Programs & Examples On #Bitwise operators

Operators which are used to perform manipulation at bit-level.The programming languages are Byte oriented whereas the hardware is bit oriented.Therefore, being able to operate on bit level can be very important in programming,especially when the program directly interact with the hardware.

how to do bitwise exclusive or of two strings in python?

I've found that the ''.join(chr(ord(a)^ord(b)) for a,b in zip(s,m)) method is pretty slow. Instead, I've been doing this:

fmt = '%dB' % len(source)
s = struct.unpack(fmt, source)
m = struct.unpack(fmt, xor_data)
final = struct.pack(fmt, *(a ^ b for a, b in izip(s, m)))

What does a bitwise shift (left or right) do and what is it used for?

Here is an example:

#include"stdio.h"
#include"conio.h"

void main()
{
    int rm, vivek;
    clrscr();
    printf("Enter any numbers\t(E.g., 1, 2, 5");
    scanf("%d", &rm); // rm = 5(0101) << 2 (two step add zero's), so the value is 10100
    printf("This left shift value%d=%d", rm, rm<<4);
    printf("This right shift value%d=%d", rm, rm>>2);
    getch();
}

What is the difference between & and && in Java?

It depends on the type of the arguments...

For integer arguments, the single ampersand ("&")is the "bit-wise AND" operator. The double ampersand ("&&") is not defined for anything but two boolean arguments.

For boolean arguments, the single ampersand constitutes the (unconditional) "logical AND" operator while the double ampersand ("&&") is the "conditional logical AND" operator. That is to say that the single ampersand always evaluates both arguments whereas the double ampersand will only evaluate the second argument if the first argument is true.

For all other argument types and combinations, a compile-time error should occur.

Is it good practice to use the xor operator for boolean checks?

I think it'd be okay if you commented it, e.g. // ^ == XOR.

Getting each individual digit from a whole integer

Usually, this problem resolve with using the modulo of a number in a loop or convert a number to a string. For convert a number to a string, you may can use the function itoa, so considering the variant with the modulo of a number in a loop.


Content of a file get_digits.c

$ cat get_digits.c 

#include <stdio.h>
#include <stdlib.h>
#include <math.h>


// return a length of integer
unsigned long int get_number_count_digits(long int number);

// get digits from an integer number into an array
int number_get_digits(long int number, int **digits, unsigned int *len);

// for demo features
void demo_number_get_digits(long int number);


int
main()
{
    demo_number_get_digits(-9999999999999);
    demo_number_get_digits(-10000000000);
    demo_number_get_digits(-1000);
    demo_number_get_digits(-9);
    demo_number_get_digits(0);
    demo_number_get_digits(9);
    demo_number_get_digits(1000);
    demo_number_get_digits(10000000000);
    demo_number_get_digits(9999999999999);
    return EXIT_SUCCESS;
}


unsigned long int
get_number_count_digits(long int number)
{
    if (number < 0)
        number = llabs(number);
    else if (number == 0)
        return 1;

    if (number < 999999999999997)
        return floor(log10(number)) + 1;

    unsigned long int count = 0;
    while (number > 0) {
        ++count;
        number /= 10;
    }
    return count;
}


int
number_get_digits(long int number, int **digits, unsigned int *len)
{
    number = labs(number);

    // termination count digits and size of a array as well as
    *len = get_number_count_digits(number);

    *digits = realloc(*digits, *len * sizeof(int));

    // fill up the array
    unsigned int index = 0;
    while (number > 0) {
        (*digits)[index] = (int)(number % 10);
        number /= 10;
        ++index;
    }

    // reverse the array
    unsigned long int i = 0, half_len = (*len / 2);
    int swap;
    while (i < half_len) {
        swap = (*digits)[i];
        (*digits)[i] = (*digits)[*len - i - 1];
        (*digits)[*len - i - 1] = swap;
         ++i;
    }

    return 0;
}


void
demo_number_get_digits(long int number)
{
    int *digits;
    unsigned int len;

    digits = malloc(sizeof(int));

    number_get_digits(number, &digits, &len);

    printf("%ld --> [", number);
    for (unsigned int i = 0; i < len; ++i) {
        if (i == len - 1)
            printf("%d", digits[i]);
        else
            printf("%d, ", digits[i]);
    }
    printf("]\n");

    free(digits);
}

Demo with the GNU GCC

$~/Downloads/temp$ cc -Wall -Wextra -std=c11 -o run get_digits.c -lm
$~/Downloads/temp$ ./run
-9999999999999 --> [9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9]
-10000000000 --> [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
-1000 --> [1, 0, 0, 0]
-9 --> [9]
0 --> [0]
9 --> [9]
1000 --> [1, 0, 0, 0]
10000000000 --> [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
9999999999999 --> [9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9]

Demo with the LLVM/Clang

$~/Downloads/temp$ rm run
$~/Downloads/temp$ clang -std=c11 -Wall -Wextra get_digits.c -o run -lm
setivolkylany$~/Downloads/temp$ ./run
-9999999999999 --> [9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9]
-10000000000 --> [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
-1000 --> [1, 0, 0, 0]
-9 --> [9]
0 --> [0]
9 --> [9]
1000 --> [1, 0, 0, 0]
10000000000 --> [1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
9999999999999 --> [9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9, 9]

Testing environment

$~/Downloads/temp$ cc --version | head -n 1
cc (Debian 4.9.2-10) 4.9.2
$~/Downloads/temp$ clang --version
Debian clang version 3.5.0-10 (tags/RELEASE_350/final) (based on LLVM 3.5.0)
Target: x86_64-pc-linux-gnu
Thread model: posix

How does bitshifting work in Java?

byte x = 51; //00101011
byte y = (byte) (x >> 2); //00001010 aka Base(10) 10

How do you set, clear, and toggle a single bit?

Let suppose few things first
num = 55 Integer to perform bitwise operations (set, get, clear, toggle).
n = 4 0 based bit position to perform bitwise operations.

How to get a bit?

  1. To get the nth bit of num right shift num, n times. Then perform bitwise AND & with 1.
bit = (num >> n) & 1;

How it works?

       0011 0111 (55 in decimal)
    >>         4 (right shift 4 times)
-----------------
       0000 0011
     & 0000 0001 (1 in decimal)
-----------------
    => 0000 0001 (final result)

How to set a bit?

  1. To set a particular bit of number. Left shift 1 n times. Then perform bitwise OR | operation with num.
num |= (1 << n);    // Equivalent to; num = (1 << n) | num;

How it works?

       0000 0001 (1 in decimal)
    <<         4 (left shift 4 times)
-----------------
       0001 0000
     | 0011 0111 (55 in decimal)
-----------------
    => 0001 0000 (final result)

How to clear a bit?

  1. Left shift 1, n times i.e. 1 << n.
  2. Perform bitwise complement with the above result. So that the nth bit becomes unset and rest of bit becomes set i.e. ~ (1 << n).
  3. Finally, perform bitwise AND & operation with the above result and num. The above three steps together can be written as num & (~ (1 << n));

Steps to clear a bit

num &= (~(1 << n));    // Equivalent to; num = num & (~(1 << n));

How it works?

       0000 0001 (1 in decimal)
    <<         4 (left shift 4 times)
-----------------
     ~ 0001 0000
-----------------
       1110 1111
     & 0011 0111 (55 in decimal)
-----------------
    => 0010 0111 (final result)

How to toggle a bit?

To toggle a bit we use bitwise XOR ^ operator. Bitwise XOR operator evaluates to 1 if corresponding bit of both operands are different, otherwise evaluates to 0.

Which means to toggle a bit, we need to perform XOR operation with the bit you want to toggle and 1.

num ^= (1 << n);    // Equivalent to; num = num ^ (1 << n);

How it works?

  • If the bit to toggle is 0 then, 0 ^ 1 => 1.
  • If the bit to toggle is 1 then, 1 ^ 1 => 0.
       0000 0001 (1 in decimal)
    <<         4 (left shift 4 times)
-----------------
       0001 0000
     ^ 0011 0111 (55 in decimal)
-----------------
    => 0010 0111 (final result)

Recommended reading - Bitwise operator exercises

Why do we usually use || over |? What is the difference?

After carefully reading this topic is still unclear to me if using | as a logical operator is conform to Java pattern practices.

I recently modified code in a pull request addressing a comment where

if(function1() | function2()){
  ...
}

had to be changed to

boolean isChanged = function1();
isChanged |= function2();
if (isChanged){
  ...
}

What is the actual accepted version?

Java documentation is not mentioning | as a logical non-shortcircuiting OR operator.

Not interested in a vote but more in finding out the standard?! Both code versions are compiling and working as expected.

What is Bit Masking?

A mask defines which bits you want to keep, and which bits you want to clear.

Masking is the act of applying a mask to a value. This is accomplished by doing:

  • Bitwise ANDing in order to extract a subset of the bits in the value
  • Bitwise ORing in order to set a subset of the bits in the value
  • Bitwise XORing in order to toggle a subset of the bits in the value

Below is an example of extracting a subset of the bits in the value:

Mask:   00001111b
Value:  01010101b

Applying the mask to the value means that we want to clear the first (higher) 4 bits, and keep the last (lower) 4 bits. Thus we have extracted the lower 4 bits. The result is:

Mask:   00001111b
Value:  01010101b
Result: 00000101b

Masking is implemented using AND, so in C we get:

uint8_t stuff(...) {
  uint8_t mask = 0x0f;   // 00001111b
  uint8_t value = 0x55;  // 01010101b
  return mask & value;
}

Here is a fairly common use-case: Extracting individual bytes from a larger word. We define the high-order bits in the word as the first byte. We use two operators for this, &, and >> (shift right). This is how we can extract the four bytes from a 32-bit integer:

void more_stuff(uint32_t value) {             // Example value: 0x01020304
    uint32_t byte1 = (value >> 24);           // 0x01020304 >> 24 is 0x01 so
                                              // no masking is necessary
    uint32_t byte2 = (value >> 16) & 0xff;    // 0x01020304 >> 16 is 0x0102 so
                                              // we must mask to get 0x02
    uint32_t byte3 = (value >> 8)  & 0xff;    // 0x01020304 >> 8 is 0x010203 so
                                              // we must mask to get 0x03
    uint32_t byte4 = value & 0xff;            // here we only mask, no shifting
                                              // is necessary
    ...
}

Notice that you could switch the order of the operators above, you could first do the mask, then the shift. The results are the same, but now you would have to use a different mask:

uint32_t byte3 = (value & 0xff00) >> 8;

Convert to binary and keep leading zeros in Python

Use the format() function:

>>> format(14, '#010b')
'0b00001110'

The format() function simply formats the input following the Format Specification mini language. The # makes the format include the 0b prefix, and the 010 size formats the output to fit in 10 characters width, with 0 padding; 2 characters for the 0b prefix, the other 8 for the binary digits.

This is the most compact and direct option.

If you are putting the result in a larger string, use an formatted string literal (3.6+) or use str.format() and put the second argument for the format() function after the colon of the placeholder {:..}:

>>> value = 14
>>> f'The produced output, in binary, is: {value:#010b}'
'The produced output, in binary, is: 0b00001110'
>>> 'The produced output, in binary, is: {:#010b}'.format(value)
'The produced output, in binary, is: 0b00001110'

As it happens, even for just formatting a single value (so without putting the result in a larger string), using a formatted string literal is faster than using format():

>>> import timeit
>>> timeit.timeit("f_(v, '#010b')", "v = 14; f_ = format")  # use a local for performance
0.40298633499332936
>>> timeit.timeit("f'{v:#010b}'", "v = 14")
0.2850222919951193

But I'd use that only if performance in a tight loop matters, as format(...) communicates the intent better.

If you did not want the 0b prefix, simply drop the # and adjust the length of the field:

>>> format(14, '08b')
'00001110'

How does the bitwise complement operator (~ tilde) work?

As others mentioned ~ just flipped bits (changes one to zero and zero to one) and since two's complement is used you get the result you saw.

One thing to add is why two's complement is used, this is so that the operations on negative numbers will be the same as on positive numbers. Think of -3 as the number to which 3 should be added in order to get zero and you'll see that this number is 1101, remember that binary addition is just like elementary school (decimal) addition only you carry one when you get to two rather than 10.

 1101 +
 0011 // 3
    =
10000
    =
 0000 // lose carry bit because integers have a constant number of bits.

Therefore 1101 is -3, flip the bits you get 0010 which is two.

Differences in boolean operators: & vs && and | vs ||

&& ; || are logical operators.... short circuit

& ; | are boolean logical operators.... Non-short circuit

Moving to differences in execution on expressions. Bitwise operators evaluate both sides irrespective of the result of left hand side. But in the case of evaluating expressions with logical operators, the evaluation of the right hand expression is dependent on the left hand condition.

For Example:

int i = 25;
int j = 25;
if(i++ < 0 && j++ > 0)
    System.out.println("OK");
System.out.printf("i = %d ; j = %d",i,j);

This will print i=26 ; j=25, As the first condition is false the right hand condition is bypassed as the result is false anyways irrespective of the right hand side condition.(short circuit)

int i = 25;
int j = 25;
if(i++ < 0 & j++ > 0)
    System.out.println("OK");
System.out.printf("i = %d ; j = %d",i,j);

But, this will print i=26; j=26,

What is (x & 1) and (x >>= 1)?

These are Bitwise Operators (reference).

x & 1 produces a value that is either 1 or 0, depending on the least significant bit of x: if the last bit is 1, the result of x & 1 is 1; otherwise, it is 0. This is a bitwise AND operation.

x >>= 1 means "set x to itself shifted by one bit to the right". The expression evaluates to the new value of x after the shift.

Note: The value of the most significant bit after the shift is zero for values of unsigned type. For values of signed type the most significant bit is copied from the sign bit of the value prior to shifting as part of sign extension, so the loop will never finish if x is a signed type, and the initial value is negative.

What does AND 0xFF do?

Anding an integer with 0xFF leaves only the least significant byte. For example, to get the first byte in a short s, you can write s & 0xFF. This is typically referred to as "masking". If byte1 is either a single byte type (like uint8_t) or is already less than 256 (and as a result is all zeroes except for the least significant byte) there is no need to mask out the higher bits, as they are already zero.

See tristopiaPatrick Schlüter's answer below when you may be working with signed types. When doing bitwise operations, I recommend working only with unsigned types.

Store output of subprocess.Popen call in a string

subprocess.Popen: http://docs.python.org/2/library/subprocess.html#subprocess.Popen

import subprocess

command = "ntpq -p"  # the shell command
process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=None, shell=True)

#Launch the shell command:
output = process.communicate()

print output[0]

In the Popen constructor, if shell is True, you should pass the command as a string rather than as a sequence. Otherwise, just split the command into a list:

command = ["ntpq", "-p"]  # the shell command
process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=None)

If you need to read also the standard error, into the Popen initialization, you can set stderr to subprocess.PIPE or to subprocess.STDOUT:

import subprocess

command = "ntpq -p"  # the shell command
process = subprocess.Popen(command, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True)

#Launch the shell command:
output, error = process.communicate()

How to extract file name from path?

Here's a simple VBA solution I wrote that works with Windows, Unix, Mac, and URL paths.

sFileName = Mid(Mid(sPath, InStrRev(sPath, "/") + 1), InStrRev(sPath, "\") + 1)

sFolderName = Left(sPath, Len(sPath) - Len(sFileName))

You can test the output using this code:

'Visual Basic for Applications 
http = "https://www.server.com/docs/Letter.txt"
unix = "/home/user/docs/Letter.txt"
dos = "C:\user\docs\Letter.txt"
win = "\\Server01\user\docs\Letter.txt"
blank = ""

sPath = unix 
sFileName = Mid(Mid(sPath, InStrRev(sPath, "/") + 1), InStrRev(sPath, "\") + 1)
sFolderName = Left(sPath, Len(sPath) - Len(sFileName))

Debug.print "Folder: " & sFolderName & " File: " & sFileName

Also see: Wikipedia - Path (computing)

Java compiler level does not match the version of the installed Java project facet

You can change project facet from Project --> Properties --> Project Facet --> Java --> {required JDK version}

Restoring Nuget References?

This script will reinstall all packages of a project without messing up dependencies or installing dependencies that may have been intentianlyz removed. (More for their part package developers.)

Update-Package -Reinstall -ProjectName Proteus.Package.LinkedContent -IgnoreDependencies

Reference member variables as class members

It's called dependency injection via constructor injection: class A gets the dependency as an argument to its constructor and saves the reference to dependent class as a private variable.

There's an interesting introduction on wikipedia.

For const-correctness I'd write:

using T = int;

class A
{
public:
  A(const T &thing) : m_thing(thing) {}
  // ...

private:
   const T &m_thing;
};

but a problem with this class is that it accepts references to temporary objects:

T t;
A a1{t};    // this is ok, but...

A a2{T()};  // ... this is BAD.

It's better to add (requires C++11 at least):

class A
{
public:
  A(const T &thing) : m_thing(thing) {}
  A(const T &&) = delete;  // prevents rvalue binding
  // ...

private:
  const T &m_thing;
};

Anyway if you change the constructor:

class A
{
public:
  A(const T *thing) : m_thing(*thing) { assert(thing); }
  // ...

private:
   const T &m_thing;
};

it's pretty much guaranteed that you won't have a pointer to a temporary.

Also, since the constructor takes a pointer, it's clearer to users of A that they need to pay attention to the lifetime of the object they pass.


Somewhat related topics are:

Why is the apt-get function not working in the terminal on Mac OS X v10.9 (Mavericks)?

As Homebrew is my favorite for macOS although it is possible to have apt-get on macOS using Fink.

Android AlertDialog Single Button

In Mono for Android you can do this:

var ad = new AlertDialog.Builder(this);
ad.SetTitle("Title");
ad.SetMessage("Message");
ad.SetPositiveButton("OK", delegate { ad.Dispose(); });
ad.Show();

Show compose SMS view in Android

I add my SMS method if it can help someone. Be careful with smsManager.sendTextMessage, If the text is too long, the message does not go away. You have to respect max length depending of encoding. More information here SMS Manager send mutlipart message when there is less than 160 characters

//TO USE EveryWhere

SMSUtils.sendSMS(context, phoneNumber, message);

//Manifest

<!-- SMS -->
<uses-permission android:name="android.permission.SEND_SMS"/>
<uses-permission android:name="android.permission.READ_PHONE_STATE"/>

 <receiver
     android:name=".SMSUtils"
     android:enabled="true"
     android:exported="true">
     <intent-filter>
         <action android:name="SMS_SENT"/>
         <action android:name="SMS_DELIVERED"/>
      </intent-filter>
 </receiver>

//JAVA

public class SMSUtils extends BroadcastReceiver {

    public static final String SENT_SMS_ACTION_NAME = "SMS_SENT";
    public static final String DELIVERED_SMS_ACTION_NAME = "SMS_DELIVERED";

    @Override
    public void onReceive(Context context, Intent intent) {
        //Detect l'envoie de sms
        if (intent.getAction().equals(SENT_SMS_ACTION_NAME)) {
            switch (getResultCode()) {
                case Activity.RESULT_OK: // Sms sent
                    Toast.makeText(context, context.getString(R.string.sms_send), Toast.LENGTH_LONG).show();
                    break;
                case SmsManager.RESULT_ERROR_GENERIC_FAILURE: // generic failure
                    Toast.makeText(context, context.getString(R.string.sms_not_send), Toast.LENGTH_LONG).show();
                    break;
                case SmsManager.RESULT_ERROR_NO_SERVICE: // No service
                    Toast.makeText(context, context.getString(R.string.sms_not_send_no_service), Toast.LENGTH_LONG).show();
                    break;
                case SmsManager.RESULT_ERROR_NULL_PDU: // null pdu
                    Toast.makeText(context, context.getString(R.string.sms_not_send), Toast.LENGTH_LONG).show();
                    break;
                case SmsManager.RESULT_ERROR_RADIO_OFF: //Radio off
                    Toast.makeText(context, context.getString(R.string.sms_not_send_no_radio), Toast.LENGTH_LONG).show();
                    break;
            }
        }
        //detect la reception d'un sms
        else if (intent.getAction().equals(DELIVERED_SMS_ACTION_NAME)) {
            switch (getResultCode()) {
                case Activity.RESULT_OK:
                    Toast.makeText(context, context.getString(R.string.sms_receive), Toast.LENGTH_LONG).show();
                    break;
                case Activity.RESULT_CANCELED:
                    Toast.makeText(context, context.getString(R.string.sms_not_receive), Toast.LENGTH_LONG).show();
                    break;
            }
        }
    }

    /**
     * Test if device can send SMS
     * @param context
     * @return
     */
    public static boolean canSendSMS(Context context) {
        return context.getPackageManager().hasSystemFeature(PackageManager.FEATURE_TELEPHONY);
    }

    public static void sendSMS(final Context context, String phoneNumber, String message) {

        if (!canSendSMS(context)) {
            Toast.makeText(context, context.getString(R.string.cannot_send_sms), Toast.LENGTH_LONG).show();
            return;
        }

        PendingIntent sentPI = PendingIntent.getBroadcast(context, 0, new Intent(SENT_SMS_ACTION_NAME), 0);
        PendingIntent deliveredPI = PendingIntent.getBroadcast(context, 0, new Intent(DELIVERED_SMS_ACTION_NAME), 0);

        final SMSUtils smsUtils = new SMSUtils();
        //register for sending and delivery
        context.registerReceiver(smsUtils, new IntentFilter(SMSUtils.SENT_SMS_ACTION_NAME));
        context.registerReceiver(smsUtils, new IntentFilter(DELIVERED_SMS_ACTION_NAME));

        SmsManager sms = SmsManager.getDefault();
        ArrayList<String> parts = sms.divideMessage(message);

        ArrayList<PendingIntent> sendList = new ArrayList<>();
        sendList.add(sentPI);

        ArrayList<PendingIntent> deliverList = new ArrayList<>();
        deliverList.add(deliveredPI);

        sms.sendMultipartTextMessage(phoneNumber, null, parts, sendList, deliverList);

        //we unsubscribed in 10 seconds 
        new Handler().postDelayed(new Runnable() {
            @Override
            public void run() {
                context.unregisterReceiver(smsUtils);
            }
        }, 10000);

    }
}

Converting ArrayList to HashMap

The general methodology would be to iterate through the ArrayList, and insert the values into the HashMap. An example is as follows:

HashMap<String, Product> productMap = new HashMap<String, Product>();
for (Product product : productList) {
   productMap.put(product.getProductCode(), product);
}

How to combine results of two queries into a single dataset

This is what you can do. Assuming that your ProductName column have common values.

SELECT 
     Table1.ProductName, 
     Table1.NumberofProducts, 
     Table2.ProductName, 
     Table2.NumberofProductssold
FROM Table1
INNER JOIN Table2
ON Table1.ProductName= Table2.ProductName

Angularjs - display current date

You have to create a date object in your controller first:

controller:

function Ctrl($scope)
{
    $scope.date = new Date();
}

view:

<div ng-app ng-controller="Ctrl">
    {{date | date:'yyyy-MM-dd'}}
</div>

JSFiddle example

Angular Date Filter Ref

How do you express binary literals in Python?

>>> print int('01010101111',2)
687
>>> print int('11111111',2)
255

Another way.

Change Title of Javascript Alert

As others have said, you can't do that either using alert()or confirm().

You can, however, create an external HTML document containing your error message and an OK button, set its <title> element to whatever you want, then display it in a modal dialog box using showModalDialog().

Generate .pem file used to set up Apple Push Notifications

$ cd Desktop
$ openssl x509 -in aps_development.cer -inform der -out PushChatCert.pem

Google OAUTH: The redirect URI in the request did not match a registered redirect URI

I thought I had this configured but it turns out I set the URL in the wrong place. I followed the URL provided in the Google error page and added my URL here. Stupid mistake from my part, but easily done. Hope this helps

When is layoutSubviews called?

https://developer.apple.com/library/prerelease/tvos/documentation/WindowsViews/Conceptual/ViewPG_iPhoneOS/CreatingViews/CreatingViews.html#//apple_ref/doc/uid/TP40009503-CH5-SW1

Layout changes can occur whenever any of the following events happens in a view:

a. The size of a view’s bounds rectangle changes.
b. An interface orientation change occurs, which usually triggers a change in the root view’s bounds rectangle.
c. The set of Core Animation sublayers associated with the view’s layer changes and requires layout.
d. Your application forces layout to occur by calling the setNeedsLayout or layoutIfNeeded method of a view.
e. Your application forces layout by calling the setNeedsLayout method of the view’s underlying layer object.

Prevent div from moving while resizing the page

1 - remove the margin from your BODY CSS.

2 - wrap all of your html in a wrapper <div id="wrapper"> ... all your body content </div>

3 - Define the CSS for the wrapper:

This will hold everything together, centered on the page.

#wrapper {
    margin-left:auto;
    margin-right:auto;
    width:960px;
}

Calculating a 2D Vector's Cross Product

In short: It's a shorthand notation for a mathematical hack.

Long explanation:

You can't do a cross product with vectors in 2D space. The operation is not defined there.

However, often it is interesting to evaluate the cross product of two vectors assuming that the 2D vectors are extended to 3D by setting their z-coordinate to zero. This is the same as working with 3D vectors on the xy-plane.

If you extend the vectors that way and calculate the cross product of such an extended vector pair you'll notice that only the z-component has a meaningful value: x and y will always be zero.

That's the reason why the z-component of the result is often simply returned as a scalar. This scalar can for example be used to find the winding of three points in 2D space.

From a pure mathematical point of view the cross product in 2D space does not exist, the scalar version is the hack and a 2D cross product that returns a 2D vector makes no sense at all.

Declaring a xsl variable and assigning value to it

No, unlike in a lot of other languages, XSLT variables cannot change their values after they are created. You can however, avoid extraneous code with a technique like this:

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" indent="yes" omit-xml-declaration="yes"/>

  <xsl:variable name="mapping">
    <item key="1" v1="A" v2="B" />
    <item key="2" v1="X" v2="Y" />
  </xsl:variable>
  <xsl:variable name="mappingNode"
                select="document('')//xsl:variable[@name = 'mapping']" />

  <xsl:template match="....">
    <xsl:variable name="testVariable" select="'1'" />

    <xsl:variable name="values" select="$mappingNode/item[@key = $testVariable]" />

    <xsl:variable name="variable1" select="$values/@v1" />
    <xsl:variable name="variable2" select="$values/@v2" />
  </xsl:template>
</xsl:stylesheet>

In fact, once you've got the values variable, you may not even need separate variable1 and variable2 variables. You could just use $values/@v1 and $values/@v2 instead.

Resize a picture to fit a JLabel

i have done the following and it worked perfectly

try {
        JFileChooser jfc = new JFileChooser();
        jfc.showOpenDialog(null);
        File f = jfc.getSelectedFile();
        Image bi = ImageIO.read(f);
        image1.setText("");
        image1.setIcon(new ImageIcon(bi.getScaledInstance(int width, int width, int width)));

    } catch (Exception e) {
    } 

Why do abstract classes in Java have constructors?

All the classes including the abstract classes can have constructors.Abstract class constructors will be called when its concrete subclass will be instantiated

How to return a custom object from a Spring Data JPA GROUP BY query

Get data with column name and its values (in key-value pair) using JDBC:

/*Template class with a basic set of JDBC operations, allowing the use
  of named parameters rather than traditional '?' placeholders.
 
  This class delegates to a wrapped {@link #getJdbcOperations() JdbcTemplate}
  once the substitution from named parameters to JDBC style '?' placeholders is
  done at execution time. It also allows for expanding a {@link java.util.List}
  of values to the appropriate number of placeholders.
 
  The underlying {@link org.springframework.jdbc.core.JdbcTemplate} is
  exposed to allow for convenient access to the traditional
  {@link org.springframework.jdbc.core.JdbcTemplate} methods.*/


@Autowired
protected  NamedParameterJdbcTemplate jdbc;


@GetMapping("/showDataUsingQuery/{Query}")
    public List<Map<String,Object>> ShowColumNameAndValue(@PathVariable("Query")String Query) throws SQLException {

      /* MapSqlParameterSource class is intended for passing in a simple Map of parameter values
        to the methods of the {@link NamedParameterJdbcTemplate} class*/

       MapSqlParameterSource msp = new MapSqlParameterSource();

       // this query used for show column name and columnvalues....
        List<Map<String,Object>> css = jdbc.queryForList(Query,msp);

        return css;
    }

what is right way to do API call in react js?

1) You can use Fetch API to fetch data from Endd Points:

Example fetching all Github repose for a user

  /* Fetch GitHub Repos */
  fetchData = () => {

       //show progress bar
      this.setState({ isLoading: true });

      //fetch repos
      fetch(`https://api.github.com/users/hiteshsahu/repos`)
      .then(response => response.json())
      .then(data => {
        if (Array.isArray(data)) {
          console.log(JSON.stringify(data));
          this.setState({ repos: data ,
                         isLoading: false});
        } else {
          this.setState({ repos: [],
                          isLoading: false  
                        });
        }
      });
  };

2) Other Alternative is Axios

Using axios you can cut out the middle step of passing the results of the http request to the .json() method. Axios just returns the data object you would expect.

  import axios from "axios";

 /* Fetch GitHub Repos */
  fetchDataWithAxios = () => {

     //show progress bar
      this.setState({ isLoading: true });

      // fetch repos with axios
      axios
          .get(`https://api.github.com/users/hiteshsahu/repos`)
          .then(result => {
            console.log(result);
            this.setState({
              repos: result.data,
              isLoading: false
            });
          })
          .catch(error =>
            this.setState({
              error,
              isLoading: false
            })
          );
}

Now you can choose to fetch data using any of this strategies in componentDidMount

class App extends React.Component {
  state = {
    repos: [],
   isLoading: false
  };

  componentDidMount() {
    this.fetchData ();
  }

Meanwhile you can show progress bar while data is loading

   {this.state.isLoading && <LinearProgress />}

Check if EditText is empty.

You can use length() from EditText.

public boolean isEditTextEmpty(EditText mInput){
   return mInput.length() == 0;
}

How do I pass multiple attributes into an Angular.js attribute directive?

You could pass an object as attribute and read it into the directive like this:

<div my-directive="{id:123,name:'teo',salary:1000,color:red}"></div>

app.directive('myDirective', function () {
    return {            
        link: function (scope, element, attrs) {
           //convert the attributes to object and get its properties
           var attributes = scope.$eval(attrs.myDirective);       
           console.log('id:'+attributes.id);
           console.log('id:'+attributes.name);
        }
    };
});

How to set height property for SPAN

Give it a display:inline-block in CSS - that should let it do what you want.
In terms of compatibility: IE6/7 will work with this, as quirks mode suggests:

IE 6/7 accepts the value only on elements with a natural display: inline.

Delete files in subfolder using batch script

You can use the /s switch for del to delete in subfolders as well.

Example

del D:\test\*.* /s

Would delete all files under test including all files in all subfolders.

To remove folders use rd, same switch applies.

rd D:\test\folder /s /q

rd doesn't support wildcards * though so if you want to recursively delete all subfolders under the test directory you can use a for loop.

for /r /d D:\test %a in (*) do rd %a /s /q

If you are using the for option in a batch file remember to use 2 %'s instead of 1.

How to make inactive content inside a div?

div[disabled]
{
  pointer-events: none;
  opacity: 0.6;
  background: rgba(200, 54, 54, 0.5);  
  background-color: yellow;
  filter: alpha(opacity=50);
  zoom: 1;  
  -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=50)";  
  -moz-opacity: 0.5; 
  -khtml-opacity: 0.5;  
}

How does += (plus equal) work?

1 += 2 is a syntax error (left-side must be a variable).

x += y is shorthand for x = x + y.

How to submit http form using C#

Your HTML file is not going to interact with C# directly, but you can write some C# to behave as if it were the HTML file.

For example: there is a class called System.Net.WebClient with simple methods:

using System.Net;
using System.Collections.Specialized;

...
using(WebClient client = new WebClient()) {

    NameValueCollection vals = new NameValueCollection();
    vals.Add("test", "test string");
    client.UploadValues("http://www.someurl.com/page.php", vals);
}

For more documentation and features, refer to the MSDN page.

Convert .pfx to .cer

I wanted to add a method which I think was simplest of all.

  1. Simply right click the pfx file, click "Install" follow the wizard, and add it to a store (I added to the Personal store).

  2. In start menu type certmgr.msc and go to CertManager program.

  3. Find your pfx certificate (tabs at top are the various stores), click the export button and follow the wizard (there is an option to export as .CER)

Essentially it does the same thing as Andrew's answer, but it avoids using Windows Management Console (goes straight to the import/export).

Reading e-mails from Outlook with Python through MAPI

I had the same issue. Combining various approaches from the internet (and above) come up with the following approach (checkEmails.py)

class CheckMailer:

        def __init__(self, filename="LOG1.txt", mailbox="Mailbox - Another User Mailbox", folderindex=3):
            self.f = FileWriter(filename)
            self.outlook = win32com.client.Dispatch("Outlook.Application").GetNamespace("MAPI").Folders(mailbox)
            self.inbox = self.outlook.Folders(folderindex)


        def check(self):                
        #===============================================================================
        # for i in xrange(1,100):                           #Uncomment this section if index 3 does not work for you
        #     try:
        #         self.inbox = self.outlook.Folders(i)     # "6" refers to the index of inbox for Default User Mailbox
        #         print "%i %s" % (i,self.inbox)            # "3" refers to the index of inbox for Another user's mailbox
        #     except:
        #         print "%i does not work"%i
        #===============================================================================

                self.f.pl(time.strftime("%H:%M:%S"))
                tot = 0                
                messages = self.inbox.Items
                message = messages.GetFirst()
                while message:
                    self.f.pl (message.Subject)
                    message = messages.GetNext()
                    tot += 1
                self.f.pl("Total Messages found: %i" % tot)
                self.f.pl("-" * 80)
                self.f.flush()

if __name__ == "__main__":
    mail = CheckMailer()
    for i in xrange(320):  # this is 10.6 hours approximately
            mail.check()
            time.sleep(120.00)

For concistency I include also the code for the FileWriter class (found in FileWrapper.py). I needed this because trying to pipe UTF8 to a file in windows did not work.

class FileWriter(object):
    '''
    convenient file wrapper for writing to files
    '''


    def __init__(self, filename):
        '''
        Constructor
        '''
        self.file = open(filename, "w")

    def pl(self, a_string):
        str_uni = a_string.encode('utf-8')
        self.file.write(str_uni)
        self.file.write("\n")

    def flush(self):
        self.file.flush()

How do SO_REUSEADDR and SO_REUSEPORT differ?

Mecki's answer is absolutly perfect, but it's worth adding that FreeBSD also supports SO_REUSEPORT_LB, which mimics Linux' SO_REUSEPORT behaviour - it balances the load; see setsockopt(2)

Upload folder with subfolders using S3 and the AWS console

I do not see Python answers here. You can script folder upload using Python/boto3. Here's how to recursively get all file names from directory tree:

def recursive_glob(treeroot, extention):
    results = [os.path.join(dirpath, f)
        for dirpath, dirnames, files in os.walk(treeroot)
        for f in files if f.endswith(extention)]
    return results

Here's how to upload a file to S3 using Python/boto:

k = Key(bucket)
k.key = s3_key_name
k.set_contents_from_file(file_handle, cb=progress, num_cb=20, reduced_redundancy=use_rr )

I used these ideas to write Directory-Uploader-For-S3

Using Python, how can I access a shared folder on windows network?

How did you try it? Maybe you are working with \ and omit proper escaping.

Instead of

open('\\HOST\share\path\to\file')

use either Johnsyweb's solution with the /s, or try one of

open(r'\\HOST\share\path\to\file')

or

open('\\\\HOST\\share\\path\\to\\file')

.

PHP is_numeric or preg_match 0-9 validation

is_numeric would accept "-0.5e+12" as a valid ID.

Selecting last element in JavaScript array

So, a lot of people are answering with pop(), but most of them don't seem to realize that's a destructive method.

var a = [1,2,3]
a.pop()
//3
//a is now [1,2]

So, for a really silly, nondestructive method:

var a = [1,2,3]
a[a.push(a.pop())-1]
//3

a push pop, like in the 90s :)

push appends a value to the end of an array, and returns the length of the result. so

d=[]
d.push('life') 
//=> 1
d 
//=>['life']

pop returns the value of the last item of an array, prior to it removing that value at that index. so

c = [1,2,1]
c.pop() 
//=> 1
c 
//=> [1,2]

arrays are 0 indexed, so c.length => 3, c[c.length] => undefined (because you're looking for the 4th value if you do that(this level of depth is for any hapless newbs that end up here)).

Probably not the best, or even a good method for your application, what with traffic, churn, blah. but for traversing down an array, streaming it onto another, just being silly with inefficient methods, this. Totally this.

How to printf a 64-bit integer as hex?

Edit: Use printf("val = 0x%" PRIx64 "\n", val); instead.

Try printf("val = 0x%llx\n", val);. See the printf manpage:

ll (ell-ell). A following integer conversion corresponds to a long long int or unsigned long long int argument, or a following n conversion corresponds to a pointer to a long long int argument.

Edit: Even better is what @M_Oehm wrote: There is a specific macro for that, because unit64_t is not always a unsigned long long: PRIx64 see also this stackoverflow answer

Swift: Convert enum value to String?

Starting from Swift 3.0 you can

var str = String(describing: Audience.friends)

LaTeX: Multiple authors in a two-column article

I put together a little test here:

\documentclass[10pt,twocolumn]{article}

\title{Article Title}
\author{
    First Author\\
    Department\\
    school\\
    email@edu
  \and
    Second Author\\
    Department\\
    school\\
    email@edu
    \and
    Third Author\\
    Department\\
    school\\
    email@edu
    \and
    Fourth Author\\
    Department\\
    school\\
    email@edu
}
\date{\today}

\begin{document}

\maketitle

\begin{abstract}
\ldots
\end{abstract}

\section{Introduction}
\ldots

\end{document}

Things to note, the title, author and date fields are declared before \begin{document}. Also, the multicol package is likely unnecessary in this case since you have declared twocolumn in the document class.

This example puts all four authors on the same line, but if your authors have longer names, departments or emails, this might cause it to flow over onto another line. You might be able to change the font sizes around a little bit to make things fit. This could be done by doing something like {\small First Author}. Here's a more detailed article on \LaTeX font sizes:

https://engineering.purdue.edu/ECN/Support/KB/Docs/LaTeXChangingTheFont

To italicize you can use {\it First Name} or \textit{First Name}.

Be careful though, if the document is meant for publication often times journals or conference proceedings have their own formatting guidelines so font size trickery might not be allowed.

How to get the difference between two arrays in JavaScript?

If you're array contains objects it becomes a bit more difficult if you want to compare an attribute.

Luckily lodash makes this pretty easy using _contains and _.pluck:

var list1 = [{id: 1},{id: 2}];
var list1 = [{id: 1},{id: 2}, {id: 3}];

//es6
var results = list2.filter(item => {
  return !_.contains(_.pluck(list1, 'id'), item.id);
});

//es5
var results = list2.filter(function(item){
  return !_.contains(_.pluck(list1, 'id'), item.id);
});

//results contains [{id: 3}]

time data does not match format

No need to use datetime library. Using the dateutil library there is no need of any format:

>>> from dateutil import parser
>>> s= '25 April, 2020, 2:50, pm, IST'
>>> parser.parse(s)
datetime.datetime(2020, 4, 25, 14, 50)

how to show alternate image if source image is not found? (onerror working in IE but not in mozilla)

I think this is very nice and short

<img src="imagenotfound.gif" alt="Image not found" onerror="this.src='imagefound.gif';" />

But, be careful. The user's browser will be stuck in an endless loop if the onerror image itself generates an error.


EDIT To avoid endless loop, remove the onerror from it at once.

<img src="imagenotfound.gif" alt="Image not found" onerror="this.onerror=null;this.src='imagefound.gif';" />

By calling this.onerror=null it will remove the onerror then try to get the alternate image.


NEW I would like to add a jQuery way, if this can help anyone.

<script>
$(document).ready(function()
{
    $(".backup_picture").on("error", function(){
        $(this).attr('src', './images/nopicture.png');
    });
});
</script>

<img class='backup_picture' src='./images/nonexistent_image_file.png' />

You simply need to add class='backup_picture' to any img tag that you want a backup picture to load if it tries to show a bad image.

Rename a column in MySQL

for mysql version 5

alter table *table_name* change column *old_column_name* *new_column_name* datatype();

Anaconda export Environment file

  1. First activate your conda environment (the one u want to export/backup)
conda activate myEnv
  1. Export all packages to a file (myEnvBkp.txt)
conda list --explicit > myEnvBkp.txt
  1. Restore/import the environment:
conda create --name myEnvRestored --file myEnvBkp.txt

Key hash for Android-Facebook app

The simplest solution I have found is this:

  • Open up Log Cat
  • Try and access Facebook with the Android SDK
  • Look for the line in the log that looks like this:

    04-24 01:14:08.605: I/System.out(31395): invalid_key:Android key mismatch. 
    Your key "abcdefgHIJKLMN+OPqrstuvwzyz" does not match the allowed keys specified in your
    application settings. Check your application settings at 
    http://www.facebook.com/developers
    
  • Copy "abcdefgHIJKLMN+OPqrstuvwzyz" and paste it into the Facebook Android Key Hash area.

Server configuration is missing in Eclipse

I faced the same problem once. THe reason for this is that even though the server is available, the config files are missing. You can see the server at Windows -> Show view -> Servers. Their configuration files can be seen at Project Explorer -> Servers. For some reason this second mentioned config files were missing.

I simply deleted the existing server and created a new one with this the config files were also created and the problem was solved!

Similar solution is given at here by Emertana EM java.lang.NoClassDefFoundError: org/apache/juli/logging/LogFactory

How to find file accessed/created just few minutes ago

If you know the file is in your current directory, I would use:

ls -lt | head

This lists your most recently modified files and directories in order. In fact, I use it so much I have it aliased to 'lh'.

How to set up devices for VS Code for a Flutter emulator

From version 2.13.0 of Dart Code, emulators can be launched directly from within Code but This feature relies on support from the Flutter tools which means it will only show emulators when using a very recent Flutter SDK. Flutter’s master channel already has this change, but it may take a little longer to filter through to the dev and beta channels.

I tested this feature and worked very well on flutter version 0.5.6-pre.61 (master channel)

enter image description here

How can I implement a theme from bootswatch or wrapbootstrap in an MVC 5 project?

All what you have to do is to select and download the bootstrap.css and bootstrap.js files from Bootswatch website, and then replace the original files with them.

Of course you have to add the paths to your layout page after the jQuery path that is all.

IntelliJ shortcut to show a popup of methods in a class that can be searched

Use Navigate (View in older versions) | File Structure Popup (Ctrl+F12 on Windows, ?+F12 on OS X). Start typing method/symbol name to either narrow down the list or highlight the desired element. Press Enter to navigate to the selected element.

Hidden features of Python

The getattr built-in function :

>>> class C():
    def getMontys(self):
        self.montys = ['Cleese','Palin','Idle','Gilliam','Jones','Chapman']
        return self.montys


>>> c = C()
>>> getattr(c,'getMontys')()
['Cleese', 'Palin', 'Idle', 'Gilliam', 'Jones', 'Chapman']
>>> 

Useful if you want to dispatch function depending on the context. See examples in Dive Into Python (Here)

Repeat a string in JavaScript a number of times

In ES2015/ES6 you can use "*".repeat(n)

So just add this to your projects, and your are good to go.

  String.prototype.repeat = String.prototype.repeat || 
    function(n) {
      if (n < 0) throw new RangeError("invalid count value");
      if (n == 0) return "";
      return new Array(n + 1).join(this.toString()) 
    };

Ignore .pyc files in git repository

If you want to ignore '.pyc' files globally (i.e. if you do not want to add the line to .gitignore file in every git directory), try the following:

$ cat ~/.gitconfig 
[core]
    excludesFile = ~/.gitignore
$ cat ~/.gitignore
**/*.pyc

[Reference]
https://git-scm.com/docs/gitignore

  • Patterns which a user wants Git to ignore in all situations (e.g., backup or temporary files generated by the user’s editor of choice) generally go into a file specified by core.excludesFile in the user’s ~/.gitconfig.

  • A leading "**" followed by a slash means match in all directories. For example, "**/foo" matches file or directory "foo" anywhere, the same as pattern "foo". "**/foo/bar" matches file or directory "bar" anywhere that is directly under directory "foo".

setting content between div tags using javascript

If the number of your messages is limited then the following may help. I used jQuery for the following example, but it works with plain js too.

The innerHtml property did not work for me. So I experimented with ...

    <div id=successAndErrorMessages-1>100% OK</div>
    <div id=successAndErrorMessages-2>This is an error mssg!</div>

and toggled one of the two on/off ...

 $("#successAndErrorMessages-1").css('display', 'none')
 $("#successAndErrorMessages-2").css('display', '')

For some reason I had to fiddle around with the ordering before it worked in all types of browsers.

How do I extract the contents of an rpm?

The powerful text-based file manager mc (Midnight Commander, vaguely reminding the Norton Commander of old DOS times) has the built-in capability of inspecting and unpacking .rpm and .rpms files, just "open" the .rpm(s) file within mc and select CONTENTS.cpio: for an rpm you get access to the install tree, for an rpms you get access to the .spec file and all the source packages.

Multiple lines of text in UILabel

The best solution I have found (to an otherwise frustrating problem that should have been solved in the framework) is similar to vaychick's.

Just set number of lines to 0 in either IB or code

myLabel.numberOfLines = 0;

This will display the lines needed but will reposition the label so its centered horizontally (so that a 1 line and 3 line label are aligned in their horizontal position). To fix that add:

CGRect currentFrame = myLabel.frame;
CGSize max = CGSizeMake(myLabel.frame.size.width, 500);
CGSize expected = [myString sizeWithFont:myLabel.font constrainedToSize:max lineBreakMode:myLabel.lineBreakMode]; 
currentFrame.size.height = expected.height;
myLabel.frame = currentFrame;

Responsively change div size keeping aspect ratio

(function( $ ) {
  $.fn.keepRatio = function(which) {
      var $this = $(this);
      var w = $this.width();
      var h = $this.height();
      var ratio = w/h;
      $(window).resize(function() {
          switch(which) {
              case 'width':
                  var nh = $this.width() / ratio;
                  $this.css('height', nh + 'px');
                  break;
              case 'height':
                  var nw = $this.height() * ratio;
                  $this.css('width', nw + 'px');
                  break;
          }
      });

  }
})( jQuery );      

$(document).ready(function(){
    $('#foo').keepRatio('width');
});

Working example: http://jsfiddle.net/QtftX/1/

Customize the Authorization HTTP header

In the case of CROSS ORIGIN request read this:

I faced this situation and at first I chose to use the Authorization Header and later removed it after facing the following issue.

Authorization Header is considered a custom header. So if a cross-domain request is made with the Autorization Header set, the browser first sends a preflight request. A preflight request is an HTTP request by the OPTIONS method, this request strips all the parameters from the request. Your server needs to respond with Access-Control-Allow-Headers Header having the value of your custom header (Authorization header).

So for each request the client (browser) sends, an additional HTTP request(OPTIONS) was being sent by the browser. This deteriorated the performance of my API. You should check if adding this degrades your performance. As a workaround I am sending tokens in http parameters, which I know is not the best way of doing it but I couldn't compromise with the performance.

What happened to console.log in IE8?

I'm using Walter's approach from above (see: https://stackoverflow.com/a/14246240/3076102)

I mix in a solution I found here https://stackoverflow.com/a/7967670 to properly show Objects.

This means the trap function becomes:

function trap(){
    if(debugging){
        // create an Array from the arguments Object           
        var args = Array.prototype.slice.call(arguments);
        // console.raw captures the raw args, without converting toString
        console.raw.push(args);
        var index;
        for (index = 0; index < args.length; ++index) {
            //fix for objects
            if(typeof args[index] === 'object'){ 
                args[index] = JSON.stringify(args[index],null,'\t').replace(/\n/g,'<br>').replace(/\t/g,'&nbsp;&nbsp;&nbsp;');
            }
        }
        var message = args.join(' ');
        console.messages.push(message);
        // instead of a fallback function we use the next few lines to output logs
        // at the bottom of the page with jQuery
        if($){
            if($('#_console_log').length == 0) $('body').append($('<div />').attr('id', '_console_log'));
            $('#_console_log').append(message).append($('<br />'));
        }
    }
} 

I hope this is helpful:-)

getActivity() returns null in Fragment function

You can using onAttach or if you do not want to put onAttach everywhere then you can put a method that returns ApplicationContext on the main App class :

public class App {
    ...  
    private static Context context;

    @Override
    public void onCreate() {
        super.onCreate();
        context = this;
    }

    public static Context getContext() {
        return context;
    }
    ...
}

After that you can re-use it everywhere in all over your project, like this :

App.getContext().getString(id)

Please let me know if this does not work for you.

HTML Button Close Window

November 2019: onclick="self.close()" still works in Chrome while Edge gives a warning that must be confirmed before it will close.

On the other hand the solution onclick="window.open('', '_self', ''); window.close();" works in both.

Could not load file or assembly 'Newtonsoft.Json' or one of its dependencies. Manifest definition does not match the assembly reference

I struggled with this recently with and older project.

I managed to track down the problem after checking what version of the dll that actually was in the bin folder.

I had a post-build script that copied dependent assemblies from a dll library folder to the bin folder. A common setup from the days before nuget.

So every time I built the post-build script replaced the correct version of Json.net with the older one

How to filter by string in JSONPath?

The browser testing tools while convenient can be a bit deceiving. Consider:

{
  "resourceType": "Encounter",
  "id": "EMR56788",
  "text": {
    "status": "generated",
    "div": "Patient admitted with chest pains</div>"
  },
  "status": "in-progress",
  "class": "inpatient",
  "patient": {
    "reference": "Patient/P12345",
    "display": "Roy Batty"
  }
}

Most tools returned this as false:

$[?(@.class==inpatient)]

But when I executed against

<dependency>
    <groupId>com.jayway.jsonpath</groupId>
    <artifactId>json-path</artifactId>
    <version>1.2.0</version>
</dependency>

It returned true. I recommend writing a simple unit test to verify rather than rely on the browser testing tools.

sql: check if entry in table A exists in table B

This also works

SELECT *
FROM tableB
WHERE ID NOT IN (
  SELECT ID FROM tableA
);

Fastest way to check if a string matches a regexp in ruby?

This is a simple benchmark:

require 'benchmark'

"test123" =~ /1/
=> 4
Benchmark.measure{ 1000000.times { "test123" =~ /1/ } }
=>   0.610000   0.000000   0.610000 (  0.578133)

"test123"[/1/]
=> "1"
Benchmark.measure{ 1000000.times { "test123"[/1/] } }
=>   0.718000   0.000000   0.718000 (  0.750010)

irb(main):019:0> "test123".match(/1/)
=> #<MatchData "1">
Benchmark.measure{ 1000000.times { "test123".match(/1/) } }
=>   1.703000   0.000000   1.703000 (  1.578146)

So =~ is faster but it depends what you want to have as a returned value. If you just want to check if the text contains a regex or not use =~

How can I iterate over the elements in Hashmap?

Need Key & Value in Iteration

Use entrySet() to iterate through Map and need to access value and key:

Map<String, Person> hm = new HashMap<String, Person>();

hm.put("A", new Person("p1"));
hm.put("B", new Person("p2"));
hm.put("C", new Person("p3"));
hm.put("D", new Person("p4"));
hm.put("E", new Person("p5"));

Set<Map.Entry<String, Person>> set = hm.entrySet();

for (Map.Entry<String, Person> me : set) {
  System.out.println("Key :"+me.getKey() +" Name : "+ me.getValue().getName()+"Age :"+me.getValue().getAge());

}

Need Key in Iteration

If you want just to iterate over keys of map you can use keySet()

for(String key: map.keySet()) {
     Person value = map.get(key); 
}

Need Value in Iteration

If you just want to iterate over values of map you can use values()

for(Person person: map.values()) {

}

When should I use Async Controllers in ASP.NET MVC?

Asynchronous action methods are useful when an action must perform several independent long running operations.

A typical use for the AsyncController class is long-running Web service calls.

Should my database calls be asynchronous ?

The IIS thread pool can often handle many more simultaneous blocking requests than a database server. If the database is the bottleneck, asynchronous calls will not speed up the database response. Without a throttling mechanism, efficiently dispatching more work to an overwhelmed database server by using asynchronous calls merely shifts more of the burden to the database. If your DB is the bottleneck, asynchronous calls won’t be the magic bullet.

You should have a look at 1 and 2 references

Derived from @PanagiotisKanavos comments:

Moreover, async doesn't mean parallel. Asynchronous execution frees a valuable threadpool thread from blocking for an external resource, for no complexity or performance cost. This means the same IIS machine can handle more concurrent requests, not that it will run faster.

You should also consider that blocking calls start with a CPU-intensive spinwait. During stress times, blocking calls will result in escalating delays and app pool recycling. Asynchronous calls simply avoid this

An App ID with Identifier '' is not available. Please enter a different string

For me, I was trying to create an app ID for an Enterprise app. The app ID had "xxx.ios.yyy" in it and it did not like the .ios. bit in the middle. As soon as I removed the ".ios" part I was able to successfully register it. This happened to me twice with two different app IDs of different length, and in each case, removing the ".ios" segment fixed the problem.

How do I correctly use "Not Equal" in MS Access?

Like this

SELECT DISTINCT Table1.Column1
FROM Table1
WHERE NOT EXISTS( SELECT * FROM Table2
    WHERE Table1.Column1 = Table2.Column1  )

You want NOT EXISTS, not "Not Equal"


By the way, you rarely want to write a FROM clause like this:

FROM Table1, Table2

as this means "FROM all combinations of every row in Table1 with every row in Table2..." Usually that's a lot more result rows than you ever want to see. And in the rare case that you really do want to do that, the more accepted syntax is:

FROM Table1 CROSS JOIN Table2

How to pad a string to a fixed length with spaces in Python?

You can use rjust and ljust functions to add specific characters before or after a string to reach a specific length.

numStr = '69' 
numStr = numStr.rjust(5, '*')

The result is 69*****

And for the left:

numStr = '69' 
numStr = numStr.ljust(3, '#')

The result will be ###69

Also to add zeros you can simply use:

numstr.zfill(8)

Which gives you 69000000 as the result.

How to quickly clear a JavaScript Object?

You can delete the props, but don't delete variables. delete abc; is invalid in ES5 (and throws with use strict).

You can assign it to null to set it for deletion to the GC (it won't if you have other references to properties)

Setting length property on an object does not change anything. (it only, well, sets the property)

How do I select last 5 rows in a table without sorting?

Well, the "last five rows" are actually the last five rows depending on your clustered index. Your clustered index, by definition, is the way that he rows are ordered. So you really can't get the "last five rows" without some order. You can, however, get the last five rows as it pertains to the clustered index.

SELECT TOP 5 * FROM MyTable
ORDER BY MyCLusteredIndexColumn1, MyCLusteredIndexColumnq, ..., MyCLusteredIndexColumnN DESC

C++ Returning reference to local variable

This code snippet:

int& func1()
{
    int i;
    i = 1;
    return i;
}

will not work because you're returning an alias (a reference) to an object with a lifetime limited to the scope of the function call. That means once func1() returns, int i dies, making the reference returned from the function worthless because it now refers to an object that doesn't exist.

int main()
{
    int& p = func1();
    /* p is garbage */
}

The second version does work because the variable is allocated on the free store, which is not bound to the lifetime of the function call. However, you are responsible for deleteing the allocated int.

int* func2()
{
    int* p;
    p = new int;
    *p = 1;
    return p;
}

int main()
{
    int* p = func2();
    /* pointee still exists */
    delete p; // get rid of it
}

Typically you would wrap the pointer in some RAII class and/or a factory function so you don't have to delete it yourself.

In either case, you can just return the value itself (although I realize the example you provided was probably contrived):

int func3()
{
    return 1;
}

int main()
{
    int v = func3();
    // do whatever you want with the returned value
}

Note that it's perfectly fine to return big objects the same way func3() returns primitive values because just about every compiler nowadays implements some form of return value optimization:

class big_object 
{ 
public:
    big_object(/* constructor arguments */);
    ~big_object();
    big_object(const big_object& rhs);
    big_object& operator=(const big_object& rhs);
    /* public methods */
private:
    /* data members */
};

big_object func4()
{
    return big_object(/* constructor arguments */);
}

int main()
{
     // no copy is actually made, if your compiler supports RVO
    big_object o = func4();    
}

Interestingly, binding a temporary to a const reference is perfectly legal C++.

int main()
{
    // This works! The returned temporary will last as long as the reference exists
    const big_object& o = func4();    
    // This does *not* work! It's not legal C++ because reference is not const.
    // big_object& o = func4();  
}

Array to String PHP?

You can use json_encode()

<?php
$arr = array('a' => 1, 'b' => 2, 'c' => 3, 'd' => 4, 'e' => 5);

echo json_encode($arr);
?>

Later just use json_decode() to decode the string from your DB. Anything else is useless, JSON keeps the array relationship intact for later usage!

PHP random string generator

There are better alternatives to this. Many was already posted so I give you only your stuff back with fixes:

<?php
    function RandomString()
    {
        global $randstring ;
        $characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
        $randstring = '';
        for ($i = 0; $i < 10; $i++) {
            $randstring .= $characters[rand(0, strlen($characters))];
        }
        return $randstring;
    }

    RandomString();

    echo $randstring;
?>

Also you may be interested in:

<?php
    function RandomString()
    {
        global $randstring;
        $characters = str_split('0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ');
           array_filter ($characters,function($var)use($characters,&$randstring){
                $randstring .= $characters[rand(0, count($characters)-1)];
        });
        return $randstring;
    }

    RandomString();
    echo $randstring.'<hr>';

    //.. OR  ..
    $randstring = '';
    echo(RandomString());
?>

Or another one:

<?php
    function s($length){
      for($i=0;
          ($i<$length) and
          (
              ($what=rand(1,3))

              and

              (
                  (
                      ($what==1) and
                      ($t=rand(48, 57)
                  )
                  ) or

                  (
                      ($what==2) and
                      ($t=rand(65, 90))
                  ) or

                  (
                      ($what==3) and
                      ($t=rand(97, 122)
                  )
                  )
              ) and
              (print chr($t))
          );

          $i++)

              ;
    }
    s(10);
?>

Difference between using bean id and name in Spring configuration file

Either one would work. It depends on your needs:
If your bean identifier contains special character(s) for example (/viewSummary.html), it wont be allowed as the bean id, because it's not a valid XML ID. In such cases you could skip defining the bean id and supply the bean name instead.
The name attribute also helps in defining aliases for your bean, since it allows specifying multiple identifiers for a given bean.

How can I copy a Python string?

Copying a string can be done two ways either copy the location a = "a" b = a or you can clone which means b wont get affected when a is changed which is done by a = 'a' b = a[:]

What is the T-SQL syntax to connect to another SQL Server?

If you are connecting to multiple servers you should add a 'GO' before switching servers, or your sql statements will run against the wrong server.

e.g.

:CONNECT SERVER1
Select * from Table
GO
enter code here
:CONNECT SERVER1
Select * from Table
GO

http://www.sqlmatters.com/Articles/Changing%20the%20SQL%20Server%20connection%20within%20an%20SSMS%20Query%20Windows%20using%20SQLCMD%20Mode.aspx

What's better at freeing memory with PHP: unset() or $var = null

PHP 7 is already worked on such memory management issues and its reduced up-to minimal usage.

<?php
  $start = microtime(true);
  for ($i = 0; $i < 10000000; $i++) {
    $a = 'a';
    $a = NULL;
  }
  $elapsed = microtime(true) - $start;

  echo "took $elapsed seconds\r\n";

  $start = microtime(true);
  for ($i = 0; $i < 10000000; $i++) {
     $a = 'a';
     unset($a);
  }
  $elapsed = microtime(true) - $start;

  echo "took $elapsed seconds\r\n";

?>

PHP 7.1 Outpu:

took 0.16778993606567 seconds took 0.16630101203918 seconds

PHP: Get key from array?


$array = array(0 => 100, "color" => "red");
print_r(array_keys($array));

How to stop creating .DS_Store on Mac?

Put following line into your ".profile" file.

Open .profile file and copy this line

find ~/ -name '.DS_Store' -delete

When you open terminal window it will automatically delete your .DS_Store file for you.

How to get a unix script to run every 15 seconds?

I wrote a scheduler faster than cron. I have also implemented an overlapping guard. You can configure the scheduler to not start new process if previous one is still running. Take a look at https://github.com/sioux1977/scheduler/wiki

How to set default font family for entire Android app

Not talk about performance, for custom font you can have a recursive method loop through all the views and set typeface if it's a TextView:

public class Font {
    public static void setAllTextView(ViewGroup parent) {
        for (int i = parent.getChildCount() - 1; i >= 0; i--) {
            final View child = parent.getChildAt(i);
            if (child instanceof ViewGroup) {
                setAllTextView((ViewGroup) child);
            } else if (child instanceof TextView) {
                ((TextView) child).setTypeface(getFont());
            }
        }
    }

    public static Typeface getFont() {
        return Typeface.createFromAsset(YourApplicationContext.getInstance().getAssets(), "fonts/whateverfont.ttf");
    }
}

In all your activity, pass current ViewGroup to it after setContentView and it's done:

ViewGroup group = (ViewGroup) getWindow().getDecorView().findViewById(android.R.id.content);
Font.setAllTextView(group);

For fragment you can do something similar.

Where is android_sdk_root? and how do I set it.?

android_sdk_root is a system variable which points to root folder of android sdk tools. You probably get the error because the variable is not set. To set it in Android Studio go to:

  1. File -> project Structure into Project Structure
  2. Left -> SDK Location
  3. SDK location select Android SDK location

If you have installed android SDK please refer to this answer to find the path to it: https://stackoverflow.com/a/15702396/3625900

Any way to make plot points in scatterplot more transparent in R?

If you decide to use ggplot2, you can set transparency of overlapping points using the alpha argument.

e.g.

library(ggplot2)
ggplot(diamonds, aes(carat, price)) + geom_point(alpha = 1/40)

What's the difference between Instant and LocalDateTime?

One main difference is the Local part of LocalDateTime. If you live in Germany and create a LocalDateTime instance and someone else lives in USA and creates another instance at the very same moment (provided the clocks are properly set) - the value of those objects would actually be different. This does not apply to Instant, which is calculated independently from time zone.

LocalDateTime stores date and time without timezone, but it's initial value is timezone dependent. Instant's is not.

Moreover, LocalDateTime provides methods for manipulating date components like days, hours, months. An Instant does not.

apart from the nanosecond precision advantage of Instant and the time-zone part of LocalDateTime

Both classes have the same precision. LocalDateTime does not store timezone. Read javadocs thoroughly, because you may make a big mistake with such invalid assumptions: Instant and LocalDateTime.

Casting to string in JavaScript

According to this JSPerf test, they differ in speed. But unless you're going to use them in huge amounts, any of them should perform fine.

For completeness: As asawyer already mentioned, you can also use the .toString() method.

How to change int into int64?

This is probably obvious, but simplest:

i64 := int64(23)

How to convert float number to Binary?

The float value is stored in IEEE 754 format so we can't convert it directly like integer, char to binary.

But we can convert float to binary through a pointer.

#include <stdio.h>

int main()
{
    float a = 7.5;
    int i;
    int * p;

    p = &a;
    for (i = sizeof(int) * 8 - 1; i >= 0; i--)
    {   
        printf("%d", (*p) >> i & 1); 
    }   

    return 0;
}

Output

0 10000001 11100000000000000000000

Spaces added for clarification, they are not included as part of the program.

sql searching multiple words in a string

Oracle SQL :

select * 
from MY_TABLE
where REGEXP_LIKE (company , 'Microsodt industry | goglge auto car | oracles    database')
  • company - is the database column name.
  • results - this SQL will show you if company column rows contain one of those companies (OR phrase) please note that : no wild characters are needed, it's built in.

more info at : http://www.techonthenet.com/oracle/regexp_like.php

How do I capitalize first letter of first name and last name in C#?

CultureInfo.CurrentCulture.TextInfo.ToTitleCase("hello world");

How to find GCD, LCM on a set of numbers

for gcd you cad do as below:

    String[] ss = new Scanner(System.in).nextLine().split("\\s+");
    BigInteger bi,bi2 = null;
    bi2 = new BigInteger(ss[1]);
    for(int i = 0 ; i<ss.length-1 ; i+=2 )
    {
        bi = new BigInteger(ss[i]);
        bi2 = bi.gcd(bi2);
    }
    System.out.println(bi2.toString());

Responsive css styles on mobile devices ONLY

Yes, this can be done via javascript feature detection ( or browser detection , e.g. Modernizr ) . Then, use yepnope.js to load required resources ( JS and/or CSS )

How to extract this specific substring in SQL Server?

An alternative to the answer provided by @Marc

SELECT SUBSTRING(LEFT(YOUR_FIELD, CHARINDEX('[', YOUR_FIELD) - 1), CHARINDEX(';', YOUR_FIELD) + 1, 100)
FROM YOUR_TABLE
WHERE CHARINDEX('[', YOUR_FIELD) > 0 AND
    CHARINDEX(';', YOUR_FIELD) > 0;

This makes sure the delimiters exist, and solves an issue with the currently accepted answer where doing the LEFT last is working with the position of the last delimiter in the original string, rather than the revised substring.

sprintf like functionality in Python

Something like...

greetings = 'Hello {name}'.format(name = 'John')

Hello John

Reading a binary file with python

I too found Python lacking when it comes to reading and writing binary files, so I wrote a small module (for Python 3.6+).

With binaryfile you'd do something like this (I'm guessing, since I don't know Fortran):

import binaryfile

def particle_file(f):
    f.array('group_ids')  # Declare group_ids to be an array (so we can use it in a loop)
    f.skip(4)  # Bytes 1-4
    num_particles = f.count('num_particles', 'group_ids', 4)  # Bytes 5-8
    f.int('num_groups', 4)  # Bytes 9-12
    f.skip(8)  # Bytes 13-20
    for i in range(num_particles):
        f.struct('group_ids', '>f')  # 4 bytes x num_particles
    f.skip(4)

with open('myfile.bin', 'rb') as fh:
    result = binaryfile.read(fh, particle_file)
print(result)

Which produces an output like this:

{
    'group_ids': [(1.0,), (0.0,), (2.0,), (0.0,), (1.0,)],
    '__skipped': [b'\x00\x00\x00\x08', b'\x00\x00\x00\x08\x00\x00\x00\x14', b'\x00\x00\x00\x14'],
    'num_particles': 5,
    'num_groups': 3
}

I used skip() to skip the additional data Fortran adds, but you may want to add a utility to handle Fortran records properly instead. If you do, a pull request would be welcome.

Nginx: Job for nginx.service failed because the control process exited

Try set a user in nginx.conf, maybe that's why he can not start the service:

User www-data;

How can I do SELECT UNIQUE with LINQ?

The Distinct() is going to mess up the ordering, so you'll have to the sorting after that.

var uniqueColors = 
               (from dbo in database.MainTable 
                 where dbo.Property == true 
                 select dbo.Color.Name).Distinct().OrderBy(name=>name);

What is the preferred Bash shebang?

#!/bin/sh

as most scripts do not need specific bash feature and should be written for sh.

Also, this makes scripts work on the BSDs, which do not have bash per default.

tqdm in Jupyter Notebook prints new progress bars repeatedly

None of the above works for me. I find that running the following sorts this issue after error (It just clears all the instances of progress bars in the background):

from tqdm import tqdm

# blah blah your code errored

tqdm._instances.clear()

Maximum size of a varchar(max) variable

As far as I can tell there is no upper limit in 2008.

In SQL Server 2005 the code in your question fails on the assignment to the @GGMMsg variable with

Attempting to grow LOB beyond maximum allowed size of 2,147,483,647 bytes.

the code below fails with

REPLICATE: The length of the result exceeds the length limit (2GB) of the target large type.

However it appears these limitations have quietly been lifted. On 2008

DECLARE @y VARCHAR(MAX) = REPLICATE(CAST('X' AS VARCHAR(MAX)),92681); 

SET @y = REPLICATE(@y,92681);

SELECT LEN(@y) 

Returns

8589767761

I ran this on my 32 bit desktop machine so this 8GB string is way in excess of addressable memory

Running

select internal_objects_alloc_page_count
from sys.dm_db_task_space_usage
WHERE session_id = @@spid

Returned

internal_objects_alloc_page_co 
------------------------------ 
2144456    

so I presume this all just gets stored in LOB pages in tempdb with no validation on length. The page count growth was all associated with the SET @y = REPLICATE(@y,92681); statement. The initial variable assignment to @y and the LEN calculation did not increase this.

The reason for mentioning this is because the page count is hugely more than I was expecting. Assuming an 8KB page then this works out at 16.36 GB which is obviously more or less double what would seem to be necessary. I speculate that this is likely due to the inefficiency of the string concatenation operation needing to copy the entire huge string and append a chunk on to the end rather than being able to add to the end of the existing string. Unfortunately at the moment the .WRITE method isn't supported for varchar(max) variables.

Addition

I've also tested the behaviour with concatenating nvarchar(max) + nvarchar(max) and nvarchar(max) + varchar(max). Both of these allow the 2GB limit to be exceeded. Trying to then store the results of this in a table then fails however with the error message Attempting to grow LOB beyond maximum allowed size of 2147483647 bytes. again. The script for that is below (may take a long time to run).

DECLARE @y1 VARCHAR(MAX) = REPLICATE(CAST('X' AS VARCHAR(MAX)),2147483647); 
SET @y1 = @y1 + @y1;
SELECT LEN(@y1), DATALENGTH(@y1)  /*4294967294, 4294967292*/


DECLARE @y2 NVARCHAR(MAX) = REPLICATE(CAST('X' AS NVARCHAR(MAX)),1073741823); 
SET @y2 = @y2 + @y2;
SELECT LEN(@y2), DATALENGTH(@y2)  /*2147483646, 4294967292*/


DECLARE @y3 NVARCHAR(MAX) = @y2 + @y1
SELECT LEN(@y3), DATALENGTH(@y3)   /*6442450940, 12884901880*/

/*This attempt fails*/
SELECT @y1 y1, @y2 y2, @y3 y3
INTO Test

What is the difference between JOIN and JOIN FETCH when using JPA and Hibernate

In this two queries, you are using JOIN to query all employees that have at least one department associated.

But, the difference is: in the first query you are returning only the Employes for the Hibernate. In the second query, you are returning the Employes and all Departments associated.

So, if you use the second query, you will not need to do a new query to hit the database again to see the Departments of each Employee.

You can use the second query when you are sure that you will need the Department of each Employee. If you not need the Department, use the first query.

I recomend read this link if you need to apply some WHERE condition (what you probably will need): How to properly express JPQL "join fetch" with "where" clause as JPA 2 CriteriaQuery?

Update

If you don't use fetch and the Departments continue to be returned, is because your mapping between Employee and Department (a @OneToMany) are setted with FetchType.EAGER. In this case, any HQL (with fetch or not) query with FROM Employee will bring all Departments. Remember that all mapping *ToOne (@ManyToOne and @OneToOne) are EAGER by default.

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

What about combining coalesce and nullif?

SET @PreviousStartDate = coalesce(nullif(@PreviousStartDate, ''), '01/01/2010')

What is the difference/usage of homebrew, macports or other package installation tools?

Currently, Macports has many more packages (~18.6 K) than there are Homebrew formulae (~3.1K), owing to its maturity. Homebrew is slowly catching up though.

Macport packages tend to be maintained by a single person.

Macports can keep multiple versions of packages around, and you can enable or disable them to test things out. Sometimes this list can get corrupted and you have to manually edit it to get things back in order, although this is not too hard.

Both package managers will ask to be regularly updated. This can take some time.

Note: you can have both package managers on your system! It is not one or the other. Brew might complain but Macports won't.

Also, if you are dealing with python or ruby packages, use a virtual environment wherever possible.

What's the difference between __PRETTY_FUNCTION__, __FUNCTION__, __func__?

For those, who wonder how it goes in VS.

MSVC 2015 Update 1, cl.exe version 19.00.24215.1:

#include <iostream>

template<typename X, typename Y>
struct A
{
  template<typename Z>
  static void f()
  {
    std::cout << "from A::f():" << std::endl
      << __FUNCTION__ << std::endl
      << __func__ << std::endl
      << __FUNCSIG__ << std::endl;
  }
};

void main()
{
  std::cout << "from main():" << std::endl
    << __FUNCTION__ << std::endl
    << __func__ << std::endl
    << __FUNCSIG__ << std::endl << std::endl;

  A<int, float>::f<bool>();
}

output:

from main():
main
main
int __cdecl main(void)

from A::f():
A<int,float>::f
f
void __cdecl A<int,float>::f<bool>(void)

Using of __PRETTY_FUNCTION__ triggers undeclared identifier error, as expected.

Unable to create Android Virtual Device

For Ubuntu and running android-studio run to install the packages (these are not installed by default):

android update sdk

Link to download apache http server for 64bit windows.

Check out the link given it has Apache HTTP Server 2.4.2 x86 and x64 Windows Installers http://www.anindya.com/apache-http-server-2-4-2-x86-and-x64-windows-installers/

How do I show the schema of a table in a MySQL database?

Perhaps the question needs to be slightly more precise here about what is required because it can be read it two different ways. i.e.

  1. How do I get the structure/definition for a table in mysql?
  2. How do I get the name of the schema/database this table resides in?

Given the accepted answer, the OP clearly intended it to be interpreted the first way. For anybody reading the question the other way try

SELECT `table_schema` 
FROM `information_schema`.`tables` 
WHERE `table_name` = 'whatever';

Proper usage of .net MVC Html.CheckBoxFor

I had trouble getting this to work and added another solution for anyone wanting/ needing to use FromCollection.

Instead of:

@Html.CheckBoxFor(model => true, item.TemplateId) 

Format html helper like so:

@Html.CheckBoxFor(model => model.SomeProperty, new { @class = "form-control", Name = "SomeProperty"})

Then in the viewmodel/model wherever your logic is:

public void Save(FormCollection frm)
{   
    // to do instantiate object.

    instantiatedItem.SomeProperty = (frm["SomeProperty"] ?? "").Equals("true", StringComparison.CurrentCultureIgnoreCase);

    // to do and save changes in database.
}

How to run cron job every 2 hours

0 */2 * * *

The answer is from https://crontab.guru/every-2-hours. It is interesting.

Unable to load DLL 'SQLite.Interop.dll'

Copy "SQLite.Interop.dll" files for both x86 and x64 in debug folder. these files should copy into "x86" and "x64 folders in debug folder.

How to print an exception in Python 3?

Although if you want a code that is compatible with both python2 and python3 you can use this:

import logging
try:
    1/0
except Exception as e:
    if hasattr(e, 'message'):
        logging.warning('python2')
        logging.error(e.message)
    else:
        logging.warning('python3')
        logging.error(e)

Date Difference in php on days?

Below code will give the output for number of days, by taking out the difference between two dates..

$str = "Jul 02 2013";
$str = strtotime(date("M d Y ")) - (strtotime($str));
echo floor($str/3600/24);

Regular Expression to reformat a US phone number in Javascript

var numbers = "(123) 456-7890".replace(/[^\d]/g, ""); //This strips all characters that aren't digits
if (numbers.length != 10) //wrong format
    //handle error
var phone = "(" + numbers.substr(0, 3) + ") " + numbers.substr(3, 3) + "-" + numbers.substr(6); //Create format with substrings

500 internal server error, how to debug

You can turn on your PHP errors with error_reporting:

error_reporting(E_ALL);
ini_set('display_errors', 'on');

Edit: It's possible that even after putting this, errors still don't show up. This can be caused if there is a fatal error in the script. From PHP Runtime Configuration:

Although display_errors may be set at runtime (with ini_set()), it won't have any affect if the script has fatal errors. This is because the desired runtime action does not get executed.

You should set display_errors = 1 in your php.ini file and restart the server.

R Apply() function on specific dataframe columns

I think what you want is mapply. You could apply the function to all columns, and then just drop the columns you don't want. However, if you are applying different functions to different columns, it seems likely what you want is mutate, from the dplyr package.

Printing prime numbers from 1 through 100

I check if a number is prime or not with the following code( of course using sqrt ):

bool IsPrime(const unsigned int x)
{
  const unsigned int TOP
  = static_cast<int>(
      std::sqrt( static_cast<double>( x ) )
    ) + 1;

  for ( int i=2; i != TOP; ++i )
  {
    if (x % i == 0) return false;
  }
  return true;
}

I use this method to determine the primes:

#include <iostream>

using std::cout;
using std::cin;
using std::endl;

#include <cmath>

void initialize( unsigned int *, const unsigned int );
void show_list( const unsigned int *, const unsigned int );
void criba( unsigned int *, const unsigned int );
void setItem ( unsigned int *, const unsigned int, const unsigned int );

bool IsPrime(const unsigned int x)
{
  const unsigned int TOP
  = static_cast<int>(
      std::sqrt( static_cast<double>( x ) )
    ) + 1;

  for ( int i=2; i != TOP; ++i )
  {
    if (x % i == 0) return false;
  }
  return true;
}

int main()
{

    unsigned int *l;
    unsigned int n;

    cout << "Ingrese tope de criba" << endl;
    cin >> n;

    l = new unsigned int[n];

    initialize( l, n );

    cout << "Esta es la lista" << endl;
    show_list( l, n );

    criba( l, n );  

    cout << "Estos son los primos" << endl;
    show_list( l, n );
}

void initialize( unsigned int *l, const unsigned int n)
{
    for( int i = 0; i < n - 1; i++ )
        *( l + i ) = i + 2;
}

void show_list( const unsigned int *l, const unsigned int n)
{
    for( int i = 0; i < n - 1; i++ )
    {
        if( *( l + i ) != 0)
            cout << l[i] << " - ";
    }
    cout << endl;
}

void setItem( unsigned int *l, const unsigned int n, const unsigned int p)
{
    unsigned int i = 2;
    while( p * i <= n)
    {
        *( l + (i * p - 2) ) = 0;
        i++;
    }
}

void criba( unsigned int *l, const unsigned int n)
{
    for( int i = 0;  i * i <= n ; i++ )
     if( IsPrime ( *( l + i) ) )
        setItem( l, n, *(l + i) );      
}

Is there a way to access an iteration-counter in Java's for-each loop?

Here is an example of how I did this. This gets the index at the for each loop. Hope this helps.

public class CheckForEachLoop {

    public static void main(String[] args) {

        String[] months = new String[] { "JANUARY", "FEBRUARY", "MARCH", "APRIL", "MAY", "JUNE", "JULY", "AUGUST",
                "SEPTEMBER", "OCTOBER", "NOVEMBER", "DECEMBER" };
        for (String s : months) {
            if (s == months[2]) { // location where you can change
              doSomethingWith(s); // however many times s and months
                                  // doSomethingWith(s) will be completed and 
                                  // added together instead of counter
            }

        }
        System.out.println(s); 


    }
}

AltGr key not working, instead I have to use Ctrl+AltGr

I found a solution for my problem while writing my question !

Going into my remote session i tried two key combinations, and it solved the problem on my Desktop : Alt+Enter and Ctrl+Enter (i don't know which one solved the problem though)

I tried to reproduce the problem, but i couldn't... but i'm almost sure it's one of the key combinations described in the question above (since i experienced this problem several times)

So it seems the problem comes from the use of RDP (windows7 and 8)

Update 2017: Problem occurs on Windows 10 aswell.

What is the most efficient way to get first and last line of a text file?

Nobody mentioned using reversed:

f=open(file,"r")
r=reversed(f.readlines())
last_line_of_file = r.next()

Socket.IO handling disconnect event

For those like @sha1 wondering why the OP's code doesn't work -

OP's logic for deleting player at server side is in the handler for DelPlayer event, and the code that emits this event (DelPlayer) is in inside disconnected event callback of client.

The server side code that emits this disconnected event is inside the disconnect event callback which is fired when the socket loses connection. Since the socket already lost connection, disconnected event doesn't reach the client.


Accepted solution executes the logic on disconnect event at server side, which is fired when the socket disconnects, hence works.

how to get selected row value in the KendoUI

If you want to select particular element use below code

var gridRowData = $("<your grid name>").data("kendoGrid");
var selectedItem = gridRowData.dataItem(gridRowData.select());
var quote = selectedItem["<column name>"];

What is a good naming convention for vars, methods, etc in C++?

There are probably as many naming conventions as there are individuals, the debate being as endless (and sterile) as to which brace style to use and so forth.

So I'll have 2 advices:

  • be consistent within a project
  • don't use reserved identifiers (anything with two underscores or beginning with an underscore followed by an uppercase letter)

The rest is up to you.

When should we implement Serializable interface?

The answer to this question is, perhaps surprisingly, never, or more realistically, only when you are forced to for interoperability with legacy code. This is the recommendation in Effective Java, 3rd Edition by Joshua Bloch:

There is no reason to use Java serialization in any new system you write

Oracle's chief architect, Mark Reinhold, is on record as saying removing the current Java serialization mechanism is a long-term goal.


Why Java serialization is flawed

Java provides as part of the language a serialization scheme you can opt in to, by using the Serializable interface. This scheme however has several intractable flaws and should be treated as a failed experiment by the Java language designers.

  • It fundamentally pretends that one can talk about the serialized form of an object. But there are infinitely many serialization schemes, resulting in infinitely many serialized forms. By imposing one scheme, without any way of changing the scheme, applications can not use a scheme most appropriate for them.
  • It is implemented as an additional means of constructing objects, which bypasses any precondition checks your constructors or factory methods perform. Unless tricky, error prone, and difficult to test extra deserialization code is written, your code probably has a gaping security weakness.
  • Testing interoperability of different versions of the serialized form is very difficult.
  • Handling of immutable objects is troublesome.

What to do instead

Instead, use a serialization scheme that you can explicitly control. Such as Protocol Buffers, JSON, XML, or your own custom scheme.

How to detect page zoom level in all modern browsers?

I have a solution for this as of Jan 2016. Tested working in Chrome, Firefox and MS Edge browsers.

The principle is as follows. Collect 2 MouseEvent points that are far apart. Each mouse event comes with screen and document coordinates. Measure the distance between the 2 points in both coordinate systems. Although there are variable fixed offsets between the coordinate systems due to the browser furniture, the distance between the points should be identical if the page is not zoomed. The reason for specifying "far apart" (I put this as 12 pixels) is so that small zoom changes (e.g. 90% or 110%) are detectable.

Reference: https://developer.mozilla.org/en/docs/Web/Events/mousemove

Steps:

  1. Add a mouse move listener

    window.addEventListener("mousemove", function(event) {
        // handle event
    });
    
  2. Capture 4 measurements from mouse events:

    event.clientX, event.clientY, event.screenX, event.screenY
    
  3. Measure the distance d_c between the 2 points in the client system

  4. Measure the distance d_s between the 2 points in the screen system

  5. If d_c != d_s then zoom is applied. The difference between the two tells you the amount of zoom.

N.B. Only do the distance calculations rarely, e.g. when you can sample a new mouse event that's far from the previous one.

Limitations: Assumes user will move the mouse at least a little, and zoom is unknowable until this time.

Format of the initialization string does not conform to specification starting at index 0

My problem wasn't that the connection string I was providing was wrong, or that the connection string in the app.config I thought I was using was wrong, but that I was using the wrong app.config.

Cannot find name 'require' after upgrading to Angular4

Still not sure the answer, but a possible workaround is

import * as Chart from 'chart.js';

How can I Remove .DS_Store files from a Git repository?

Combining benzado and webmat's answers, updating with git rm, not failing on files found that aren't in repo, and making it paste-able generically for any user:

# remove any existing files from the repo, skipping over ones not in repo
find . -name .DS_Store -print0 | xargs -0 git rm --ignore-unmatch
# specify a global exclusion list
git config --global core.excludesfile ~/.gitignore
# adding .DS_Store to that list
echo .DS_Store >> ~/.gitignore

Appending a list or series to a pandas DataFrame as a row?

Sometimes it's easier to do all the appending outside of pandas, then, just create the DataFrame in one shot.

>>> import pandas as pd
>>> simple_list=[['a','b']]
>>> simple_list.append(['e','f'])
>>> df=pd.DataFrame(simple_list,columns=['col1','col2'])
   col1 col2
0    a    b
1    e    f

What does the keyword Set actually do in VBA?

set is used to assign a reference to an object. The C equivalent would be

 int i;
int* ref_i;

i = 4; // Assigning a value (in VBA: i = 4)
ref_i = &i; //assigning a reference (in VBA: set ref_i = i)

How do I create a comma delimited string from an ArrayList?

Something like:

String.Join(",", myArrayList.toArray(string.GetType()) );

Which basically loops ya know...

EDIT

how about:

string.Join(",", Array.ConvertAll<object, string>(a.ToArray(), Convert.ToString));

Android emulator: could not get wglGetExtensionsStringARB error

just change your JDK I installed the JDK of SUN not Oracle and it works for me....

How to change a string into uppercase

For questions on simple string manipulation the dir built-in function comes in handy. It gives you, among others, a list of methods of the argument, e.g., dir(s) returns a list containing upper.

Environment variables in Mac OS X

If you want to change environment variables permanently on macOS, set them in /etc/paths. Note, this file is read-only by default, so you'll have to chmod for write permissions.

How to sum the values of one column of a dataframe in spark/scala

Not sure this was around when this question was asked but:

df.describe().show("columnName")

gives mean, count, stdtev stats on a column. I think it returns on all columns if you just do .show()

Run JavaScript in Visual Studio Code

The shortcut for the integrated terminal is ctrl + `, then type node <filename>.

Alternatively you can create a task. This is the only code in my tasks.json:

{
// See https://go.microsoft.com/fwlink/?LinkId=733558
// for the documentation about the tasks.json format
"version": "0.1.0",
"command": "node",
"isShellCommand": true,
"args": ["${file}"],
"showOutput": "always"
}

From here create a shortcut. This is my keybindings.json:

// Place your key bindings in this file to overwrite the defaults
[
{   "key": "cmd+r",
"command": "workbench.action.tasks.runTask"
},
{   "key": "cmd+e",
"command": "workbench.action.output.toggleOutput"
}
]

This will open 'run' in the Command Pallete, but you still have to type or select with the mouse the task you want to run, in this case node. The second shortcut toggles the output panel, there's already a shortcut for it but these keys are next to each other and easier to work with.

How to convert C# nullable int to int

Int nullable to int conversion can be done like so:

v2=(int)v1;

Is there a label/goto in Python?

I found this in the official python Design and History FAQ.

Why is there no goto?

You can use exceptions to provide a “structured goto” that even works across function calls. Many feel that exceptions can conveniently emulate all reasonable uses of the “go” or “goto” constructs of C, Fortran, and other languages. For example:

class label(Exception): pass  # declare a label

try:
    ...
    if condition: raise label()  # goto label
    ...
except label:  # where to goto
    pass
... 

This doesn’t allow you to jump into the middle of a loop, but that’s usually considered an abuse of goto anyway. Use sparingly.

It's very nice that this is even mentioned in the official FAQ, and that a nice solution sample is provided. I really like python because its community is treating even goto like this ;)

Understanding string reversal via slicing

[::-1] gives a slice of the string a. the full syntax is a[begin:end:step] which gives a[begin], a[begin+step], ... a[end-1]. WHen step is negative, you start at end and move to begin.

Finally, begin defaults to the beginning of the sequence, end to the end, and step to -1.

MySQL: #126 - Incorrect key file for table

I got this message when writing to a table after reducing the ft_min_word_len (full text min word length). To solve it, re-create the index by repairing the table.

Why are only final variables accessible in anonymous class?

There is a trick that allows anonymous class to update data in the outer scope.

private void f(Button b, final int a) {
    final int[] res = new int[1];
    b.addClickHandler(new ClickHandler() {
        @Override
        public void onClick(ClickEvent event) {
            res[0] = a * 5;
        }
    });

    // But at this point handler is most likely not executed yet!
    // How should we now res[0] is ready?
}

However, this trick is not very good due to the synchronization issues. If handler is invoked later, you need to 1) synchronize access to res if handler was invoked from the different thread 2) need to have some sort of flag or indication that res was updated

This trick works OK, though, if anonymous class is invoked in the same thread immediately. Like:

// ...

final int[] res = new int[1];
Runnable r = new Runnable() { public void run() { res[0] = 123; } };
r.run();
System.out.println(res[0]);

// ...

How do I use T-SQL's Case/When?

SELECT
   CASE 
   WHEN xyz.something = 1 THEN 'SOMETEXT'
   WHEN xyz.somethingelse = 1 THEN 'SOMEOTHERTEXT'
   WHEN xyz.somethingelseagain = 2 THEN 'SOMEOTHERTEXTGOESHERE'
   ELSE 'SOMETHING UNKNOWN'
   END AS ColumnName;

Show/Hide Div on Scroll

i have a pretty answer try this code ;)

<div id="DivID">
</div>

$("#DivID").scrollview({ direction: 'y' });
$("#DivID > .ui-scrollbar").addClass("ui-scrollbar-visible");

Can I create view with parameter in MySQL?

Actually if you create func:

create function p1() returns INTEGER DETERMINISTIC NO SQL return @p1;

and view:

create view h_parm as
select * from sw_hardware_big where unit_id = p1() ;

Then you can call a view with a parameter:

select s.* from (select @p1:=12 p) parm , h_parm s;

I hope it helps.

show and hide divs based on radio button click

The hide selector was incorrect. I hid the blocks at page load and showed the selected value. I also changed the car div id's to make it easier to append the radio button value and create the proper id selector.

<div id="myRadioGroup">
  2 Cars<input type="radio" name="cars" checked="checked" value="2"  />
  3 Cars<input type="radio" name="cars" value="3" />
  <div id="car-2">
  2 Cars
  </div>
  <div id="car-3">
  3 Cars
  </div>
</div>

<script type="text/javascript">
$(document).ready(function(){ 
  $("div div").hide();
  $("#car-2").show();
  $("input[name$='cars']").click(function() {
      var test = $(this).val();
      $("div div").hide();
      $("#car-"+test).show();
  }); 
});
</script>

Colspan all columns

For IE 6, you'll want to equal colspan to the number of columns in your table. If you have 5 columns, then you'll want: colspan="5".

The reason is that IE handles colspans differently, it uses the HTML 3.2 specification:

IE implements the HTML 3.2 definition, it sets colspan=0 as colspan=1.

The bug is well documented.

Rails :include vs. :joins

I was recently reading more on difference between :joins and :includes in rails. Here is an explaination of what I understood (with examples :))

Consider this scenario:

  • A User has_many comments and a comment belongs_to a User.

  • The User model has the following attributes: Name(string), Age(integer). The Comment model has the following attributes:Content, user_id. For a comment a user_id can be null.

Joins:

:joins performs a inner join between two tables. Thus

Comment.joins(:user)

#=> <ActiveRecord::Relation [#<Comment id: 1, content: "Hi I am Aaditi.This is my first   comment!", user_id: 1, created_at: "2014-11-12 18:29:24", updated_at: "2014-11-12 18:29:24">, 
     #<Comment id: 2, content: "Hi I am Ankita.This is my first comment!", user_id: 2, created_at: "2014-11-12 18:29:29", updated_at: "2014-11-12 18:29:29">,    
     #<Comment id: 3, content: "Hi I am John.This is my first comment!", user_id: 3, created_at: "2014-11-12 18:30:25", updated_at: "2014-11-12 18:30:25">]>

will fetch all records where user_id (of comments table) is equal to user.id (users table). Thus if you do

Comment.joins(:user).where("comments.user_id is null")

#=> <ActiveRecord::Relation []>

You will get a empty array as shown.

Moreover joins does not load the joined table in memory. Thus if you do

comment_1 = Comment.joins(:user).first

comment_1.user.age
#=>?[1m?[36mUser Load (0.0ms)?[0m  ?[1mSELECT "users".* FROM "users" WHERE "users"."id" = ? ORDER BY "users"."id" ASC LIMIT 1?[0m  [["id", 1]]
#=> 24

As you see, comment_1.user.age will fire a database query again in the background to get the results

Includes:

:includes performs a left outer join between the two tables. Thus

Comment.includes(:user)

#=><ActiveRecord::Relation [#<Comment id: 1, content: "Hi I am Aaditi.This is my first comment!", user_id: 1, created_at: "2014-11-12 18:29:24", updated_at: "2014-11-12 18:29:24">,
   #<Comment id: 2, content: "Hi I am Ankita.This is my first comment!", user_id: 2, created_at: "2014-11-12 18:29:29", updated_at: "2014-11-12 18:29:29">,
   #<Comment id: 3, content: "Hi I am John.This is my first comment!", user_id: 3, created_at: "2014-11-12 18:30:25", updated_at: "2014-11-12 18:30:25">,    
   #<Comment id: 4, content: "Hi This is an anonymous comment!", user_id: nil, created_at: "2014-11-12 18:31:02", updated_at: "2014-11-12 18:31:02">]>

will result in a joined table with all the records from comments table. Thus if you do

Comment.includes(:user).where("comment.user_id is null")
#=> #<ActiveRecord::Relation [#<Comment id: 4, content: "Hi This is an anonymous comment!", user_id: nil, created_at: "2014-11-12 18:31:02", updated_at: "2014-11-12 18:31:02">]>

it will fetch records where comments.user_id is nil as shown.

Moreover includes loads both the tables in the memory. Thus if you do

comment_1 = Comment.includes(:user).first

comment_1.user.age
#=> 24

As you can notice comment_1.user.age simply loads the result from memory without firing a database query in the background.

How to create a popup windows in javafx

Have you looked into ControlsFx Popover control.


import org.controlsfx.control.PopOver;
import org.controlsfx.control.PopOver.ArrowLocation;

private PopOver item;

final Scene scene = addItemButton.getScene();

final Point2D windowCoord = new Point2D(scene.getWindow()
        .getX(), scene.getWindow().getY());

final Point2D sceneCoord = new Point2D(scene.getX(), scene.
                getY());

final Point2D nodeCoord = addItemButton.localToScene(0.0,
                        0.0);
final double clickX = Math.round(windowCoord.getX()
    + sceneCoord.getY() + nodeCoord.getX());

final double clickY = Math.round(windowCoord.getY()
        + sceneCoord.getY() + nodeCoord.getY());
item.setContentNode(addItemScreen);
item.setArrowLocation(ArrowLocation.BOTTOM_LEFT);
item.setCornerRadius(4);                            
item.setDetachedTitle("Add New Item");
item.show(addItemButton.getParent(), clickX, clickY);

This is only an example but a PopOver sounds like it could accomplish what you want. Check out the documentation for more info.

Important note: ControlsFX will only work on JavaFX 8.0 b118 or later.

WPF Timer Like C# Timer

The usual WPF timer is the DispatcherTimer, which is not a control but used in code. It basically works the same way like the WinForms timer:

System.Windows.Threading.DispatcherTimer dispatcherTimer = new System.Windows.Threading.DispatcherTimer();
dispatcherTimer.Tick += dispatcherTimer_Tick;
dispatcherTimer.Interval = new TimeSpan(0,0,1);
dispatcherTimer.Start();


private void dispatcherTimer_Tick(object sender, EventArgs e)
{
  // code goes here
}

More on the DispatcherTimer can be found here

C# Inserting Data from a form into an access Database

This answer will help in case, If you are working with Data Bases then mostly take the help of try-catch block statement, which will help and guide you with your code. Here i am showing you that how to insert some values in Data Base with a Button Click Event.

 private void button2_Click(object sender, EventArgs e)
    {
        System.Data.OleDb.OleDbConnection conn = new System.Data.OleDb.OleDbConnection();
        conn.ConnectionString = @"Provider=Microsoft.ACE.OLEDB.12.0;" +
    @"Data source= C:\Users\pir fahim shah\Documents\TravelAgency.accdb";

     try
       {
           conn.Open();
           String ticketno=textBox1.Text.ToString();                 
           String Purchaseprice=textBox2.Text.ToString();
           String sellprice=textBox3.Text.ToString();
           String my_querry = "INSERT INTO Table1(TicketNo,Sellprice,Purchaseprice)VALUES('"+ticketno+"','"+sellprice+"','"+Purchaseprice+"')";

            OleDbCommand cmd = new OleDbCommand(my_querry, conn);
            cmd.ExecuteNonQuery();

            MessageBox.Show("Data saved successfuly...!");
          }
         catch (Exception ex)
         {
             MessageBox.Show("Failed due to"+ex.Message);
         }
         finally
         {
             conn.Close();
         }

How do I execute a bash script in Terminal?

cd to the directory that contains the script, or put it in a bin folder that is in your $PATH

then type

./scriptname.sh

if in the same directory or

scriptname.sh

if it's in the bin folder.

How to get the focused element with jQuery?

If you want to confirm if focus is with an element then

if ($('#inputId').is(':focus')) {
    //your code
}

ngFor with index as value in attribute

Just an update to this, Thierry's answer is still correct, but there has been an update to Angular2 with regards to:

<ul *ngFor="let item of items; let i = index" [attr.data-index]="i">
  <li>{{item}}</li>
</ul>

The #i = index should now be let i = index

EDIT/UPDATE:

The *ngFor should be on the element you're wanting to foreach, so for this example it should be:

<ul>
  <li *ngFor="let item of items; let i = index" [attr.data-index]="i">{{item}}</li>
</ul>

EDIT/UPDATE

Angular 5

<ul>
  <li *ngFor="let item of items; index as i" [attr.data-index]="i">{{item}}</li>
</ul>

EDIIT/UPDATE

Angular 7/8

<ul *ngFor="let item of items; index as i">
  <li [attr.data-index]="i">{{item}}</li>
</ul>

How to generate XML file dynamically using PHP?

I'd use SimpleXMLElement.

<?php

$xml = new SimpleXMLElement('<xml/>');

for ($i = 1; $i <= 8; ++$i) {
    $track = $xml->addChild('track');
    $track->addChild('path', "song$i.mp3");
    $track->addChild('title', "Track $i - Track Title");
}

Header('Content-type: text/xml');
print($xml->asXML());

Tell Ruby Program to Wait some amount of time

Like this:

sleep(num_secs)

The num_secs value can be an integer or float.

Also, if you're writing this within a Rails app, or have included the ActiveSupport library in your project, you can construct longer intervals using the following convenience syntax:

sleep(4.minutes)
# or, even longer...
sleep(2.hours); sleep(3.days) # etc., etc.
# or shorter
sleep(0.5) # half a second

jQuery: more than one handler for same event

Both handlers will run, the jQuery event model allows multiple handlers on one element, therefore a later handler does not override an older handler.

The handlers will execute in the order in which they were bound.

Pass variable to function in jquery AJAX success callback

I've meet the probleme recently. The trouble is coming when the filename lenght is greather than 20 characters. So the bypass is to change your filename length, but the trick is also a good one.

$.ajaxSetup({async: false}); // passage en mode synchrone
$.ajax({
   url: pathpays,
   success: function(data) {
      //debug(data);
      $(data).find("a:contains(.png),a:contains(.jpg)").each(function() {
         var image = $(this).attr("href");
         // will loop through
         debug("Found a file: " + image);
         text +=  '<img class="arrondie" src="' + pathpays + image + '" />';
      });
      text = text + '</div>';
      //debug(text);
   }
});

After more investigation the trouble is coming from ajax request: Put an eye to the html code returned by ajax:

<a href="Paris-Palais-de-la-cite%20-%20Copie.jpg">Paris-Palais-de-la-c..&gt;</a>
</td>
<td align="right">2015-09-05 09:50 </td>
<td align="right">4.3K</td>
<td>&nbsp;</td>
</tr>

As you can see the filename is splitted after the character 20, so the $(data).find("a:contains(.png)) is not able to find the correct extention.

But if you check the value of the href parameter it contents the fullname of the file.

I dont know if I can to ask to ajax to return the full filename in the text area?

Hope to be clear

I've found the right test to gather all files:

$(data).find("[href$='.jpg'],[href$='.png']").each(function() {  
var image = $(this).attr("href");

Fixed GridView Header with horizontal and vertical scrolling in asp.net

It is possible to apply the specific GridView / Table layout via custom CSS rules (as it was discussed in the <table><tbody> scrollable? thread) to fix GridView's Header. However, this approach will not work in all browsers. The 3-rd ASP.NET GridView controls (such as the ASPxGridView from DevExpress component vendor provide this functionality.

Check also the following CodeProject solutions:

Printing hexadecimal characters in C

You are probably printing from a signed char array. Either print from an unsigned char array or mask the value with 0xff: e.g. ar[i] & 0xFF. The c0 values are being sign extended because the high (sign) bit is set.

How to install PyQt5 on Windows?

If you are facing problem with pip3 install pyqt5 then try pip3 install pyqt5==5.12.0
This solved the problem for me

How can you search Google Programmatically Java API

Indeed there is an API to search google programmatically. The API is called google custom search. For using this API, you will need an Google Developer API key and a cx key. A simple procedure for accessing google search from java program is explained in my blog.

Now dead, here is the Wayback Machine link.

How do I use su to execute the rest of the bash script as that user?

Use sudo instead

EDIT: As Douglas pointed out, you can not use cd in sudo since it is not an external command. You have to run the commands in a subshell to make the cd work.

sudo -u $USERNAME -H sh -c "cd ~/$PROJECT; svn update"

sudo -u $USERNAME -H cd ~/$PROJECT
sudo -u $USERNAME svn update

You may be asked to input that user's password, but only once.

How can I add a Google search box to my website?

No need to embed! Just simply send the user to google and add the var in the search like this: (Remember, code might not work on this, so try in a browser if it doesn't.) Hope it works!

<textarea id="Blah"></textarea><button onclick="search()">Search</button>
<script>
function search() {
var Blah = document.getElementById("Blah").value;
location.replace("https://www.google.com/search?q=" + Blah + "");
}
</script>

_x000D_
_x000D_
    function search() {_x000D_
    var Blah = document.getElementById("Blah").value;_x000D_
    location.replace("https://www.google.com/search?q=" + Blah + "");_x000D_
    }
_x000D_
<textarea id="Blah"></textarea><button onclick="search()">Search</button>
_x000D_
_x000D_
_x000D_

Creating lowpass filter in SciPy - understanding methods and units

A few comments:

  • The Nyquist frequency is half the sampling rate.
  • You are working with regularly sampled data, so you want a digital filter, not an analog filter. This means you should not use analog=True in the call to butter, and you should use scipy.signal.freqz (not freqs) to generate the frequency response.
  • One goal of those short utility functions is to allow you to leave all your frequencies expressed in Hz. You shouldn't have to convert to rad/sec. As long as you express your frequencies with consistent units, the scaling in the utility functions takes care of the normalization for you.

Here's my modified version of your script, followed by the plot that it generates.

import numpy as np
from scipy.signal import butter, lfilter, freqz
import matplotlib.pyplot as plt


def butter_lowpass(cutoff, fs, order=5):
    nyq = 0.5 * fs
    normal_cutoff = cutoff / nyq
    b, a = butter(order, normal_cutoff, btype='low', analog=False)
    return b, a

def butter_lowpass_filter(data, cutoff, fs, order=5):
    b, a = butter_lowpass(cutoff, fs, order=order)
    y = lfilter(b, a, data)
    return y


# Filter requirements.
order = 6
fs = 30.0       # sample rate, Hz
cutoff = 3.667  # desired cutoff frequency of the filter, Hz

# Get the filter coefficients so we can check its frequency response.
b, a = butter_lowpass(cutoff, fs, order)

# Plot the frequency response.
w, h = freqz(b, a, worN=8000)
plt.subplot(2, 1, 1)
plt.plot(0.5*fs*w/np.pi, np.abs(h), 'b')
plt.plot(cutoff, 0.5*np.sqrt(2), 'ko')
plt.axvline(cutoff, color='k')
plt.xlim(0, 0.5*fs)
plt.title("Lowpass Filter Frequency Response")
plt.xlabel('Frequency [Hz]')
plt.grid()


# Demonstrate the use of the filter.
# First make some data to be filtered.
T = 5.0         # seconds
n = int(T * fs) # total number of samples
t = np.linspace(0, T, n, endpoint=False)
# "Noisy" data.  We want to recover the 1.2 Hz signal from this.
data = np.sin(1.2*2*np.pi*t) + 1.5*np.cos(9*2*np.pi*t) + 0.5*np.sin(12.0*2*np.pi*t)

# Filter the data, and plot both the original and filtered signals.
y = butter_lowpass_filter(data, cutoff, fs, order)

plt.subplot(2, 1, 2)
plt.plot(t, data, 'b-', label='data')
plt.plot(t, y, 'g-', linewidth=2, label='filtered data')
plt.xlabel('Time [sec]')
plt.grid()
plt.legend()

plt.subplots_adjust(hspace=0.35)
plt.show()

lowpass example

Logging with Retrofit 2

You can also add Facebook's Stetho and look at the network traces in Chrome: http://facebook.github.io/stetho/

final OkHttpClient.Builder builder = new OkHttpClient.Builder();
if (BuildConfig.DEBUG) {
    builder.networkInterceptors().add(new StethoInterceptor());
}

Then open "chrome://inspect" in Chrome...

Best way to get identity of inserted row?

I'm saying the same thing as the other guys, so everyone's correct, I'm just trying to make it more clear.

@@IDENTITY returns the id of the last thing that was inserted by your client's connection to the database.
Most of the time this works fine, but sometimes a trigger will go and insert a new row that you don't know about, and you'll get the ID from this new row, instead of the one you want

SCOPE_IDENTITY() solves this problem. It returns the id of the last thing that you inserted in the SQL code you sent to the database. If triggers go and create extra rows, they won't cause the wrong value to get returned. Hooray

IDENT_CURRENT returns the last ID that was inserted by anyone. If some other app happens to insert another row at an unforunate time, you'll get the ID of that row instead of your one.

If you want to play it safe, always use SCOPE_IDENTITY(). If you stick with @@IDENTITY and someone decides to add a trigger later on, all your code will break.

How to dynamically remove items from ListView on a button click?

Well you just remove the desired item from the list using the remove() method of your ArrayAdapter.

A possible way to do that would be:

Object toRemove = arrayAdapter.getItem([POSITION]);
arrayAdapter.remove(toRemove);

Another way would be to modify the ArrayList and call notifyDataSetChanged() on the ArrayAdapter.

arrayList.remove([INDEX]);
arrayAdapter.notifyDataSetChanged();

How to download fetch response in react as file

You can use these two libs to download files http://danml.com/download.html https://github.com/eligrey/FileSaver.js/#filesaverjs

example

//  for FileSaver
import FileSaver from 'file-saver';
export function exportRecordToExcel(record) {
      return ({fetch}) => ({
        type: EXPORT_RECORD_TO_EXCEL,
        payload: {
          promise: fetch('/records/export', {
            credentials: 'same-origin',
            method: 'post',
            headers: {'Content-Type': 'application/json'},
            body: JSON.stringify(data)
          }).then(function(response) {
            return response.blob();
          }).then(function(blob) {
            FileSaver.saveAs(blob, 'nameFile.zip');
          })
        }
      });

//  for download 
let download = require('./download.min');
export function exportRecordToExcel(record) {
      return ({fetch}) => ({
        type: EXPORT_RECORD_TO_EXCEL,
        payload: {
          promise: fetch('/records/export', {
            credentials: 'same-origin',
            method: 'post',
            headers: {'Content-Type': 'application/json'},
            body: JSON.stringify(data)
          }).then(function(response) {
            return response.blob();
          }).then(function(blob) {
            download (blob);
          })
        }
      });

How to hide .php extension in .htaccess

The other option for using PHP scripts sans extension is

Options +MultiViews

Or even just following in the directories .htaccess:

DefaultType application/x-httpd-php

The latter allows having all filenames without extension script being treated as PHP scripts. While MultiViews makes the webserver look for alternatives, when just the basename is provided (there's a performance hit with that however).

How to display raw html code in PRE or something like it but without escaping it

echo '<pre>' . htmlspecialchars("<div><b>raw HTML</b></div>") . '</pre>';

I think that's what you're looking for?

In other words, use htmlspecialchars() in PHP

How to parse float with two decimal places in javascript?

You can use toFixed() to do that

var twoPlacedFloat = parseFloat(yourString).toFixed(2)

What is the difference between JavaScript and ECMAScript?

What is ECMAScript i.e. ES?

ECMAScript is a standard for a scripting language and the Javascript language is based on the ECMAScript standard.

Is Javascript exactly the same as ECMAScript?

  • No, Javascript is not exactly equivalent to ECMAScript.
  • The core features of Javascript are based on the ECMAScript standard, but Javascript also has other additional features that are not in the ECMA specifications/standard.

JavaScript = ECMAScript + DOM API;

DOM API like: document.getElementById('id');

Do other languages use the ECMAScript standard?

  • Yes, there are languages other than JavaScript that also implement the ECMAScript Standard as their core.
  • ActionScript (used by Adobe Flash) and JScript (used by Microsoft) are both languages that implement the ECMAScript standard.

Why is it called ECMAScript?

  • Javascript was originally created at Netscape, and they wanted to standardize the language. So, they submitted the language to the European Computer Manufacturer’s Association (ECMA) for standardization.
  • But, there were trademark issues with the name Javascript, and the standard became called ECMAScript, which is the name it holds today as well.
  • Because of trademark issues, Microsoft’s version of the language is called JScript – even though JScript is, at its core, the same language as Javascript.

How to right-align and justify-align in Markdown?

Aligning text in native markdown is not possible. However, you can align the text using inline HTML tags.

<div style="text-align: right"> your-text-here </div>

To justify, replace right with justify in the above.

I am getting an "Invalid Host header" message when connecting to webpack-dev-server remotely

The more secure option would be to add allowedHosts to your Webpack config like this:

module.exports = {
devServer: {
 allowedHosts: [
  'host.com',
  'subdomain.host.com',
  'subdomain2.host.com',
  'host2.com'
   ]
  }
};

The array contains all allowed host, you can also specify subdomians. check out more here

Provide an image for WhatsApp link sharing

Following actions helped in my case.

Putting image under the same host.

<meta property="og:url" content="https://www.same-host.com/whatsapp-image.png" />

Passing needed image to WhatsApp specifically by detecting its user agent by leading substring, example

WhatsApp/2.18.380 A

Waiting few seconds before actually pushing send button, so WhatsApp will have time to retrieve image and description from og metadata.

Enabling error display in PHP via htaccess only

If you want to see only fatal runtime errors:

php_value display_errors on
php_value error_reporting 4

Entity Framework throws exception - Invalid object name 'dbo.BaseCs'

If everything is fine with your ConnectionString check your DbSet collection name in you db context file. If that and database table names aren't matching you will also get this error.

So, for example, Categories, Products

public class ProductContext : DbContext 
{ 
    public DbSet<Category> Categories { get; set; } 
    public DbSet<Product> Products { get; set; } 
}

should match with actual database table names:

enter image description here

Spark DataFrame TimestampType - how to get Year, Month, Day values from field?

Actually, we really do not need to import any python library. We can separate the year, month, date using simple SQL. See the below example,

+----------+
|       _c0|
+----------+
|1872-11-30|
|1873-03-08|
|1874-03-07|
|1875-03-06|
|1876-03-04|
|1876-03-25|
|1877-03-03|
|1877-03-05|
|1878-03-02|
|1878-03-23|
|1879-01-18|

I have a date column in my data frame which contains the date, month and year and assume I want to extract only the year from the column.

df.createOrReplaceTempView("res")
sqlDF = spark.sql("SELECT EXTRACT(year from `_c0`) FROM res ")

Here I'm creating a temporary view and store the year values using this single line and the output will be,

+-----------------------+
|year(CAST(_c0 AS DATE))|
+-----------------------+
|                   1872|
|                   1873|
|                   1874|
|                   1875|
|                   1876|
|                   1876|
|                   1877|
|                   1877|
|                   1878|
|                   1878|
|                   1879|
|                   1879|
|                   1879|

Closure in Java 7

Java Closures are going to be a part of J2SE 8 and is set to be released by the end of 2012.

Java 8's closures support include the concept of Lambda Expressions, Method Reference, Constructor Reference and the Default Methods.

For more information and working examples for this please visit: http://amitrp.blogspot.in/2012/08/at-first-sight-with-closures-in-java.html

Matplotlib: "Unknown projection '3d'" error

Just to add to Joe Kington's answer (not enough reputation for a comment) there is a good example of mixing 2d and 3d plots in the documentation at http://matplotlib.org/examples/mplot3d/mixed_subplots_demo.html which shows projection='3d' working in combination with the Axes3D import.

from mpl_toolkits.mplot3d import Axes3D
...
ax = fig.add_subplot(2, 1, 1)
...
ax = fig.add_subplot(2, 1, 2, projection='3d')

In fact as long as the Axes3D import is present the line

from mpl_toolkits.mplot3d import Axes3D
...
ax = fig.gca(projection='3d')

as used by the OP also works. (checked with matplotlib version 1.3.1)

IOException: The process cannot access the file 'file path' because it is being used by another process

I had this problem and it was solved by following the code below

var _path=MyFile.FileName;
using (var stream = new FileStream
    (_path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
  { 
    // Your Code! ;
  }

Programmatically select a row in JTable

You can do it calling setRowSelectionInterval :

table.setRowSelectionInterval(0, 0);

to select the first row.

What should I do if the current ASP.NET session is null?

If your Session instance is null and your in an 'ashx' file, just implement the 'IRequiresSessionState' interface.

This interface doesn't have any members so you just need to add the interface name after the class declaration (C#):

public class MyAshxClass : IHttpHandler, IRequiresSessionState

Call a "local" function within module.exports from another function in module.exports?

To fix your issue, i have made few changes in bla.js and it is working,

var foo= function (req, res, next) {
  console.log('inside foo');
  return ("foo");
}

var  bar= function(req, res, next) {
  this.foo();
}
module.exports = {bar,foo};

and no modification in app.js

var bla = require('./bla.js');
console.log(bla.bar());

How to overlay images

You might want to check out this tutorial: http://www.webdesignerwall.com/tutorials/css-decorative-gallery/

In it the writer uses an empty span element to add an overlaying image. You can use jQuery to inject said span elements, if you'd like to keep your code as clean as possible. An example is also given in the aforementioned article.

Hope this helps!

-Dave

Disabling Warnings generated via _CRT_SECURE_NO_DEPRECATE

Combination of @[macbirdie] and @[Adrian Borchardt] answer. Which proves to be very useful in production environment (not messing up previously existing warning, especially during cross-platform compile)

#if (_MSC_VER >= 1400)         // Check MSC version
#pragma warning(push)
#pragma warning(disable: 4996) // Disable deprecation
#endif 
//...                          // ...
strcat(base, cat);             // Sample depreciated code
//...                          // ...
#if (_MSC_VER >= 1400)         // Check MSC version
#pragma warning(pop)           // Renable previous depreciations
#endif

Passing Multiple route params in Angular2

      new AsyncRoute({path: '/demo/:demoKey1/:demoKey2', loader: () => {
      return System.import('app/modules/demo/demo').then(m =>m.demoComponent);
       }, name: 'demoPage'}),
       export class demoComponent {
       onClick(){
            this._router.navigate( ['/demoPage', {demoKey1: "123", demoKey2: "234"}]);
          }
        }

PHP split alternative?

If you want to split a string into words, you can use explode() or str_word_count().

How can I adjust DIV width to contents

One way you can achieve this is setting display: inline-block; on the div. It is by default a block element, which will always fill the width it can fill (unless specifying width of course).

inline-block's only downside is that IE only supports it correctly from version 8. IE 6-7 only allows setting it on naturally inline elements, but there are hacks to solve this problem.

There are other options you have, you can either float it, or set position: absolute on it, but these also have other effects on layout, you need to decide which one fits your situation better.

instantiate a class from a variable in PHP?

If You Use Namespaces

In my own findings, I think it's good to mention that you (as far as I can tell) must declare the full namespace path of a class.

MyClass.php

namespace com\company\lib;
class MyClass {
}

index.php

namespace com\company\lib;

//Works fine
$i = new MyClass();

$cname = 'MyClass';

//Errors
//$i = new $cname;

//Works fine
$cname = "com\\company\\lib\\".$cname;
$i = new $cname;

Converting xml to string using C#

There's a much simpler way to convert your XmlDocument to a string; use the OuterXml property. The OuterXml property returns a string version of the xml.

public string GetXMLAsString(XmlDocument myxml)
{
    return myxml.OuterXml;
}

How to get year, month, day, hours, minutes, seconds and milliseconds of the current moment in Java?

Use the formatting pattern 'dd-MM-yyyy HH:mm:ss aa' to get date as 21-10-2020 20:53:42 pm

ImportError: No module named request

The SpeechRecognition library requires Python 3.3 or up:

Requirements

[...]

The first software requirement is Python 3.3 or better. This is required to use the library.

and from the Trove classifiers:

Programming Language :: Python
Programming Language :: Python :: 3
Programming Language :: Python :: 3.3
Programming Language :: Python :: 3.4

The urllib.request module is part of the Python 3 standard library; in Python 2 you'd use urllib2 here.

Is java.sql.Timestamp timezone specific?

You can use the below method to store the timestamp in database specific to your desired zone/zone Id.

ZonedDateTime zdt = ZonedDateTime.now(ZoneId.of("Asia/Calcutta")) ;
Timestamp timestamp = Timestamp.valueOf(zdt.toLocalDateTime());

A common mistake people do is use LocaleDateTime to get the timestamp of that instant which discards any information specif to your zone even if you try to convert it later. It does not understand the Zone.

Please note Timestamp is of the class java.sql.Timestamp.

What's the difference between ".equals" and "=="?

The equals( ) method and the == operator perform two different operations. The equals( ) method compares the characters inside a String object. The == operator compares two object references to see whether they refer to the same instance. The following program shows how two different String objects can contain the same characters, but references to these objects will not compare as equal:

// equals() vs ==
class EqualsNotEqualTo {
     public static void main(String args[]) {
          String s1 = "Hello";
          String s2 = new String(s1);
          System.out.println(s1 + " equals " + s2 + " -> " +
          s1.equals(s2));
          System.out.println(s1 + " == " + s2 + " -> " + (s1 == s2));
     }
}

The variable s1 refers to the String instance created by “Hello”. The object referred to by s2 is created with s1 as an initializer. Thus, the contents of the two String objects are identical, but they are distinct objects. This means that s1 and s2 do not refer to the same objects and are, therefore, not ==, as is shown here by the output of the preceding example:

Hello equals Hello -> true
Hello == Hello -> false