Programs & Examples On #Null

Null means *nothing* or *unknown*, depending on context.

How do I check for null values in JavaScript?

Strict equality operator:-

We can check null by ===

if ( value === null ){


Just by using if

if( value ) {


will evaluate to true if value is not:

  • null
  • undefined
  • NaN
  • empty string ("")
  • false
  • 0

When should I use nil and NULL in Objective-C?

To expand on a comment from @cobbal:

MacTypes.h contains:

#ifndef nil
   #define nil NULL

IllegalArgumentException or NullPointerException for a null parameter?

In this case, IllegalArgumentException conveys clear information to the user using your API that the " should not be null". As other forum users pointed out you could use NPE if you want to as long as you convey the right information to the user using your API.

GaryF and tweakt dropped "Effective Java" (which I swear by) references which recommends using NPE. And looking at how other good APIs are constructed is the best way to see how to construct your API.

Another good example is to look at the Spring APIs. For example, org.springframework.beans.BeanUtils.instantiateClass(Constructor ctor, Object[] args) has a Assert.notNull(ctor, "Constructor must not be null") line. org.springframework.util.Assert.notNull(Object object, String message) method checks to see if the argument (object) passed in is null and if it is it throws a new IllegalArgumentException(message) which is then caught in the org.springframework.beans.BeanUtils.instantiateClass(...) method.

How to check for empty value in Javascript?

First, I would check what i gets initialized to, to see if the elements returned by getElementsByName are what you think they are. Maybe split the problem by trying it with a hard-coded name like timetemp0, without the concatenation. You can also run the code through a browser debugger (FireBug, Chrome Dev Tools, IE Dev Tools).

Also, for your if-condition, this should suffice:

if (!timetemp[0].value) {
    // The value is empty.
else {
    // The value is not empty.

The empty string in Javascript is a falsey value, so the logical negation of that will get you into the if-block.

Check if object exists in JavaScript

You could use "typeof".

if(typeof maybeObject != "undefined")
    alert("GOT HERE");

How to do ToString for a possibly null object?

I disagree with that this:

String s = myObj == null ? "" : myObj.ToString();

is a hack in any way. I think it's a good example of clear code. It's absolutely obvious what you want to achieve and that you're expecting null.


I see now that you were not saying that this was a hack. But it's implied in the question that you think this way is not the way to go. In my mind it's definitely the clearest solution.

Create unique constraint with null columns

Create two partial indexes:

CREATE UNIQUE INDEX favo_3col_uni_idx ON favorites (user_id, menu_id, recipe_id)

CREATE UNIQUE INDEX favo_2col_uni_idx ON favorites (user_id, recipe_id)
WHERE menu_id IS NULL;

This way, there can only be one combination of (user_id, recipe_id) where menu_id IS NULL, effectively implementing the desired constraint.

Possible drawbacks: you cannot have a foreign key referencing (user_id, menu_id, recipe_id), you cannot base CLUSTER on a partial index, and queries without a matching WHERE condition cannot use the partial index. (It seems unlikely you'd want a FK reference three columns wide - use the PK column instead).

If you need a complete index, you can alternatively drop the WHERE condition from favo_3col_uni_idx and your requirements are still enforced.
The index, now comprising the whole table, overlaps with the other one and gets bigger. Depending on typical queries and the percentage of NULL values, this may or may not be useful. In extreme situations it might even help to maintain all three indexes (the two partial ones and a total on top).

Aside: I advise not to use mixed case identifiers in PostgreSQL.

SQL is null and = null

In SQL, a comparison between a null value and any other value (including another null) using a comparison operator (eg =, !=, <, etc) will result in a null, which is considered as false for the purposes of a where clause (strictly speaking, it's "not true", rather than "false", but the effect is the same).

The reasoning is that a null means "unknown", so the result of any comparison to a null is also "unknown". So you'll get no hit on rows by coding where my_column = null.

SQL provides the special syntax for testing if a column is null, via is null and is not null, which is a special condition to test for a null (or not a null).

Here's some SQL showing a variety of conditions and and their effect as per above.

create table t (x int, y int);
insert into t values (null, null), (null, 1), (1, 1);

select 'x = null' as test , x, y from t where x = null
union all
select 'x != null', x, y from t where x != null
union all
select 'not (x = null)', x, y from t where not (x = null)
union all
select 'x = y', x, y from t where x = y
union all
select 'not (x = y)', x, y from t where not (x = y);

returns only 1 row (as expected):

TEST    X   Y
x = y   1   1

See this running on SQLFiddle

MySQL: selecting rows where a column is null

Had the same issue where query:

SELECT * FROM 'column' WHERE 'column' IS NULL; 

returned no values. Seems to be an issue with MyISAM and the same query on the data in InnoDB returned expected results.

Went with:

SELECT * FROM 'column' WHERE 'column' = ' '; 

Returned all expected results.

How to check a string against null in java?

If we look at the implementation of the equalsIgnoreCase method, we find this part:

if (string == null || count != string.count) {
    return false;

So it will always return false if the argument is null. And this is obviously right, because the only case where it should return true is when equalsIgnoreCase was invoked on a null String, but

String nullString = null;

will definitely result in a NullPointerException.

So equals methods are not designed to test whether an object is null, just because you can't invoke them on null.

object==null or null==object?

Compare with the following code:

    String pingResult = "asd";
    long s = System.nanoTime ( );
    if ( null != pingResult )
        System.out.println ( "null != pingResult" );
    long e = System.nanoTime ( );
    System.out.println ( e - s );

    long s1 = System.nanoTime ( );
    if ( pingResult != null )
        System.out.println ( "pingResult != null" );
    long e1 = System.nanoTime ( );
    System.out.println ( e1 - s1 );

Output (After multiple executions):

null != pingResult
pingResult != null

Therefore, pingResult != null is the winner.

Checking for NULL pointer in C/C++

I'll start off with this: consistency is king, the decision is less important than the consistency in your code base.

In C++

NULL is defined as 0 or 0L in C++.

If you've read The C++ Programming Language Bjarne Stroustrup suggests using 0 explicitly to avoid the NULL macro when doing assignment, I'm not sure if he did the same with comparisons, it's been a while since I read the book, I think he just did if(some_ptr) without an explicit comparison but I am fuzzy on that.

The reason for this is that the NULL macro is deceptive (as nearly all macros are) it is actually 0 literal, not a unique type as the name suggests it might be. Avoiding macros is one of the general guidelines in C++. On the other hand, 0 looks like an integer and it is not when compared to or assigned to pointers. Personally I could go either way, but typically I skip the explicit comparison (though some people dislike this which is probably why you have a contributor suggesting a change anyway).

Regardless of personal feelings this is largely a choice of least evil as there isn't one right method.

This is clear and a common idiom and I prefer it, there is no chance of accidentally assigning a value during the comparison and it reads clearly:

if (some_ptr) {}

This is clear if you know that some_ptr is a pointer type, but it may also look like an integer comparison:

if (some_ptr != 0) {}

This is clear-ish, in common cases it makes sense... But it's a leaky abstraction, NULL is actually 0 literal and could end up being misused easily:

if (some_ptr != NULL) {}

C++11 has nullptr which is now the preferred method as it is explicit and accurate, just be careful about accidental assignment:

if (some_ptr != nullptr) {}

Until you are able to migrate to C++0x I would argue it's a waste of time worrying about which of these methods you use, they are all insufficient which is why nullptr was invented (along with generic programming issues which came up with perfect forwarding.) The most important thing is to maintain consistency.

In C

C is a different beast.

In C NULL can be defined as 0 or as ((void *)0), C99 allows for implementation defined null pointer constants. So it actually comes down to the implementation's definition of NULL and you will have to inspect it in your standard library.

Macros are very common and in general they are used a lot to make up for deficiencies in generic programming support in the language and other things as well. The language is much simpler and reliance on the preprocessor more common.

From this perspective I'd probably recommend using the NULL macro definition in C.

Difference between null and empty string

No method can be invoked on a object which is assigned a NULL value. It will give a nullPointerException. Hence, s2.length() is giving an exception.

DateTime "null" value

Just be warned - When using a Nullable its obviously no longer a 'pure' datetime object, as such you cannot access the DateTime members directly. I'll try and explain.

By using Nullable<> you're basically wrapping DateTime in a container (thank you generics) of which is nullable - obviously its purpose. This container has its own properties which you can call that will provide access to the aforementioned DateTime object; after using the correct property - in this case Nullable.Value - you then have access to the standard DateTime members, properties etc.

So - now the issue comes to mind as to the best way to access the DateTime object. There are a few ways, number 1 is by FAR the best and 2 is "dude why".

  1. Using the Nullable.Value property,

    DateTime date = myNullableObject.Value.ToUniversalTime(); //Works

    DateTime date = myNullableObject.ToUniversalTime(); //Not a datetime object, fails

  2. Converting the nullable object to datetime using Convert.ToDateTime(),

    DateTime date = Convert.ToDateTime(myNullableObject).ToUniversalTime(); //works but why...

Although the answer is well documented at this point, I believe the usage of Nullable was probably worth posting about. Sorry if you disagree.

edit: Removed a third option as it was a bit overly specific and case dependent.

Checking for a null int value from a Java ResultSet

Just an update with Java Generics.

You could create an utility method to retrieve an optional value of any Java type from a given ResultSet, previously casted.

Unfortunately, getObject(columnName, Class) does not return null, but the default value for given Java type, so 2 calls are required

public <T> T getOptionalValue(final ResultSet rs, final String columnName, final Class<T> clazz) throws SQLException {
    final T value = rs.getObject(columnName, clazz);
    return rs.wasNull() ? null : value;

In this example, your code could look like below:

final Integer columnValue = getOptionalValue(rs, Integer.class);
if (columnValue == null) {
    //null handling
} else {
    //use int value of columnValue with autoboxing

Happy to get feedback

Origin null is not allowed by Access-Control-Allow-Origin

Origin null is the local file system, so that suggests that you're loading the HTML page that does the load call via a file:/// URL (e.g., just double-clicking it in a local file browser or similar). Different browsers take different approaches to applying the Same Origin Policy to local files.

My guess is that you're seeing this using Chrome. Chrome's rules for applying the SOP to local files are very tight, it disallows even loading files from the same directory as the document. So does Opera. Some other browsers, such as Firefox, allow limited access to local files. But basically, using ajax with local resources isn't going to work cross-browser.

If you're just testing something locally that you'll really be deploying to the web, rather than use local files, install a simple web server and test via http:// URLs instead. That gives you a much more accurate security picture.

NULL vs nullptr (Why was it replaced?)

nullptr is always a pointer type. 0 (aka. C's NULL bridged over into C++) could cause ambiguity in overloaded function resolution, among other things:

f(foo *);

Is it possible in Java to check if objects fields are null and then add default value to all those attributes?

This is not to check for null, instead this will be helpful in converting an existing object to an empty object(fresh object). I dont know whether this is relevant or not, but I had such a requirement.

@SuppressWarnings({ "unchecked" })
static void emptyObject(Object obj) 
    Class c1 = obj.getClass();
    Field[] fields = c1.getDeclaredFields();

    for(Field field : fields)
            if(field.getType().getCanonicalName() == "boolean")
                field.set(obj, false);
            else if(field.getType().getCanonicalName() == "char")
                field.set(obj, '\u0000');
            else if((field.getType().isPrimitive()))
                field.set(obj, 0);
                field.set(obj, null);
        catch(Exception ex)


Unable to cast object of type 'System.DBNull' to type 'System.String`

Since I got an instance which isn't null and if I compared to DBNULL I got Operator '==' cannot be applied to operands of type 'string' and 'system.dbnull' exeption, and if I tried to change to compare to NULL, it simply didn't work ( since DBNull is an object) even that's the accepted answer.

I decided to simply use the 'is' keyword. So the result is very readable:

data = (item is DBNull) ? String.Empty : item

JavaScript check if value is only undefined, null or false

Try like Below

var Boolify = require('node-boolify').Boolify;
if (!Boolify(val)) {
    //your instruction

Refer node-boolify

What is the difference between NULL, '\0' and 0?

All three define the meaning of zero in different context.

  • pointer context - NULL is used and means the value of the pointer is 0, independent of whether it is 32bit or 64bit (one case 4 bytes the other 8 bytes of zeroes).
  • string context - the character representing the digit zero has a hex value of 0x30, whereas the NUL character has hex value of 0x00 (used for terminating strings).

These three are always different when you look at the memory:

NULL - 0x00000000 or 0x00000000'00000000 (32 vs 64 bit)
NUL - 0x00 or 0x0000 (ascii vs 2byte unicode)
'0' - 0x20

I hope this clarifies it.

How to check if a string is null in python

Try this:

if cookie and not cookie.isspace():
    # the string is non-empty
    # the string is empty

The above takes in consideration the cases where the string is None or a sequence of white spaces.

How to use NULL or empty string in SQL

You can simply do this:

FROM   yourTable
WHERE  yourColumn IS NULL OR yourColumn = ''

Shortest way to check for null and assign another value if not

My guess is the best you can come up with is

this.approved_by = IsNullOrEmpty(planRec.approved_by) ? string.Empty
                                                      : planRec.approved_by.ToString();

Of course since you're hinting at the fact that approved_by is an object (which cannot equal ""), this would be rewritten as

this.approved_by = (planRec.approved_by ?? string.Empty).ToString();

How do I assign a null value to a variable in PowerShell?

If the goal simply is to list all computer objects with an empty description attribute try this

import-module activedirectory  
$domain = "" 
Get-ADComputer -Filter '*' -Properties Description | where { $_.Description -eq $null }

How to filter empty or NULL names in a QuerySet?

Firstly, the Django docs strongly recommend not using NULL values for string-based fields such as CharField or TextField. Read the documentation for the explanation:

Solution: You can also chain together methods on QuerySets, I think. Try this:


That should give you the set you're looking for.

check if variable empty

To check for null values you can use is_null() as is demonstrated below.

if (is_null($value)) {
   $value = "MY TEXT"; //define to suit

Checking for a null object in C++

A C++ reference is not a pointer nor a Java/C# style reference and cannot be NULL. They behave as if they were an alias to another existing object.

In some cases, if there are bugs in your code, you might get a reference into an already dead or non-existent object, but the best thing you can do is hope that the program dies soon enough to be able to debug what happened and why your program got corrupted.

That is, I have seen code checking for 'null references' doing something like: if ( &reference == 0 ), but the standard is clear that there cannot be null references in a well-formed program. If a reference is bound to a null object the program is ill-formed and should be corrected. If you need optional values, use pointers (or some higher level construct like boost::optional), not references.

Filter values only if not null using lambda in Java8

you can use this

List<Car> requiredCars =
    .filter (t->  t!= null && StringUtils.startsWith(t.getName(),"M"))

How can I determine if a variable is 'undefined' or 'null'?

If the variable you want to check is a global, do

if (window.yourVarName) {
    // Your code here

This way to check will not throw an error even if the yourVarName variable doesn't exist.

Example: I want to know if my browser supports History API

if (window.history) {

How this works:

window is an object which holds all global variables as its properties, and in JavaScript it is legal to try to access a non-existing object property. If history doesn't exist then window.history returns undefined. undefined is falsey, so code in an if(undefined){} block won't run.

MySQL CONCAT returns NULL if any field contain NULL

To have the same flexibility in CONCAT_WS as in CONCAT (if you don't want the same separator between every member for instance) use the following:

SELECT CONCAT_WS("",affiliate_name,':',model,'-',ip,... etc)

What is null in Java?

Is null an instance of anything?

No, there is no type which null is an instanceof.

15.20.2 Type Comparison Operator instanceof

    RelationalExpression instanceof ReferenceType

At run time, the result of the instanceof operator is true if the value of the RelationalExpression is not null and the reference could be cast to the ReferenceType without raising a ClassCastException. Otherwise the result is false.

This means that for any type E and R, for any E o, where o == null, o instanceof R is always false.

What set does 'null' belong to?

JLS 4.1 The Kinds of Types and Values

There is also a special null type, the type of the expression null, which has no name. Because the null type has no name, it is impossible to declare a variable of the null type or to cast to the null type. The null reference is the only possible value of an expression of null type. The null reference can always be cast to any reference type. In practice, the programmer can ignore the null type and just pretend that null is merely a special literal that can be of any reference type.

What is null?

As the JLS quote above says, in practice you can simply pretend that it's "merely a special literal that can be of any reference type".

In Java, null == null (this isn't always the case in other languages). Note also that by contract, it also has this special property (from java.lang.Object):

public boolean equals(Object obj)

For any non-null reference value x, x.equals(null) should return false.

It is also the default value (for variables that have them) for all reference types:

JLS 4.12.5 Initial Values of Variables

  • Each class variable, instance variable, or array component is initialized with a default value when it is created:
    • For all reference types, the default value is null.

How this is used varies. You can use it to enable what is called lazy initialization of fields, where a field would have its initial value of null until it's actually used, where it's replaced by the "real" value (which may be expensive to compute).

There are also other uses. Let's take a real example from java.lang.System:

public static Console console()

Returns: The system console, if any, otherwise null.

This is a very common use pattern: null is used to denote non-existence of an object.

Here's another usage example, this time from

public String readLine() throws IOException

Returns: A String containing the contents of the line, not including any line-termination characters, or null if the end of the stream has been reached.

So here, readLine() would return instanceof String for each line, until it finally returns a null to signify the end. This allows you to process each line as follows:

String line;
while ((line = reader.readLine()) != null) {

One can design the API so that the termination condition doesn't depend on readLine() returning null, but one can see that this design has the benefit of making things concise. Note that there is no problem with empty lines, because an empty line "" != null.

Let's take another example, this time from java.util.Map<K,V>:

V get(Object key)

Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

If this map permits null values, then a return value of null does not necessarily indicate that the map contains no mapping for the key; it's also possible that the map explicitly maps the key to null. The containsKey operation may be used to distinguish these two cases.

Here we start to see how using null can complicate things. The first statement says that if the key isn't mapped, null is returned. The second statement says that even if the key is mapped, null can also be returned.

In contrast, java.util.Hashtable keeps things simpler by not permitting null keys and values; its V get(Object key), if returns null, unambiguously means that the key isn't mapped.

You can read through the rest of the APIs and find where and how null is used. Do keep in mind that they aren't always the best practice examples.

Generally speaking, null are used as a special value to signify:

  • Uninitialized state
  • Termination condition
  • Non-existing object
  • An unknown value

How is it represented in the memory?

In Java? None of your concern. And it's best kept that way.

Is null a good thing?

This is now borderline subjective. Some people say that null causes many programmer errors that could've been avoided. Some say that in a language that catches NullPointerException like Java, it's good to use it because you will fail-fast on programmer errors. Some people avoid null by using Null object pattern, etc.

This is a huge topic on its own, so it's best discussed as answer to another question.

I will end this with a quote from the inventor of null himself, C.A.R Hoare (of quicksort fame):

I call it my billion-dollar mistake. It was the invention of the null reference in 1965. At that time, I was designing the first comprehensive type system for references in an object oriented language (ALGOL W). My goal was to ensure that all use of references should be absolutely safe, with checking performed automatically by the compiler. But I couldn't resist the temptation to put in a null reference, simply because it was so easy to implement. This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years.

The video of this presentation goes deeper; it's a recommended watch.

JavaScript null check

In JavaScript, null is a special singleton object which is helpful for signaling "no value". You can test for it by comparison and, as usual in JavaScript, it's a good practice to use the === operator to avoid confusing type coercion:

var a = null;
alert(a === null); // true

As @rynah mentions, "undefined" is a bit confusing in JavaScript. However, it's always safe to test if the typeof(x) is the string "undefined", even if "x" is not a declared variable:

alert(typeof(x) === 'undefined'); // true

Also, variables can have the "undefined value" if they are not initialized:

var y;
alert(typeof(y) === 'undefined'); // true

Putting it all together, your check should look like this:

if ((typeof(data) !== 'undefined') && (data !== null)) {
  // ...

However, since the variable "data" is always defined since it is a formal function parameter, using the "typeof" operator is unnecessary and you can safely compare directly with the "undefined value".

function(data) {
  if ((data !== undefined) && (data !== null)) {
    // ...

This snippet amounts to saying "if the function was called with an argument which is defined and is not null..."

How to check if String is null

To sure, you should use function to check is null and empty as below:

string str = ...
if (!String.IsNullOrEmpty(str))

How to check if a double is null?

I believe Double.NaN might be able to cover this. That is the only 'null' value double contains.

How to convert empty spaces into null values, using SQL Server?

SQL Server ignores trailing whitespace when comparing strings, so ' ' = ''. Just use the following query for your update

UPDATE table
SET col1 = NULL
WHERE col1 = ''

NULL values in your table will stay NULL, and col1s with any number on space only characters will be changed to NULL.

If you want to do it during your copy from one table to another, use this:

INSERT INTO newtable ( col1, othercolumn )
   NULLIF(col1, ''),
FROM table

how to check if a datareader is null or empty

In addition to the suggestions given, you can do this directly from your query like this -

SELECT ISNULL([Additional], -1) AS [Additional]

This way you can write the condition to check whether the field value is < 0 or >= 0.

Best way to check if a Data Table has a null value in it

I will do like....


Check array position for null/empty

There is no bound checking in array in C programming. If you declare array as

int arr[50];

Then you can even write as

arr[51] = 10;

The compiler would not throw an error. Hope this answers your question.

How to check if my string is equal to null?

Okay this is how datatypes work in Java. (You have to excuse my English, I am prob. not using the right vocab. You have to differentiate between two of them. The base datatypes and the normal datatypes. Base data types pretty much make up everything that exists. For example, there are all numbers, char, boolean etc. The normal data types or complex data types is everything else. A String is an array of chars, therefore a complex data type.

Every variable that you create is actually a pointer on the value in your memory. For example:

String s = new String("This is just a test");

the variable "s" does NOT contain a String. It is a pointer. This pointer points on the variable in your memory. When you call System.out.println(anyObject), the toString() method of that object is called. If it did not override toString from Object, it will print the pointer. For example:

public class Foo{
    public static void main(String[] args) {
        Foo f = new Foo();


Everything behind the "@" is the pointer. This only works for complex data types. Primitive datatypes are DIRECTLY saved in their pointer. So actually there is no pointer and the values are stored directly.

For example:

int i = 123;

i does NOT store a pointer in this case. i will store the integer value 123 (in byte ofc).

Okay so lets come back to the == operator. It always compares the pointer and not the content saved at the pointer's position in the memory.


String s1 = new String("Hallo");
String s2 = new String("Hallo");

System.out.println(s1 == s2);

>>>>> false

This both String have a different pointer. String.equals(String other) however compares the content. You can compare primitive data types with the '==' operator because the pointer of two different objects with the same content is equal.

Null would mean that the pointer is empty. An empty primitive data type by default is 0 (for numbers). Null for any complex object however means, that object does not exist.


Which @NotNull Java annotation should I use?

One of the nice things about IntelliJ is that you don't need to use their annotations. You can write your own, or you can use those of whatever other tool you like. You're not even limited to a single type. If you're using two libraries that use different @NotNull annotations, you can tell IntelliJ to use both of them. To do this, go to "Configure Inspections", click on the "Constant Conditions & Exceptions" inspection, and hit the "Configure inspections" button. I use the Nullness Checker wherever I can, so I set up IntelliJ to use those annotations, but you can make it work with whatever other tool you want. (I have no opinion on the other tools because I've been using IntelliJ's inspections for years, and I love them.)

How do I get SUM function in MySQL to return '0' if no values are found?

if sum of column is 0 then display empty

select if(sum(column)>0,sum(column),'')
from table 

Is null reference possible?


#include <iostream>
#include <functional>

struct null_ref_t {
   template <typename T>
   operator T&() {
      union TypeSafetyBreaker {
         T *ptr;

         // see
         std::reference_wrapper<T> ref; 

      TypeSafetyBreaker ptr = {.ptr = nullptr};

      // unwrap the reference
      return ptr.ref.get();

null_ref_t nullref;

int main() {
   int &a = nullref;

   // Segmentation fault
   a = 4;
   return 0;

Check if a parameter is null or empty in a stored procedure

If you want a "Null, empty or white space" check, you can avoid unnecessary string manipulation with LTRIM and RTRIM like this.

IF COALESCE(PATINDEX('%[^ ]%', @parameter), 0) > 0

Why is null an object and what's the difference between null and undefined?

Comparison of many different null checks in JavaScript:

// Variables to test
var myNull = null;
var myObject = {};
var myStringEmpty = "";
var myStringWhiteSpace = " ";
var myStringHello = "hello";
var myIntZero = 0;
var myIntOne = 1;
var myBoolTrue = true;
var myBoolFalse = false;
var myUndefined;


JavaScript Null Check Comparison Chart

SQL Inner Join On Null Values

If you want null values to be included from Y.QID then Fastest way is


Note: this solution is applicable only if you need null values from Left table i.e. Y (in above case).

Otherwise INNER JOIN x ON x.qid IS NOT DISTINCT FROM y.qid is right way to do

How to store NULL values in datetime fields in MySQL?

Specifically relating to the error you're getting, you can't do something like this in PHP for a nullable field in MySQL:

$sql = 'INSERT INTO table (col1, col2) VALUES(' . $col1 . ', ' . null . ')';

Because null in PHP will equate to an empty string which is not the same as a NULL value in MysQL. Instead you want to do this:

$sql = 'INSERT INTO table (col1, col2) VALUES(' . $col1 . ', ' . (is_null($col2) ? 'NULL' : $col2). ')';

Of course you don't have to use is_null but I figure that it demonstrates the point a little better. Probably safer to use empty() or something like that. And if $col2 happens to be a string which you would enclose in double quotes in the query, don't forget not to include those around the 'NULL' string, otherwise it wont work.

Hope that helps!

Null vs. False vs. 0 in PHP

I have just wasted 1/2 a day trying to get either a 0, null, false to return from strops!

Here's all I was trying to do, before I found that the logic wasn't flowing in the right direction, seeming that there was a blackhole in php coding:

Concept take a domain name hosted on a server, and make sure it's not root level, OK several different ways to do this, but I chose different due to other php functions/ constructs I have done.

Anyway here was the basis of the cosing:

if (strpos($_SERVER ['SERVER_NAME'], dirBaseNAME ()) 
    do this 
} else {
    or that

echo strpos(, mydomain);  

if ( strpos(mydomain, xmas) == null ) 
        echo "\n1 is null"; 

if ( (strpos(, mydomain)) == 0 ) 
        echo "\n2 is 0"; 
    } else {
        echo "\n2 Something is WRONG"; 

if ( (, mydomain)) != 0 ) 
        echo "\n3 is 0"; 
    } else {
        echo "\n3 it is not 0"; 

if ( (, mydomain)) == null ) 
        echo "\n4 is null"; 
    } else {
        echo "\n4 Something is WRONG"; 

FINALLY after reading this Topic, I found that this worked!!!

if ((, mydomain)) !== false ) 
        echo "\n5 is True"; 
    } else {
        echo "\n5 is False"; 

Thanks for this article, I now understand that even though it's Christmas, it may not be Christmas as false, as its also can be a NULL day!

After wasting a day of debugging some simple code, wished I had known this before, as I would have been able to identify the problem, rather than going all over the place trying to get it to work. It didn't work, as False, NULL and 0 are not all the same as True or False or NULL?

javax.persistence.NoResultException: No entity found for query

String hql="from DrawUnusedBalance where unusedBalanceDate= :today";
DrawUnusedBalance drawUnusedBalance = em.unwrap(Session.class)
    .createQuery(hql, DrawUnusedBalance.class)
    .setParameter("today",new LocalDate())

SQL Server String Concatenation with Null

I just wanted to contribute this should someone be looking for help with adding separators between the strings, depending on whether a field is NULL or not.

So in the example of creating a one line address from separate fields

Address1, Address2, Address3, City, PostCode

in my case, I have the following Calculated Column which seems to be working as I want it:

    when [Address1] IS NOT NULL 
    then (((          [Address1]      + 
          isnull(', '+[Address2],'')) +
          isnull(', '+[Address3],'')) +
          isnull(', '+[City]    ,'')) +
          isnull(', '+[PostCode],'')  

Hope that helps someone!

how do you insert null values into sql server

If you're using SSMS (or old school Enterprise Manager) to edit the table directly, press CTRL+0 to add a null.

Is null check needed before calling instanceof?

Just as a tidbit:

Even (((A)null)instanceof A) will return false.

(If typecasting null seems surprising, sometimes you have to do it, for example in situations like this:

public class Test
  public static void test(A a)
    System.out.println("a instanceof A: " + (a instanceof A));

  public static void test(B b) {
    // Overloaded version. Would cause reference ambiguity (compile error)
    // if Test.test(null) was called without casting.
    // So you need to call Test.test((A)null) or Test.test((B)null).

So Test.test((A)null) will print a instanceof A: false.)

P.S.: If you are hiring, please don't use this as a job interview question. :D

When is null or undefined used in JavaScript?

The DOM methods getElementById(), nextSibling(), childNodes[n], parentNode() and so on return null (defined but having no value) when the call does not return a node object.

The property is defined, but the object it refers to does not exist.

This is one of the few times you may not want to test for equality-

if(x!==undefined) will be true for a null value

but if(x!= undefined) will be true (only) for values that are not either undefined or null.

Identifying and removing null characters in UNIX

I’d use tr:

tr < file-with-nulls -d '\000' > file-without-nulls

If you are wondering if input redirection in the middle of the command arguments works, it does. Most shells will recognize and deal with I/O redirection (<, >, …) anywhere in the command line, actually.

Checking for an empty field with MySQL

There's a difference between an empty string (email != "") and NULL. NULL is null and an Empty string is something.

How should we manage jdk8 stream for null values

Stuart's answer provides a great explanation, but I'd like to provide another example.

I ran into this issue when attempting to perform a reduce on a Stream containing null values (actually it was LongStream.average(), which is a type of reduction). Since average() returns OptionalDouble, I assumed the Stream could contain nulls but instead a NullPointerException was thrown. This is due to Stuart's explanation of null v. empty.

So, as the OP suggests, I added a filter like so:
    .filter(o -> o != null)

Or as tangens pointed out below, use the predicate provided by the Java API:

From the mailing list discussion Stuart linked: Brian Goetz on nulls in Streams

Explicitly set column value to null SQL Developer

Use Shift+Del.

More info: Shift+Del combination key set a field to null when you filled a field by a value and you changed your decision and you want to make it null. It is useful and I amazed from the other answers that give strange solutions.

Java "?" Operator for checking null - What is it? (Not Ternary!)

Java does not have the exact syntax but as of JDK-8, we have the Optional API with various methods at our disposal. So, the C# version with the use of null conditional operator:

return person?.getName()?.getGivenName(); 

can be written as follows in Java with the Optional API:

 return Optional.ofNullable(person)
                .map(e -> e.getName())
                .map(e -> e.getGivenName())

if any of person, getName or getGivenName is null then null is returned.

Check if a string is null or empty in XSLT

If there is a possibility that the element does not exist in the XML I would test both that the element is present and that the string-length is greater than zero:

    <xsl:when test="categoryName and string-length(categoryName) &gt; 0">
        <xsl:value-of select="categoryName " />
        <xsl:value-of select="other" />

MySql Query Replace NULL with Empty String in Select

Try this, this should also get rid of those empty lines also:

SELECT prereq FROM test WHERE prereq IS NOT NULL;

How to I say Is Not Null in VBA

you can do like follows. Remember, IsNull is a function which returns TRUE if the parameter passed to it is null, and false otherwise.

Not IsNull(Fields!W_O_Count.Value)

How to set enum to null

Color? color = null;

or you can use

Color? color = new Color?();

example where assigning null wont work

color = x == 5 ? Color.Red : x == 9 ? Color.Black : null ; 

so you can use :

 color = x == 5 ? Color.Red : x == 9 ? Color.Black : new Color?(); 

Best way to check for null values in Java?

Method 4 is far and away the best as it clearly indicates what will happen and uses the minimum of code.

Method 3 is just wrong on every level. You know the item may be null so it's not an exceptional situation it's something you should check for.

Method 2 is just making it more complicated than it needs to be.

Method 1 is just method 4 with an extra line of code.

Referring to the null object in Python

In Python, the 'null' object is the singleton None.

The best way to check things for "Noneness" is to use the identity operator, is:

if foo is None:

PHP/MySQL Insert null values

This is one example where using prepared statements really saves you some trouble.

In MySQL, in order to insert a null value, you must specify it at INSERT time or leave the field out which requires additional branching:

INSERT INTO table2 (f1, f2)
  VALUES ('String Value', NULL);

However, if you want to insert a value in that field, you must now branch your code to add the single quotes:

INSERT INTO table2 (f1, f2)
  VALUES ('String Value', 'String Value');

Prepared statements automatically do that for you. They know the difference between string(0) "" and null and write your query appropriately:

$stmt = $mysqli->prepare("INSERT INTO table2 (f1, f2) VALUES (?, ?)");
$stmt->bind_param('ss', $field1, $field2);

$field1 = "String Value";
$field2 = null;


It escapes your fields for you, makes sure that you don't forget to bind a parameter. There is no reason to stay with the mysql extension. Use mysqli and it's prepared statements instead. You'll save yourself a world of pain.

What is the use of adding a null key or value to a HashMap in Java?

A null key can also be helpful when the map stores data for UI selections where the map key represents a bean field.

A corresponding null field value would for example be represented as "(please select)" in the UI selection.

What is the correct way to represent null XML elements?

You use xsi:nil when your schema semantics indicate that an element has a default value, and that the default value should be used if the element isn't present. I have to assume that there are smart people to whom the preceding sentence is not a self-evidently terrible idea, but it sounds like nine kinds of bad to me. Every XML format I've ever worked with represents null values by omitting the element. (Or attribute, and good luck marking an attribute with xsi:nil.)

ALTER TABLE, set null in not null column, PostgreSQL 9.1

First, Set :

Check if AJAX response data is empty/blank/null/undefined/0

The following correct answer was provided in the comment section of the question by Felix Kling:

if (!$.trim(data)){   
    alert("What follows is blank: " + data);
    alert("What follows is not blank: " + data);

Error checking for NULL in VBScript

I see lots of confusion in the comments. Null, IsNull() and vbNull are mainly used for database handling and normally not used in VBScript. If it is not explicitly stated in the documentation of the calling object/data, do not use it.

To test if a variable is uninitialized, use IsEmpty(). To test if a variable is uninitialized or contains "", test on "" or Empty. To test if a variable is an object, use IsObject and to see if this object has no reference test on Is Nothing.

In your case, you first want to test if the variable is an object, and then see if that variable is Nothing, because if it isn't an object, you get the "Object Required" error when you test on Nothing.

snippet to mix and match in your code:

If IsObject(provider) Then
    If Not provider Is Nothing Then
        ' Code to handle a NOT empty object / valid reference
        ' Code to handle an empty object / null reference
    End If
    If IsEmpty(provider) Then
        ' Code to handle a not initialized variable or a variable explicitly set to empty
    ElseIf provider = "" Then
        ' Code to handle an empty variable (but initialized and set to "")
        ' Code to handle handle a filled variable
    End If
End If

What is the difference between null and undefined in JavaScript?

Null is ALWAYS an unknown object that exists in memory, whereas undefined is not.

What is the PostgreSQL equivalent for ISNULL()

Create the following function

    "is null) WHEN true THEN $2 ELSE $1 END) AS RESULT' LANGUAGE 'sql'

And it'll work.

You may to create different versions with different parameter types.

Can I use if (pointer) instead of if (pointer != NULL)?

The relevant use cases for null pointers are

  • Redirection to something like a deeper tree node, which may not exist or has not been linked yet. That's something you should always keep closely encapsulated in a dedicated class, so readability or conciseness isn't that much of an issue here.
  • Dynamic casts. Casting a base-class pointer to a particular derived-class one (something you should again try to avoid, but may at times find necessary) always succeeds, but results in a null pointer if the derived class doesn't match. One way to check this is

    Derived* derived_ptr = dynamic_cast<Derived*>(base_ptr);
    if(derived_ptr != nullptr) { ... }

    (or, preferrably, auto derived_ptr = ...). Now, this is bad, because it leaves the (possibly invalid, i.e. null) derived pointer outside of the safety-guarding if block's scope. This isn't necessary, as C++ allows you to introduce boolean-convertable variables inside an if-condition:

    if(auto derived_ptr = dynamic_cast<Derived*>(base_ptr)) { ... }

    which is not only shorter and scope-safe, it's also much more clear in its intend: when you check for null in a separate if-condition, the reader wonders "ok, so derived_ptr must not be null here... well, why would it be null?" Whereas the one-line version says very plainly "if you can safely cast base_ptr to Derived*, then use it for...".

    The same works just as well for any other possible-failure operation that returns a pointer, though IMO you should generally avoid this: it's better to use something like boost::optional as the "container" for results of possibly failing operations, rather than pointers.

So, if the main use case for null pointers should always be written in a variation of the implicit-cast-style, I'd say it's good for consistency reasons to always use this style, i.e. I'd advocate for if(ptr) over if(ptr!=nullptr).

I'm afraid I have to end with an advert: the if(auto bla = ...) syntax is actually just a slightly cumbersome approximation to the real solution to such problems: pattern matching. Why would you first force some action (like casting a pointer) and then consider that there might be a failure... I mean, it's ridiculous, isn't it? It's like, you have some foodstuff and want to make soup. You hand it to your assistant with the task to extract the juice, if it happens to be a soft vegetable. You don't first look it at it. When you have a potato, you still give it to your assistant but they slap it back in your face with a failure note. Ah, imperative programming!

Much better: consider right away all the cases you might encounter. Then act accordingly. Haskell:

makeSoupOf :: Foodstuff -> Liquid
makeSoupOf p@(Potato{..}) = mash (boil p) <> water
makeSoupOf vegetable
 | isSoft vegetable  = squeeze vegetable <> salt
makeSoupOf stuff  = boil (throwIn (water<>salt) stuff)

Haskell also has special tools for when there is really a serious possibility of failure (as well as for a whole bunch of other stuff): monads. But this isn't the place for explaining those.


How to test for $null array in PowerShell

You can reorder the operands:

$null -eq $foo

Note that -eq in PowerShell is not an equivalence relation.

Why use Optional.of over Optional.ofNullable?

This depends upon scenarios.

Let's say you have some business functionality and you need to process something with that value further but having null value at time of processing would impact it.

Then, in that case, you can use Optional<?>.

String nullName = null;

String name = Optional.ofNullable(nullName)
                      .orElse("Default value in case of null");

Handling NULL values in Hive

Try to include length > 0 as well.

column1 is not NULL AND column1 <> '' AND length(column1) > 0 

Undefined or null for AngularJS

My suggestion to you is to write your own utility service. You can include the service in each controller or create a parent controller, assign the utility service to your scope and then every child controller will inherit this without you having to include it.


var app = angular.module('plunker', []);

app.controller('MainCtrl', function($scope, Utils) {
    $scope.utils = Utils;

app.controller('ChildCtrl', function($scope, Utils) {
   $scope.undefined1 = Utils.isUndefinedOrNull(1);  // standard DI
   $scope.undefined2 = $scope.utils.isUndefinedOrNull(1);  // MainCtrl is parent


app.factory('Utils', function() {
  var service = {
     isUndefinedOrNull: function(obj) {
         return !angular.isDefined(obj) || obj===null;


  return service;

Or you could add it to the rootScope as well. Just a few options for extending angular with your own utility functions.

How to set null value to int in c#?

Additionally, you cannot use "null" as a value in a conditional assignment. e.g...

bool testvalue = false;
int? myint = (testvalue == true) ? 1234 : null;

FAILS with: Type of conditional expression cannot be determined because there is no implicit conversion between 'int' and '<null>'.

So, you have to cast the null as well... This works:

int? myint = (testvalue == true) ? 1234 : (int?)null;

Method call if not null in C#

A quick extension method:

    public static void IfNotNull<T>(this T obj, Action<T> action, Action actionIfNull = null) where T : class {
        if(obj != null) {
        } else if ( actionIfNull != null ) {


  string str = null;
  str.IfNotNull(s => Console.Write(s.Length));
  str.IfNotNull(s => Console.Write(s.Length), () => Console.Write("null"));

or alternatively:

    public static TR IfNotNull<T, TR>(this T obj, Func<T, TR> func, Func<TR> ifNull = null) where T : class {
        return obj != null ? func(obj) : (ifNull != null ? ifNull() : default(TR));


    string str = null;
    Console.Write(str.IfNotNull(s => s.Length.ToString());
    Console.Write(str.IfNotNull(s => s.Length.ToString(), () =>  "null"));

Returning null in a method whose signature says return int?

int is a primitive, null is not a value that it can take on. You could change the method return type to return java.lang.Integer and then you can return null, and existing code that returns int will get autoboxed.

Nulls are assigned only to reference types, it means the reference doesn't point to anything. Primitives are not reference types, they are values, so they are never set to null.

Using the object wrapper java.lang.Integer as the return value means you are passing back an Object and the object reference can be null.

Why does NULL = NULL evaluate to false in SQL server

NULL isn't equal to anything, not even itself. My personal solution to understanding the behavior of NULL is to avoid using it as much as possible :).

How can I check for an empty/undefined/null string in JavaScript?

A lot of answers, and a lot of different possibilities!

Without a doubt for quick and simple implementation the winner is: if (!str.length) {...}

However, as many other examples are available. The best functional method to go about this, I would suggest:

function empty(str)
    if (typeof str == 'undefined' || !str || str.length === 0 || str === "" || !/[^\s]/.test(str) || /^\s*$/.test(str) || str.replace(/\s/g,"") === "")
        return true;
        return false;

A bit excessive, I know.

HQL "is null" And "!= null" on an Oracle column

That is a binary operator in hibernate you should use

is not null

Have a look at 14.10. Expressions

What is a NullReferenceException, and how do I fix it?

You can fix NullReferenceException in a clean way using Null-conditional Operators in c#6 and write less code to handle null checks.

It's used to test for null before performing a member access (?.) or index (?[) operation.


  var name = p?.Spouse?.FirstName;

is equivalent to:

    if (p != null)
        if (p.Spouse != null)
            name = p.Spouse.FirstName;

The result is that the name will be null when p is null or when p.Spouse is null.

Otherwise, the variable name will be assigned the value of the p.Spouse.FirstName.

For More details : Null-conditional Operators

Removing "NUL" characters

I was having same problem. The above put me on the right track but was not quite correct in my case. What did work was closely related:

  • Open your file in Notepad++
  • Type Control-A (select all)
  • Type Control-H (replace)
  • In 'Find What' type \x00
  • In 'Replace With' leave BLANK
  • In 'Search Mode' Selected 'Extended'
  • Then Click on 'Replace All'

Javascript document.getElementById("id").value returning null instead of empty string when the element is an empty text box

Posting your HTML might help a bit. Instead, you can get the element first and then check if it is null or not and then ask for its value rather than just asking for the value directly without knowing if the element is visible on the HTML or not.

element1 = document.getElementById(id);

if(element1 != null)
    //code to set the value variable.

What is the PHP syntax to check "is not null" or an empty string?

Null OR an empty string?

if (!empty($user)) {}

Use empty().

After realizing that $user ~= $_POST['user'] (thanks matt):

var uservariable='<?php 
    echo ((array_key_exists('user',$_POST)) || (!empty($_POST['user']))) ? $_POST['user'] : 'Empty Username Input';

Best way to check if a character array is empty

Depends on whether or not your array is holding a null-terminated string. If so, then

if(text[0] == '\0') {}

should be sufficient.

Edit: Another method would be...

if (strcmp(text, "") == 0)

which is potentially less efficient but clearly expresses your intent.

JavaScript checking for null vs. undefined and difference between == and ===

How do I check a variable if it's null or undefined...

Is the variable null:

if (a === null)
// or
if (a == null) // but see note below

...but note the latter will also be true if a is undefined.

Is it undefined:

if (typeof a === "undefined")
// or
if (a === undefined)
// or
if (a == undefined) // but see note below

...but again, note that the last one is vague; it will also be true if a is null.

Now, despite the above, the usual way to check for those is to use the fact that they're falsey:

if (!a) {
    // `a` is falsey, which includes `undefined` and `null`
    // (and `""`, and `0`, and `NaN`, and [of course] `false`)

This is defined by ToBoolean in the spec.

...and what is the difference between the null and undefined?

They're both values usually used to indicate the absence of something. undefined is the more generic one, used as the default value of variables until they're assigned some other value, as the value of function arguments that weren't provided when the function was called, and as the value you get when you ask an object for a property it doesn't have. But it can also be explicitly used in all of those situations. (There's a difference between an object not having a property, and having the property with the value undefined; there's a difference between calling a function with the value undefined for an argument, and leaving that argument off entirely.)

null is slightly more specific than undefined: It's a blank object reference. JavaScript is loosely typed, of course, but not all of the things JavaScript interacts with are loosely typed. If an API like the DOM in browsers needs an object reference that's blank, we use null, not undefined. And similarly, the DOM's getElementById operation returns an object reference — either a valid one (if it found the DOM element), or null (if it didn't).

Interestingly (or not), they're their own types. Which is to say, null is the only value in the Null type, and undefined is the only value in the Undefined type.

What is the difference between "==" and "==="

The only difference between them is that == will do type coercion to try to get the values to match, and === won't. So for instance "1" == 1 is true, because "1" coerces to 1. But "1" === 1 is false, because the types don't match. ("1" !== 1 is true.) The first (real) step of === is "Are the types of the operands the same?" and if the answer is "no", the result is false. If the types are the same, it does exactly what == does.

Type coercion uses quite complex rules and can have surprising results (for instance, "" == 0 is true).

More in the spec:

How to check null objects in jQuery

jquery $() function always return non null value - mean elements matched you selector cretaria. If the element was not found it will return an empty array. So your code will look something like this -

if ($("#btext" + i).length){
        //alert($("#btext" + i).text());
    $("#btext" + i).text("Branch " + i);

Why I am getting Cannot pass parameter 2 by reference error when I am using bindParam with a constant value?

Try This.

$stmt->bindValue(':v1', null, PDO::PARAM_NULL); // --> insert null

Combine two columns and add into one new column

Did you check the string concatenation function? Something like:

update table_c set column_a = column_b || column_c 

should work. More here

What is the `zero` value for time.Time in Go?

You should use the Time.IsZero() function instead:

func (Time) IsZero

func (t Time) IsZero() bool
IsZero reports whether t represents the zero time instant, January 1, year 1, 00:00:00 UTC.

How to check for null in a single statement in scala?

Although I'm sure @Ben Jackson's asnwer with Option(getObject).foreach is the preferred way of doing it, I like to use an AnyRef pimp that allows me to write:

getObject ifNotNull ( QueueManager.add(_) )

I find it reads better.

And, in a more general way, I sometimes write

val returnVal = getObject ifNotNull { obj =>
} otherwise {

... replacing ifNotNull with ifSome if I'm dealing with an Option. I find it clearer than first wrapping in an option and then pattern-matching it.

(For the implementation, see Implementing ifTrue, ifFalse, ifSome, ifNone, etc. in Scala to avoid if(...) and simple pattern matching and the Otherwise0/Otherwise1 classes.)

Using Thymeleaf when the value is null

Sure there is. You can for example use the conditional expressions. For example:

<span th:text="${someObject.someProperty != null} ? ${someObject.someProperty} : 'null value!'">someValue</span>

You can even omit the "else" expression:

<span th:text="${someObject.someProperty != null} ? ${someObject.someProperty}">someValue</span>

You can also take a look at the Elvis operator to display default values.

nil detection in Go

I have created some sample code which creates new variables using a variety of ways that I can think of. It looks like the first 3 ways create values, and the last two create references.

package main

import "fmt"

type Config struct {
    host string
    port float64

func main() {
    var c1 Config
    c2 := Config{}
    c3 := *new(Config)

    c4 := &Config{}
    c5 := new(Config)

    fmt.Println(&c1 == nil)
    fmt.Println(&c2 == nil)
    fmt.Println(&c3 == nil)
    fmt.Println(c4 == nil)
    fmt.Println(c5 == nil)

    fmt.Println(c1, c2, c3, c4, c5)

which outputs:

{ 0} { 0} { 0} &{ 0} &{ 0}

where to place CASE WHEN column IS NULL in this query

That looks like it might belong in the select statement:

SELECT id, col1, col2, col3, (CASE WHEN table3.col3 IS NULL THEN table2.col3 AS col4 ELSE table3.col3 as col4 END)
FROM table1
ON =
ON =

How to select rows where column value IS NOT NULL using CodeIgniter's ActiveRecord?

And just to give you yet another option, you can use NOT ISNULL(archived) as your WHERE filter.


One should NEVER treat "BLANK" and NULL as the same.

Back in the olden days before there was a SQL standard, Oracle made the design decision that empty strings in VARCHAR/ VARCHAR2 columns were NULL and that there was only one sense of NULL (there are relational theorists that would differentiate between data that has never been prompted for, data where the answer exists but is not known by the user, data where there is no answer, etc. all of which constitute some sense of NULL). By the time that the SQL standard came around and agreed that NULL and the empty string were distinct entities, there were already Oracle users that had code that assumed the two were equivalent. So Oracle was basically left with the options of breaking existing code, violating the SQL standard, or introducing some sort of initialization parameter that would change the functionality of potentially large number of queries. Violating the SQL standard (IMHO) was the least disruptive of these three options.

Oracle has left open the possibility that the VARCHAR data type would change in a future release to adhere to the SQL standard (which is why everyone uses VARCHAR2 in Oracle since that data type's behavior is guaranteed to remain the same going forward).

How do I convert ticks to minutes?

A single tick represents one hundred nanoseconds or one ten-millionth of a second. FROM MSDN.

So 28 000 000 000 * 1/10 000 000 = 2 800 sec. 2 800 sec /60 = 46.6666min

Or you can do it programmaticly with TimeSpan:

    static void Main()
        TimeSpan ts = TimeSpan.FromTicks(28000000000);
        double minutesFromTs = ts.TotalMinutes;

Both give me 46 min and not 480 min...

Convert a string to a datetime

You should have to use Date.ParseExact or Date.TryParseExact with correct format string.

 Dim edate = "10/12/2009"
 Dim expenddt As Date = Date.ParseExact(edate, "dd/MM/yyyy", 


 Dim format() = {"dd/MM/yyyy", "d/M/yyyy", "dd-MM-yyyy"}
 Dim expenddt As Date = Date.ParseExact(edate, format,  


Dim format() = {"dd/MM/yyyy", "d/M/yyyy", "dd-MM-yyyy"}
Dim expenddt As Date
Date.TryParseExact(edate, format, 
    Globalization.DateTimeStyles.None, expenddt)

How do you clone an Array of Objects in Javascript?

The issue with your shallow copy is that all the objects aren't cloned. While the references to each object are unique in each array, once you ultimately grab onto it you're dealing with the same object as before. There is nothing wrong with the way you cloned it... the same result would occur using Array.slice().

The reason your deep copy is having problems is because you're ending up with circular object references. Deep will go as deep as it can go, and if you've got a circle, it'll keep going infinitely until the browser faints.

If the data structure cannot be represented as a directed acyclic graph, then I'm not sure you're going to be able to find an all-purpose method for deep cloning. Cyclic graphs provide many tricky corner cases, and since it's not a common operation I doubt anyone has written a full solution (if it's even possible - it might not be! But I have no time to try to write a rigorous proof now.). I found some good comments on the issue on this page.

If you need a deep copy of an Array of Objects with circular references I believe you're going to have to code your own method to handle your specialized data structure, such that it is a multi-pass clone:

  1. On round one, make a clone of all objects that don't reference other objects in the array. Keep a track of each object's origins.
  2. On round two, link the objects together.

Regular Expression for any number greater than 0?

The simple answer is: ^[1-9][0-9]*$

Is Python strongly typed?

It's already been answered a few times, but Python is a strongly typed language:

>>> x = 3
>>> y = '4'
>>> print(x+y)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: 'int' and 'str'

The following in JavaScript:

var x = 3    
var y = '4'
alert(x + y) //Produces "34"

That's the difference between weak typing and strong typing. Weak types automatically try to convert from one type to another, depending on context (e.g. Perl). Strong types never convert implicitly.

Your confusion lies in a misunderstanding of how Python binds values to names (commonly referred to as variables).

In Python, names have no types, so you can do things like:

bob = 1
bob = "bob"
bob = "An Ex-Parrot!"

And names can be bound to anything:

>>> def spam():
...     print("Spam, spam, spam, spam")
>>> spam_on_eggs = spam
>>> spam_on_eggs()
Spam, spam, spam, spam

For further reading:

and the slightly related but more advanced:

Disable browser cache for entire ASP.NET website

Create a class that inherits from IActionFilter.

public class NoCacheAttribute : ActionFilterAttribute
    public override void OnResultExecuting(ResultExecutingContext filterContext)


Then put attributes where needed...

public class AccountController : Controller
    public ActionResult ChangePassword()
        return View();

Adding 30 minutes to time formatted as H:i in PHP

$time = strtotime('10:00');
$startTime = date("H:i", strtotime('-30 minutes', $time));
$endTime = date("H:i", strtotime('+30 minutes', $time));

PowerMockito mock single static method and return object

What you want to do is a combination of part of 1 and all of 2.

You need to use the PowerMockito.mockStatic to enable static mocking for all static methods of a class. This means make it possible to stub them using the when-thenReturn syntax.

But the 2-argument overload of mockStatic you are using supplies a default strategy for what Mockito/PowerMock should do when you call a method you haven't explicitly stubbed on the mock instance.

From the javadoc:

Creates class mock with a specified strategy for its answers to interactions. It's quite advanced feature and typically you don't need it to write decent tests. However it can be helpful when working with legacy systems. It is the default answer so it will be used only when you don't stub the method call.

The default default stubbing strategy is to just return null, 0 or false for object, number and boolean valued methods. By using the 2-arg overload, you're saying "No, no, no, by default use this Answer subclass' answer method to get a default value. It returns a Long, so if you have static methods which return something incompatible with Long, there is a problem.

Instead, use the 1-arg version of mockStatic to enable stubbing of static methods, then use when-thenReturn to specify what to do for a particular method. For example:

import static org.mockito.Mockito.*;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.invocation.InvocationOnMock;
import org.mockito.stubbing.Answer;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

class ClassWithStatics {
  public static String getString() {
    return "String";

  public static int getInt() {
    return 1;

public class StubJustOneStatic {
  public void test() {


    System.out.println("String: " + ClassWithStatics.getString());
    System.out.println("Int: " + ClassWithStatics.getInt());

The String-valued static method is stubbed to return "Hello!", while the int-valued static method uses the default stubbing, returning 0.

Inline Form nested within Horizontal Form in Bootstrap 3

To make it work in Chrome (and bootply) i had to change code in this way:

<form class="form-horizontal">
  <div class="form-group">
    <label for="name" class="col-xs-2 control-label">Name</label>
    <div class="col-xs-10">
      <input type="text" class="form-control col-sm-10" name="name" placeholder="name" />

  <div class="form-group">
    <label for="birthday" class="col-xs-2 control-label">Birthday</label>
    <div class="col-xs-10">
      <div class="form-inline">
        <input type="text" class="form-control" placeholder="year" />
        <input type="text" class="form-control" placeholder="month" />
        <input type="text" class="form-control" placeholder="day" />

How to get build time stamp from Jenkins build variables?

Generate environment variables from script (Unix script) :

echo "BUILD_DATE=$(date +%F-%T)"

HQL "is null" And "!= null" on an Oracle column

That is a binary operator in hibernate you should use

is not null

Have a look at 14.10. Expressions

Refresh/reload the content in Div using jquery/ajax

What you want is to load the data again but not reload the div.

You need to make an Ajax query to get data from the server and fill the DIV.

.NET: Simplest way to send POST with data and read response

Personally, I think the simplest approach to do an http post and get the response is to use the WebClient class. This class nicely abstracts the details. There's even a full code example in the MSDN documentation.

In your case, you want the UploadData() method. (Again, a code sample is included in the documentation)

UploadString() will probably work as well, and it abstracts it away one more level.

Shortcuts in Objective-C to concatenate NSStrings

Two answers I can think of... neither is particularly as pleasant as just having a concatenation operator.

First, use an NSMutableString, which has an appendString method, removing some of the need for extra temp strings.

Second, use an NSArray to concatenate via the componentsJoinedByString method.

How can I create a unique constraint on my column (SQL Server 2008 R2)?

One thing not clearly covered is that microsoft sql is creating in the background an unique index for the added constraint

create table Customer ( id int primary key identity (1,1) , name nvarchar(128) ) 

--Commands completed successfully.

sp_help Customer

---> index
--index_name    index_description   index_keys
--PK__Customer__3213E83FCC4A1DFA    clustered, unique, primary key located on PRIMARY   id

---> constraint
--constraint_type   constraint_name delete_action   update_action   status_enabled  status_for_replication  constraint_keys
--PRIMARY KEY (clustered)   PK__Customer__3213E83FCC4A1DFA  (n/a)   (n/a)   (n/a)   (n/a)   id

---- now adding the unique constraint


-- Commands completed successfully.

sp_help Customer

---> index
---index_name   index_description   index_keys
---PK__Customer__3213E83FCC4A1DFA   clustered, unique, primary key located on PRIMARY   id
---U_Name   nonclustered, unique, unique key located on PRIMARY name

---> constraint
---constraint_type  constraint_name delete_action   update_action   status_enabled  status_for_replication  constraint_keys
---PRIMARY KEY (clustered)  PK__Customer__3213E83FCC4A1DFA  (n/a)   (n/a)   (n/a)   (n/a)   id
---UNIQUE (non-clustered)   U_Name  (n/a)   (n/a)   (n/a)   (n/a)   name

as you can see , there is a new constraint and a new index U_Name

After Spring Boot 2.0 migration: jdbcUrl is required with driverClassName

In case you do need to define dataSource(), for example when you have multiple data sources, you can use:

@Autowired Environment env;

public DataSource customDataSource() {

    DriverManagerDataSource dataSource = new DriverManagerDataSource();

    return dataSource;


By setting up the dataSource yourself (instead of using DataSourceBuilder), it fixed my problem which you also had.

The always knowledgeable Baeldung has a tutorial which explains in depth.

How to set TextView textStyle such as bold, italic

try this to set your TextView style by java code


How to replace deprecated

Adding only android-support-v7-appcompat.jar to library dependencies is not enough, you have also to import in your project the module that you can find in your SDK at the path \android-sdk\extras\android\support\v7\appcompatand after that add module dependencies configuring the project structure in this way

enter image description here

otherwise are included only the class files of support library and the app is not able to load the other resources causing the error.

In addition as reVerse suggested replace this

public CustomActionBarDrawerToggle(Activity mActivity,
                                           DrawerLayout mDrawerLayout) {
            super(mActivity, mDrawerLayout,new Toolbar(MyActivity.this) ,
                    R.string.ns_menu_open, R.string.ns_menu_close);


public CustomActionBarDrawerToggle(Activity mActivity,
                                           DrawerLayout mDrawerLayout) {
            super(mActivity, mDrawerLayout, R.string.ns_menu_open, R.string.ns_menu_close);

Value cannot be null. Parameter name: source

It could be as silly as in my case where savechanges was erroring bcoz the db did not have foreign keys and associations were added to EDM tables. I added foreign keys in the db and regenerated EDM for a fix.

The errors I was seeing are as follows: Case 1 -> when using DBContext for EDM Message=Value cannot be null. Parameter name: source at System.Linq.Enumerable.Any[TSource](IEnumerable1 source, Func2 predicate)

Case 2 -> when using ObjectContext for EDM Message=Unable to update the EntitySet 'Contact' because it has a DefiningQuery and no element exists in the element to support the current operation.

(Just wanted to throw it in there in case it helps someone).

jQuery UI Sortable, then write order into a database

I can change the rows by following the accepted answer and associated example on jsFiddle. But due to some unknown reasons, I couldn't get the ids after "stop or change" actions. But the example posted in the JQuery UI page works fine for me. You can check that link here.

How can I list all tags for a Docker image on a remote registry?

If folks want to read tags from the RedHat registry at then the steps are:

# example nodejs-12 image
# Get an oAuth token based on a service account username and password
TOKEN=$(curl --silent -u "$REGISTRY_USER":"$REGISTRY_PASSWORD" "" |  jq --raw-output '.token')
# Grab the tags
wget -q --header="Accept: application/json" --header="Authorization: Bearer $TOKEN" -O - "$REDHAT_REGISTRY_API/tags/list" | jq -r '."tags"[]' 

If you want to compare what you have in your local openshift registry against what is in the upstream then here is a complete script.

Facebook API error 191

For me, it was a missing app domain. Go into the app, and make sure that you have the root of your site set up as an app domain. See screenshot.

app domains is in the basic settings of your app

setContentView(R.layout.main); error

is this already solved?

i also had this problem. I solved it just by cleaning the project.

Project>Clean>Clean projects selected below>Check [your project's name]

How to check a channel is closed or not without reading it?

You could set your channel to nil in addition to closing it. That way you can check if it is nil.

example in the playground:

edit: This is actually a bad solution as demonstrated in the next example, because setting the channel to nil in a function would break it:

Get contentEditable caret index position

window.getSelection - vs - document.selection

This one works for me:

function getCaretCharOffset(element) {_x000D_
  var caretOffset = 0;_x000D_
  if (window.getSelection) {_x000D_
    var range = window.getSelection().getRangeAt(0);_x000D_
    var preCaretRange = range.cloneRange();_x000D_
    preCaretRange.setEnd(range.endContainer, range.endOffset);_x000D_
    caretOffset = preCaretRange.toString().length;_x000D_
  } _x000D_
  else if (document.selection && document.selection.type != "Control") {_x000D_
    var textRange = document.selection.createRange();_x000D_
    var preCaretTextRange = document.body.createTextRange();_x000D_
    preCaretTextRange.setEndPoint("EndToEnd", textRange);_x000D_
    caretOffset = preCaretTextRange.text.length;_x000D_
  return caretOffset;_x000D_
// Demo:_x000D_
var elm = document.querySelector('[contenteditable]');_x000D_
elm.addEventListener('click', printCaretPosition)_x000D_
elm.addEventListener('keydown', printCaretPosition)_x000D_
function printCaretPosition(){_x000D_
  console.log( getCaretCharOffset(elm), 'length:', this.textContent.trim().length )_x000D_
<div contenteditable>some text here <i>italic text here</i> some other text here <b>bold text here</b> end of text</div>

The calling line depends on event type, for key event use this:

getCaretCharOffsetInDiv( + ($(window.getSelection().getRangeAt(0).startContainer.parentNode).index());

for mouse event use this:

getCaretCharOffsetInDiv( + ($(

on these two cases I take care for break lines by adding the target index

Why is the minidlna database not being refreshed?

There is a patch for the sourcecode of minidlna at sourceforge available that does not make a full rescan, but a kind of incremental scan. That worked fine, but with some later version, the patch is broken. See here Link to SF

Regards Gerry

Converting a sentence string to a string array of words in Java

You can just split your string like that using this regular expression

String l = "sofia, malgré tout aimait : la laitue et le choux !" <br/>
l.split("[[ ]*|[,]*|[\\.]*|[:]*|[/]*|[!]*|[?]*|[+]*]+");

What does <![CDATA[]]> in XML mean?

I once had to use CDATA when my xml element needed to store HTML code. Something like

  <div> <p> my para </p> </div> 

So CDATA means it will ignore any character which could otherwise be interpreted as XML tag like < and > etc.

Python constructors and __init__

Classes are simply blueprints to create objects from. The constructor is some code that are run every time you create an object. Therefor it does'nt make sense to have two constructors. What happens is that the second over write the first.

What you typically use them for is create variables for that object like this:

>>> class testing:
...     def __init__(self, init_value):
...         self.some_value = init_value

So what you could do then is to create an object from this class like this:

>>> testobject = testing(5)

The testobject will then have an object called some_value that in this sample will be 5.

>>> testobject.some_value

But you don't need to set a value for each object like i did in my sample. You can also do like this:

>>> class testing:
...     def __init__(self):
...         self.some_value = 5

then the value of some_value will be 5 and you don't have to set it when you create the object.

>>> testobject = testing()
>>> testobject.some_value

the >>> and ... in my sample is not what you write. It's how it would look in pyshell...

How to get PID of process I've just started within java program?

Since Java 9 class Process has new method long pid(), so it is as simple as

ProcessBuilder pb = new ProcessBuilder("cmd", "/c", "path");
try {
    Process p = pb.start();
    long pid =;      
} catch (IOException ex) {
    // ...

Cannot find either column "dbo" or the user-defined function or aggregate "dbo.Splitfn", or the name is ambiguous

Since people will be coming from Google, make sure you're in the right database.

Running SQL in the 'master' database will often return this error.

Creating composite primary key in SQL Server

How about something like

CREATE TABLE testRequest (
        wardNo nchar(5),
        BHTNo nchar(5),
        testID nchar(5),
        reqDateTime datetime,
        PRIMARY KEY (wardNo, BHTNo, testID)

Have a look at this example


Filter object properties by key in ES6

I'm surprised how nobody has suggested this yet. It's super clean and very explicit about which keys you want to keep.

const unfilteredObj = {a: ..., b:..., c:..., x:..., y:...}

const filterObject = ({a,b,c}) => ({a,b,c})
const filteredObject = filterObject(unfilteredObject)

Or if you want a dirty one liner:

const unfilteredObj = {a: ..., b:..., c:..., x:..., y:...}

const filteredObject = (({a,b,c})=>({a,b,c}))(unfilteredObject);

How can I change a button's color on hover?

Seems your selector is wrong, try using:

     background: #383;

Your code

a.button a:hover

Means it is going to search for an a element inside a with class button.

Adjust UILabel height depending on the text

UILabel *itemTitle = [[UILabel alloc] initWithFrame:CGRectMake(10.0f, 10,100, 200.0f)];
itemTitle.text = @"aseruy56uiytitfesh";
itemTitle.adjustsFontSizeToFitWidth = NO;
itemTitle.autoresizingMask = UIViewAutoresizingFlexibleWidth;
itemTitle.font = [UIFont boldSystemFontOfSize:18.0];
itemTitle.textColor = [UIColor blackColor];
itemTitle.shadowColor = [UIColor whiteColor];
itemTitle.shadowOffset = CGSizeMake(0, 1);
itemTitle.backgroundColor = [UIColor blueColor];
itemTitle.lineBreakMode = UILineBreakModeWordWrap;
itemTitle.numberOfLines = 0;
[itemTitle sizeToFit];
[self.view addSubview:itemTitle];

use this here all the properties are used on the label and test it by increasing the text in the itemTitle.text as

itemTitle.text = @"diofgorigjveghnhkvjteinughntivugenvitugnvkejrfgnvkhv";

it will show the perfetc answer as you need

String concatenation of two pandas columns

You could also use

df['bar'] = df['bar']['foo'].values.astype(str), sep=' is ')

Export JAR with Netbeans

  1. Right click your project folder.
  2. Select Properties.
  3. Expand Build option.
  4. Select Packaging.
  5. Now Clean and Build your project (Shift +F11).
  6. jar file will be created at your_project_folder\dist folder.

How to list files inside a folder with SQL Server

Very easy, just use the SQLCMD-syntax.

Remember to enable SQLCMD-mode in the SSMS, look under Query -> SQLCMD Mode

Try execute:


or maybe:
!!DIR "c:/temp"

Why doesn't Java allow overriding of static methods?

Here is a simple explanation. A static method is associated with a class while an instance method is associated with a particular object. Overrides allow calling the different implementation of the overridden methods associated with the particular object. So it is counter-intuitive to override static method which is not even associated with objects but the class itself in the first place. So static methods cannot be overridden based on what object is calling it, it will always be associated with the class where it was created.

How to a convert a date to a number and back again in MATLAB


>> datestr(40189)
ans =

Unfortunately, Excel starts counting at 1-Jan-1900. Find out how to convert serial dates from Matlab to Excel by using DATENUM

>> datenum(2010,1,11)
ans =
>> datenum(2010,1,11)-40189
ans =
>> datestr(40189+693960)
ans =

In other words, to convert any serial Excel date, call

datestr(excelSerialDate + 693960)


To get the date in mm/dd/yyyy format, call datestr with the specified format

excelSerialDate = 40189;
datestr(excelSerialDate + 693960,'mm/dd/yyyy')
ans =

Also, if you want to get rid of the leading zero for the month, you can use REGEXPREP to fix things

excelSerialDate = 40189;
regexprep(datestr(excelSerialDate + 693960,'mm/dd/yyyy'),'^0','')
ans =

Excel VBA Run-time Error '32809' - Trying to Understand it

It seems that 32809 is a general error message. After struggling for some time, I found that I had not clicked on the "Enable Macros" security button at the below the workbook ribbon. Once I did this, everything worked fine.

node.js, with SSL

If your server certificated file is not trusted, (for example, you may generate the keystore by yourself with keytool command in java), you should add the extra option rejectUnauthorized

var socket = io.connect('https://localhost', {rejectUnauthorized: false});

There are No resources that can be added or removed from the server

The issue is incompatible web application version with the targeted server. So project facets needs to be changed. In most of the cases the "Dynamic Web Module" property. This should be the value of the servlet-api version supported by the server.

In my case,

I tried changing the web_app value in web.xml. It did not worked.

I tried changing the project facet by right clicking on project properties(as mentioned above), did not work.

What worked is: Changing "version" value as in jst.web to right version from

org.eclipse.wst.common.project.facet.core.xml file. This file is present in the .setting folder under your project root directory.

You may also look at this

Is there a maximum number you can set Xmx to when trying to increase jvm memory?

Yes, there is a maximum, but it's system dependent. Try it and see, doubling until you hit a limit then searching down. At least with Sun JRE 1.6 on linux you get interesting if not always informative error messages (peregrino is netbook running 32 bit ubuntu with 2G RAM and no swap):

peregrino:$ java -Xmx4096M -cp bin WheelPrimes 
Invalid maximum heap size: -Xmx4096M
The specified size exceeds the maximum representable size.
Could not create the Java virtual machine.

peregrino:$ java -Xmx4095M -cp bin WheelPrimes 
Error occurred during initialization of VM
Incompatible minimum and maximum heap sizes specified

peregrino:$ java -Xmx4092M -cp bin WheelPrimes 
Error occurred during initialization of VM
The size of the object heap + VM data exceeds the maximum representable size

peregrino:$ java -Xmx4000M -cp bin WheelPrimes 
Error occurred during initialization of VM
Could not reserve enough space for object heap
Could not create the Java virtual machine.

(experiment reducing from 4000M until)

peregrino:$ java -Xmx2686M -cp bin WheelPrimes 
(normal execution)

Most are self explanatory, except -Xmx4095M which is rather odd (maybe a signed/unsigned comparison?), and that it claims to reserve 2686M on a 2GB machine with no swap. But it does hint that the maximum size is 4G not 2G for a 32 bit VM, if the OS allows you to address that much.

Filter Extensions in HTML form upload

I wouldnt use this attribute as most browsers ignore it as CMS points out.

By all means use client side validation but only in conjunction with server side. Any client side validation can be got round.

Slightly off topic but some people check the content type to validate the uploaded file. You need to be careful about this as an attacker can easily change it and upload a php file for example. See the example at:

Maven : error in opening zip file when running maven

Deleting the entire local m2 repo may not be advisable. As in my case I have hundreds and hundreds of jars in my local, I don't want to re-download them all just for one jar. Most of the above answers didn't work for me, here is what I did.

STEP:1: Ensure if you are downloading from the correct Maven repo in you settings.xml. In my case it was referring to as So it was getting corrupted or going otherwise?

STEP:2: Delete the folder containing the artifact and other details in your local machine.This will force it download it again upon next build

STEP:3: mvn clean install :).

Hope it helps.

JAX-RS — How to return JSON and HTTP status code together?

The answer by hisdrewness will work, but it modifies the whole approach to letting a provider such as Jackson+JAXB automatically convert your returned object to some output format such as JSON. Inspired by an Apache CXF post (which uses a CXF-specific class) I've found one way to set the response code that should work in any JAX-RS implementation: inject an HttpServletResponse context and manually set the response code. For example, here is how to set the response code to CREATED when appropriate.

public Foo setFoo(@PathParam("fooID") final String fooID, final Foo foo, @Context final HttpServletResponse response)
  //TODO store foo in persistent storage
  if(itemDidNotExistBefore) //return 201 only if new object; TODO app-specific logic
  return foo;  //TODO get latest foo from storage if needed

Improvement: After finding another related answer, I learned that one can inject the HttpServletResponse as a member variable, even for singleton service class (at least in RESTEasy)!! This is a much better approach than polluting the API with implementation details. It would look like this:

@Context  //injected response proxy supporting multiple threads
private HttpServletResponse response;

public Foo setFoo(@PathParam("fooID") final String fooID, final Foo foo)
  //TODO store foo in persistent storage
  if(itemDidNotExistBefore) //return 201 only if new object; TODO app-specific logic
  return foo;  //TODO get latest foo from storage if needed

Retrieving parameters from a URL

The url you are referring is a query type and I see that the request object supports a method called arguments to get the query arguments. You may also want try self.request.get('def') directly to get your value from the object..

Kotlin's List missing "add", "remove", Map missing "put", etc?

In concept of immutable data, maybe this is a better way:

class TempClass {
    val list: List<Int> by lazy {
    fun doSomething() {
        list += 10
        list -= 10

Fastest way to implode an associative array with keys

You can use http_build_query() to do that.

Generates a URL-encoded query string from the associative (or indexed) array provided.

Combine Date and Time columns using python pandas

My dataset had 1second resolution data for a few days and parsing by the suggested methods here was very slow. Instead I used:

dates = pandas.to_datetime(df.Date, cache=True)
times = pandas.to_timedelta(df.Time)
datetimes  = dates + times

Note the use of cache=True makes parsing the dates very efficient since there are only a couple unique dates in my files, which is not true for a combined date and time column.

VarBinary vs Image SQL Server Data Type to Store Binary Data?


Variable-length binary data from 0 through 2^31-1 (2,147,483,647) bytes. Still it IS supported to use image datatype, but be aware of:

varbinary [ ( n | max) ]

Variable-length binary data. n can be a value from 1 through 8,000. max indicates that the maximum storage size is 2^31-1 bytes. The storage size is the actual length of the data entered + 2 bytes. The data that is entered can be 0 bytes in length. The ANSI SQL synonym for varbinary is binary varying.

So both are equally in size (2GB). But be aware of:

Though the end of "image" datatype is still not determined, you should use the "future" proof equivalent.

But you have to ask yourself: why storing BLOBS in a Column?

Merge two (or more) lists into one, in C# .NET

list4 = list1.Concat(list2).Concat(list3).ToList();

How to give a Blob uploaded as FormData a file name?

For Chrome, Safari and Firefox, just use this:

form.append("blob", blob, filename);

(see MDN documentation)

Register comdlg32.dll gets Regsvr32: DllRegisterServer entry point was not found

Registering DLL for Fundsite

Outdated or missing comdlg32.ocx runtime library can be the problem of causing this error. Make sure comdlg32.ocx file is not corrupted otherwise Download the File comdlg32.ocx (~60 Kb Zip).

Download the file and extract the comdlg32.ocx to your the Windows\System32 folder or Windows\SysWOW64. In my case i started with Windows\System32 but it didn’t work at my end, so I again saved in Windows\SysWOW64.

Type following command from Start, Run dialog:“c:\windows>System32\regsvr32 Comdlg32.ocx “ or “c:\windows>SysWOW64\regsvr32 Comdlg32.ocx ”

Now Comdlg.ocx File is register and next step is to register the DLL

  1. Copy the Fundsite.Text.Encoding. dll into .Net Framework folder for 64bit on below path C:\Windows\Microsoft.NET\Framework64\v2.0.50727

  2. Then on command prompt and go to directory C:\Windows\Microsoft.NET\Framework64\v2.0.50727 and then run the following command as shown below.

This will register the dll successfully.

C:\Windows\\framework64\v2.0.50727>regasm "Dll Name".dll

how to remove css property using javascript?

removeProperty will remove a style from an element.


MDN documentation page:

Problems when trying to load a package in R due to rJava

I had a similar problem what worked for me was to set JAVA_HOME. I tired it first in R:

Sys.setenv(JAVA_HOME = "C:/Program Files/Java/jdk1.8.0_101/")

And when it actually worked I set it in

System Properties -> Advanced -> Environment Variables

by adding a new System variable. I then restarted R/RStudio and everything worked.

How to map an array of objects in React

@FurkanO has provided the right approach. Though to go for a more cleaner approach (es6 way) you can do something like this

    name: 'Sam',
    email: '[email protected]'
    name: 'Ash',
    email: '[email protected]'
].map( ( {name, email} ) => {
    return <p key={email}>{name} - {email}</p>


How to force Hibernate to return dates as java.util.Date instead of Timestamp?

There are some classes in the Java platform libraries that do extend an instantiable class and add a value component. For example, java.sql.Timestamp extends java.util.Date and adds a nanoseconds field. The equals implementation for Timestamp does violate symmetry and can cause erratic behavior if Timestamp and Date objects are used in the same collection or are otherwise intermixed. The Timestamp class has a disclaimer cautioning programmers against mixing dates and timestamps. While you won’t get into trouble as long as you keep them separate, there’s nothing to prevent you from mixing them, and the resulting errors can be hard to debug. This behavior of the Timestamp class was a mistake and should not be emulated.

check out this link

How can I access localhost from another computer in the same network?

localhost is a special hostname that almost always resolves to If you ask someone else to connect to http://localhost they'll be connecting to their computer instead or yours.

To share your web server with someone else you'll need to find your IP address or your hostname and provide that to them instead. On windows you can find this with ipconfig /all on a command line.

You'll also need to make sure any firewalls you may have configured allow traffic on port 80 to connect to the WAMP server.

Do checkbox inputs only post data if they're checked?

Is it standard behaviour for browsers to only send the checkbox input value data if it is checked upon form submission?

Yes, because otherwise there'd be no solid way of determining if the checkbox was actually checked or not (if it changed the value, the case may exist when your desired value if it were checked would be the same as the one that it was swapped to).

And if no value data is supplied, is the default value always "on"?

Other answers confirm that "on" is the default. However, if you are not interested in the value, just use:

if (isset($_POST['the_checkbox'])){
    // name="the_checkbox" is checked

How to enable file upload on React's Material UI simple input?

Here an example:

return (
    <Box alignItems='center' display='flex' justifyContent='center' flexDirection='column'>
        <input accept="image/*" id="upload-company-logo" type='file' hidden />
        <label htmlFor="upload-company-logo">
          <Button component="span" >
            <Paper elevation={5}>
              <Avatar src={formik.values.logo} className={classes.avatar} variant='rounded' />

jQuery .search() to any string

Ah, that would be because RegExp is not jQuery. :)

Try this page. jQuery.attr doesn't return a String so that would certainly cause in this regard. Fortunately I believe you can just use .text() to return the String representation.

Something like:


Append text to textarea with javascript

Give this a try:

<!DOCTYPE html>
    <title>List Test</title>
        li:hover {
            cursor: hand; cursor: pointer;
    <script src=""></script>

    <h2>List items</h2>
        <textarea id="alltext"></textarea>


How do I toggle an element's class in pure JavaScript?

This one works in earlier versions of IE also.

function toogleClass(ele, class1) {_x000D_
  var classes = ele.className;_x000D_
  var regex = new RegExp('\\b' + class1 + '\\b');_x000D_
  var hasOne = classes.match(regex);_x000D_
  class1 = class1.replace(/\s+/g, '');_x000D_
  if (hasOne)_x000D_
    ele.className = classes.replace(regex, '');_x000D_
    ele.className = classes + class1;_x000D_
.red {_x000D_
  background-color: red_x000D_
div {_x000D_
  width: 100px;_x000D_
  height: 100px;_x000D_
  margin-bottom: 10px;_x000D_
  border: 1px solid black;_x000D_
<div class="does red redAnother " onclick="toogleClass(this, 'red')"></div>_x000D_
<div class="does collapse navbar-collapse " onclick="toogleClass(this, 'red')"></div>

How to test an Internet connection with bash?

Similarly to @Jesse's answer, this option might be much faster than any solution using ping and perhaps slightly more efficient than @Jesse's answer.

find /sys/class/net/ -maxdepth 1 -mindepth 1 ! -name "*lo*" -exec sh -c 'cat "$0"/carrier 2>&1' {} \; | grep -q '1'


This command uses find with -exec to run command on all files not named *lo* in /sys/class/net/. These should be links to directories containing information about the available network interfaces on your machine.

The command being ran is an sh command that checks the contents of the file carrier in those directories. The value of $interface/carrier has 3 meanings - Quoting:

It seems there are three states:

  • ./carrier not readable (for instance when the interface is disabled in Network Manager).
  • ./carrier contain "1" (when the interface is activated and it is connected to a WiFi network)
  • ./carrier contain "0" (when the interface is activated and it is not connected to a WiFi network)

The first option is not taken care of in @Jesse's answer. The sh command striped out is:

# Note: $0 == $interface
cat "$0"/carrier 2>&1

cat is being used to check the contents of carrier and redirect all output to standard output even when it fails because the file is not readable. If grep -q finds "1" among those files it means there is at least 1 interface connected. The exit code of grep -q will be the final exit code.


For example, using this command's exit status, you can use it start a gnubiff in your ~/.xprofile only if you have an internet connection.

online() {
    find /sys/class/net/ -maxdepth 1 -mindepth 1 ! -name "*lo*" -exec sh -c 'cat "$0"/carrier 2>&1 > /dev/null | grep -q "1" && exit 0' {} \;
online && gnubiff --systemtray --noconfigure &


CSS centred header image

If you set the margin to be margin:0 auto the image will be centered.

This will give top + bottom a margin of 0, and left and right a margin of 'auto'. Since the div has a width (200px), the image will be 200px wide and the browser will auto set the left and right margin to half of what is left on the page, which will result in the image being centered.

start MySQL server from command line on Mac OS Lion

111028 16:57:43 [ERROR] Fatal error: Please read "Security" section of the manual to find out how to run mysqld as root!

Have you set a root password for your mysql installation? This is different to your sudo root password. Try /usr/local/mysql/bin/mysql_secure_installation

How to assign pointer address manually in C programming language?

let's say you want a pointer to point at the address 0x28ff4402, the usual way is

uint32_t *ptr;
ptr = (uint32_t*) 0x28ff4402 //type-casting the address value to uint32_t pointer
*ptr |= (1<<13) | (1<<10); //access the address how ever you want

So the short way is to use a MACRO,

#define ptr *(uint32_t *) (0x28ff4402)

How to make URL/Phone-clickable UILabel?

extension UITapGestureRecognizer {

    func didTapAttributedTextInLabel(label: UILabel, inRange targetRange: NSRange) -> Bool {

        let layoutManager = NSLayoutManager()
        let textContainer = NSTextContainer(size:
        let textStorage = NSTextStorage(attributedString: label.attributedText!)

        // Configure layoutManager and textStorage

        // Configure textContainer
        textContainer.lineFragmentPadding = 0.0
        textContainer.lineBreakMode = label.lineBreakMode
        textContainer.maximumNumberOfLines = label.numberOfLines
        textContainer.size = label.bounds.size

        // main code
        let locationOfTouchInLabel = self.location(in: label)

        let indexOfCharacter = layoutManager.characterIndex(for: locationOfTouchInLabel, in: textContainer, fractionOfDistanceBetweenInsertionPoints: nil)
        let indexOfCharacterRange = NSRange(location: indexOfCharacter, length: 1)
        let indexOfCharacterRect = layoutManager.boundingRect(forGlyphRange: indexOfCharacterRange, in: textContainer)
        let deltaOffsetCharacter = indexOfCharacterRect.origin.x + indexOfCharacterRect.size.width

        if locationOfTouchInLabel.x > deltaOffsetCharacter {
            return false
        } else {
            return NSLocationInRange(indexOfCharacter, targetRange)

Outline effect to text

You could try stacking multiple blured shadows until the shadows look like a stroke, like so:

.shadowOutline {
  text-shadow: 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black, 0 0 4px black;

Here's a fiddle:

I mention it just in case someone's interested, although I wouldn't call it a solution because it fails in various ways:

  • it doesn't work in old IE
  • it renders quite differently in every browser
  • applying so many shadows is very heavy to process :S

How to apply `git diff` patch without Git installed?

git diff > patchfile


patch -p1 < patchfile

work but as many people noticed in comments and other answers patch does not understand adds, deletes and renames. There is no option but git apply patchfile if you need handle file adds, deletes and renames.

EDIT December 2015

Latest versions of patch command (2.7, released in September 2012) support most features of the "diff --git" format, including renames and copies, permission changes, and symlink diffs (but not yet binary diffs) (release announcement).

So provided one uses current/latest version of patch there is no need to use git to be able to apply its diff as a patch.

Retrieving a random item from ArrayList

anyItem has never been declared as a variable, so it makes sense that it causes an error. But more importantly, you have code after a return statement and this will cause an unreachable code error.

How to set at runtime?

You can use System.setProperty("" , "true");

This is equivalent to passing it in the command line via

Import / Export database with SQL Server Server Management Studio

for Microsoft SQL Server Management Studio 2012,2008.. First Copy your database file .mdf and log file .ldf & Paste in your sql server install file in Programs Files->Microsoft SQL Server->MSSQL10.SQLEXPRESS->MSSQL->DATA. Then open Microsoft Sql Server . Right Click on Databases -> Select Attach...option.

How to make type="number" to positive numbers only

(function ($) {
  $.fn.inputFilter = function (inputFilter) {
    return this.on('input keydown keyup mousedown mouseup select contextmenu drop', function () {
      if (inputFilter(this.value)) {
        this.oldValue = this.value;
        this.oldSelectionStart = this.selectionStart;
        this.oldSelectionEnd = this.selectionEnd;
      } else if (this.hasOwnProperty('oldValue')) {
        this.value = this.oldValue;
        //this.setSelectionRange(this.oldSelectionStart, this.oldSelectionEnd);
      } else {
        this.value = '';

$('.positive_int').inputFilter(function (value) {
  return /^\d*[.]?\d{0,2}$/.test(value);
<script src=""></script>
<input type="number" class="positive_int"/>

Above code works fine for all !!! And it will also prevent inserting more than 2 decimal points. And if you don't need this just remove\d{0,2} or if need more limited decimal point just change number 2

Have log4net use application config file for configuration data

All appender names must be reflected in the root section.
In your case the appender name is EventLogAppender but in the <root> <appender-ref .. section it is named as ConsoleAppender. They need to match.

You can add multiple appenders to your log config but you need to register each of them in the <root> section.

<appender-ref ref="ConsoleAppender" />
<appender-ref ref="EventLogAppender" />

You can also refer to the apache documentation on configuring log4net.

How to get position of a certain element in strings vector, to use it as an index in ints vector?

I am a beginner so here is a beginners answer. The if in the for loop gives i which can then be used however needed such as Numbers[i] in another vector. Most is fluff for examples sake, the for/if really says it all.

int main(){
vector<string>names{"Sara", "Harold", "Frank", "Taylor", "Sasha", "Seymore"};
string req_name;
cout<<"Enter search name: "<<'\n';
    for(int i=0; i<=names.size()-1; ++i) {
            cout<<"The index number for "<<req_name<<" is "<<i<<'\n';
            return 0;
        else if(names[i]!=req_name && i==names.size()-1) {
            cout<<"That name is not an element in this vector"<<'\n';
        } else {

How to extract HTTP response body from a Python requests call?

Your code is correct. I tested:

r = requests.get("")

And it returned plenty of content. Check the url, try "". Cheers!

Use dynamic (variable) string as regex pattern in JavaScript

I found I had to double slash the \b to get it working. For example to remove "1x" words from a string using a variable, I needed to use:

    str = "1x";
    var regex = new RegExp("\\b"+str+"\\b","g"); // same as inv.replace(/\b1x\b/g, "")
    inv=inv.replace(regex, "");

Empty an array in Java / processing

I just want to add something to Mark's comment. If you want to reuse array without additional allocation, just use it again and override existing values with new ones. It will work if you fill the array sequentially. In this case just remember the last initialized element and use array until this index. It is does not matter that there is some garbage in the end of the array.

Programmatically change the src of an img tag

Give your img tag an id, then you can


PHP cURL custom headers

curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    'X-Apple-Tz: 0',
    'X-Apple-Store-Front: 143444,12'

List submodules in a Git repository

I use this one:

git submodule status | cut -d' ' -f3-4 

Output (path + version):

tools/deploy_utils (0.2.4)

How do I list all the columns in a table?

Microsoft SQL Server Management Studio 2008 R2:

In a query editor, if you highlight the text of table name (ex dbo.MyTable) and hit ALT+F1, you'll get a list of column names, type, length, etc.

ALT+F1 while you've highlighted dbo.MyTable is the equivalent of running EXEC sp_help 'dbo.MyTable' according to this site

I can't get the variations on querying INFORMATION_SCHEMA.COLUMNS to work, so I use this instead.

MD5 is 128 bits but why is it 32 characters?

MD5 yields hexadecimal digits (0-15 / 0-F), so they are four bits each. 128 / 4 = 32 characters.

SHA-1 yields hexadecimal digits too (0-15 / 0-F), so 160 / 4 = 40 characters.

(Since they're mathematical operations, most hashing functions' output is commonly represented as hex digits.)

You were probably thinking of ASCII text characters, which are 8 bits.

How to cast Object to boolean?

Assuming that yourObject.toString() returns "true" or "false", you can try

boolean b = Boolean.valueOf(yourObject.toString())

Export to csv/excel from kibana

FYI : How to download data in CSV from Kibana:

In Kibana--> 1. Go to 'Discover' in left side

  1. Select Index Field (based on your dashboard data) (*** In case if you are not sure which index to select-->go to management tab-->Saved Objects-->Dashboard-->select dashboard name-->scroll down to JSON-->you will see the Index name )

  2. left side you see all the variables available in the data-->click over the variable name that you want to have in csv-->click add-->this variable will be added on the right side of the columns avaliable

  3. Top right section of the kibana-->there is the time filter-->click -->select the duration for which you want the csv

  4. Top upper right -->Reporting-->save this time/variable selection with a new report-->click generate CSV

  5. Go to 'Management' in left side--> 'Reporting'-->download your csv

Encrypt and Decrypt in Java

If you use a static key, encrypt and decrypt always give the same result;

public static final String CRYPTOR_KEY = "your static key here";
byte[] keyByte = Base64.getDecoder().decode(CRYPTOR_KEY);
key = new SecretKeySpec(keyByte, "AES");

Splitting on last delimiter in Python string?

Use .rsplit() or .rpartition() instead:

s.rsplit(',', 1)

str.rsplit() lets you specify how many times to split, while str.rpartition() only splits once but always returns a fixed number of elements (prefix, delimiter & postfix) and is faster for the single split case.


>>> s = "a,b,c,d"
>>> s.rsplit(',', 1)
['a,b,c', 'd']
>>> s.rsplit(',', 2)
['a,b', 'c', 'd']
>>> s.rpartition(',')
('a,b,c', ',', 'd')

Both methods start splitting from the right-hand-side of the string; by giving str.rsplit() a maximum as the second argument, you get to split just the right-hand-most occurrences.

How to select all the columns of a table except one column?

I just wanted to echo @Luann's comment as I use this approach always.

Just right click on the table > Script table as > Select to > New Query window.

You will see the select query. Just take out the column you want to exclude and you have your preferred select query. enter image description here

Plot multiple columns on the same graph in R

A very simple solution:

df <- read.csv("df.csv",sep=",",head=T)
x <- cbind(df$Xax,df$Xax,df$Xax,df$Xax)
y <- cbind(df$A,df$B,df$C,df$D)

please note it just plots the data and it does not plot any regression line.

Sublime 3 - Set Key map for function Goto Definition

I'm using Sublime portable version (for Windows) and this (placing the mousemap in SublimeText\Packages\User folder) did not work for me.

I had to place the mousemap file in SublimeText\Data\Packages\User folder to get it to work where SublimeText is the installation directory for my portable version. Data\Packages\User is where I found the keymap file as well.

Finish an activity from another activity

I think i have the easiest approach... on pressing new in B..

Intent intent = new Intent(B.this, A.class);
intent.putExtra("NewClicked", true);

and in A get it

  if (getIntent().getBooleanExtra("NewClicked", false)) {
        finish();// finish yourself and make a create a new Instance of yours.
      Intent intent = new Intent(A.this,A.class);

How can I combine two HashMap objects containing the same types?

If you don't need mutability for your final map, there is Guava's ImmutableMap with its Builder and putAll method which, in contrast to Java's Map interface method, can be chained.

Example of use:

Map<String, Integer> mergeMyTwoMaps(Map<String, Integer> map1, Map<String, Integer> map2) {
  return ImmutableMap.<String, Integer>builder()

Of course, this method can be more generic, use varargs and loop to putAll Maps from arguments etc. but I wanted to show a concept.

Also, ImmutableMap and its Builder have few limitations (or maybe features?):

  • they are null hostile (throw NullPointerException - if any key or value in map is null)
  • Builder don't accept duplicate keys (throws IllegalArgumentException if duplicate keys were added).

How to deserialize xml to object

Your classes should look like this

public class StepList
    public List<Step> Steps { get; set; }

public class Step
    public string Name { get; set; }
    public string Desc { get; set; }

Here is my testcode.

string testData = @"<StepList>

XmlSerializer serializer = new XmlSerializer(typeof(StepList));
using (TextReader reader = new StringReader(testData))
    StepList result = (StepList) serializer.Deserialize(reader);

If you want to read a text file you should load the file into a FileStream and deserialize this.

using (FileStream fileStream = new FileStream("<PathToYourFile>", FileMode.Open)) 
    StepList result = (StepList) serializer.Deserialize(fileStream);

grunt: command not found when running from terminal

My fix for this on Mountain Lion was: -

npm install -g grunt-cli 

Saw it on

How to scroll to the bottom of a RecyclerView? scrollToPosition doesn't work

Just set setStackFromEnd=true or setReverseLayout=true so that LLM will layout items from end.

The difference between these two is that setStackFromEnd will set the view to show the last element, the layout direction will remain the same. (So, in an left-to-right horizontal Recycler View, the last element will be shown and scrolling to the left will show the earlier elements)

Whereas setReverseLayout will change the order of the elements added by the Adapter. The layout will start from the last element, which will be the left-most in an LTR Recycler View and then, scrolling to the right will show the earlier elements.


final LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getActivity());

See documentation for details.

Pandas DataFrame to List of Dictionaries

Use df.to_dict('records') -- gives the output without having to transpose externally.

In [2]: df.to_dict('records')
[{'customer': 1L, 'item1': 'apple', 'item2': 'milk', 'item3': 'tomato'},
 {'customer': 2L, 'item1': 'water', 'item2': 'orange', 'item3': 'potato'},
 {'customer': 3L, 'item1': 'juice', 'item2': 'mango', 'item3': 'chips'}]

How to take a first character from the string

Try this..

Dim S As String
Dim answer As Char
answer = S.Substring(0, 1)

HTML form do some "action" when hit submit button

Ok, I'll take a stab at this. If you want to work with PHP, you will need to install and configure both PHP and a webserver on your machine. This article might get you started: PHP Manual: Installation on Windows systems

Once you have your environment setup, you can start working with webforms. Directly From the article: Processing form data with PHP:

For this example you will need to create two pages. On the first page we will create a simple HTML form to collect some data. Here is an example:

 <title>Test Page</title>
    <h2>Data Collection</h2><p>
    <form action="process.php" method="post">  
                <td><input type="text" name="Name"/></td>
                <td><input type="text" name="Age"/></td>
                <td colspan="2" align="center">
                <input type="submit"/>

This page will send the Name and Age data to the page process.php. Now lets create process.php to use the data from the HTML form we made:

    print "Your name is ". $Name;   
    print "<br />";   
    print "You are ". $Age . " years old";   
    print "<br />";   $old = 25 + $Age;
    print "In 25 years you will be " . $old . " years old";   

As you may be aware, if you leave out the method="post" part of the form, the URL with show the data. For example if your name is Bill Jones and you are 35 years old, our process.php page will display as If you want, you can manually change the URL in this way and the output will change accordingly.

Additional JavaScript Example

This single file example takes the html from your question and ties the onSubmit event of the form to a JavaScript function that pulls the values of the 2 textboxes and displays them in an alert box.

Note: document.getElementById("fname").value gets the object with the ID tag that equals fname and then pulls it's value - which in this case is the text in the First Name textbox.

     <script type="text/javascript">
     function ExampleJS(){
        var jFirst = document.getElementById("fname").value;
        var jLast = document.getElementById("lname").value;
        alert("Your name is: " + jFirst + " " + jLast);

        <FORM NAME="myform" onSubmit="JavaScript:ExampleJS()">

             First name: <input type="text" id="fname" name="firstname" /><br />
             Last name:  <input type="text" id="lname" name="lastname" /><br />
            <input name="Submit"  type="submit" value="Update" />

Delete all the records

I can see the that the others answers shown above are right, but I'll make your life easy.

I even created an example for you. I added some rows and want delete them.

You have to right click on the table and as shown in the figure Script Table a> Delete to> New query Editor widows:

enter image description here

Then another window will open with a script. Delete the line of "where", because you want to delete all rows. Then click Execute.

enter image description here

To make sure you did it right right click over the table and click in "Select Top 1000 rows". Then you can see that the query is empty.

Test iOS app on device without apple developer program or jailbreak

Go to Build Settings, under Code Signing, set Code Signing Identity as iOS Developer & Provisioning Profile as Automatic.

Select your device (now visible) from drop down list and run your app.

enter image description here

How do I create an HTML table with a fixed/frozen left column and a scrollable body?

Opera was buggy for all of the previous answers when I tested them on my mac. If you scroll through the table the fixed column disappears after you pass the first unfixed column. I went ahead and wrote the code below. It works in all the browsers I have locally installed. I don't know how ie handles it though.

Just keep that in mind that if you intend to skip rows in one table and not the other or change the heights of the rows you might need to adjust this code.

<table class = "fixedColumns">
    <tr><td> row 1 </td></tr>
    <tr><td> row 2 </td></tr>
<table class = "scrollableTable">
    <tr><td> col 1 </td> <td> col 2 </td><td> col 3 </td><td> col 4 </td></tr>
    <tr><td> col 1 </td> <td> col 2 </td><td> col 3 </td><td> col 4 </td></tr>

<style type = "text/css" >
        display: inline-block;
        display: inline-block;
        white-space: nowrap;
        overflow-x: scroll;

How to convert/parse from String to char in java?

The simplest way to convert a String to a char is using charAt():

String stringAns="hello";
char charAns=stringAns.charAt(0);//Gives You 'h'
char charAns=stringAns.charAt(1);//Gives You 'e'
char charAns=stringAns.charAt(2);//Gives You 'l'
char charAns=stringAns.charAt(3);//Gives You 'l'
char charAns=stringAns.charAt(4);//Gives You 'o'
char charAns=stringAns.charAt(5);//Gives You:: Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 5

Here is a full script:

import java.util.Scanner;

class demo {
    String accNo,name,fatherName,motherName;
    int age;
    static double rate=0.25;
    static double balance=1000;
    Scanner scanString=new Scanner(;
    Scanner scanNum=new Scanner(;

    void input()
        System.out.print("Account Number:");
        System.out.print("Father's Name:");
        System.out.print("Mother's Name:");

    void withdraw() {
        System.out.print("How Much:");
        double withdraw=scanNum.nextDouble();
            System.out.println("Invalid Data Entry\n Balance below Rs 1000 not allowed");

    void deposit() {
        System.out.print("How Much:");
        double deposit=scanNum.nextDouble();

    void display() {
        System.out.println("Your  Balnce:Rs "+balance);

    void oneYear() {
        System.out.println("After one year:");

    public static void main(String args[]) {
        demo d1=new demo();
        while(true) {//Withdraw/Deposit
            System.out.println("Withdraw/Deposit Press W/D:");
            String reply1= ((d1.scanString.nextLine()).toLowerCase()).trim();
            char reply=reply1.charAt(0);
            if(reply=='w') {
            else if(reply=='d') {
            else {
                System.out.println("Invalid Entry");
            //More Manipulation 
            System.out.println("Want More Manipulations: Y/N:");
            String manipulation1= ((d1.scanString.nextLine()).toLowerCase()).trim();

            char manipulation=manipulation1.charAt(0);

            if(manipulation=='y') { }
            else if(manipulation=='n') {
            else {
                System.out.println("Invalid Entry");


Automatically start forever (node) on system restart

The problem with rc.local is that the commands are accessed as root which is different than logging to as a user and using sudo.

I solved this problem by adding a .sh script with the startup commands i want to etc/profile.d. Any .sh file in profile.d will load automatically and any command will be treated as if you used the regular sudo.

The only downside to this is the specified user needs to loggin for things to start which in my situation was always the case.

How to set tint for an image view programmatically in android?

Random random=new Random;
ImageView imageView = (ImageView) view.findViewById(;
ColorFilter cf = new PorterDuffColorFilter(Color.rgb(random.nextInt(255), random.nextInt(255), random.nextInt(255)),Mode.OVERLAY);


Laravel: Error [PDOException]: Could not Find Driver in PostgreSQL

For PDOException: could not find driver for MySQL, and if it is Debian based OS,

sudo apt-get -y install php5-mysql

java.lang.UnsatisfiedLinkError no *****.dll in java.library.path

It is simple just write java -XshowSettings:properties on your command line in windows and then paste all the files in the path shown by the java.library.path.

How do I create a chart with multiple series using different X values for each series?

You need to use the Scatter chart type instead of Line. That will allow you to define separate X values for each series.

Get each line from textarea

Use PHP DOM to parse and add <br/> in it. Like this:

$html = '<textarea> put returns between paragraphs
for linebreak add 2 spaces at end
indent code by 4 spaces
quote by placing > at start of line

//parsing begins here:
$doc = new DOMDocument();
$nodes = $doc->getElementsByTagName('textarea');

//get text and add <br/> then remove last <br/>
$lines = $nodes->item(0)->nodeValue;

//split it by newlines
$lines = explode("\n", $lines);

//add <br/> at end of each line
foreach($lines as $line)
    $output .= $line . "<br/>";

//remove last <br/>
$output = rtrim($output, "<br/>");

//display it

This outputs:

string ' put returns between paragraphs
<br/>for linebreak add 2 spaces at end
<br/>indent code by 4 spaces
<br/>quote by placing > at start of line
' (length=141)

What is the difference between T(n) and O(n)?

one is Big "O"

one is Big Theta

Big O means your algorithm will execute in no more steps than in given expression(n^2)

Big Omega means your algorithm will execute in no fewer steps than in the given expression(n^2)

When both condition are true for the same expression, you can use the big theta notation....

Is it possible to get the index you're sorting over in Underscore.js?

The iterator of _.each is called with 3 parameters (element, index, list). So yes, for _.each you cab get the index.

You can do the same in sortBy

What does LPCWSTR stand for and how should it be handled with?

It's a long pointer to a constant, wide string (i.e. a string of wide characters).

Since it's a wide string, you want to make your constant look like: L"TestWindow". I wouldn't create the intermediate a either, I'd just pass L"TestWindow" for the parameter:

ghTest = FindWindowEx(NULL, NULL, NULL, L"TestWindow");

If you want to be pedantically correct, an "LPCTSTR" is a "text" string -- a wide string in a Unicode build and a narrow string in an ANSI build, so you should use the appropriate macro:

ghTest = FindWindow(NULL, NULL, NULL, _T("TestWindow"));

Few people care about producing code that can compile for both Unicode and ANSI character sets though, and if you don't getting it to really work correctly can be quite a bit of extra work for little gain. In this particular case, there's not much extra work, but if you're manipulating strings, there's a whole set of string manipulation macros that resolve to the correct functions.

fcntl substitute on Windows

Although this does not help you right away, there is an alternative that can work with both Unix (fcntl) and Windows (win32 api calls), called: portalocker

It describes itself as a cross-platform (posix/nt) API for flock-style file locking for Python. It basically maps fcntl to win32 api calls.

The original code at can now be installed as a separate package -

Download data url file

There are several solutions but they depend on HTML5 and haven't been implemented completely in some browsers yet. Examples below were tested in Chrome and Firefox (partly works).

  1. Canvas example with save to file support. Just set your document.location.href to the data URI.
  2. Anchor download example. It uses <a href="your-data-uri" download="filename.txt"> to specify file name.

Convert a Unicode string to a string in Python (containing extra symbols)

>>> text=u'abcd'
>>> str(text)

If the string only contains ascii characters.

Most efficient solution for reading CLOB to String, and String to CLOB in Java?

A friendly helper method using apache

Reader reader = clob.getCharacterStream();
StringWriter writer = new StringWriter();
IOUtils.copy(reader, writer);
String clobContent = writer.toString();

how to configure hibernate config file for sql server

We also need to mention default schema for SQSERVER: dbo

<property name="hibernate.default_schema">dbo</property>

Tested with hibernate 4

Xcode: Could not locate device support files

Here is the correct way of handling support errors from Xcode. All you have to do is add support to Xcode's DeviceSupport folder.

Open this link, extract the zip and copy the folder.

NOTE: A new version of iOS 13.0 beta recently released. If your Xcode throws iOS 13.0 support files needed, then click the link below:

Then, go to Applications -> Xcode. Right click and open Show Package Contents. Then, paste to Contents -> Developer -> Platforms -> iPhoneOS.platform -> DeviceSupport and restart Xcode.

Note: If you have a problem with any other version of iOS, then download the right iOS Developer Disk Image and paste it in the above-mentioned folder.

This will work. Press this to visually see the path.

Should I always use a parallel stream when possible?

The Stream API was designed to make it easy to write computations in a way that was abstracted away from how they would be executed, making switching between sequential and parallel easy.

However, just because its easy, doesn't mean its always a good idea, and in fact, it is a bad idea to just drop .parallel() all over the place simply because you can.

First, note that parallelism offers no benefits other than the possibility of faster execution when more cores are available. A parallel execution will always involve more work than a sequential one, because in addition to solving the problem, it also has to perform dispatching and coordinating of sub-tasks. The hope is that you'll be able to get to the answer faster by breaking up the work across multiple processors; whether this actually happens depends on a lot of things, including the size of your data set, how much computation you are doing on each element, the nature of the computation (specifically, does the processing of one element interact with processing of others?), the number of processors available, and the number of other tasks competing for those processors.

Further, note that parallelism also often exposes nondeterminism in the computation that is often hidden by sequential implementations; sometimes this doesn't matter, or can be mitigated by constraining the operations involved (i.e., reduction operators must be stateless and associative.)

In reality, sometimes parallelism will speed up your computation, sometimes it will not, and sometimes it will even slow it down. It is best to develop first using sequential execution and then apply parallelism where

(A) you know that there's actually benefit to increased performance and

(B) that it will actually deliver increased performance.

(A) is a business problem, not a technical one. If you are a performance expert, you'll usually be able to look at the code and determine (B), but the smart path is to measure. (And, don't even bother until you're convinced of (A); if the code is fast enough, better to apply your brain cycles elsewhere.)

The simplest performance model for parallelism is the "NQ" model, where N is the number of elements, and Q is the computation per element. In general, you need the product NQ to exceed some threshold before you start getting a performance benefit. For a low-Q problem like "add up numbers from 1 to N", you will generally see a breakeven between N=1000 and N=10000. With higher-Q problems, you'll see breakevens at lower thresholds.

But the reality is quite complicated. So until you achieve experthood, first identify when sequential processing is actually costing you something, and then measure if parallelism will help.

Start index for iterating Python list

You can use slicing:

for item in some_list[2:]:
    # do stuff

This will start at the third element and iterate to the end.

SVG rounded corner

You are using a path element, why don't you just give the path a curve? See here for how to make curves using path elements:

Java - Convert String to valid URI object

Or perhaps you could use this class:

Which is present in Android since API level 1.

Annoyingly however, it treats spaces specially (replacing them with + instead of %20). To get round this we simply use this fragment:

URLEncoder.encode(value, "UTF-8").replace("+", "%20");

Largest and smallest number in an array

Int[] number ={1,2,3,4,5,6,7,8,9,10};
Int? Result = null;
 foreach(Int i in number)

       If(!Result.HasValue || i< Result)


            Result =i;


Saving utf-8 texts with json.dumps as UTF8, not as \u escape sequence

Use the ensure_ascii=False switch to json.dumps(), then encode the value to UTF-8 manually:

>>> json_string = json.dumps("??? ????", ensure_ascii=False).encode('utf8')
>>> json_string
b'"\xd7\x91\xd7\xa8\xd7\x99 \xd7\xa6\xd7\xa7\xd7\x9c\xd7\x94"'
>>> print(json_string.decode())
"??? ????"

If you are writing to a file, just use json.dump() and leave it to the file object to encode:

with open('filename', 'w', encoding='utf8') as json_file:
    json.dump("??? ????", json_file, ensure_ascii=False)

Caveats for Python 2

For Python 2, there are some more caveats to take into account. If you are writing this to a file, you can use instead of open() to produce a file object that encodes Unicode values for you as you write, then use json.dump() instead to write to that file:

with'filename', 'w', encoding='utf8') as json_file:
    json.dump(u"??? ????", json_file, ensure_ascii=False)

Do note that there is a bug in the json module where the ensure_ascii=False flag can produce a mix of unicode and str objects. The workaround for Python 2 then is:

with'filename', 'w', encoding='utf8') as json_file:
    data = json.dumps(u"??? ????", ensure_ascii=False)
    # unicode(data) auto-decodes data to unicode if str

In Python 2, when using byte strings (type str), encoded to UTF-8, make sure to also set the encoding keyword:

>>> d={ 1: "??? ????", 2: u"??? ????" }
>>> d
{1: '\xd7\x91\xd7\xa8\xd7\x99 \xd7\xa6\xd7\xa7\xd7\x9c\xd7\x94', 2: u'\u05d1\u05e8\u05d9 \u05e6\u05e7\u05dc\u05d4'}

>>> s=json.dumps(d, ensure_ascii=False, encoding='utf8')
>>> s
u'{"1": "\u05d1\u05e8\u05d9 \u05e6\u05e7\u05dc\u05d4", "2": "\u05d1\u05e8\u05d9 \u05e6\u05e7\u05dc\u05d4"}'
>>> json.loads(s)['1']
u'\u05d1\u05e8\u05d9 \u05e6\u05e7\u05dc\u05d4'
>>> json.loads(s)['2']
u'\u05d1\u05e8\u05d9 \u05e6\u05e7\u05dc\u05d4'
>>> print json.loads(s)['1']
??? ????
>>> print json.loads(s)['2']
??? ????

How can I change the font-size of a select option?

check this fiddle,

i just edited the above fiddle, its working

.selectDefault, .selectDiv option

How to get HQ youtube thumbnails?

Are you referring to the full resolution one?:<insert-youtube-video-id-here>/maxresdefault.jpg

I don't believe you can get 'multiple' images of HQ because the one you have is the one.

Check the following answer out for more information on the URLs: How do I get a YouTube video thumbnail from the YouTube API?

For live videos use<insert-youtube-video-id-here>/maxresdefault_live.jpg

- cornips

How do I force detach Screen from another SSH session?

As Jose answered, screen -d -r should do the trick. This is a combination of two commands, as taken from the man page.

screen -d detaches the already-running screen session, and screen -r reattaches the existing session. By running screen -d -r, you force screen to detach it and then resume the session.

If you use the capital -D -RR, I quote the man page because it's too good to pass up.

Attach here and now. Whatever that means, just do it.

Note: It is always a good idea to check the status of your sessions by means of "screen -list".

Visual Studio Code includePath

I tried this and now working Configuration for c_cpp_properties.json

"configurations": [
        "name": "Win32",
        "compilerPath": "C:/MinGW/bin/g++.exe",
        "includePath": [
        "defines": [
        "cStandard": "c17",
        "cppStandard": "c++17",
        "intelliSenseMode": "windows-gcc-x64"
"version": 4

task.json configuration File

"version": "2.0.0",
"tasks": [
        "type": "cppbuild",
        "label": "C/C++: g++.exe build active file",
        "command": "C:\\MinGW\\bin\\g++.exe",
        "args": [
        "options": {
            "cwd": "C:\\MinGW\\bin"
        "problemMatcher": [
        "group": {
            "kind": "build",
            "isDefault": true
        "detail": "compiler: C:\\MinGW\\bin\\g++.exe"

Set iframe content height to auto resize dynamically

In the iframe: So that means you have to add some code in the iframe page. Simply add this script to your code IN THE IFRAME:

<body onload="parent.alertsize(document.body.scrollHeight);">

In the holding page: In the page holding the iframe (in my case with ID="myiframe") add a small javascript:

function alertsize(pixels){

What happens now is that when the iframe is loaded it triggers a javascript in the parent window, which in this case is the page holding the iframe.

To that JavaScript function it sends how many pixels its (iframe) height is.

The parent window takes the number, adds 32 to it to avoid scrollbars, and sets the iframe height to the new number.

That's it, nothing else is needed.

But if you like to know some more small tricks keep on reading...

DYNAMIC HEIGHT IN THE IFRAME? If you like me like to toggle content the iframe height will change (without the page reloading and triggering the onload). I usually add a very simple toggle script I found online:

function toggle(obj) {
    var el = document.getElementById(obj);
    if ( != 'block' ) = 'block';
    else = 'none';

to that script just add:

function toggle(obj) {
    var el = document.getElementById(obj);
    if ( != 'block' ) = 'block';
    else = 'none';
    parent.alertsize(document.body.scrollHeight); // ADD THIS LINE!

How you use the above script is easy:

<a href="javascript:toggle('moreheight')">toggle height?</a><br />
<div style="display:none;" id="moreheight">
more height!<br />
more height!<br />
more height!<br />

For those that like to just cut and paste and go from there here is the two pages. In my case I had them in the same folder, but it should work cross domain too (I think...)

Complete holding page code:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "">
<meta http-equiv="content-type" content="text/html; charset=iso-8859-1">
<title>THE IFRAME HOLDER</title>
function alertsize(pixels){

<body style="background:silver;">
<iframe src='theiframe.htm' style='width:458px;background:white;' frameborder='0' id="myiframe" scrolling="auto"></iframe>

Complete iframe code: (this iframe named "theiframe.htm")

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "">
<meta http-equiv="content-type" content="text/html; charset=iso-8859-1">
<title>IFRAME CONTENT</title>
function toggle(obj) {
    var el = document.getElementById(obj);
    if ( != 'block' ) = 'block';
    else = 'none';

<body onload="parent.alertsize(document.body.scrollHeight);">
<a href="javascript:toggle('moreheight')">toggle height?</a><br />
<div style="display:none;" id="moreheight">
more height!<br />
more height!<br />
more height!<br />
text<br />
text<br />
text<br />
text<br />
text<br />
text<br />
text<br />
text<br />



Understanding React-Redux and mapStateToProps()

import React from 'react';
import {connect} from 'react-redux';
import Userlist from './Userlist';

class Userdetails extends React.Component{

            <p>Name : <span>{}</span></p>
            <p>ID : <span>{}</span></p>
            <p>Working : <span>{this.props.user.Working}</span></p>
            <p>Age : <span>{this.props.user.age}</span></p>


 function mapStateToProps(state){  
  return {


  export default connect(mapStateToProps, null)(Userdetails);

Uri not Absolute exception getting while calling Restful Webservice

The problem is likely that you are calling URLEncoder.encode() on something that already is a URI.

How can I escape white space in a bash loop list?

Why not just put


in front of the for command? This changes the field separator from < Space>< Tab>< Newline> to just < Newline>

How to set background color of view transparent in React Native

Here is my solution to a modal that can be rendered on any screen and initialized in App.tsx


import React, { Component } from 'react';
import { Modal, Text, TouchableHighlight, View, StyleSheet, Platform } from 'react-native';
import EventEmitter from 'events';
// I keep localization files for strings and device metrics like height and width which are used for styling 
import strings from '../../config/strings';
import metrics from '../../config/metrics';

const emitter = new EventEmitter();
export const _modalEmitter = emitter

export class ModalView extends Component {
    state: {
        modalVisible: boolean,
        text: string, 
        callbackSubmit: any, 
        callbackCancel: any,
        animation: any

    constructor(props) {
        this.state = {
            modalVisible: false,
            text: "", 
            callbackSubmit: (() => {}), 
            callbackCancel: (() => {}),
            animation: new Animated.Value(0)

    componentDidMount() {
        _modalEmitter.addListener(strings.modalOpen, (event) => {
            var state = {
                modalVisible: true,
                text: event.text, 
                callbackSubmit: event.onSubmit, 
                callbackCancel: event.onClose,
                animation: new Animated.Value(0)
        _modalEmitter.addListener(strings.modalClose, (event) => {
            var state = {
                modalVisible: false,
                text: "", 
                callbackSubmit: (() => {}), 
                callbackCancel: (() => {}),
                animation: new Animated.Value(0)

    componentWillUnmount() {
        var state = {
            modalVisible: false,
            text: "", 
            callbackSubmit: (() => {}), 
            callbackCancel: (() => {})

    closeModal = () => {

        Animated.timing(this.state.animation, {
            toValue : 0.5,
            duration : 500

    body = () => {
        const animatedOpacity ={
            opacity : this.state.animation
        return (
            <View style={{ height: 0 }}>

                    // render a transparent gray background over the whole screen and animate it to fade in, touchable opacity to close modal on click out

                    <Animated.View style={[styles.modalBackground, animatedOpacity]} > 
                        <TouchableOpacity onPress={() => this.closeModal()} activeOpacity={1} style={[styles.modalBackground, {opacity: 1} ]} > 

                    // render an absolutely positioned modal component over that background
                    <View style={styles.modalContent}>

                        <View key="text_container">
                        <View key="options_container">
                            // keep in mind the content styling is very minimal for this example, you can put in your own component here or style and make it behave as you wish
                                onPress={() => {

                                onPress={() => {


    render() {
        return this.body()

// to center the modal on your screen 
// top: metrics.DEVICE_HEIGHT/2 positions the top of the modal at the center of your screen
// however you wanna consider your modal's height and subtract half of that so that the 
// center of the modal is centered not the top, additionally for 'ios' taking into consideration
// the 20px top bunny ears offset hence - (Platform.OS == 'ios'? 120 : 100)
// where 100 is half of the modal's height of 200
const styles = StyleSheet.create({
    modalBackground: {
        height: '100%', 
        width: '100%', 
        backgroundColor: 'gray', 
        zIndex: -1 
    modalContent: { 
        position: 'absolute', 
        alignSelf: 'center', 
        zIndex: 1, 
        top: metrics.DEVICE_HEIGHT/2 - (Platform.OS == 'ios'? 120 : 100), 
        justifyContent: 'center', 
        alignItems: 'center', 
        display: 'flex', 
        height: 200, 
        width: '80%', 
        borderRadius: 27,
        backgroundColor: 'white', 
        opacity: 1 

App.tsx render and import

import { ModalView } from './{your_path}/ModalComponent';

render() {
    return (
            <StatusBar barStyle={'dark-content'} />
            <AppRouter />
            <ModalView />

and to use it from any component


import { _modalEmitter } from './{your_path}/ModalComponent'

// Some functions within your component

showModal(modalText, callbackOnSubmit, callbackOnClose) {
    _modalEmitter.emit(strings.modalOpen, { text: modalText, onSubmit: callbackOnSubmit.bind(this), onClose: callbackOnClose.bind(this) })

closeModal() {

Hope I was able to help some of you, I used a very similar structure for in-app notifications

Happy coding

Check if a given key already exists in a dictionary and increment it

This isn't directly answering the question, but to me, it looks like you might want the functionality of collections.Counter.

from collections import Counter

to_count = ["foo", "foo", "bar", "baz", "foo", "bar"]

count = Counter(to_count)


print("acts just like the desired dictionary:")
print("bar occurs {} times".format(count["bar"]))

print("any item that does not occur in the list is set to 0:")
print("dog occurs {} times".format(count["dog"]))

print("can iterate over items from most frequent to least:")
for item, times in count.most_common():
    print("{} occurs {} times".format(item, times))

This results in the output

Counter({'foo': 3, 'bar': 2, 'baz': 1})
acts just like the desired dictionary:
bar occurs 2 times
any item that does not occur in the list is set to 0:
dog occurs 0 times
can iterate over items from most frequent to least:
foo occurs 3 times
bar occurs 2 times
baz occurs 1 times

"Cannot instantiate the type..."

You can use

Queue thequeue = new linkedlist();


Queue thequeue = new Priorityqueue();

Reason: Queue is an interface. So you can instantiate only its concrete subclass.

Reducing video size with same format and reducing frame size

Instead of chosing fixed bit rates, with the H.264 codec, you can also chose a different preset as described at I also found Video encoder comparison at KeyJ's blog (archived version) an interesting read, it compares H.264 against Theora and others.

Following is a comparison of various options I tried. The recorded video was originally 673M in size, taken on an iPad using RecordMyScreen. It has a duration of about 20 minutes with a resolution of 1024x768 (with half of the video being blank, so I cropped it to 768x768). In order to reduce size, I lowered the resolution to 480x480. There is no audio.

The results, taking the same 1024x768 as base (and applying cropping, scaling and a filter):

  • With no special options: 95M (encoding time: 1m19s).
  • With only -b 512k added, the size dropped to 77M (encoding time: 1m17s).
  • With only -preset veryslow (and no -b), it became 70M (encoding time: 6m14s)
  • With both -b 512k and -preset veryslow, the size becomes 77M (100K smaller than just -b 512k).
  • With -preset veryslow -crf 28, I get a file of 39M which took 5m47s (with no visual quality difference to me).

N=1, so take the results with a grain of salt and perform your own tests.

How to center canvas in html5

Give the canvas the following css style properties:

canvas {
    padding-left: 0;
    padding-right: 0;
    margin-left: auto;
    margin-right: auto;
    display: block;
    width: 800px;


Since this answer is quite popular, let me add a little bit more details.

The above properties will horizontally center the canvas, div or whatever other node you have relative to it's parent. There is no need to change the top or bottom margins and paddings. You specify a width and let the browser fill the remaining space with the auto margins.

However, if you want to type less, you could use whatever css shorthand properties you wish, such as

canvas {
    padding: 0;
    margin: auto;
    display: block;
    width: 800px;

Centering the canvas vertically requires a different approach however. You need to use absolute positioning, and specify both the width and the height. Then set the left, right, top and bottom properties to 0 and let the browser fill the remaining space with the auto margins.

canvas {
    padding: 0;
    margin: auto;
    display: block;
    width: 800px;
    height: 600px;
    position: absolute;
    top: 0;
    bottom: 0;
    left: 0;
    right: 0;

The canvas will center itself based on the first parent element that has position set to relative or absolute, or the body if none is found.

Another approach would be to use display: flex, that is available in IE11

Also, make sure you use a recent doctype such as xhtml or html 5.

How to play .mp4 video in videoview in android?

In Kotlin you can do as

 val videoView = findViewById<VideoView>(

       // If url is from raw
   /* val url = "android.resource://" + packageName
        .toString() + "/" +*/

    // If url is from network
    val url = ""

    val video =

git push: permission denied (public key)

None of the above solutions worked for me. For context, I'm running ubuntu, and I had already gone through the ssh-key setup documentation. The fix for me was to run ssh-add in the terminal. This fixed the issue.


Name attribute in @Entity and @Table

@Entity is useful with model classes to denote that this is the entity or table

@Table is used to provide any specific name to your table if you want to provide any different name

Note: if you don't use @Table then hibernate consider that @Entity is your table name by default and @Entity must

@Table(name = "emp")     
public class Employee implements    


Check if an array is empty or exists

If you want to test whether the image array variable had been defined you can do it like this

if(typeof image_array === 'undefined') {
    // it is not defined yet
} else if (image_array.length > 0) {
    // you have a greater than zero length array

What is the difference between a token and a lexeme?

CS researchers, as those from Math, are fond of creating "new" terms. The answers above are all nice but apparently, there is no such a great need to distinguish tokens and lexemes IMHO. They are like two ways to represent the same thing. A lexeme is concrete -- here a set of char; a token, on the other hand, is abstract -- usually referring to the type of a lexeme together with its semantic value if that makes sense. Just my two cents.

React native text going off my screen, refusing to wrap. What to do?

Another solution that I found to this issue is by wrapping the Text inside a View. Also set the style of the View to flex: 1.

How to simulate a touch event in Android?

When using Monkey Script I noticed that DispatchPress(KEYCODE_BACK) is doing nothing which really suck. In many cases this is due to the fact that the Activity doesn't consume the Key event. The solution to this problem is to use a mix of monkey script and adb shell input command in a sequence.

1 Using monkey script gave some great timing control. Wait a certain amount of second for the activity and is a blocking adb call.
2 Finally sending adb shell input keyevent 4 will end the running APK.


adb shell monkey -p -v -v -v -f /sdcard/monkey_script.txt 1
adb shell input keyevent 4

Pdf.js: rendering a pdf file using a base64 file source instead of url

Used the Accepted Answer to do a check for IE and convert the dataURI to UInt8Array; an accepted form by PDFJS

        Ext.isIE ? pdfAsDataUri = me.convertDataURIToBinary(pdfAsDataUri): '';_x000D_
        convertDataURIToBinary: function(dataURI) {_x000D_
          var BASE64_MARKER = ';base64,',_x000D_
            base64Index = dataURI.indexOf(BASE64_MARKER) + BASE64_MARKER.length,_x000D_
            base64 = dataURI.substring(base64Index),_x000D_
            raw = window.atob(base64),_x000D_
            rawLength = raw.length,_x000D_
            array = new Uint8Array(new ArrayBuffer(rawLength));_x000D_
          for (var i = 0; i < rawLength; i++) {_x000D_
            array[i] = raw.charCodeAt(i);_x000D_
          return array;_x000D_

JavaScript check if variable exists (is defined/initialized)

I prefer this method for it's accuracy and succinctness:

var x
if (x === void 0) {
  console.log(`x is undefined`)
} else {
  console.log(`x is defined`)

As has been mentioned in other comments and answers, undefined isn't guaranteed to be undefined. Because it's not a keyword, it can be redefined as a variable in scopes other than the global scope. Here's little example that demonstrates this nuance:

var undefined = 'bar'
console.log(`In the global scope: ${undefined}`)

function foo() {
  var undefined = 'defined'
  var x
  if (x === undefined) {
    console.log(`x === undefined`)
  } else {
    console.log(`x !== undefined`)
  if (x === void 0) {
    console.log(`x === void 0`)
  } else {
    console.log(`x !== void 0`)


See void for compatibility (supported in IE5!?!! Wow!).

Why powershell does not run Angular commands?

script1.ps1 cannot be loaded because running scripts is disabled on this system. For more information, see about_Execution_Policies at

This error happens due to a security measure which won't let scripts be executed on your system without you having approved of it. You can do so by opening up a powershell with administrative rights (search for powershell in the main menu and select Run as administrator from the context menu) and entering:

set-executionpolicy remotesigned

ActivityCompat.requestPermissions not showing dialog box

For me the issue was I had an invalid request code. I choose 0xDEADBEEF as a request code and it was silently failing (maybe it's cast to something smaller than 32-bit somewhere internally?) If I choose 255 everything worked fine as NightSkyDev described above.

Array to Hash Ruby

Enumerator includes Enumerable. Since 2.1, Enumerable also has a method #to_h. That's why, we can write :-

a = ["item 1", "item 2", "item 3", "item 4"]
# => {"item 1"=>"item 2", "item 3"=>"item 4"}

Because #each_slice without block gives us Enumerator, and as per the above explanation, we can call the #to_h method on the Enumerator object.

Are HTTP cookies port specific?

According to RFC2965 3.3.1 (which might or might not be followed by browsers), unless the port is explicitly specified via the port parameter of the Set-Cookie header, cookies might or might not be sent to any port.

Google's Browser Security Handbook says: by default, cookie scope is limited to all URLs on the current host name - and not bound to port or protocol information. and some lines later There is no way to limit cookies to a single DNS name only [...] likewise, there is no way to limit them to a specific port. (Also, keep in mind, that IE does not factor port numbers into its same-origin policy at all.)

So it does not seem to be safe to rely on any well-defined behavior here.

A table name as a variable

For static queries, like the one in your question, table names and column names need to be static.

For dynamic queries, you should generate the full SQL dynamically, and use sp_executesql to execute it.

Here is an example of a script used to compare data between the same tables of different databases:

Static query:


Since I want to easily change the name of table and schema, I have created this dynamic query:

declare @schema varchar(50)
declare @table varchar(50)
declare @query nvarchar(500)

set @schema = 'dbo'
set @table = 'ACTY'

set @query = 'SELECT * FROM [DB_ONE].[' + @schema + '].[' + @table + '] EXCEPT SELECT * FROM [DB_TWO].[' + @schema + '].[' + @table + ']'

EXEC sp_executesql @query

Since dynamic queries have many details that need to be considered and they are hard to maintain, I recommend that you read: The curse and blessings of dynamic SQL

Why binary_crossentropy and categorical_crossentropy give different performances for the same problem?

I came across an "inverted" issue — I was getting good results with categorical_crossentropy (with 2 classes) and poor with binary_crossentropy. It seems that problem was with wrong activation function. The correct settings were:

  • for binary_crossentropy: sigmoid activation, scalar target
  • for categorical_crossentropy: softmax activation, one-hot encoded target

jQuery $("#radioButton").change(...) not firing during de-selection

You can bind to all of the radio buttons at once by name:


Working example here:

npm throws error without sudo

Also you will need the write permission in node_modules directory:

sudo chown -R $USER /usr/local/lib/node_modules

Export multiple classes in ES6 modules

For multiple classes in the same js file, extending Component from @wordpress/element, you can do that :

// classes.js
import { Component } from '@wordpress/element';

const Class1 = class extends Component {

const Class2 = class extends Component {

export { Class1, Class2 }

And import them in another js file :

import { Class1, Class2 } from './classes';

Get min and max value in PHP Array

Option 1. First you map the array to get those numbers (and not the full details):

$numbers = array_column($array, 'weight')

Then you get the min and max:

$min = min($numbers);
$max = max($numbers);

Option 2. (Only if you don't have PHP 5.5 or better) The same as option 1, but to pluck the values, use array_map:

$numbers = array_map(function($details) {
  return $details['Weight'];
}, $array);

Option 3.

Option 4. If you only need a min OR max, array_reduce() might be faster:

$min = array_reduce($array, function($min, $details) {
  return min($min, $details['weight']);

This does more min()s, but they're very fast. The PHP_INT_MAX is to start with a high, and get lower and lower. You could do the same for $max, but you'd start at 0, or -PHP_INT_MAX.

How to get numeric position of alphabets in java?

String str = "abcdef";
char[] ch  = str.toCharArray();
for(char c : ch){
    int temp = (int)c;
    int temp_integer = 96; //for lower case
    if(temp<=122 & temp>=97)



@Shiki for Capital/UpperCase letters use the following code:

String str = "DEFGHI";
char[] ch  = str.toCharArray();
for(char c : ch){
    int temp = (int)c;
    int temp_integer = 64; //for upper case
    if(temp<=90 & temp>=65)



Resize background image in div using css

i would recommend using this:

  background-image: url(your file location here);
  background-size:cover;(will only work with css3)

hope it helps :D

And if this doesnt support your needs just say it: i can make a jquery for multibrowser support.

GET and POST methods with the same Action name in the same Controller

You received the good answer to this question, but I want to add my two cents. You could use one method and process requests according to request type:

public ActionResult Index()
        Some Code--Some Code---Some Code for GET
    else if("POST"==this.HttpContext.Request.RequestType)
        Some Code--Some Code---Some Code for POST

    return View();

Convert InputStream to JSONObject

The best solution in my opinion is to encapsulate the InputStream in a JSONTokener object. Something like this:

JSONObject jsonObject = new JSONObject(new JSONTokener(inputStream));

Can two or more people edit an Excel document at the same time?

Yes you can. I've used it with Word and PowerPoint. You will need Office 2010 client apps and SharePoint 2010 foundation at least. You must also allow editing without checking out on the document library.

It's quite cool, you can mark regions as 'locked' so no-one can change them and you can see what other people have changed every time you save your changes to the server. You also get to see who's working on the document from the Office app. The merging happens on SharePoint 2010.

How do I start my app on startup?


I would like to add one point in this question which I was facing for couple of days. I tried all the answers but those were not working for me. If you are using android version 5.1 please change these settings.

If you are using android version 5.1 then you have to dis-select (Restrict to launch) from app settings.

settings> app > your app > Restrict to launch (dis-select)

bootstrap 3 tabs not working properly

My problem was with extra </div> tag inside the first tab.

XMLHttpRequest Origin null is not allowed Access-Control-Allow-Origin for file:/// to file:/// (Serverless)

Here is an applescript that will launch Chrome with the --allow-file-access-from-files switch turned on, for OSX/Chrome devs out there:

set chromePath to POSIX path of "/Applications/Google Chrome"    
set switch to " --allow-file-access-from-files"
do shell script (quoted form of chromePath) & switch & " > /dev/null 2>&1 &"

The forked VM terminated without saying properly goodbye. VM crash or System.exit called

I had the same issue today and for me the real problem was reported further up in the log with message Cannot use a threadCount parameter less than 1; 1 > 0. When adding <threadCount>1</threadCount> in the surefire-plugin config the other error disappeared.

Full plugin config:

...and yes, I am using both junit and testng in this test framework for backward compatibility reasons.

How to prevent buttons from submitting forms

Set your button in normal way and use event.preventDefault like..

   <button onclick="myFunc(e)"> Remove </button>  

   In function...

   function myFunc(e){

Remove all files except some from a directory

A little late for the OP, but hopefully useful for anyone who gets here much later by google...

I found the answer by @awi and comment on -delete by @Jamie Bullock really useful. A simple utility so you can do this in different directories ignoring different file names/types each time with minimal typing:

rm_except (or whatever you want to name it)



for fignore in "$@"; do
  ignore=${ignore}"-not -name ${fignore} "

find . -type f $ignore -delete

e.g. to delete everything except for text files and

rm_except *.txt 

Similar to @mishunika, but without the if clause.

Create a Date with a set timezone without using a string representation

Best Solution I have seen from this came from

Print Time Function

<script language="javascript" type="text/javascript">
//borrowed from echoecho
workDate = new Date()
UTCDate = new Date()

function printTime(offset) {
    tempDate = new Date()
    timeValue = ((tempDate.getHours()<10) ? ("0"+tempDate.getHours()) : (""+tempDate.getHours()))
    timeValue += ((tempDate.getMinutes()<10) ? ("0"+tempDate.getMinutes()) : tempDate.getMinutes())
    timeValue += " hrs."
    return timeValue
    var now = new Date()
    var seed = now.getTime() % 0xfffffff
    var same = rand(12)

Banff, Canada:
<script language="JavaScript">document.write(printTime("-7"))</script>

Full Code Example


<script language="javascript" type="text/javascript">
//borrowed from echoecho
workDate = new Date()
UTCDate = new Date()

function printTime(offset) {
tempDate = new Date()
timeValue = ((tempDate.getHours()<10) ? ("0"+tempDate.getHours()) : (""+tempDate.getHours()))
timeValue += ((tempDate.getMinutes()<10) ? ("0"+tempDate.getMinutes()) : tempDate.getMinutes())
timeValue += " hrs."
return timeValue
var now = new Date()
var seed = now.getTime() % 0xfffffff
var same = rand(12)


Banff, Canada:
<script language="JavaScript">document.write(printTime("-7"))</script>
<script language="JavaScript">document.write(printTime("-5"))</script>
Greenwich, England(UTC):
<script language="JavaScript">document.write(printTime("-0"))</script>
Tokyo, Japan:
<script language="JavaScript">document.write(printTime("+9"))</script>
Berlin, Germany:
<script language="JavaScript">document.write(printTime("+1"))</script>


How to generate serial version UID in Intellij

IntelliJ IDEA Plugins / GenerateSerialVersionUID

very nice, very easy to install. you can install that from plugins menu, select install from disk, select the jar file you unpacked in the lib folder. restart, control + ins, and it pops up to generate serial UID from menu. love it. :-)

Git "error: The branch 'x' is not fully merged"

Easiest Solution With Explanation (double checked solution) (faced the problem before)

Problem is:

1- I can't delete a branch

2- The terminal keep display a warning message that there are some commits that are not approved yet

3- knowing that I checked the master and branch and they are identical (up to date)


git checkout master
git merge branch_name
git checkout branch_name
git push
git checkout master
git branch -d branch_name


when your branch is connected to upstream remote branch (on Github, bitbucket or whatever), you need to merge (push) it into the master, and you need to push the new changes (commits) to the remote repo (Github, bitbucket or whatever) from the branch,

what I did in my code is that I switched to master, then merge the branch into it (to make sure they're identical on your local machine), then I switched to the branch again and pushed the updates or changes into the remote online repo using "git push".

after that, I switched to the master again, and tried to delete the branch, and the problem (warning message) disappeared, and the branch deleted successfully

Entity Framework change connection at runtime

In my case I'm using the ObjectContext as opposed to the DbContext so I tweaked the code in the accepted answer for that purpose.

public static class ConnectionTools
    public static void ChangeDatabase(
        this ObjectContext source,
        string initialCatalog = "",
        string dataSource = "",
        string userId = "",
        string password = "",
        bool integratedSecuity = true,
        string configConnectionStringName = "")
            // use the const name if it's not null, otherwise
            // using the convention of connection string = EF contextname
            // grab the type name and we're done
            var configNameEf = string.IsNullOrEmpty(configConnectionStringName)
                ? Source.GetType().Name
                : configConnectionStringName;

            // add a reference to System.Configuration
            var entityCnxStringBuilder = new EntityConnectionStringBuilder

            // init the sqlbuilder with the full EF connectionstring cargo
            var sqlCnxStringBuilder = new SqlConnectionStringBuilder

            // only populate parameters with values if added
            if (!string.IsNullOrEmpty(initialCatalog))
                sqlCnxStringBuilder.InitialCatalog = initialCatalog;
            if (!string.IsNullOrEmpty(dataSource))
                sqlCnxStringBuilder.DataSource = dataSource;
            if (!string.IsNullOrEmpty(userId))
                sqlCnxStringBuilder.UserID = userId;
            if (!string.IsNullOrEmpty(password))
                sqlCnxStringBuilder.Password = password;

            // set the integrated security status
            sqlCnxStringBuilder.IntegratedSecurity = integratedSecuity;

            // now flip the properties that were changed
                = sqlCnxStringBuilder.ConnectionString;
        catch (Exception ex)
            // set log item if required

C#: How do you edit items and subitems in a listview?

Click the items in the list view. Add a button that will edit the selected items. Add the code

    LSTDEDUCTION.SelectedItems[0].SubItems[1].Text = txtcarName.Text;
    LSTDEDUCTION.SelectedItems[0].SubItems[0].Text = txtcarBrand.Text;
    LSTDEDUCTION.SelectedItems[0].SubItems[2].Text = txtCarName.Text;

calculating number of days between 2 columns of dates in data frame

You need to use the as.Date formats correctly.


x = '2012/07/25'
xd = as.Date(x,'%Y/%m/%d')
xd    # Prints "2012-07-25"

R date formats are similary to *nix ones.

Doing a typeof(xd) shows it as a double ie. days since 1970.

Correct way to write loops for promise.

Use async and await (es6):

function taskAsync(paramets){
 return new Promise((reslove,reject)=>{
 //your logic after reslove(respoce) or reject(error)

async function fName(){
let arry=['list of items'];
  for(var i=0;i<arry.length;i++){
   let result=await(taskAsync('parameters'));


How to represent matrices in python

Python doesn't have matrices. You can use a list of lists or NumPy

Objective-C - Remove last character from string

In your controller class, create an action method you will hook the button up to in Interface Builder. Inside that method you can trim your string like this:

if ([string length] > 0) {
    string = [string substringToIndex:[string length] - 1];
} else {
    //no characters to delete... attempting to do so will result in a crash

If you want a fancy way of doing this in just one line of code you could write it as:

string = [string substringToIndex:string.length-(string.length>0)];

*Explanation of fancy one-line code snippet:

If there is a character to delete (i.e. the length of the string is greater than 0)
     (string.length>0) returns 1 thus making the code return:
          string = [string substringToIndex:string.length-1];

If there is NOT a character to delete (i.e. the length of the string is NOT greater than 0)
     (string.length>0) returns 0 thus making the code return:
          string = [string substringToIndex:string.length-0];
     Which prevents crashes.

setTimeout in for-loop does not print consecutive values

You could use bind method

for (var i = 1, j = 1; i <= 3; i++, j++) {
    setTimeout(function() {
    }.bind(i), j * 100);

Calling a method inside another method in same class

It is just an overload. The add method is from the ArrayList class. Look that Staff inherits from it.

Oracle Not Equals Operator

Developers using a mybatis-like framework will prefer != over <>. Reason being the <> will need to be wrapped in CDATA as it could be interpreted as xml syntax. Easier on the eyes too.

Twig ternary operator, Shorthand if-then-else

{{ ( in company_abilities) ? 'selected' : '' }}

The ternary operator is documented under 'other operators'

numpy matrix vector multiplication

Simplest solution

Use or See the documentation here.

>>> a = np.array([[ 5, 1 ,3], 
                  [ 1, 1 ,1], 
                  [ 1, 2 ,1]])
>>> b = np.array([1, 2, 3])
>>> print
array([16, 6, 8])

This occurs because numpy arrays are not matrices, and the standard operations *, +, -, / work element-wise on arrays. Instead, you could try using numpy.matrix, and * will be treated like matrix multiplication.

Other Solutions

Also know there are other options:

  • As noted below, if using python3.5+ the @ operator works as you'd expect:

    >>> print(a @ b)
    array([16, 6, 8])
  • If you want overkill, you can use numpy.einsum. The documentation will give you a flavor for how it works, but honestly, I didn't fully understand how to use it until reading this answer and just playing around with it on my own.

    >>> np.einsum('ji,i->j', a, b)
    array([16, 6, 8])
  • As of mid 2016 (numpy 1.10.1), you can try the experimental numpy.matmul, which works like with two major exceptions: no scalar multiplication but it works with stacks of matrices.

    >>> np.matmul(a, b)
    array([16, 6, 8])
  • numpy.inner functions the same way as for matrix-vector multiplication but behaves differently for matrix-matrix and tensor multiplication (see Wikipedia regarding the differences between the inner product and dot product in general or see this SO answer regarding numpy's implementations).

    >>> np.inner(a, b)
    array([16, 6, 8])
    # Beware using for matrix-matrix multiplication though!
    >>> b = a.T
    >>>, b)
    array([[35,  9, 10],
           [ 9,  3,  4],
           [10,  4,  6]])
    >>> np.inner(a, b) 
    array([[29, 12, 19],
           [ 7,  4,  5],
           [ 8,  5,  6]])

Rarer options for edge cases

  • If you have tensors (arrays of dimension greater than or equal to one), you can use numpy.tensordot with the optional argument axes=1:

    >>> np.tensordot(a, b, axes=1)
    array([16,  6,  8])
  • Don't use numpy.vdot if you have a matrix of complex numbers, as the matrix will be flattened to a 1D array, then it will try to find the complex conjugate dot product between your flattened matrix and vector (which will fail due to a size mismatch n*m vs n).

Difference between filter and filter_by in SQLAlchemy

filter_by uses keyword arguments, whereas filter allows pythonic filtering arguments like filter("john")

Remove a child with a specific attribute, in SimpleXML for PHP

If you extend the base SimpleXMLElement class, you can use this method:

class MyXML extends SimpleXMLElement {

    public function find($xpath) {
        $tmp = $this->xpath($xpath);
        return isset($tmp[0])? $tmp[0]: null;

    public function remove() {
        $dom = dom_import_simplexml($this);
        return $dom->parentNode->removeChild($dom);


// Example: removing the <bar> element with id = 1
$foo = new MyXML('<foo><bar id="1"/><bar id="2"/></foo>');
print $foo->asXML(); // <foo><bar id="2"/></foo>

How to import local packages without gopath

To add a "local" package to your project, add a folder (for example "package_name"). And put your implementation files in that folder.

 +-- main.go
       +-- whatever_name1.go
       +-- whatever_name2.go

In your package main do this:

import ""

Where package_name is the folder name and it must match the package name used in files whatever_name1.go and whatever_name2.go. In other words all files with a sub-directory should be of the same package.

You can further nest more subdirectories as long as you specify the whole path to the parent folder in the import.

How to load a resource from WEB-INF directory of a web archive

Here is how it works for me with no Servlet use.

Let's say I am trying to access web.xml in project/WebContent/WEB-INF/web.xml

  1. In project property Source-tab add source folder by pointing to the parent container for WEB-INF folder (in my case WebContent )

  2. Now let's use class loader:

    InputStream inStream = class.getClass().getClassLoader().getResourceAsStream("Web-INF/web.xml")

PHP Include for HTML?

Try to get some debugging information, could be that the file path is wrong, for example.

Try these two things:- Add this line to the top of your sample page:

<?php error_reporting(E_ALL);?>

This will print all errors/warnings/notices in the page so if there is any problem you get a text message describing it instead of a blank page

Additionally you can change include() to require()

<?php require ('headings.php'); ?>
<?php require ('navbar.php'); ?>
<?php require ('image.php'); ?>

This will throw a FATAL error PHP is unable to load required pages, and should help you in getting better tracing what is going wrong..

You can post the error descriptions here, if you get any, and you are unable to figure out what it means..

Execute command on all files in a directory

Based on @Jim Lewis's approach:

Here is a quick solution using find and also sorting files by their modification date:

$ find  directory/ -maxdepth 1 -type f -print0 | \
  xargs -r0 stat -c "%y %n" | \
  sort | cut -d' ' -f4- | \
  xargs -d "\n" -I{} cmd -op1 {} 

For sorting see:

How to search JSON tree with jQuery

var json = {
    "people": {
        "person": [{
            "name": "Peter",
            "age": 43,
            "sex": "male"},
            "name": "Zara",
            "age": 65,
            "sex": "female"}]
$.each(json.people.person, function(i, v) {
    if ( == "Peter") {


Based on this answer, you could use something like:

$(function() {
    var json = {
        "people": {
            "person": [{
                "name": "Peter",
                "age": 43,
                "sex": "male"},
                "name": "Zara",
                "age": 65,
                "sex": "female"}]
    $.each(json.people.person, function(i, v) {
        if ( RegExp(/peter/i)) != -1) {

Example 2

How to style icon color, size, and shadow of Font Awesome Icons

text-shadow: 1px 1px 3px rgba(0,0,0,0.5);

How to deal with SQL column names that look like SQL keywords?

Your question seems to be well answered here, but I just want to add one more comment to this subject.

Those designing the database should be well aware of the reserved keywords and avoid using them. If you discover someone using it, inform them about it (in a polite way). The keyword here is reserved word.

More information:

"Reserved keywords should not be used as object names. Databases upgraded from earlier versions of SQL Server may contain identifiers that include words not reserved in the earlier version, but that are reserved words for the current version of SQL Server. You can refer to the object by using delimited identifiers until the name can be changed."


"If your database does contain names that match reserved keywords, you must use delimited identifiers when you refer to those objects. For more information, see Identifiers (DMX)."

pip installs packages successfully, but executables not found from command line

When you install Python or Python3 using MacOS installer (downloaded from Python website) - it adds an exporter to your ~/.profile script. All you need to do is just source it. Restarting all the terminals should also do the trick.

WARNING - I believe it's better to just use pip3 with Python3 - for future benefits.

If you already have Python3 installed, the following steps work for me on macOS Mojave:

  1. Install ansible first using sudo - sudo -H pip3 install ansible

  2. you create a symlink to the Python's bin path

sudo ln -s /Library/Frameworks/Python.framework/Versions/Current/bin /Library/Frameworks/Python.framework/current_python_bin

and staple it to .profile

export PATH=$PATH:/Library/Frameworks/Python.framework/current_python_bin

  1. run source ~/.profile and restart all terminal shells.

  2. Type ansible --version

Where does Vagrant download its .box files to?

As mentioned in the docs, boxes are stored at:

  • Mac OS X and Linux: ~/.vagrant.d/boxes
  • Windows: C:/Users/USERNAME/.vagrant.d/boxes

How can I select rows with most recent timestamp for each key value?

I had mostly the same problem and ended up a a different solution that makes this type of problem trivial to query.

I have a table of sensor data (1 minute data from about 30 sensors)


and I have a sensor table that has lots of mostly static stuff about the sensor but the relevant fields are these:


The tvLastupdate and tvLastValue are set in a trigger on inserts to the SensorReadings table. I always have direct access to these values without needing to do any expensive queries. This does denormalize slightly. The query is trivial:

SELECT idSensor,Description,tvLastUpdate,tvLastValue 
FROM Sensors

I use this method for data that is queried often. In my case I have a sensor table, and a large event table, that have data coming in at the minute level AND dozens of machines are updating dashboards and graphs with that data. With my data scenario the trigger-and-cache method works well.

How to use AND in IF Statement

If there are no typos in the question, you got the conditions wrong:

You said this:

IF cells (i,"A") contains the text 'Miami'

...but your code says:

If Cells(i, "A") <> "Miami"

--> <> means that the value of the cell is not equal to "Miami", so you're not checking what you think you are checking.

I guess you want this instead:

If Cells(i, "A") like "*Miami*"


Sorry, but I can't really help you more. As I already said in a comment, I'm no Excel VBA expert.
Normally I would open Excel now and try your code myself, but I don't even have Excel on any of my machines at home (I use OpenOffice).

Just one general thing: can you identify the row that does not work?
Maybe this helps someone else to answer the question.

Does it ever execute (or at least try to execute) the Cells(i, "C").Value = "BA" line?
Or is the If Cells(i, "A") like "*Miami*" stuff already False?
If yes, try checking just one cell and see if that works.

How to send a "multipart/form-data" with requests in python?

You need to use the name attribute of the upload file that is in the HTML of the site. Example:

autocomplete="off" name="image">

You see name="image">? You can find it in the HTML of a site for uploading the file. You need to use it to upload the file with Multipart/form-data


import requests

site = '' # the site where you upload the file
filename = 'image.jpg'  # name example

Here, in the place of image, add the name of the upload file in HTML

up = {'image':(filename, open(filename, 'rb'), "multipart/form-data")}

If the upload requires to click the button for upload, you can use like that:

data = {
     "Button" : "Submit",

Then start the request

request =, files=up, data=data)

And done, file uploaded succesfully

Ruby get object keys as array

Like taro said, keys returns the array of keys of your Hash:

You'll find all the different methods available for each class.

If you don't know what you're dealing with:

 puts my_unknown_variable.class.to_s

This will output the class name.