types, checking for null wouldn't work - the indexer for Dictionary<,> will throw an exception if you request a missing key, rather than returning null. (This is a big difference between Dictionary<,> and Hashtable.)

batch script - run command on each file in directory

you can run something like this (paste the code bellow in a .bat, or if you want it to run interractively replace the %% by % :

for %%i in (c:\directory\*.xls) do ssconvert %%i %%i.xlsx

If you can run powershell it will be :

Get-ChildItem -Path c:\directory -filter *.xls | foreach {ssconvert $($_.FullName) $($_.baseName).xlsx }

phpmyadmin.pma_table_uiprefs doesn't exist

Clear your cookies

When using PHPMyAdmin configured with multiple databases, one having the phpmyadmin table and another not having it; phpmyadmin will store preferences for the database with the table in your cookies then try to load them with the database that doesn't have the table.

To test, try using an incognito window.

Temporarily change current working directory in bash to run a command

You can run the cd and the executable in a subshell by enclosing the command line in a pair of parentheses:

(cd SOME_PATH && exec_some_command)

Demo:

$ pwd
/home/abhijit
$ (cd /tmp && pwd)  # directory changed in the subshell
/tmp 
$ pwd               # parent shell's pwd is still the same
/home/abhijit

What are some examples of commonly used practices for naming git branches?

Here are some branch naming conventions that I use and the reasons for them

Branch naming conventions

  1. Use grouping tokens (words) at the beginning of your branch names.
  2. Define and use short lead tokens to differentiate branches in a way that is meaningful to your workflow.
  3. Use slashes to separate parts of your branch names.
  4. Do not use bare numbers as leading parts.
  5. Avoid long descriptive names for long-lived branches.

Group tokens

Use "grouping" tokens in front of your branch names.

group1/foo
group2/foo
group1/bar
group2/bar
group3/bar
group1/baz

The groups can be named whatever you like to match your workflow. I like to use short nouns for mine. Read on for more clarity.

Short well-defined tokens

Choose short tokens so they do not add too much noise to every one of your branch names. I use these:

wip       Works in progress; stuff I know won't be finished soon
feat      Feature I'm adding or expanding
bug       Bug fix or experiment
junk      Throwaway branch created to experiment

Each of these tokens can be used to tell you to which part of your workflow each branch belongs.

It sounds like you have multiple branches for different cycles of a change. I do not know what your cycles are, but let's assume they are 'new', 'testing' and 'verified'. You can name your branches with abbreviated versions of these tags, always spelled the same way, to both group them and to remind you which stage you're in.

new/frabnotz
new/foo
new/bar
test/foo
test/frabnotz
ver/foo

You can quickly tell which branches have reached each different stage, and you can group them together easily using Git's pattern matching options.

$ git branch --list "test/*"
test/foo
test/frabnotz

$ git branch --list "*/foo"
new/foo
test/foo
ver/foo

$ gitk --branches="*/foo"

Use slashes to separate parts

You may use most any delimiter you like in branch names, but I find slashes to be the most flexible. You might prefer to use dashes or dots. But slashes let you do some branch renaming when pushing or fetching to/from a remote.

$ git push origin 'refs/heads/feature/*:refs/heads/phord/feat/*'
$ git push origin 'refs/heads/bug/*:refs/heads/review/bugfix/*'

For me, slashes also work better for tab expansion (command completion) in my shell. The way I have it configured I can search for branches with different sub-parts by typing the first characters of the part and pressing the TAB key. Zsh then gives me a list of branches which match the part of the token I have typed. This works for preceding tokens as well as embedded ones.

$ git checkout new<TAB>
Menu:  new/frabnotz   new/foo   new/bar


$ git checkout foo<TAB>
Menu:  new/foo   test/foo   ver/foo

(Zshell is very configurable about command completion and I could also configure it to handle dashes, underscores or dots the same way. But I choose not to.)

It also lets you search for branches in many git commands, like this:

git branch --list "feature/*"
git log --graph --oneline --decorate --branches="feature/*" 
gitk --branches="feature/*" 

Caveat: As Slipp points out in the comments, slashes can cause problems. Because branches are implemented as paths, you cannot have a branch named "foo" and another branch named "foo/bar". This can be confusing for new users.

Do not use bare numbers

Do not use use bare numbers (or hex numbers) as part of your branch naming scheme. Inside tab-expansion of a reference name, git may decide that a number is part of a sha-1 instead of a branch name. For example, my issue tracker names bugs with decimal numbers. I name my related branches CRnnnnn rather than just nnnnn to avoid confusion.

$ git checkout CR15032<TAB>
Menu:   fix/CR15032    test/CR15032

If I tried to expand just 15032, git would be unsure whether I wanted to search SHA-1's or branch names, and my choices would be somewhat limited.

Avoid long descriptive names

Long branch names can be very helpful when you are looking at a list of branches. But it can get in the way when looking at decorated one-line logs as the branch names can eat up most of the single line and abbreviate the visible part of the log.

On the other hand long branch names can be more helpful in "merge commits" if you do not habitually rewrite them by hand. The default merge commit message is Merge branch 'branch-name'. You may find it more helpful to have merge messages show up as Merge branch 'fix/CR15032/crash-when-unformatted-disk-inserted' instead of just Merge branch 'fix/CR15032'.

Usage of unicode() and encode() functions in Python

Make sure you've set your locale settings right before running the script from the shell, e.g.

$ locale -a | grep "^en_.\+UTF-8"
en_GB.UTF-8
en_US.UTF-8
$ export LC_ALL=en_GB.UTF-8
$ export LANG=en_GB.UTF-8

Docs: man locale, man setlocale.

MSSQL Error 'The underlying provider failed on Open'

I had the same problem but what worked for me was removing this from the Connection String:

persist security info=True

How to convert DOS/Windows newline (CRLF) to Unix newline (LF) in a Bash script?

This worked for me

tr "\r" "\n" < sampledata.csv > sampledata2.csv 

Install tkinter for Python

The situation on macOS is still a bit complicated, but do-able:

Python.org strongly suggest downloading tkinter from ActiveState, but you should read their license first (hint: don't redistribute or want Support).

When the download is opened OS X 10.11 rejected it because it couldn't find my receipt: "ActiveTcl-8.6.pkg can’t be opened because it is from an unidentified developer".

I followed an OSXDaily fix from 2012 which suggested allowing from anywhere. But OS X has now added an "Open Anyway" option to allow (e.g.) Active-Tcl as a once off, and the "Anywhere" option has gained a timeout.

New warning for "Anywhere"

How to evaluate a boolean variable in an if block in bash?

Note that the if $myVar; then ... ;fi construct has a security problem you might want to avoid with

case $myvar in
  (true)    echo "is true";;
  (false)   echo "is false";;
  (rm -rf*) echo "I just dodged a bullet";;
esac

You might also want to rethink why if [ "$myvar" = "true" ] appears awkward to you. It's a shell string comparison that beats possibly forking a process just to obtain an exit status. A fork is a heavy and expensive operation, while a string comparison is dead cheap. Think a few CPU cycles versus several thousand. My case solution is also handled without forks.

Python3 project remove __pycache__ folders and .pyc files

The command I've used:

find . -type d -name "__pycache__" -exec rm -r {} +

Explains:

  1. First finds all __pycache__ folders in current directory.

  2. Execute rm -r {} + to delete each folder at step above ({} signify for placeholder and + to end the command)

Edited 1:

I'm using Linux, to reuse the command I've added the line below to the ~/.bashrc file

alias rm-pycache='find . -type d -name  "__pycache__" -exec rm -r {} +'

Edited 2: If you're using VS Code, you don't need to remove __pycache__ manually. You can add the snippet below to settings.json file. After that, VS Code will hide all __pycache__ folders for you

"files.exclude": {
     "**/__pycache__": true
}

Hope it helps !!!

Max size of an iOS application

With the release of iOS 7 (September 18th, 2013) apple increased the over-the-air cellular download limit to 100MBs.

Maximum app size remains 2GBs.

Source

How to open local files in Swagger-UI

With Firefox, I:

  1. Downloaded and unpacked a version of Swagger.IO to C:\Swagger\
  2. Created a folder called Definitions in C:\Swagger\dist
  3. Copied my swagger.json definition file there, and
  4. Entered "Definitions/MyDef.swagger.json" in the Explore box

Be careful of your slash directions!!

It seems you can drill down in folder structure but not up, annoyingly.

How do I find Waldo with Mathematica?

I don't know Mathematica . . . too bad. But I like the answer above, for the most part.

Still there is a major flaw in relying on the stripes alone to glean the answer (I personally don't have a problem with one manual adjustment). There is an example (listed by Brett Champion, here) presented which shows that they, at times, break up the shirt pattern. So then it becomes a more complex pattern.

I would try an approach of shape id and colors, along with spacial relations. Much like face recognition, you could look for geometric patterns at certain ratios from each other. The caveat is that usually one or more of those shapes is occluded.

Get a white balance on the image, and red a red balance from the image. I believe Waldo is always the same value/hue, but the image may be from a scan, or a bad copy. Then always refer to an array of the colors that Waldo actually is: red, white, dark brown, blue, peach, {shoe color}.

There is a shirt pattern, and also the pants, glasses, hair, face, shoes and hat that define Waldo. Also, relative to other people in the image, Waldo is on the skinny side.

So, find random people to obtain an the height of people in this pic. Measure the average height of a bunch of things at random points in the image (a simple outline will produce quite a few individual people). If each thing is not within some standard deviation from each other, they are ignored for now. Compare the average of heights to the image's height. If the ratio is too great (e.g., 1:2, 1:4, or similarly close), then try again. Run it 10(?) of times to make sure that the samples are all pretty close together, excluding any average that is outside some standard deviation. Possible in Mathematica?

This is your Waldo size. Walso is skinny, so you are looking for something 5:1 or 6:1 (or whatever) ht:wd. However, this is not sufficient. If Waldo is partially hidden, the height could change. So, you are looking for a block of red-white that ~2:1. But there has to be more indicators.

  1. Waldo has glasses. Search for two circles 0.5:1 above the red-white.
  2. Blue pants. Any amount of blue at the same width within any distance between the end of the red-white and the distance to his feet. Note that he wears his shirt short, so the feet are not too close.
  3. The hat. Red-white any distance up to twice the top of his head. Note that it must have dark hair below, and probably glasses.
  4. Long sleeves. red-white at some angle from the main red-white.
  5. Dark hair.
  6. Shoe color. I don't know the color.

Any of those could apply. These are also negative checks against similar people in the pic -- e.g., #2 negates wearing a red-white apron (too close to shoes), #5 eliminates light colored hair. Also, shape is only one indicator for each of these tests . . . color alone within the specified distance can give good results.

This will narrow down the areas to process.

Storing these results will produce a set of areas that should have Waldo in it. Exclude all other areas (e.g., for each area, select a circle twice as big as the average person size), and then run the process that @Heike laid out with removing all but red, and so on.

Any thoughts on how to code this?


Edit:

Thoughts on how to code this . . . exclude all areas but Waldo red, skeletonize the red areas, and prune them down to a single point. Do the same for Waldo hair brown, Waldo pants blue, Waldo shoe color. For Waldo skin color, exclude, then find the outline.

Next, exclude non-red, dilate (a lot) all the red areas, then skeletonize and prune. This part will give a list of possible Waldo center points. This will be the marker to compare all other Waldo color sections to.

From here, using the skeletonized red areas (not the dilated ones), count the lines in each area. If there is the correct number (four, right?), this is certainly a possible area. If not, I guess just exclude it (as being a Waldo center . . . it may still be his hat).

Then check if there is a face shape above, a hair point above, pants point below, shoe points below, and so on.

No code yet -- still reading the docs.

Java equivalent of unsigned long long?

Java 8 provides a set of unsigned long operations that allows you to directly treat those Long variables as unsigned Long, here're some commonly used ones:

And additions, subtractions, and multiplications are the same for signed and unsigned longs.

Get month and year from date cells Excel

I had a requirement to provide a report showing details by month where the date field was formatted as date & time, I simply changed the formatting of the date column to "General" and then used the following formula in a new column,

=CONCATENATE(YEAR(C2),MONTH(C2)) 

Declaring an enum within a class

If you are creating a code library, then I would use namespace. However, you can still only have one Color enum inside that namespace. If you need an enum that might use a common name, but might have different constants for different classes, use your approach.

Make a link in the Android browser start up my app?

This method doesn't call the disambiguation dialog asking you to open either your app or a browser.

If you register the following in your Manifest

<manifest package="com.myApp" .. >
  <application ...>
    <activity ...>
      <intent-filter>
        <action android:name="android.intent.action.VIEW" />
        <category android:name="android.intent.category.DEFAULT" />
        <category android:name="android.intent.category.BROWSABLE" />
        <data
          android:host="gallery"
          android:scheme="myApp" />
      </intent-filter>
    </activity>
    ..

and click this url from an email on your phone for example

<a href="intent://gallery?directLink=true#Intent;scheme=myApp;package=com.myApp;end"> 
  Click me 
</a>

then android will try to find an app with the package com.myApp that responds to your gallery intent and has a myApp scheme. In case it can't, it will take you to the store, looking for com.myApp, which should be your app.

Total number of items defined in an enum

You can use the static method Enum.GetNames which returns an array representing the names of all the items in the enum. The length property of this array equals the number of items defined in the enum

var myEnumMemberCount = Enum.GetNames(typeof(MyEnum)).Length;

Dealing with nginx 400 "The plain HTTP request was sent to HTTPS port" error

I ran into a similar problem. It works on one server and does not on another server with same Nginx configuration. Found the the solution which is answered by Igor here http://forum.nginx.org/read.php?2,1612,1627#msg-1627

Yes. Or you may combine SSL/non-SSL servers in one server:

server {
  listen 80;
  listen 443 default ssl;

  # ssl on   - remember to comment this out

}

What exactly is a Context in Java?

A Context represents your environment. It represents the state surrounding where you are in your system.

For example, in web programming in Java, you have a Request, and a Response. These are passed to the service method of a Servlet.

A property of the Servlet is the ServletConfig, and within that is a ServletContext.

The ServletContext is used to tell the servlet about the Container that the Servlet is within.

So, the ServletContext represents the servlets environment within its container.

Similarly, in Java EE, you have EBJContexts that elements (like session beans) can access to work with their containers.

Those are two examples of contexts used in Java today.

Edit --

You mention Android.

Look here: http://developer.android.com/reference/android/content/Context.html

You can see how this Context gives you all sorts of information about where the Android app is deployed and what's available to it.

What range of values can integer types store in C++

The size of the numerical types is not defined in the C++ standard, although the minimum sizes are. The way to tell what size they are on your platform is to use numeric limits

For example, the maximum value for a int can be found by:

std::numeric_limits<int>::max();

Computers don't work in base 10, which means that the maximum value will be in the form of 2n-1 because of how the numbers of represent in memory. Take for example eight bits (1 byte)

  0100 1000

The right most bit (number) when set to 1 represents 20, the next bit 21, then 22 and so on until we get to the left most bit which if the number is unsigned represents 27.

So the number represents 26 + 23 = 64 + 8 = 72, because the 4th bit from the right and the 7th bit right the left are set.

If we set all values to 1:

11111111

The number is now (assuming unsigned)
128 + 64 + 32 + 16 + 8 + 4 + 2 + 1 = 255 = 28 - 1
And as we can see, that is the largest possible value that can be represented with 8 bits.

On my machine and int and a long are the same, each able to hold between -231 to 231 - 1. In my experience the most common size on modern 32 bit desktop machine.

docker command not found even though installed with apt-get

sudo apt-get install docker # DO NOT do this

is a different library on ubuntu.

Use sudo apt-get install docker-ce to install the correct docker.

How can I submit a POST form using the <a href="..."> tag?

There really seems no way for fooling the <a href= .. into a POST method. However, given that you have access to CSS of a page, this can be substituted by using a form instead.

Unfortunately, the obvious way of just styling the button in CSS as an anchor tag, is not cross-browser compatible, since different browsers treat <button value= ... differently.

Incorrect:

<form action='actbusy.php' method='post'>
  <button type='submit' name='parameter' value='One'>Two</button>
</form>

The above example will be showing 'Two' and transmit 'parameter:One' in FireFox, while it will show 'One' and transmit also 'parameter:One' in IE8.

The way around is to use hidden input field(s) for delivering data and the button just for submitting it.

<form action='actbusy.php' method='post'>
   <input class=hidden name='parameter' value='blaah'>
   <button type='submit' name='delete' value='Delete'>Delete</button>
</form>

Note, that this method has a side effect that besides 'parameter:blaah' it will also deliver 'delete:Delete' as surplus parameters in POST.

You want to keep for a button the value attribute and button label between tags both the same ('Delete' on this case), since (as stated above) some browsers will display one and some display another as a button label.

Escape string for use in Javascript regex

Short 'n Sweet

function escapeRegExp(string) {
  return string.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'); // $& means the whole matched string
}

Example

escapeRegExp("All of these should be escaped: \ ^ $ * + ? . ( ) | { } [ ]");

>>> "All of these should be escaped: \\ \^ \$ \* \+ \? \. \( \) \| \{ \} \[ \] "

(NOTE: the above is not the original answer; it was edited to show the one from MDN. This means it does not match what you will find in the code in the below npm, and does not match what is shown in the below long answer. The comments are also now confusing. My recommendation: use the above, or get it from MDN, and ignore the rest of this answer. -Darren,Nov 2019)

Install

Available on npm as escape-string-regexp

npm install --save escape-string-regexp

Note

See MDN: Javascript Guide: Regular Expressions

Other symbols (~`!@# ...) MAY be escaped without consequence, but are not required to be.

.

.

.

.

Test Case: A typical url

escapeRegExp("/path/to/resource.html?search=query");

>>> "\/path\/to\/resource\.html\?search=query"

The Long Answer

If you're going to use the function above at least link to this stack overflow post in your code's documentation so that it doesn't look like crazy hard-to-test voodoo.

var escapeRegExp;

(function () {
  // Referring to the table here:
  // https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/regexp
  // these characters should be escaped
  // \ ^ $ * + ? . ( ) | { } [ ]
  // These characters only have special meaning inside of brackets
  // they do not need to be escaped, but they MAY be escaped
  // without any adverse effects (to the best of my knowledge and casual testing)
  // : ! , = 
  // my test "~!@#$%^&*(){}[]`/=?+\|-_;:'\",<.>".match(/[\#]/g)

  var specials = [
        // order matters for these
          "-"
        , "["
        , "]"
        // order doesn't matter for any of these
        , "/"
        , "{"
        , "}"
        , "("
        , ")"
        , "*"
        , "+"
        , "?"
        , "."
        , "\\"
        , "^"
        , "$"
        , "|"
      ]

      // I choose to escape every character with '\'
      // even though only some strictly require it when inside of []
    , regex = RegExp('[' + specials.join('\\') + ']', 'g')
    ;

  escapeRegExp = function (str) {
    return str.replace(regex, "\\$&");
  };

  // test escapeRegExp("/path/to/res?search=this.that")
}());

How can I list ALL DNS records?

  1. A zone transfer is the only way to be sure you have all the subdomain records. If the DNS is correctly configured you should not normally be able to perform an external zone transfer.

  2. The scans.io project has a database of DNS records that can be downloaded and searched for subdomains. This requires downloading the 87GB of DNS data, alternatively you can try the online search of the data at https://hackertarget.com/find-dns-host-records/

What is a 'multi-part identifier' and why can't it be bound?

Mine was putting the schema on the table Alias by mistake:

SELECT * FROM schema.CustomerOrders co
WHERE schema.co.ID = 1  -- oops!

Expression must be a modifiable lvalue

The assignment operator has lower precedence than &&, so your condition is equivalent to:

if ((match == 0 && k) = m)

But the left-hand side of this is an rvalue, namely the boolean resulting from the evaluation of the sub­expression match == 0 && k, so you cannot assign to it.

By contrast, comparison has higher precedence, so match == 0 && k == m is equivalent to:

if ((match == 0) && (k == m))

Calling a Javascript Function from Console

An example of where the console will return ReferenceError is putting a function inside a JQuery document ready function

//this will fail
$(document).ready(function () {
          myFunction(alert('doing something!'));
          //other stuff
}

To succeed move the function outside the document ready function

//this will work
myFunction(alert('doing something!'));
$(document).ready(function () {

          //other stuff
}

Then in the console window, type the function name with the '()' to execute the function

myFunction()

Also of use is being able to print out the function body to remind yourself what the function does. Do this by leaving off the '()' from the function name

function myFunction(alert('doing something!'))

Of course if you need the function to be registered after the document is loaded then you couldn't do this. But you might be able to work around that.

Going from MM/DD/YYYY to DD-MMM-YYYY in java

Try this,

Date currDate = new Date();
DateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy");
String strCurrDate = dateFormat.format(currDate);
System.out.println("strCurrDate->"+strCurrDate);

Eclipse error: 'Failed to create the Java Virtual Machine'

Some time it's not your eclipse.ini; it's your JDK which is crashed. You can check it by writing following command in a command prompt:

c:\> java -version

If this command shows the following error:

Error occurred during initialization of VM

java/lang/NoClassDefFoundError: java/lang/Object

Then first uninstall JDK and reinstall it.

Eclipse will be in action again ;) As today I have got the same problem, and the above is suggested by Itachi Uchiha.

Auto increment in phpmyadmin

Just run a simple MySQL query and set the auto increment number to whatever you want.

ALTER TABLE `table_name` AUTO_INCREMENT=10000

In terms of a maximum, as far as I am aware there is not one, nor is there any way to limit such number.

It is perfectly safe, and common practice to set an id number as a primiary key, auto incrementing int. There are alternatives such as using PHP to generate membership numbers for you in a specific format and then checking the number does not exist prior to inserting, however for me personally I'd go with the primary id auto_inc value.

Read values into a shell variable from a pipe

I'm no expert in Bash, but I wonder why this hasn't been proposed:

stdin=$(cat)

echo "$stdin"

One-liner proof that it works for me:

$ fortune | eval 'stdin=$(cat); echo "$stdin"'

Reading string by char till end of line C/C++

If you are using C function fgetc then you should check a next character whether it is equal to the new line character or to EOF. For example

unsigned int count = 0;
while ( 1 )
{
   int c = fgetc( FileStream );

   if ( c == EOF || c == '\n' )
   {
      printF( "The length of the line is %u\n", count );
      count = 0;
      if ( c == EOF ) break;
   }
   else
   {
      ++count;
   }
}    

or maybe it would be better to rewrite the code using do-while loop. For example

unsigned int count = 0;
do
{
   int c = fgetc( FileStream );

   if ( c == EOF || c == '\n' )
   {
      printF( "The length of the line is %u\n", count );
      count = 0;
   }
   else
   {
      ++count;
   }
} while ( c != EOF );

Of course you need to insert your own processing of read xgaracters. It is only an example how you could use function fgetc to read lines of a file.

But if the program is written in C++ then it would be much better if you would use std::ifstream and std::string classes and function std::getline to read a whole line.

Getting Hour and Minute in PHP

print date('H:i');
$var = date('H:i');

Should do it, for the current time. Use a lower case h for 12 hour clock instead of 24 hour.

More date time formats listed here.

How to connect to a remote Windows machine to execute commands using python?

I have personally found pywinrm library to be very effective. However, it does require some commands to be run on the machine and some other setup before it will work.

Responsive css background images

background:url("img/content-bg.jpg") no-repeat;
background-position:center; 
background-size:cover;

or

background-size:100%;

Randomize numbers with jQuery?

You don't need jQuery, just use javascript's Math.random function.

edit: If you want to have a number from 1 to 6 show randomly every second, you can do something like this:

<span id="number"></span>

<script language="javascript">
  function generate() {
    $('#number').text(Math.floor(Math.random() * 6) + 1);
  }
  setInterval(generate, 1000);
</script>

Extracting columns from text file with different delimiters in Linux

You can use cut with a delimiter like this:

with space delim:

cut -d " " -f1-100,1000-1005 infile.csv > outfile.csv

with tab delim:

cut -d$'\t' -f1-100,1000-1005 infile.csv > outfile.csv

I gave you the version of cut in which you can extract a list of intervals...

Hope it helps!

Best practice for REST token-based authentication with JAX-RS and Jersey

This answer is all about authorization and it is a complement of my previous answer about authentication

Why another answer? I attempted to expand my previous answer by adding details on how to support JSR-250 annotations. However the original answer became the way too long and exceeded the maximum length of 30,000 characters. So I moved the whole authorization details to this answer, keeping the other answer focused on performing authentication and issuing tokens.


Supporting role-based authorization with the @Secured annotation

Besides authentication flow shown in the other answer, role-based authorization can be supported in the REST endpoints.

Create an enumeration and define the roles according to your needs:

public enum Role {
    ROLE_1,
    ROLE_2,
    ROLE_3
}

Change the @Secured name binding annotation created before to support roles:

@NameBinding
@Retention(RUNTIME)
@Target({TYPE, METHOD})
public @interface Secured {
    Role[] value() default {};
}

And then annotate the resource classes and methods with @Secured to perform the authorization. The method annotations will override the class annotations:

@Path("/example")
@Secured({Role.ROLE_1})
public class ExampleResource {

    @GET
    @Path("{id}")
    @Produces(MediaType.APPLICATION_JSON)
    public Response myMethod(@PathParam("id") Long id) {
        // This method is not annotated with @Secured
        // But it's declared within a class annotated with @Secured({Role.ROLE_1})
        // So it only can be executed by the users who have the ROLE_1 role
        ...
    }

    @DELETE
    @Path("{id}")    
    @Produces(MediaType.APPLICATION_JSON)
    @Secured({Role.ROLE_1, Role.ROLE_2})
    public Response myOtherMethod(@PathParam("id") Long id) {
        // This method is annotated with @Secured({Role.ROLE_1, Role.ROLE_2})
        // The method annotation overrides the class annotation
        // So it only can be executed by the users who have the ROLE_1 or ROLE_2 roles
        ...
    }
}

Create a filter with the AUTHORIZATION priority, which is executed after the AUTHENTICATION priority filter defined previously.

The ResourceInfo can be used to get the resource Method and resource Class that will handle the request and then extract the @Secured annotations from them:

@Secured
@Provider
@Priority(Priorities.AUTHORIZATION)
public class AuthorizationFilter implements ContainerRequestFilter {

    @Context
    private ResourceInfo resourceInfo;

    @Override
    public void filter(ContainerRequestContext requestContext) throws IOException {

        // Get the resource class which matches with the requested URL
        // Extract the roles declared by it
        Class<?> resourceClass = resourceInfo.getResourceClass();
        List<Role> classRoles = extractRoles(resourceClass);

        // Get the resource method which matches with the requested URL
        // Extract the roles declared by it
        Method resourceMethod = resourceInfo.getResourceMethod();
        List<Role> methodRoles = extractRoles(resourceMethod);

        try {

            // Check if the user is allowed to execute the method
            // The method annotations override the class annotations
            if (methodRoles.isEmpty()) {
                checkPermissions(classRoles);
            } else {
                checkPermissions(methodRoles);
            }

        } catch (Exception e) {
            requestContext.abortWith(
                Response.status(Response.Status.FORBIDDEN).build());
        }
    }

    // Extract the roles from the annotated element
    private List<Role> extractRoles(AnnotatedElement annotatedElement) {
        if (annotatedElement == null) {
            return new ArrayList<Role>();
        } else {
            Secured secured = annotatedElement.getAnnotation(Secured.class);
            if (secured == null) {
                return new ArrayList<Role>();
            } else {
                Role[] allowedRoles = secured.value();
                return Arrays.asList(allowedRoles);
            }
        }
    }

    private void checkPermissions(List<Role> allowedRoles) throws Exception {
        // Check if the user contains one of the allowed roles
        // Throw an Exception if the user has not permission to execute the method
    }
}

If the user has no permission to execute the operation, the request is aborted with a 403 (Forbidden).

To know the user who is performing the request, see my previous answer. You can get it from the SecurityContext (which should be already set in the ContainerRequestContext) or inject it using CDI, depending on the approach you go for.

If a @Secured annotation has no roles declared, you can assume all authenticated users can access that endpoint, disregarding the roles the users have.

Supporting role-based authorization with JSR-250 annotations

Alternatively to defining the roles in the @Secured annotation as shown above, you could consider JSR-250 annotations such as @RolesAllowed, @PermitAll and @DenyAll.

JAX-RS doesn't support such annotations out-of-the-box, but it could be achieved with a filter. Here are a few considerations to keep in mind if you want to support all of them:

So an authorization filter that checks JSR-250 annotations could be like:

@Provider
@Priority(Priorities.AUTHORIZATION)
public class AuthorizationFilter implements ContainerRequestFilter {

    @Context
    private ResourceInfo resourceInfo;

    @Override
    public void filter(ContainerRequestContext requestContext) throws IOException {

        Method method = resourceInfo.getResourceMethod();

        // @DenyAll on the method takes precedence over @RolesAllowed and @PermitAll
        if (method.isAnnotationPresent(DenyAll.class)) {
            refuseRequest();
        }

        // @RolesAllowed on the method takes precedence over @PermitAll
        RolesAllowed rolesAllowed = method.getAnnotation(RolesAllowed.class);
        if (rolesAllowed != null) {
            performAuthorization(rolesAllowed.value(), requestContext);
            return;
        }

        // @PermitAll on the method takes precedence over @RolesAllowed on the class
        if (method.isAnnotationPresent(PermitAll.class)) {
            // Do nothing
            return;
        }

        // @DenyAll can't be attached to classes

        // @RolesAllowed on the class takes precedence over @PermitAll on the class
        rolesAllowed = 
            resourceInfo.getResourceClass().getAnnotation(RolesAllowed.class);
        if (rolesAllowed != null) {
            performAuthorization(rolesAllowed.value(), requestContext);
        }

        // @PermitAll on the class
        if (resourceInfo.getResourceClass().isAnnotationPresent(PermitAll.class)) {
            // Do nothing
            return;
        }

        // Authentication is required for non-annotated methods
        if (!isAuthenticated(requestContext)) {
            refuseRequest();
        }
    }

    /**
     * Perform authorization based on roles.
     *
     * @param rolesAllowed
     * @param requestContext
     */
    private void performAuthorization(String[] rolesAllowed, 
                                      ContainerRequestContext requestContext) {

        if (rolesAllowed.length > 0 && !isAuthenticated(requestContext)) {
            refuseRequest();
        }

        for (final String role : rolesAllowed) {
            if (requestContext.getSecurityContext().isUserInRole(role)) {
                return;
            }
        }

        refuseRequest();
    }

    /**
     * Check if the user is authenticated.
     *
     * @param requestContext
     * @return
     */
    private boolean isAuthenticated(final ContainerRequestContext requestContext) {
        // Return true if the user is authenticated or false otherwise
        // An implementation could be like:
        // return requestContext.getSecurityContext().getUserPrincipal() != null;
    }

    /**
     * Refuse the request.
     */
    private void refuseRequest() {
        throw new AccessDeniedException(
            "You don't have permissions to perform this action.");
    }
}

Note: The above implementation is based on the Jersey RolesAllowedDynamicFeature. If you use Jersey, you don't need to write your own filter, just use the existing implementation.

How does functools partial do what it does?

In my opinion, it's a way to implement currying in python.

from functools import partial
def add(a,b):
    return a + b

def add2number(x,y,z):
    return x + y + z

if __name__ == "__main__":
    add2 = partial(add,2)
    print("result of add2 ",add2(1))
    add3 = partial(partial(add2number,1),2)
    print("result of add3",add3(1))

The result is 3 and 4.

Java GUI frameworks. What to choose? Swing, SWT, AWT, SwingX, JGoodies, JavaFX, Apache Pivot?

I would go with Swing. For layout I would use JGoodies form layout. Its worth studying the white paper on the Form Layout here - http://www.jgoodies.com/freeware/forms/

Also if you are going to start developing a huge desktop application, you will definitely need a framework. Others have pointed out the netbeans framework. I didnt like it much so wrote a new one that we now use in my company. I have put it onto sourceforge, but didnt find the time to document it much. Here's the link to browse the code:

http://swingobj.svn.sourceforge.net/viewvc/swingobj/

The showcase should show you how to do a simple logon actually..

Let me know if you have any questions on it I could help.

How to get pandas.DataFrame columns containing specific dtype

Someone will give you a better answe than this possibly, but one thing I tend to do is if all my numeric data are int64 or float64 objects, then you can create a dict of the column data types and then use the values to create your list of columns.

So for example, in a dataframe where I have columns of type float64, int64 and object firstly you can look at the data types as so:

DF.dtypes

and if they conform to the standard whereby the non-numeric columns of data are all object types (as they are in my dataframes), then you can do the following to get a list of the numeric columns:

[key for key in dict(DF.dtypes) if dict(DF.dtypes)[key] in ['float64', 'int64']]

Its just a simple list comprehension. Nothing fancy. Again, though whether this works for you will depend upon how you set up you dataframe...

What are the differences between Abstract Factory and Factory design patterns?

Factory Method relies on inheritance: Object creation is delegated to subclasses, which implement the factory method to create objects.

Abstract Factory relies on object composition: object creation is implemented in methods exposed in the factory interface.

High level diagram of Factory and Abstract factory pattern,

diagram

For more information about the Factory method, refer this article.

For more information about Abstract factory method, refer this article.

Python Matplotlib figure title overlaps axes label when using twiny

A temporary solution if you don't want to get into the x, y position of your title.

Following worked for me.

plt.title('Capital Expenditure\n') # Add a next line after your title

kudos.

Redirect Windows cmd stdout and stderr to a single file

You want:

dir > a.txt 2>&1

The syntax 2>&1 will redirect 2 (stderr) to 1 (stdout). You can also hide messages by redirecting to NUL, more explanation and examples on MSDN.

What do the different readystates in XMLHttpRequest mean, and how can I use them?

The full list of readyState values is:

State  Description
0      The request is not initialized
1      The request has been set up
2      The request has been sent
3      The request is in process
4      The request is complete

(from https://www.w3schools.com/js/js_ajax_http_response.asp)

In practice you almost never use any of them except for 4.

Some XMLHttpRequest implementations may let you see partially received responses in responseText when readyState==3, but this isn't universally supported and shouldn't be relied upon.

svn cleanup: sqlite: database disk image is malformed

The SVN cleanup didn't work. The SVN folder on my local system got corrupted. So I just deleted the folder, recreated a new one, and updated from SVN. That solved the problem!

Does C# have extension properties?

No they do not exist in C# 3.0 and will not be added in 4.0. It's on the list of feature wants for C# so it may be added at a future date.

At this point the best you can do is GetXXX style extension methods.

How do I get to IIS Manager?

First of all, you need to check that the IIS is installed in your machine, for that you can go to:

Control Panel --> Add or Remove Programs --> Windows Features --> And Check if Internet Information Services is installed with at least the 'Web Administration Tools' Enabled and The 'World Wide Web Service'

If not, check it, and Press Accept to install it.

Once that is done, you need to go to Administrative Tools in Control Panel and the IIS Will be there. Or simply run inetmgr (after Win+R).

Edit: You should have something like this: enter image description here

CSS/Javascript to force html table row on a single line

I wonder if it might be worth using PHP (or another server-side scripting language) or Javascript to truncate the strings to the right length (although calculating the right length is tricky, unless you use a fixed-width font)?

Cannot GET / Nodejs Error

Much like leonardocsouza, I had the same problem. To clarify a bit, this is what my folder structure looked like when I ran node server.js

node_modules/
app/
  index.html
  server.js

After printing out the __dirname path, I realized that the __dirname path was where my server was running (app/).

So, the answer to your question is this:

If your server.js file is in the same folder as the files you are trying to render, then

app.use( express.static( path.join( application_root, 'site') ) );

should actually be

app.use(express.static(application_root));

The only time you would want to use the original syntax that you had would be if you had a folder tree like so:

app/
  index.html
node_modules
server.js

where index.html is in the app/ directory, whereas server.js is in the root directory (i.e. the same level as the app/ directory).

Side note: Intead of calling the path utility, you can use the syntax application_root + 'site' to join a path.

Overall, your code could look like:

// Module dependencies.
var application_root = __dirname,
express = require( 'express' ), //Web framework
mongoose = require( 'mongoose' ); //MongoDB integration

//Create server
var app = express();

// Configure server
app.configure( function() {

    //Don't change anything here...

    //Where to serve static content
    app.use( express.static( application_root ) );

    //Nothing changes here either...
});

//Start server --- No changes made here
var port = 5000;
app.listen( port, function() {
    console.log( 'Express server listening on port %d in %s mode', port, app.settings.env );
});

SQL permissions for roles

USE DataBaseName; GO --------- CREATE ROLE --------- CREATE ROLE Doctors ; GO  ---- Assign Role To users -------  CREATE USER [Username] FOR LOGIN [Domain\Username] EXEC sp_addrolemember N'Doctors', N'Username'  ----- GRANT Permission to Users Assinged with this Role----- GRANT ALL ON Table1, Table2, Table3 TO Doctors; GO 

Convert List to Pandas Dataframe Column

if your list looks like this: [1,2,3] you can do:

lst = [1,2,3]
df = pd.DataFrame([lst])
df.columns =['col1','col2','col3']
df

to get this:

    col1    col2    col3
0   1       2       3

alternatively you can create a column as follows:

import numpy as np
df = pd.DataFrame(np.array([lst]).T)
df.columns =['col1']
df

to get this:

  col1
0   1
1   2
2   3

SQL selecting rows by most recent date with two unique columns

SELECT chargeId, chargeType, MAX(serviceMonth) AS serviceMonth 
FROM invoice
GROUP BY chargeId, chargeType

Check if something is (not) in a list in Python

How do I check if something is (not) in a list in Python?

The cheapest and most readable solution is using the in operator (or in your specific case, not in). As mentioned in the documentation,

The operators in and not in test for membership. x in s evaluates to True if x is a member of s, and False otherwise. x not in s returns the negation of x in s.

Additionally,

The operator not in is defined to have the inverse true value of in.

y not in x is logically the same as not y in x.

Here are a few examples:

'a' in [1, 2, 3]
# False

'c' in ['a', 'b', 'c']
# True

'a' not in [1, 2, 3]
# True

'c' not in ['a', 'b', 'c']
# False

This also works with tuples, since tuples are hashable (as a consequence of the fact that they are also immutable):

(1, 2) in [(3, 4), (1, 2)]
#  True

If the object on the RHS defines a __contains__() method, in will internally call it, as noted in the last paragraph of the Comparisons section of the docs.

... in and not in, are supported by types that are iterable or implement the __contains__() method. For example, you could (but shouldn't) do this:

[3, 2, 1].__contains__(1)
# True

in short-circuits, so if your element is at the start of the list, in evaluates faster:

lst = list(range(10001))
%timeit 1 in lst
%timeit 10000 in lst  # Expected to take longer time.

68.9 ns ± 0.613 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)
178 µs ± 5.01 µs per loop (mean ± std. dev. of 7 runs, 10000 loops each)

If you want to do more than just check whether an item is in a list, there are options:

  • list.index can be used to retrieve the index of an item. If that element does not exist, a ValueError is raised.
  • list.count can be used if you want to count the occurrences.

The XY Problem: Have you considered sets?

Ask yourself these questions:

  • do you need to check whether an item is in a list more than once?
  • Is this check done inside a loop, or a function called repeatedly?
  • Are the items you're storing on your list hashable? IOW, can you call hash on them?

If you answered "yes" to these questions, you should be using a set instead. An in membership test on lists is O(n) time complexity. This means that python has to do a linear scan of your list, visiting each element and comparing it against the search item. If you're doing this repeatedly, or if the lists are large, this operation will incur an overhead.

set objects, on the other hand, hash their values for constant time membership check. The check is also done using in:

1 in {1, 2, 3} 
# True

'a' not in {'a', 'b', 'c'}
# False

(1, 2) in {('a', 'c'), (1, 2)}
# True

If you're unfortunate enough that the element you're searching/not searching for is at the end of your list, python will have scanned the list upto the end. This is evident from the timings below:

l = list(range(100001))
s = set(l)

%timeit 100000 in l
%timeit 100000 in s

2.58 ms ± 58.9 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)
101 ns ± 9.53 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)

As a reminder, this is a suitable option as long as the elements you're storing and looking up are hashable. IOW, they would either have to be immutable types, or objects that implement __hash__.

Laravel - Form Input - Multiple select for a one to many relationship

My solution, it´s make with jquery-chosen and bootstrap, the id is for jquery chosen, tested and working, I had problems concatenating @foreach but now work with a double @foreach and double @if:

  <div class="form-group">
    <label for="tagLabel">Tags: </label>
    <select multiple class="chosen-tag" id="tagLabel" name="tag_id[]" required>
      @foreach($tags as $id => $name)
        @if (is_array(Request::old('tag_id')))
                <option value="{{ $id }}" 
                @foreach (Request::old('tag_id') as $idold)
                  @if($idold==$id)
                    selected
                  @endif 
                @endforeach
                style="padding:5px;">{{ $name }}</option>
        @else
          <option value="{{ $id }}" style="padding:5px;">{{ $name }}</option>
        @endif
      @endforeach
    </select>
  </div>

this is the code por jquery chosen (the blade.php code doesn´t need this code to work)

    $(".chosen-tag").chosen({
  placeholder_text_multiple: "Selecciona alguna etiqueta",
  no_results_text: "No hay resultados para la busqueda",
  search_contains: true,
  width: '500px'
});

Add custom icons to font awesome

Give Icomoon a try. You can upload your own SVGs, add them to the library, then create a custom font combining FontAwesome with your own icons.

Show data on mouseover of circle

You can pass in the data to be used in the mouseover like this- the mouseover event uses a function with your previously entered data as an argument (and the index as a second argument) so you don't need to use enter() a second time.

vis.selectAll("circle")
.data(datafiltered).enter().append("svg:circle")
.attr("cx", function(d) { return x(d.x);})
.attr("cy", function(d) {return y(d.y)})
.attr("fill", "red").attr("r", 15)
.on("mouseover", function(d,i) {
    d3.select(this).append("text")
        .text( d.x)
        .attr("x", x(d.x))
        .attr("y", y(d.y)); 
});

Kendo grid date column not formatting

As far as I'm aware in order to format a date value you have to handle it in parameterMap,

$('#listDiv').kendoGrid({
            dataSource: {
                type: 'json',
                serverPaging: true,
                pageSize: 10,
                transport: {
                    read: {
                        url: '@Url.Action("_ListMy", "Placement")',
                        data: refreshGridParams,
                        type: 'POST'
                    },
                    parameterMap: function (options, operation) {
                        if (operation != "read") {
                            var d = new Date(options.StartDate);
                            options.StartDate = kendo.toString(new Date(d), "dd/MM/yyyy");
                            return options;
                        }
                        else { return options; }

                    }
                },
                schema: {
                    model: {
                        id: 'Id',
                        fields: {
                            Id: { type: 'number' },
                            StartDate: { type: 'date', format: 'dd/MM/yyyy' },
                            Area: { type: 'string' },
                            Length: { type: 'string' },
                            Display: { type: 'string' },
                            Status: { type: 'string' },
                            Edit: { type: 'string' }
                        }
                    },
                    data: "Data",
                    total: "Count"
                }
            },
            scrollable: false,
            columns:
                [
                    {
                        field: 'StartDate',
                        title: 'Start Date',
                        format: '{0:dd/MM/yyyy}',
                        width: 100
                    },

If you follow the above example and just renames objects like 'StartDate' then it should work (ignore 'data: refreshGridParams,')

For further details check out below link or just search for kendo grid parameterMap ans see what others have done.

http://docs.kendoui.com/api/framework/datasource#configuration-transport.parameterMap

Remove a file from the list that will be committed

You want to do this:

git add -u
git reset HEAD path/to/file
git commit

Be sure and do this from the top level of the repo; add -u adds changes in the current directory (recursively).

The key line tells git to reset the version of the given path in the index (the staging area for the commit) to the version from HEAD (the currently checked-out commit).

And advance warning of a gotcha for others reading this: add -u stages all modifications, but doesn't add untracked files. This is the same as what commit -a does. If you want to add untracked files too, use add . to recursively add everything.

How to print a string multiple times?

rows = int(input('How many stars in each row do you want?'))
columns = int(input('How many columns do you want?'))
i = 0

for i in range(columns): 
    print ("*" * rows)

i = i + 1

Send a SMS via intent

Hope this is work, this is working in my app

SmsManager.getDefault().sendTextMessage("Phone Number", null, "Message", null, null);

UITapGestureRecognizer - single tap and double tap

You need to use the requireGestureRecognizerToFail: method. Something like this:

[singleTapRecognizer requireGestureRecognizerToFail:doubleTapRecognizer];

How do I retrieve an HTML element's actual width and height?

You only need to calculate it for IE7 and older (and only if your content doesn't have fixed size). I suggest using HTML conditional comments to limit hack to old IEs that don't support CSS2. For all other browsers use this:

<style type="text/css">
    html,body {display:table; height:100%;width:100%;margin:0;padding:0;}
    body {display:table-cell; vertical-align:middle;}
    div {display:table; margin:0 auto; background:red;}
</style>
<body><div>test<br>test</div></body>

This is the perfect solution. It centers <div> of any size, and shrink-wraps it to size of its content.

Sending Email in Android using JavaMail API without using the default/built-in app

You can use JavaMail API to handle your email tasks. JavaMail API is available in JavaEE package and its jar is available for download. Sadly it cannot be used directly in an Android application since it uses AWT components which are completely incompatible in Android.

You can find the Android port for JavaMail at the following location: http://code.google.com/p/javamail-android/

Add the jars to your application and use the SMTP method

How to call getResources() from a class which has no context?

The normal solution to this is to pass an instance of the context to the class as you create it, or after it is first created but before you need to use the context.

Another solution is to create an Application object with a static method to access the application context although that couples the Droid object fairly tightly into the code.

Edit, examples added

Either modify the Droid class to be something like this

 public Droid(Context context,int x, int y) {
    this.bitmap = BitmapFactory.decodeResource(context.getResources(), R.drawable.birdpic);
    this.x = x;
    this.y = y;
    }   

Or create an Application something like this:

public class App extends android.app.Application
{
    private static App mApp = null;
    /* (non-Javadoc)
     * @see android.app.Application#onCreate()
     */
    @Override
    public void onCreate()
    {
        super.onCreate();
        mApp = this;
    }
    public static Context context()
    {
        return mApp.getApplicationContext();
    }
}

And call App.context() wherever you need a context - note however that not all functions are available on an application context, some are only available on an activity context but it will certainly do with your need for getResources().

Please note that you'll need to add android:name to your application definition in your manifest, something like this:

<application
    android:icon="@drawable/icon"
    android:label="@string/app_name"
    android:name=".App" >

Distinct pair of values SQL

What you mean is either

SELECT DISTINCT a, b FROM pairs;

or

SELECT a, b FROM pairs GROUP BY a, b;

Vertical Text Direction

This works as well:

transform: rotate(90deg);

Print ArrayList

This helped to me:

System.out.println(Arrays.toString(codeLangArray.toArray()));

Firebug-like debugger for Google Chrome

You can set this bookmarklet in your "Bookmarks Bar" in order to have Firebug lite always available in Chrome/Chromium browser (put this as the URL):

javascript:var firebug=document.createElement('script');firebug.setAttribute('src','http://getfirebug.com/releases/lite/1.2/firebug-lite-compressed.js');document.body.appendChild(firebug);(function(){if(window.firebug.version){firebug.init();}else{setTimeout(arguments.callee);}})();void(firebug);

Remove last item from array

I would consider .pop() to be the most 'correct' solution, however, sometimes it might not work since you need to use array without the last element right there...

In such a case you might want to use the following, it will return [1,2,3]

_x000D_
_x000D_
var arr = [1,2,3,4];_x000D_
console.log(arr.splice(0,arr.length-1));
_x000D_
_x000D_
_x000D_

while .pop() would return 4:

_x000D_
_x000D_
var arr = [1,2,3,4];_x000D_
console.log(arr.pop());
_x000D_
_x000D_
_x000D_

which might not be desirable...

Hope this saves you some time.

6 digits regular expression

  ^\d{1,6}$

....................

How do I horizontally center an absolute positioned element inside a 100% width div?

Was missing the use of calc in the answers, which is a cleaner solution.

#logo {
  position: absolute;
  left: calc(50% - 25px);
  height: 50px;
  width: 50px;
  background: red;
}

jsFiddle

Works in most modern browsers: http://caniuse.com/calc

Maybe it's too soon to use it without a fallback, but I thought maybe for future visitors it would be helpful.

How to delete columns in pyspark dataframe

Adding to @Patrick's answer, you can use the following to drop multiple columns

columns_to_drop = ['id', 'id_copy']
df = df.drop(*columns_to_drop)

PHP how to get value from array if key is in a variable

$value = ( array_key_exists($key, $array) && !empty($array[$key]) ) 
         ? $array[$key] 
         : 'non-existant or empty value key';

How to delete a file via PHP?

You can delete the file using

unlink($Your_file_path);

but if you are deleting a file from it's http path then this unlink is not work proper. You have to give a file path correct.

Is there anything like .NET's NotImplementedException in Java?

You could do it yourself (thats what I did) - in order to not be bothered with exception handling, you simply extend the RuntimeException, your class could look something like this:

public class NotImplementedException extends RuntimeException {

    private static final long serialVersionUID = 1L;

    public NotImplementedException(){}
}

You could extend it to take a message - but if you use the method as I do (that is, as a reminder, that there is still something to be implemented), then usually there is no need for additional messages.

I dare say, that I only use this method, while I am in the process of developing a system, makes it easier for me to not lose track of which methods are still not implemented properly :)

SQL - Update multiple records in one query

INSERT INTO tablename
    (name, salary)
    VALUES 
        ('Bob', 1125),
        ('Jane', 1200),
        ('Frank', 1100),
        ('Susan', 1175),
        ('John', 1150)
        ON DUPLICATE KEY UPDATE salary = VALUES(salary);

How can I hide or encrypt JavaScript code?

One of the best compressors (not specifically an obfuscator) is the YUI Compressor.

Add custom buttons on Slick Carousel

That's because they use an icon font for the buttons. They use "Slick" font as you can see in this image:

enter image description here

Basically, the make the letter "A" the form of an icon, the letter "B" the form of another one and so on.

For example:

enter image description here

If you want to know more about icon fonts click here

If you want to change the icons, you need to replace the whole button code or you can go to www.fontastic.me and create your own icon font. After that, replace the font file for the current one and you'll have your own icon.

Excel VBA - Delete empty rows

How about

sub foo()
  dim r As Range, rows As Long, i As Long
  Set r = ActiveSheet.Range("A1:Z50")
  rows = r.rows.Count
  For i = rows To 1 Step (-1)
    If WorksheetFunction.CountA(r.rows(i)) = 0 Then r.rows(i).Delete
  Next
End Sub

Try this

Option Explicit

Sub Sample()
    Dim i As Long
    Dim DelRange As Range

    On Error GoTo Whoa

    Application.ScreenUpdating = False

    For i = 1 To 50
        If Application.WorksheetFunction.CountA(Range("A" & i & ":" & "Z" & i)) = 0 Then
            If DelRange Is Nothing Then
                Set DelRange = Range("A" & i & ":" & "Z" & i)
            Else
                Set DelRange = Union(DelRange, Range("A" & i & ":" & "Z" & i))
            End If
        End If
    Next i

    If Not DelRange Is Nothing Then DelRange.Delete shift:=xlUp
LetsContinue:
    Application.ScreenUpdating = True

    Exit Sub
Whoa:
    MsgBox Err.Description
    Resume LetsContinue
End Sub

IF you want to delete the entire row then use this code

Option Explicit

Sub Sample()
    Dim i As Long
    Dim DelRange As Range

    On Error GoTo Whoa

    Application.ScreenUpdating = False

    For i = 1 To 50
        If Application.WorksheetFunction.CountA(Range("A" & i & ":" & "Z" & i)) = 0 Then
            If DelRange Is Nothing Then
                Set DelRange = Rows(i)
            Else
                Set DelRange = Union(DelRange, Rows(i))
            End If
        End If
    Next i

    If Not DelRange Is Nothing Then DelRange.Delete shift:=xlUp
LetsContinue:
    Application.ScreenUpdating = True

    Exit Sub
Whoa:
    MsgBox Err.Description
    Resume LetsContinue
End Sub

Convert a python UTC datetime to a local datetime using only python standard library?

You can't do it with only the standard library as the standard library doesn't have any timezones. You need pytz or dateutil.

>>> from datetime import datetime
>>> now = datetime.utcnow()
>>> from dateutil import tz
>>> HERE = tz.tzlocal()
>>> UTC = tz.gettz('UTC')

The Conversion:
>>> gmt = now.replace(tzinfo=UTC)
>>> gmt.astimezone(HERE)
datetime.datetime(2010, 12, 30, 15, 51, 22, 114668, tzinfo=tzlocal())

Or well, you can do it without pytz or dateutil by implementing your own timezones. But that would be silly.

JSON array get length

Check you have the line:

 import org.json.JSONArray;

at the top of your source code

Cannot lower case button text in android studio

There is a property in <Button> that is android:textAllCaps="false" that make characters in which you want in your own Small and caps. By Default its became True so write this code and make textAllCaps=false then you can write text on button in small and Caps letter as per your requirement. Complete code for a Button which allow use to write letters as per our requirement.

 <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/btnLogin"
            android:text="Login for Chat"
            android:textAllCaps="false"/>

What is the difference between <p> and <div>?

<p> indicates a paragraph and has semantic meaning.

<div> is simply a block container for other content.

Anything that can go in a <p> can go in a <div> but the reverse is not true. <div> tags can have block-level elements as children. <p> elements cannot.

Tae a look at the HTML DTD.

<!ENTITY % inline "#PCDATA | %fontstyle; | %phrase; | %special; | %formctrl;">
<!ENTITY % block
     "P | %heading; | %list; | %preformatted; | DL | DIV | NOSCRIPT |
      BLOCKQUOTE | FORM | HR | TABLE | FIELDSET | ADDRESS">

<!ENTITY % flow "%block; | %inline;">

<!ELEMENT DIV - - (%flow;)*            -- generic language/style container -->
<!ELEMENT P - O (%inline;)*            -- paragraph -->

Guzzle 6: no more json() method for responses

You switch to:

json_decode($response->getBody(), true)

Instead of the other comment if you want it to work exactly as before in order to get arrays instead of objects.

Locating child nodes of WebElements in selenium

The toString() method of Selenium's By-Class produces something like "By.xpath: //XpathFoo"

So you could take a substring starting at the colon with something like this:

String selector = divA.toString().substring(s.indexOf(":") + 2);

With this, you could find your element inside your other element with this:

WebElement input = driver.findElement( By.xpath( selector + "//input" ) );

Advantage: You have to search only once on the actual SUT, so it could give you a bonus in performance.

Disadvantage: Ugly... if you want to search for the parent element with css selectory and use xpath for it's childs, you have to check for types before you concatenate... In this case, Slanec's solution (using findElement on a WebElement) is much better.

Dead simple example of using Multiprocessing Queue, Pool and Locking

The best solution for your problem is to utilize a Pool. Using Queues and having a separate "queue feeding" functionality is probably overkill.

Here's a slightly rearranged version of your program, this time with only 2 processes coralled in a Pool. I believe it's the easiest way to go, with minimal changes to original code:

import multiprocessing
import time

data = (
    ['a', '2'], ['b', '4'], ['c', '6'], ['d', '8'],
    ['e', '1'], ['f', '3'], ['g', '5'], ['h', '7']
)

def mp_worker((inputs, the_time)):
    print " Processs %s\tWaiting %s seconds" % (inputs, the_time)
    time.sleep(int(the_time))
    print " Process %s\tDONE" % inputs

def mp_handler():
    p = multiprocessing.Pool(2)
    p.map(mp_worker, data)

if __name__ == '__main__':
    mp_handler()

Note that mp_worker() function now accepts a single argument (a tuple of the two previous arguments) because the map() function chunks up your input data into sublists, each sublist given as a single argument to your worker function.

Output:

Processs a  Waiting 2 seconds
Processs b  Waiting 4 seconds
Process a   DONE
Processs c  Waiting 6 seconds
Process b   DONE
Processs d  Waiting 8 seconds
Process c   DONE
Processs e  Waiting 1 seconds
Process e   DONE
Processs f  Waiting 3 seconds
Process d   DONE
Processs g  Waiting 5 seconds
Process f   DONE
Processs h  Waiting 7 seconds
Process g   DONE
Process h   DONE

Edit as per @Thales comment below:

If you want "a lock for each pool limit" so that your processes run in tandem pairs, ala:

A waiting B waiting | A done , B done | C waiting , D waiting | C done, D done | ...

then change the handler function to launch pools (of 2 processes) for each pair of data:

def mp_handler():
    subdata = zip(data[0::2], data[1::2])
    for task1, task2 in subdata:
        p = multiprocessing.Pool(2)
        p.map(mp_worker, (task1, task2))

Now your output is:

 Processs a Waiting 2 seconds
 Processs b Waiting 4 seconds
 Process a  DONE
 Process b  DONE
 Processs c Waiting 6 seconds
 Processs d Waiting 8 seconds
 Process c  DONE
 Process d  DONE
 Processs e Waiting 1 seconds
 Processs f Waiting 3 seconds
 Process e  DONE
 Process f  DONE
 Processs g Waiting 5 seconds
 Processs h Waiting 7 seconds
 Process g  DONE
 Process h  DONE

Wait for a void async method

You don't really need to do anything manually, await keyword pauses the function execution until blah() returns.

private async void SomeFunction()
{
     var x = await LoadBlahBlah(); <- Function is not paused
     //rest of the code get's executed even if LoadBlahBlah() is still executing
}

private async Task<T> LoadBlahBlah()
{
     await DoStuff();  <- function is paused
     await DoMoreStuff();
}

T is type of object blah() returns

You can't really await a void function so LoadBlahBlah() cannot be void

How to do IF NOT EXISTS in SQLite

If you want to ignore the insertion of existing value, there must be a Key field in your Table. Just create a table With Primary Key Field Like:

CREATE TABLE IF NOT EXISTS TblUsers (UserId INTEGER PRIMARY KEY, UserName varchar(100), ContactName varchar(100),Password varchar(100));

And Then Insert Or Replace / Insert Or Ignore Query on the Table Like:

INSERT OR REPLACE INTO TblUsers (UserId, UserName, ContactName ,Password) VALUES('1','UserName','ContactName','Password');

It Will Not Let it Re-Enter The Existing Primary key Value... This Is how you can Check Whether a Value exists in the table or not.

How do I return the response from an asynchronous call?

The simplest solution is create a JavaScript function and call it for the Ajax success callback.

function callServerAsync(){
    $.ajax({
        url: '...',
        success: function(response) {

            successCallback(response);
        }
    });
}

function successCallback(responseObj){
    // Do something like read the response and show data
    alert(JSON.stringify(responseObj)); // Only applicable to JSON response
}

function foo(callback) {

    $.ajax({
        url: '...',
        success: function(response) {
           return callback(null, response);
        }
    });
}

var result = foo(function(err, result){
          if (!err)
           console.log(result);    
}); 

Convert MySql DateTime stamp into JavaScript's Date format

var a=dateString.split(" ");
var b=a[0].split("-");
var c=a[1].split(":");
var date = new Date(b[0],(b[1]-1),b[2],b[0],c[1],c[2]);

"Server Tomcat v7.0 Server at localhost failed to start" without stack trace while it works in terminal

I was facing similar problem this weekend. Tried all the above mentioned tricks, but none of them worked of me. (Working in Eclipse LUNA)

Then i analysed that just before creating a particular servlet, i was running Apache Tomcat v7.0 successfully. Which was "RefreshServlet" as shown below :

RefreshServlet.java

So that practicing servlets to understand the "AutoRefresh" functioning. When i remove this servlet from my application, it works fine, but when i try to add and run this servlet, it gives the same error "Apache Tomcat v7.0 failed to start"

Don't know why, but only removing this servlet works fine for me to run the rest of my application.

So, the bottom line suggestion from me would be that if not any other trick is working, then try removing any latest servlet or any class you just created before getting this error and it may work fine for you too for the rest of the application.

Any further explanation would be appreciated. Thanks

Pass a simple string from controller to a view MVC3

To pass a string to the view as the Model, you can do:

public ActionResult Index()
{
    string myString = "This is my string";
    return View((object)myString);
}

You must cast it to an object so that MVC doesn't try to load the string as the view name, but instead pass it as the model. You could also write:

return View("Index", myString);

.. which is a bit more verbose.

Then in your view, just type it as a string:

@model string

<p>Value: @Model</p>

Then you can manipulate Model how you want.

For accessing it from a Layout page, it might be better to create an HtmlExtension for this:

public static string GetThemePath(this HtmlHelper helper)
{
    return "/path-to-theme";
}

Then inside your layout page:

<p>Value: @Html.GetThemePath()</p>

Hopefully you can apply this to your own scenario.

Edit: explicit HtmlHelper code:

namespace <root app namespace>
{
    public static class Helpers
    {
        public static string GetThemePath(this HtmlHelper helper)
        {
            return System.Web.Hosting.HostingEnvironment.MapPath("~") + "/path-to-theme";
        }
    }
}

Then in your view:

@{
    var path = Html.GetThemePath();
    // .. do stuff
}

Or: <p>Path: @Html.GetThemePath()</p>

Edit 2:

As discussed, the Helper will work if you add a @using statement to the top of your view, with the namespace pointing to the one that your helper is in.

Running an Excel macro via Python?

Hmm i was having some trouble with that part (yes still xD):

xl.Application.Run("excelsheet.xlsm!macroname.macroname")

cos im not using excel often (same with vb or macros, but i need it to use femap with python) so i finaly resolved it checking macro list: Developer -> Macros: there i saw that: this macroname.macroname should be sheet_name.macroname like in "Macros" list.

(i spend something like 30min-1h trying to solve it, so it may be helpful for noobs like me in excel) xD

How to get all keys with their values in redis

I refined the bash solution a bit, so that the more efficient scan is used instead of keys, and printing out array and hash values is supported. My solution also prints out the key name.

redis_print.sh:

#!/bin/bash

# Default to '*' key pattern, meaning all redis keys in the namespace
REDIS_KEY_PATTERN="${REDIS_KEY_PATTERN:-*}"
for key in $(redis-cli --scan --pattern "$REDIS_KEY_PATTERN")
do
    type=$(redis-cli type $key)
    if [ $type = "list" ]
    then
        printf "$key => \n$(redis-cli lrange $key 0 -1 | sed 's/^/  /')\n"
    elif [ $type = "hash" ]
    then
        printf "$key => \n$(redis-cli hgetall $key | sed 's/^/  /')\n"
    else
        printf "$key => $(redis-cli get $key)\n"
    fi
done

Note: you can formulate a one-liner of this script by removing the first line of redis_print.sh and commanding: cat redis_print.sh | tr '\n' ';' | awk '$1=$1'

React-Redux: Actions must be plain objects. Use custom middleware for async actions

The error is simply asking you to insert a Middleware in between which would help to handle async operations.

You could do that by :

npm i redux-thunk

        Inside index.js

import thunk from "redux-thunk" 
        
...createStore(rootReducers, applyMiddleware(thunk));

Now, async operations will work inside your functions.

How can I rebuild indexes and update stats in MySQL innoDB?

This is done with

ANALYZE TABLE table_name;

Read more about it here.

ANALYZE TABLE analyzes and stores the key distribution for a table. During the analysis, the table is locked with a read lock for MyISAM, BDB, and InnoDB. This statement works with MyISAM, BDB, InnoDB, and NDB tables.

Android map v2 zoom to show all the markers

I worked the same problem for showing multiple markers in Kotlin using a fragment

first declare a list of markers

private lateinit var markers: MutableList<Marker>

initialize this in the oncreate method of the frament

override fun onCreateView(
    inflater: LayoutInflater,
    container: ViewGroup?,
    savedInstanceState: Bundle?
                         ): View? {
    //initialize markers list

    markers = mutableListOf()
   
    return inflater.inflate(R.layout.fragment_driver_map, container, false)
}

on the OnMapReadyCallback add the markers to the markers list

private val callback = OnMapReadyCallback { googleMap ->

    map = googleMap

    markers.add(
        map.addMarker(
            MarkerOptions().position(riderLatLng)
                .title("Driver")
                .snippet("Driver")
                .icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_RED))))


    markers.add(
        map.addMarker(
            MarkerOptions().position(driverLatLng)
                .title("Driver")
                .snippet("Driver")
                .icon(BitmapDescriptorFactory.defaultMarker(BitmapDescriptorFactory.HUE_GREEN))))

Still on the callback

//create builder
    val builder = LatLngBounds.builder()

    //loop through the markers list
    for (marker in markers) {

        builder.include(marker.position)
    }
    //create a bound
    val bounds = builder.build()

    //set a 200 pixels padding from the edge of the screen
    val cu = CameraUpdateFactory.newLatLngBounds(bounds,200)
    
    //move and animate the camera
    map.moveCamera(cu)
    //animate camera by providing zoom and duration args, callBack set to null
    map.animateCamera(CameraUpdateFactory.zoomTo(10f), 2000, null)

Merry coding guys

The PowerShell -and conditional operator

You can simplify it to

if ($user_sam -and $user_case) {
  ...
}

because empty strings coerce to $false (and so does $null, for that matter).

What is a Windows Handle?

So at the most basic level a HANDLE of any sort is a pointer to a pointer or

#define HANDLE void **

Now as to why you would want to use it

Lets take a setup:

class Object{
   int Value;
}

class LargeObj{

   char * val;
   LargeObj()
   {
      val = malloc(2048 * 1000);
   }

}

void foo(Object bar){
    LargeObj lo = new LargeObj();
    bar.Value++;
}

void main()
{
   Object obj = new Object();
   obj.val = 1;
   foo(obj);
   printf("%d", obj.val);
}

So because obj was passed by value (make a copy and give that to the function) to foo, the printf will print the original value of 1.

Now if we update foo to:

void foo(Object * bar)
{
    LargeObj lo = new LargeObj();
    bar->val++;
}

There is a chance that the printf will print the updated value of 2. But there is also the possibility that foo will cause some form of memory corruption or exception.

The reason is this while you are now using a pointer to pass obj to the function you are also allocating 2 Megs of memory, this could cause the OS to move the memory around updating the location of obj. Since you have passed the pointer by value, if obj gets moved then the OS updates the pointer but not the copy in the function and potentially causing problems.

A final update to foo of:

void foo(Object **bar){
    LargeObj lo = LargeObj();
    Object * b = &bar;
    b->val++;
}

This will always print the updated value.

See, when the compiler allocates memory for pointers it marks them as immovable, so any re-shuffling of memory caused by the large object being allocated the value passed to the function will point to the correct address to find out the final location in memory to update.

Any particular types of HANDLEs (hWnd, FILE, etc) are domain specific and point to a certain type of structure to protect against memory corruption.

How to return data from PHP to a jQuery ajax call

based on accepted answer

$output = some_function();
  echo $output;

if it results array then use json_encode it will result json array which is supportable by javascript

$output = some_function();
  echo json_encode($output);

If someone wants to stop execution after you echo some result use exit method of php. It will work like return keyword

$output = some_function();
  echo $output;
exit;

How can I create directories recursively?

os.makedirs is what you need. For chmod or chown you'll have to use os.walk and use it on every file/dir yourself.

PostgreSQL: Modify OWNER on all tables simultaneously in PostgreSQL

Docker: Modify Owner of all Tables + Sequences

export user="your_new_owner"
export dbname="your_db_name"

cat <<EOF | docker run -i --rm --link postgres:postgres postgres sh -c "psql -h \$POSTGRES_PORT_5432_TCP_ADDR -p \$POSTGRES_PORT_5432_TCP_PORT -U postgres -d $dbname" | grep ALTER | docker run -i --rm --link postgres:postgres postgres sh -c "psql -h \$POSTGRES_PORT_5432_TCP_ADDR -p \$POSTGRES_PORT_5432_TCP_PORT -U postgres -d $dbname"
SELECT 'ALTER TABLE '||schemaname||'.'||tablename||' OWNER TO $user;' FROM pg_tables WHERE schemaname = 'public';
SELECT 'ALTER SEQUENCE '||relname||' OWNER TO $user;' FROM pg_class WHERE relkind = 'S';
EOF

Group by in LINQ

You can also Try this:

var results= persons.GroupBy(n => new { n.PersonId, n.car})
                .Select(g => new {
                               g.Key.PersonId,
                               g.Key.car)}).ToList();

Get url without querystring

This is my solution:

Request.Url.AbsoluteUri.Replace(Request.Url.Query, String.Empty);

How do I add an integer value with javascript (jquery) to a value that's returning a string?

Parse int is the tool you should use here, but like any tool it should be used correctly. When using parseInt you should always use the radix parameter to ensure the correct base is used

var currentValue = parseInt($("#replies").text(),10);

How to get the height of a body element

Simply use

$(document).height() // - $('body').offset().top

and / or

$(window).height()

instead of $('body').height();

How to handle button clicks using the XML onClick within Fragments

Though I've spotted some nice answers relying on data binding, I didn't see any going to the full extent with that approach -- in the sense of enabling fragment resolution while allowing for fragment-free layout definitions in XML's.

So assuming data binding is enabled, here's a generic solution I can propose; A bit long but it definitely works (with some caveats):

Step 1: Custom OnClick Implementation

This will run a fragment-aware search through contexts associated with the tapped-on view (e.g. button):


// CustomOnClick.kt

@file:JvmName("CustomOnClick")

package com.example

import android.app.Activity
import android.content.Context
import android.content.ContextWrapper
import android.view.View
import androidx.fragment.app.Fragment
import androidx.fragment.app.FragmentActivity
import java.lang.reflect.Method

fun onClick(view: View, methodName: String) {
    resolveOnClickInvocation(view, methodName)?.invoke(view)
}

private data class OnClickInvocation(val obj: Any, val method: Method) {
    fun invoke(view: View) {
        method.invoke(obj, view)
    }
}

private fun resolveOnClickInvocation(view: View, methodName: String): OnClickInvocation? =
    searchContexts(view) { context ->
        var invocation: OnClickInvocation? = null
        if (context is Activity) {
            val activity = context as? FragmentActivity
                    ?: throw IllegalStateException("A non-FragmentActivity is not supported (looking up an onClick handler of $view)")

            invocation = getTopFragment(activity)?.let { fragment ->
                resolveInvocation(fragment, methodName)
            }?: resolveInvocation(context, methodName)
        }
        invocation
    }

private fun getTopFragment(activity: FragmentActivity): Fragment? {
    val fragments = activity.supportFragmentManager.fragments
    return if (fragments.isEmpty()) null else fragments.last()
}

private fun resolveInvocation(target: Any, methodName: String): OnClickInvocation? =
    try {
        val method = target.javaClass.getMethod(methodName, View::class.java)
        OnClickInvocation(target, method)
    } catch (e: NoSuchMethodException) {
        null
    }

private fun <T: Any> searchContexts(view: View, matcher: (context: Context) -> T?): T? {
    var context = view.context
    while (context != null && context is ContextWrapper) {
        val result = matcher(context)
        if (result == null) {
            context = context.baseContext
        } else {
            return result
        }
    }
    return null
}

Note: loosely based on the original Android implementation (see https://android.googlesource.com/platform/frameworks/base/+/a175a5b/core/java/android/view/View.java#3025)

Step 2: Declarative application in layout files

Then, in data-binding aware XML's:

<layout>
  <data>
     <import type="com.example.CustomOnClick"/>
  </data>

  <Button
    android:onClick='@{(v) -> CustomOnClick.onClick(v, "myClickMethod")}'
  </Button>
</layout>

Caveats

  • Assumes a 'modern' FragmentActivity based implementation
  • Can only lookup method of "top-most" (i.e. last) fragment in stack (though that can be fixed, if need be)

Why do package names often begin with "com"

Wikipedia, of all places, actually discusses this.

The idea is to make sure all package names are unique world-wide, by having authors use a variant of a DNS name they own to name the package. For example, the owners of the domain name joda.org created a number of packages whose names begin with org.joda, for example:

  • org.joda.time
  • org.joda.time.base
  • org.joda.time.chrono
  • org.joda.time.convert
  • org.joda.time.field
  • org.joda.time.format

Adding a Button to a WPF DataGrid

First create a DataGridTemplateColumn to contain the button:

<DataGridTemplateColumn>
  <DataGridTemplateColumn.CellTemplate> 
    <DataTemplate> 
      <Button Click="ShowHideDetails">Details</Button> 
    </DataTemplate> 
  </DataGridTemplateColumn.CellTemplate> 
</DataGridTemplateColumn>

When the button is clicked, update the containing DataGridRow's DetailsVisibility:

void ShowHideDetails(object sender, RoutedEventArgs e)
{
    for (var vis = sender as Visual; vis != null; vis = VisualTreeHelper.GetParent(vis) as Visual)
    if (vis is DataGridRow)
    {
        var row = (DataGridRow)vis;
        row.DetailsVisibility = 
        row.DetailsVisibility == Visibility.Visible ? Visibility.Collapsed : Visibility.Visible;
        break;
    }
}

How to force maven update?

I ran into this recently and running the following fixed all the problems

mvn -fae install

How to drop SQL default constraint without knowing its name?

Drop all default contstraints in a database - safe for nvarchar(max) threshold.

/* WARNING: THE SAMPLE BELOW; DROPS ALL THE DEFAULT CONSTRAINTS IN A DATABASE */ 
/* MAY 03, 2013 - BY WISEROOT  */
declare @table_name nvarchar(128)
declare @column_name nvarchar(128)
declare @df_name nvarchar(128)
declare @cmd nvarchar(128) 

declare table_names cursor for 
 SELECT t.name TableName, c.name ColumnName
 FROM sys.columns c INNER JOIN
     sys.tables t ON c.object_id = t.object_id INNER JOIN
     sys.schemas s ON t.schema_id = s.schema_id
     ORDER BY T.name, c.name

     open table_names
fetch next from table_names into @table_name , @column_name
while @@fetch_status = 0
BEGIN

if exists (SELECT top(1) d.name from sys.tables t join sys.default_constraints d on d.parent_object_id = t.object_id join sys.columns c on c.object_id = t.object_id and c.column_id = d.parent_column_id where t.name = @table_name and c.name = @column_name)
BEGIN
    SET @df_name = (SELECT top(1) d.name from sys.tables t join sys.default_constraints d on d.parent_object_id = t.object_id join sys.columns c on c.object_id = t.object_id and c.column_id = d.parent_column_id where t.name = @table_name and c.name = @column_name)
    select @cmd = 'ALTER TABLE [' + @table_name +  '] DROP CONSTRAINT [' +  @df_name + ']'
    print @cmd
    EXEC sp_executeSQL @cmd;
END

  fetch next from table_names into @table_name , @column_name
END

close table_names 
deallocate table_names

Class has no initializers Swift

simply provide the init block for HomeCell class

it's work in my case

Class JavaLaunchHelper is implemented in two places

This happened to me when I installed Intellij IDEA 2017, go to menu Preferences -> Build, Execution, Deployment -> Debugger and disable the option: "Force Classic VM for JDK 1.3.x and earlier". This works to me.

How to create roles in ASP.NET Core and assign them to users?

I have created an action in the Accounts controller that calls a function to create the roles and assign the Admin role to the default user. (You should probably remove the default user in production):

    private async Task CreateRolesandUsers()
    {  
        bool x = await _roleManager.RoleExistsAsync("Admin");
        if (!x)
        {
            // first we create Admin rool    
            var role = new IdentityRole();
            role.Name = "Admin";
            await _roleManager.CreateAsync(role);

            //Here we create a Admin super user who will maintain the website                   

            var user = new ApplicationUser();
            user.UserName = "default";
            user.Email = "[email protected]";

            string userPWD = "somepassword";

            IdentityResult chkUser = await _userManager.CreateAsync(user, userPWD);

            //Add default User to Role Admin    
            if (chkUser.Succeeded)
            {
                var result1 = await _userManager.AddToRoleAsync(user, "Admin");
            }
        }

        // creating Creating Manager role     
        x = await _roleManager.RoleExistsAsync("Manager");
        if (!x)
        {
            var role = new IdentityRole();
            role.Name = "Manager";
            await _roleManager.CreateAsync(role);
        }

        // creating Creating Employee role     
        x = await _roleManager.RoleExistsAsync("Employee");
        if (!x)
        {
            var role = new IdentityRole();
            role.Name = "Employee";
            await _roleManager.CreateAsync(role);
        }
  }

After you could create a controller to manage roles for the users.

Android global variable

There are a few different ways you can achieve what you are asking for.

1.) Extend the application class and instantiate your controller and model objects there.

public class FavoriteColorsApplication extends Application {

    private static FavoriteColorsApplication application;
    private FavoriteColorsService service;

    public FavoriteColorsApplication getInstance() {
        return application;
    }

    @Override
    public void onCreate() {
        super.onCreate();
        application = this;
        application.initialize();
    }

    private void initialize() {
        service = new FavoriteColorsService();
    }

    public FavoriteColorsService getService() {
        return service;
    }

}

Then you can call the your singleton from your custom Application object at any time:

public class FavoriteColorsActivity extends Activity {

private FavoriteColorsService service = null;
private ArrayAdapter<String> adapter;
private List<String> favoriteColors = new ArrayList<String>();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_favorite_colors);

    service = ((FavoriteColorsApplication) getApplication()).getService();
    favoriteColors = service.findAllColors();

    ListView lv = (ListView) findViewById(R.id.favoriteColorsListView);
    adapter = new ArrayAdapter<String>(this, R.layout.favorite_colors_list_item,
            favoriteColors);
    lv.setAdapter(adapter);
}

2.) You can have your controller just create a singleton instance of itself:

public class Controller {
    private static final String TAG = "Controller";
    private static sController sController;
    private Dao mDao;

    private Controller() {
        mDao = new Dao();    
    }

    public static Controller create() {
        if (sController == null) {
            sController = new Controller();
        }
        return sController;
    }
}

Then you can just call the create method from any Activity or Fragment and it will create a new controller if one doesn't already exist, otherwise it will return the preexisting controller.

3.) Finally, there is a slick framework created at Square which provides you dependency injection within Android. It is called Dagger. I won't go into how to use it here, but it is very slick if you need that sort of thing.

I hope I gave enough detail in regards to how you can do what you are hoping for.

Add ripple effect to my button with button background color?

An alternative solution to using the <ripple> tag (which I personally prefer not to do, because the colors are not "default"), is the following:

Create a drawable for the button background, and include <item android:drawable="?attr/selectableItemBackground"> in the <layer-list>

Then (and I think this is the important part) programmatically set backgroundResource(R.drawable.custom_button) on your button instance.

Activity/Fragment

Button btn_temp = view.findViewById(R.id.btn_temp);
btn_temp.setBackgroundResource(R.drawable.custom_button);

Layout

<Button
    android:id="@+id/btn_temp"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:background="@drawable/custom_button"
    android:text="Test" />

custom_button.xml

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape android:shape="rectangle">
            <solid android:color="@android:color/white" />
            <corners android:radius="10dp" />
        </shape>
    </item>
    <item android:drawable="?attr/selectableItemBackground" />
</layer-list>

Convert dictionary to list collection in C#

If you want convert Keys:

List<string> listNumber = dicNumber.Keys.ToList();

else if you want convert Values:

List<string> listNumber = dicNumber.Values.ToList();

cURL POST command line on WINDOWS RESTful service

One more alternative cross-platform solution on powershell 6.2.3:

$headers = @{
    'Authorization' = 'Token 12d119ad48f9b70ed53846f9e3d051dc31afab27'
}

$body = @"
{
    "value":"3.92.0", 
    "product":"847"
}
"@


$params = @{
    Uri         = 'http://local.vcs:9999/api/v1/version/'
    Headers     = $headers
    Method      = 'POST'
    Body        = $body
    ContentType = 'application/json'

}

Invoke-RestMethod @params

The APK file does not exist on disk

Using Android Studio 2.2.1, I clicked the Sync Project with Gradle Files option, from the dropdown at the top, Tools>Android

Similar, to an answer posted above, see below for a screenshot of how to get to this option.

enter image description here

org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'customerService' is defined

You will have to annotate your service with @Service since you have said I am using annotations for mapping

Multidimensional Lists in C#

It's old but thought I'd add my two cents... Not sure if it will work but try using a KeyValuePair:

 List<KeyValuePair<?, ?>> LinkList = new List<KeyValuePair<?, ?>>();
 LinkList.Add(new KeyValuePair<?, ?>(Object, Object));

You'll end up with something like this:

 LinkList[0] = <Object, Object>
 LinkList[1] = <Object, Object>
 LinkList[2] = <Object, Object>

and so on...

How to add option to select list in jQuery

This is working fine, try out this.

var ob = $("#myListBox");

for (var i = 0; i < buildings.length; i++) {
     var val = buildings[i];
     var text = buildings[i];

     ob.prepend("<option value="+ val +">" + text + "</option>");
}

Copy files without overwrite

Robocopy can be downloaded here for systems where it is not installed already. (I.e. Windows Server 2003.)

http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=17657 (no reboot required for installation)

Remember to set your path to the robocopy exe. You do this by right clicking "my computer"> properties>advanced>"Environment Variables", then find the path system variable and add this to the end: ";C:\Program Files\Windows Resource Kits\Tools" or wherever you installed it. Make sure to leave the path variable strings that are already there and just append the addtional path.

once the path is set, you can run the command that belisarius suggests. It works great.

Chrome extension id - how to find it

Extension IDs can be found in:

chrome://extensions (Chrome_Hotdog >> More_tools >> Extensions) Developer mode.

For Linux: $HOME/.config/google-chrome/Default/Preferences (json file) under ["extensions"].

How to use (install) dblink in PostgreSQL?

# or even faster copy paste answer if you have sudo on the host 
sudo su - postgres  -c "psql template1 -c 'CREATE EXTENSION IF NOT EXISTS \"dblink\";'"

What is “the inverse side of the association” in a bidirectional JPA OneToMany/ManyToOne association?

Table relationships vs. entity relationships

In a relational database system, there can be only three types of table relationships:

  • one-to-many (via a Foreign Key column)
  • one-to-one (via a shared Primary Key)
  • many-to-many (via a link table with two Foreign Keys referencing two separate parent tables)

So, a one-to-many table relationship looks as follows:

one-to-many table relationship

Note that the relationship is based on the Foreign Key column (e.g., post_id) in the child table.

So, there is a single source of truth when it comes to managing a one-to-many table relationship.

Now, if you take a bidirectional entity relationship that maps on the one-to-many table relationship we saw previously:

Bidirectional One-To-Many entity association

If you take a look at the diagram above, you can see that there are two ways to manage this relationship.

In the Post entity, you have the comments collection:

@OneToMany(
    mappedBy = "post",
    cascade = CascadeType.ALL,
    orphanRemoval = true
)
private List<PostComment> comments = new ArrayList<>();

And, in the PostComment, the post association is mapped as follows:

@ManyToOne(
    fetch = FetchType.LAZY
)
@JoinColumn(name = "post_id")
private Post post;

So, you have two sides that can change the entity association:

  • By adding an entry in the comments child collection, a new post_comment row should be associated with the parent post entity via its post_id column.
  • By setting the post property of the PostComment entity, the post_id column should be updated as well.

Because there are two ways to represent the Foreign Key column, you must define which is the source of truth when it comes to translating the association state change into its equivalent Foreign Key column value modification.

MappedBy (a.k.a the inverse side)

The mappedBy attribute tells that the @ManyToOne side is in charge of managing the Foreign Key column, and the collection is used only to fetch the child entities and to cascade parent entity state changes to children (e.g., removing the parent should also remove the child entities).

It's called the inverse side because it references the child entity property that manages this table relationship.

Synchronize both sides of a bidirectional association

Now, even if you defined the mappedBy attribute and the child-side @ManyToOne association manages the Foreign Key column, you still need to synchronize both sides of the bidirectional association.

The best way to do that is to add these two utility methods:

public void addComment(PostComment comment) {
    comments.add(comment);
    comment.setPost(this);
}

public void removeComment(PostComment comment) {
    comments.remove(comment);
    comment.setPost(null);
}

The addComment and removeComment methods ensure that both sides are synchronized. So, if we add a child entity, the child entity needs to point to the parent and the parent entity should have the child contained in the child collection.

Postgres password authentication fails

pg_hba.conf entry define login methods by IP addresses. You need to show the relevant portion of pg_hba.conf in order to get proper help.

Change this line:

host    all             all             <my-ip-address>/32        md5

To reflect your local network settings. So, if your IP is 192.168.16.78 (class C) with a mask of 255.255.255.0, then put this:

host    all             all             192.168.16.0/24        md5

Make sure your WINDOWS MACHINE is in that network 192.168.16.0 and try again.

Getting time and date from timestamp with php

$timestamp='2014-11-21 16:38:00';

list($date,$time)=explode(' ',$timestamp);

// just time

preg_match("/ (\d\d:\d\d):\d\d$/",$timestamp,$match);
echo "\n<br>".$match[1];

How to write string literals in python without having to escape them?

Raw string literals:

>>> r'abc\dev\t'
'abc\\dev\\t'

How to blur background images in Android

The simplest way to achieve this is given below,

I)

Glide.with(context.getApplicationContext())
                        .load(Your Path)   
                        .override(15, 15) // (change according to your wish)
                        .error(R.drawable.placeholder)
                        .into(image.score);

else you can follow the code below..

II)

1.Create a class.(Code is given below)

public class BlurTransformation extends BitmapTransformation {

    private RenderScript rs;

    public BlurTransformation(Context context) {
        super( context );

        rs = RenderScript.create( context );
    }

    @Override
    protected Bitmap transform(BitmapPool pool, Bitmap toTransform, int outWidth, int outHeight) {
        Bitmap blurredBitmap = toTransform.copy( Bitmap.Config.ARGB_8888, true );

        // Allocate memory for Renderscript to work with
        Allocation input = Allocation.createFromBitmap(
            rs, 
            blurredBitmap, 
            Allocation.MipmapControl.MIPMAP_FULL, 
            Allocation.USAGE_SHARED
        );
        Allocation output = Allocation.createTyped(rs, input.getType());

        // Load up an instance of the specific script that we want to use.
        ScriptIntrinsicBlur script = ScriptIntrinsicBlur.create(rs, Element.U8_4(rs));
        script.setInput(input);

        // Set the blur radius
        script.setRadius(10);

        // Start the ScriptIntrinisicBlur
        script.forEach(output);

        // Copy the output to the blurred bitmap
        output.copyTo(blurredBitmap);

        toTransform.recycle();

        return blurredBitmap;
    }

    @Override
    public String getId() {
        return "blur";
    }
}

2.Set image to ImageView using Glide.

eg:

Glide.with(this)
     .load(expertViewDetailsModel.expert.image)
     .asBitmap()
     .transform(new BlurTransformation(this))
     .into(ivBackground);

Multiline TextBox multiple newline

Try this one

textBox1.Text = "Line1" + Environment.NewLine + "Line2";

Working fine for me...

Pass request headers in a jQuery AJAX GET call

Use beforeSend:

$.ajax({
         url: "http://localhost/PlatformPortal/Buyers/Account/SignIn",
         data: { signature: authHeader },
         type: "GET",
         beforeSend: function(xhr){xhr.setRequestHeader('X-Test-Header', 'test-value');},
         success: function() { alert('Success!' + authHeader); }
      });

http://api.jquery.com/jQuery.ajax/

http://www.w3.org/TR/XMLHttpRequest/#the-setrequestheader-method

How to make div appear in front of another?

You can set the z-index in css

<div style="z-index: -1"></div>

How do I combine two dataframes?

I believe you can use the append method

bigdata = data1.append(data2, ignore_index=True)

to keep their indexes just dont use the ignore_index keyword ...

How can I find all matches to a regular expression in Python?

Use re.findall or re.finditer instead.

re.findall(pattern, string) returns a list of matching strings.

re.finditer(pattern, string) returns an iterator over MatchObject objects.

Example:

re.findall( r'all (.*?) are', 'all cats are smarter than dogs, all dogs are dumber than cats')
# Output: ['cats', 'dogs']

[x.group() for x in re.finditer( r'all (.*?) are', 'all cats are smarter than dogs, all dogs are dumber than cats')]
# Output: ['all cats are', 'all dogs are']

"TypeError: (Integer) is not JSON serializable" when serializing JSON in Python?

as @JAC pointed out in the comments of the highest rated answer, the generic solution (for all numpy types) can be found in the thread Converting numpy dtypes to native python types.

Nevertheless, I´ll add my version of the solution below, as my in my case I needed a generic solution that combines these answers and with the answers of the other thread. This should work with almost all numpy types.

def convert(o):
    if isinstance(o, np.generic): return o.item()  
    raise TypeError

json.dumps({'value': numpy.int64(42)}, default=convert)

jQuery text() and newlines

You can use html instead of text and replace each occurrence of \n with <br>. You will have to correctly escape your text though.

x = x.replace(/&/g, '&amp;')
     .replace(/>/g, '&gt;')
     .replace(/</g, '&lt;')
     .replace(/\n/g, '<br>');

Find a commit on GitHub given the commit hash

A URL of the form https://github.com/<owner>/<project>/commit/<hash> will show you the changes introduced in that commit. For example here's a recent bugfix I made to one of my projects on GitHub:

https://github.com/jerith666/git-graph/commit/35e32b6a00dec02ae7d7c45c6b7106779a124685

You can also shorten the hash to any unique prefix, like so:

https://github.com/jerith666/git-graph/commit/35e32b


I know you just asked about GitHub, but for completeness: If you have the repository checked out, from the command line, you can achieve basically the same thing with either of these commands (unique prefixes work here too):

git show 35e32b6a00dec02ae7d7c45c6b7106779a124685
git log -p -1 35e32b6a00dec02ae7d7c45c6b7106779a124685

Note: If you shorten the commit hash too far, the command line gives you a helpful disambiguation message, but GitHub will just return a 404.

PHP Parse error: syntax error, unexpected T_PUBLIC

You can remove public keyword from your functions, because, you have to define a class in order to declare public, private or protected function

jQuery AJAX file upload PHP

Best File Upload Using Jquery Ajax With Materialise Click Here to Download

When you select image the image will be Converted in base 64 and you can store this in to database so it will be light weight also.

support FragmentPagerAdapter holds reference to old fragments

I faced the same issue but my ViewPager was inside a TopFragment which created and set an adapter using setAdapter(new FragmentPagerAdapter(getChildFragmentManager())).

I fixed this issue by overriding onAttachFragment(Fragment childFragment) in the TopFragment like this:

@Override
public void onAttachFragment(Fragment childFragment) {
    if (childFragment instanceof OnboardingDiamondsFragment) {
        mChildFragment = (ChildFragment) childFragment;
    }

    super.onAttachFragment(childFragment);
}

As known already (see answers above), when the childFragmentManager recreate itself, it also create the fragments which were inside the viewPager.
The important part is that after that, he calls onAttachFragment and now we have a reference to the new recreated fragment!

Hope this will help anyone getting this old Q like me :)

Print specific part of webpage

try this one.

export function printSectionOfWebpage(sectionSelector) {
    const $body = jquery('body');
    const $sectionToPrint = jquery(sectionSelector);
    const $sectionToPrintParent = $sectionToPrint.parent();
    const $printContainer = jquery('<div style="position:relative;">');

    $printContainer.height($sectionToPrint.height()).append($sectionToPrint).prependTo($body);

    const $content = $body.children().not($printContainer).not('script').detach();

    /**
     * Needed for those who use Bootstrap 3.x, because some of
     * its `@media print` styles ain't play nicely when printing.
     */
    const $patchedStyle = jquery('<style media="print">')
        .text(
            `
          img { max-width: none !important; }
          a[href]:after { content: ""; }
        `
        )
        .appendTo('head');

    window.print();

    $body.prepend($content);
    $sectionToPrintParent.prepend($sectionToPrint);

    $printContainer.remove();
    $patchedStyle.remove();
}

How to use default Android drawables

Java Usage example: myMenuItem.setIcon(android.R.drawable.ic_menu_save);

Resource Usage example: android:icon="@android:drawable/ic_menu_save"

Random character generator with a range of (A..Z, 0..9) and punctuation

Why reinvent the wheel? RandomStringUtils from Apache Commons has functions to which you can specify the character set from which characters are generated. You can take what you need to your app:

http://kickjava.com/src/org/apache/commons/lang/RandomStringUtils.java.htm

How to SELECT in Oracle using a DBLINK located in a different schema?

I had the same problem I used the solution offered above - I dropped the SYNONYM, created a VIEW with the same name as the synonym. it had a select using the dblink , and gave GRANT SELECT to the other schema It worked great.

Http Post request with content type application/x-www-form-urlencoded not working in Spring

The easiest thing to do is to set the content type of your ajax request to "application/json; charset=utf-8" and then let your API method consume JSON. Like this:

var basicInfo = JSON.stringify({
    firstName: playerProfile.firstName(),
    lastName: playerProfile.lastName(),
    gender: playerProfile.gender(),
    address: playerProfile.address(),
    country: playerProfile.country(),
    bio: playerProfile.bio()
});

$.ajax({
    url: "http://localhost:8080/social/profile/update",
    type: 'POST',
    dataType: 'json',
    contentType: "application/json; charset=utf-8",
    data: basicInfo,
    success: function(data) {
        // ...
    }
});


@RequestMapping(
    value = "/profile/update",
    method = RequestMethod.POST,
    produces = MediaType.APPLICATION_JSON_VALUE,
    consumes = MediaType.APPLICATION_JSON_VALUE)
public ResponseEntity<ResponseModel> UpdateUserProfile(
    @RequestBody User usersNewDetails,
    HttpServletRequest request,
    HttpServletResponse response
) {
    // ...
}

I guess the problem is that Spring Boot has issues submitting form data which is not JSON via ajax request.

Note: the default content type for ajax is "application/x-www-form-urlencoded".

javax.naming.NameNotFoundException: Name is not bound in this Context. Unable to find

In Tomcat 8.0.44 I did this: create the JNDI on Tomcat's server.xml between the tag "GlobalNamingResources" For example:

_x000D_
_x000D_
<GlobalNamingResources>_x000D_
    <!-- Editable user database that can also be used by_x000D_
         UserDatabaseRealm to authenticate users_x000D_
    -->_x000D_
  <!-- Other previus resouces -->_x000D_
    <Resource auth="Container" driverClassName="org.postgresql.Driver" global="jdbc/your_jndi" _x000D_
    maxActive="100" maxIdle="20" maxWait="1000" minIdle="5" name="jdbc/your_jndi" password="your_password" _x000D_
    type="javax.sql.DataSource" url="jdbc:postgresql://localhost:5432/your_database?user=postgres" username="database_username"/>_x000D_
  </GlobalNamingResources>
_x000D_
_x000D_
_x000D_ In your web application you need a link to that resource (ResourceLink):

project explore

_x000D_
_x000D_
<?xml version="1.0" encoding="UTF-8"?>_x000D_
<Context reloadable="true" >_x000D_
   <ResourceLink name="jdbc/your_jndi"_x000D_
      global="jdbc/your_jndi"_x000D_
      auth="Container"_x000D_
      type="javax.sql.DataSource" />_x000D_
</Context>
_x000D_
_x000D_
_x000D_

So if you're using Hiberte with spring you can tell to him to use the JNDI in your persistence.xml

persistence.xml location

_x000D_
_x000D_
<?xml version="1.0" encoding="UTF-8"?>_x000D_
<persistence xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"_x000D_
 xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd"_x000D_
 version="2.0" xmlns="http://java.sun.com/xml/ns/persistence">_x000D_
 <persistence-unit name="UNIT_NAME" transaction-type="RESOURCE_LOCAL">_x000D_
  <provider>org.hibernate.ejb.HibernatePersistence</provider>_x000D_
_x000D_
  <properties>_x000D_
   <property name="javax.persistence.jdbc.driver"   value="org.postgresql.Driver" />_x000D_
   <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQL82Dialect" />_x000D_
   _x000D_
   <!--  <property name="hibernate.jdbc.time_zone" value="UTC"/>-->_x000D_
   <property name="hibernate.hbm2ddl.auto" value="update" />_x000D_
   <property name="hibernate.show_sql" value="false" />_x000D_
   <property name="hibernate.format_sql" value="true"/>     _x000D_
  </properties>_x000D_
 </persistence-unit>_x000D_
</persistence>
_x000D_
_x000D_
_x000D_

So in your spring.xml you can do that:

_x000D_
_x000D_
<bean id="postGresDataSource" class="org.springframework.jndi.JndiObjectFactoryBean">_x000D_
   <property name="jndiName" value="java:comp/env/jdbc/your_jndi" />_x000D_
  </bean>_x000D_
     _x000D_
        <bean id="entityManagerFactory" class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">_x000D_
              <property name="persistenceUnitName" value="UNIT_NAME" />_x000D_
              <property name="dataSource" ref="postGresDataSource" />_x000D_
              <property name="jpaVendorAdapter"> _x000D_
                 <bean class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter" />_x000D_
              </property>_x000D_
        </bean>
_x000D_
_x000D_
_x000D_ Look above that entityManagerFactory bean refers to your UNIT_NAME configured at persistence xml and the bean postGresDataSource has a property that points to your JNDI resource in Tomcat.

_x000D_
_x000D_
<property name="jndiName" value="java:comp/env/jdbc/your_jndi" />
_x000D_
_x000D_
_x000D_

In this example I used spring with xml but you can do this programmaticaly if you prefer.

That's it, I hope helped.

"The given path's format is not supported."

Image img = Image.FromFile(System.IO.Path.GetFullPath("C:\\ File Address"));

you need getfullpath by pointed class. I had same error and fixed...

error while loading shared libraries: libncurses.so.5:

For Redhat Linux 8 try this:

sudo yum install libncurses*

Syntax error: Illegal return statement in JavaScript

return only makes sense inside a function. There is no function in your code.

Also, your code is worthy if the Department of Redundancy Department. Assuming you move it to a proper function, this would be better:

return confirm(".json_encode($message).");

EDIT much much later: Changed code to use json_encode to ensure the message contents don't break just because of an apostrophe in the message.