Programs & Examples On #Variable length array

A variable length array is an array in C99 and other languages whose size is unknown at compile time; instead, it's determined at runtime.

C compile error: "Variable-sized object may not be initialized"

I am assuming that you are using a C99 compiler (with support for dynamically sized arrays). The problem in your code is that at the time when the compilers sees your variable declaration it cannot know how many elements there are in the array (I am also assuming here, from the compiler error that length is not a compile time constant).

You must manually initialize that array:

int boardAux[length][length];
memset( boardAux, 0, length*length*sizeof(int) );

How can I initialize an array without knowing it size?

You can't... an array's size is always fixed in Java. Typically instead of using an array, you'd use an implementation of List<T> here - usually ArrayList<T>, but with plenty of other alternatives available.

You can create an array from the list as a final step, of course - or just change the signature of the method to return a List<T> to start with.

Ant if else condition?

Since ant 1.9.1 you can use a if:set condition :

How to use SVN, Branch? Tag? Trunk?

I asked myself the same questions when we came to implement Subversion here -- about 20 developers spread across 4 - 6 projects. I didn't find any one good source with ''the answer''. Here are some parts of how our answer has developed over the last 3 years:

-- commit as often as is useful; our rule of thumb is commit whenever you have done sufficient work that it would be a problem having to re-do it if the modifications got lost; sometimes I commit every 15 minutes or so, other times it might be days (yes, sometimes it takes me a day to write 1 line of code)

-- we use branches, as one of your earlier answers suggested, for different development paths; right now for one of our programs we have 3 active branches: 1 for the main development, 1 for the as-yet-unfinished effort to parallelise the program, and 1 for the effort to revise it to use XML input and output files;

-- we scarcely use tags, though we think we ought to use them to identify releases to production;

Think of development proceeding along a single path. At some time or state of development marketing decide to release the first version of the product, so you plant a flag in the path labelled '1' (or '1.0' or what have you). At some other time some bright spark decides to parallelise the program, but decides that that will take weeks and that people want to keep going down the main path in the meantime. So you build a fork in the path and different people wander off down the different forks.

The flags in the road are called 'tags' ,and the forks in the road are where 'branches' divide. Occasionally, also, branches come back together.

-- we put all material necessary to build an executable (or system) into the repository; That means at least source code and make file (or project files for Visual Studio). But when we have icons and config files and all that other stuff, that goes into the repository. Some documentation finds its way into the repo; certainly any documentation such as help files which might be integral to the program does, and it's a useful place to put developer documentation.

We even put Windows executables for our production releases in there, to provide a single location for people looking for software -- our Linux releases go to a server so don't need to be stored.

-- we don't require that the repository at all times be capable of delivering a latest version which builds and executes; some projects work that way, some don't; the decision rests with the project manager and depends on many factors but I think it breaks down when making major changes to a program.

Difference between array_map, array_walk and array_filter

The other answers demonstrate the difference between array_walk (in-place modification) and array_map (return modified copy) quite well. However, they don't really mention array_reduce, which is an illuminating way to understand array_map and array_filter.

The array_reduce function takes an array, a two-argument function and an 'accumulator', like this:

array_reduce(array('a', 'b', 'c', 'd'),

The array's elements are combined with the accumulator one at a time, using the given function. The result of the above call is the same as doing this:


If you prefer to think in terms of loops, it's like doing the following (I've actually used this as a fallback when array_reduce wasn't available):

function array_reduce($array, $function, $accumulator) {
  foreach ($array as $element) {
    $accumulator = $function($accumulator, $element);
  return $accumulator;

This looping version makes it clear why I've called the third argument an 'accumulator': we can use it to accumulate results through each iteration.

So what does this have to do with array_map and array_filter? It turns out that they're both a particular kind of array_reduce. We can implement them like this:

array_map($function, $array)    === array_reduce($array, $MAP,    array())
array_filter($array, $function) === array_reduce($array, $FILTER, array())

Ignore the fact that array_map and array_filter take their arguments in a different order; that's just another quirk of PHP. The important point is that the right-hand-side is identical except for the functions I've called $MAP and $FILTER. So, what do they look like?

$MAP = function($accumulator, $element) {
  $accumulator[] = $function($element);
  return $accumulator;

$FILTER = function($accumulator, $element) {
  if ($function($element)) $accumulator[] = $element;
  return $accumulator;

As you can see, both functions take in the $accumulator and return it again. There are two differences in these functions:

  • $MAP will always append to $accumulator, but $FILTER will only do so if $function($element) is TRUE.
  • $FILTER appends the original element, but $MAP appends $function($element).

Note that this is far from useless trivia; we can use it to make our algorithms more efficient!

We can often see code like these two examples:

// Transform the valid inputs
array_map('transform', array_filter($inputs, 'valid'))

// Get all numeric IDs
array_filter(array_map('get_id', $inputs), 'is_numeric')

Using array_map and array_filter instead of loops makes these examples look quite nice. However, it can be very inefficient if $inputs is large, since the first call (map or filter) will traverse $inputs and build an intermediate array. This intermediate array is passed straight into the second call, which will traverse the whole thing again, then the intermediate array will need to be garbage collected.

We can get rid of this intermediate array by exploiting the fact that array_map and array_filter are both examples of array_reduce. By combining them, we only have to traverse $inputs once in each example:

// Transform valid inputs
             function($accumulator, $element) {
               if (valid($element)) $accumulator[] = transform($element);
               return $accumulator;

// Get all numeric IDs
             function($accumulator, $element) {
               $id = get_id($element);
               if (is_numeric($id)) $accumulator[] = $id;
               return $accumulator;

NOTE: My implementations of array_map and array_filter above won't behave exactly like PHP's, since my array_map can only handle one array at a time and my array_filter won't use "empty" as its default $function. Also, neither will preserve keys.

It's not difficult to make them behave like PHP's, but I felt that these complications would make the core idea harder to spot.

Can I restore a single table from a full mysql mysqldump file?

This tool may be is what you want:

e.g. Restore a table from database dump file: -t yourtable -s yourdb -f backup.sql

Load a bitmap image into Windows Forms using open file dialog

You can try the following:

private void button1_Click(object sender, EventArgs e)
        OpenFileDialog fDialog = new OpenFileDialog();
        fDialog.Title = "Select file to be upload";
        fDialog.Filter = "All Files|*.*";
        //  fDialog.Filter = "PDF Files|*.pdf";
        if (fDialog.ShowDialog() == DialogResult.OK)
            textBox1.Text = fDialog.FileName.ToString();

Uncaught TypeError: undefined is not a function on loading jquery-min.js

I've run into the very same issue, when mistakenly named variable with the very same name, as function.

So this:

isLive = isLive(data);

failed, generating OP's mentioned error message.

Fix to this was as simple as changing above line to:

isItALive = isLive(data);

I don't know, how much does it helps in this situation, but I decided to put this answer for others looking for a solution for similar problems.

How to set JFrame to appear centered, regardless of monitor resolution?

If you explicitly setPreferredSize(new Dimension(X, Y)); then it is better to use:

setLocation(dim.width/2-this.getPreferredSize().width/2, dim.height/2-this.getPreferredSize().height/2);

Getting "type or namespace name could not be found" but everything seems ok?

Reinstalling nuget packages did the trick for me. After I changed .NET Framework versions to be in sync for all projects, some of the nuget packages (especially Entity Framework) were still installed for previous versions. This command in Packages Manager Console reinstalls packages for the whole solution:

Update-Package –reinstall

How can I populate a select dropdown list from a JSON feed with AngularJS?

The proper way to do it is using the ng-options directive. The HTML would look like this.

<select ng-model="selectedTestAccount" 
        ng-options="item.Id as item.Name for item in testAccounts">
    <option value="">Select Account</option>


angular.module('test', []).controller('DemoCtrl', function ($scope, $http) {
    $scope.selectedTestAccount = null;
    $scope.testAccounts = [];

            method: 'GET',
            url: '/Admin/GetTestAccounts',
            data: { applicationId: 3 }
        }).success(function (result) {
        $scope.testAccounts = result;

You'll also need to ensure angular is run on your html and that your module is loaded.

<html ng-app="test">
    <body ng-controller="DemoCtrl">

How can I inspect the file system of a failed `docker build`?

The top answer works in the case that you want to examine the state immediately prior to the failed command.

However, the question asks how to examine the state of the failed container itself. In my situation, the failed command is a build that takes several hours, so rewinding prior to the failed command and running it again takes a long time and is not very helpful.

The solution here is to find the container that failed:

$ docker ps -a
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS                          PORTS               NAMES
6934ada98de6        42e0228751b3        "/bin/sh -c './utils/"   24 minutes ago      Exited (1) About a minute ago                       sleepy_bell

Commit it to an image:

$ docker commit 6934ada98de6

And then run the image [if necessary, running bash]:

$ docker run -it 7015687976a4 [bash -il]

Now you are actually looking at the state of the build at the time that it failed, instead of at the time before running the command that caused the failure.

What's the difference between Sender, From and Return-Path?

The official RFC which defines this specification could be found here: (look at paragraph 2.1.2. and the following)

2.1.2. Header Field: From

    Mailbox of message author  
Related information:
    Specifies the author(s) of the message; that is, the mailbox(es)
    of the person(s) or system(s) responsible for the writing of the
    message. Defined as standard by RFC 822.

2.1.3. Header Field: Sender

    Mailbox of message sender  
Related information:
    Specifies the mailbox of the agent responsible for the actual
    transmission of the message.  Defined as standard by RFC 822.

2.1.22. Header Field: Return-Path

    Message return path
Related information:
    Return path for message response diagnostics. See also RFC 2821
    [17]. Defined as standard by RFC 822.

ENOENT, no such file or directory

Another possibility is that you are missing an .npmrc file if you are pulling any packages that are not publicly available.

You will need to add an .npmrc file at the root directory and add the private/internal registry inside of the .npmrc file like this:


JQUERY: Uncaught Error: Syntax error, unrecognized expression

Try this (ES5)

console.log($("#" +  d));



Can I set background image and opacity in the same property?

You can use CSS psuedo selector ::after to achieve this. Here is a working demo.

enter image description here

  width: 100%;_x000D_
  height: 300px;_x000D_
  border: 1px solid #000;_x000D_
  position: relative;_x000D_
.bg-container .content{_x000D_
  position: absolute;_x000D_
  text-align: center;_x000D_
  width: 100%;_x000D_
  content: "";_x000D_
  position: absolute;_x000D_
  top: 0px;_x000D_
  left: 0px;_x000D_
  width: 100%;_x000D_
  height: 100%;_x000D_
  background-image: url(;_x000D_
  background-size: cover;_x000D_
  opacity: 0.4;_x000D_
<div class="bg-container">_x000D_
   <div class="content">_x000D_
     <h1>Background Opacity 0.4</h1>_x000D_

symfony 2 No route found for "GET /"

I have also tried that error , I got it right by just adding /hello/any name because it is path that there must be an hello/name

example : instead of just putting http://localhost/app_dev.php

put it like this way http://localhost/name_of_your_project/web/app_dev.php/hello/ai

it will display Hello Ai . I hope I answer your question.

How to add new item to hash

hash_items = {:item => 1}
puts hash_items 
#hash_items will give you {:item => 1}

hash_items.merge!({:item => 2})
puts hash_items 
#hash_items will give you {:item => 1, :item => 2}

hash_items.merge({:item => 2})
puts hash_items 
#hash_items will give you {:item => 1, :item => 2}, but the original variable will be the same old one. 

Using Tempdata in ASP.NET MVC - Best practice

TempData is a bucket where you can dump data that is only needed for the following request. That is, anything you put into TempData is discarded after the next request completes. This is useful for one-time messages, such as form validation errors. The important thing to take note of here is that this applies to the next request in the session, so that request can potentially happen in a different browser window or tab.

To answer your specific question: there's no right way to use it. It's all up to usability and convenience. If it works, makes sense and others are understanding it relatively easy, it's good. In your particular case, the passing of a parameter this way is fine, but it's strange that you need to do that (code smell?). I'd rather keep a value like this in resources (if it's a resource) or in the database (if it's a persistent value). From your usage, it seems like a resource, since you're using it for the page title.

Hope this helps.

Resize image proportionally with CSS?

    object-fit: scale-down;

works for me. It scales down larger images to fit in the box, but leaves smaller images their original size.

Laravel 5 not finding css files

Here is the solution

  {!! Html::style('css/select2.min.css') !!}
  {!! Html::script('js/select2.min.js') !!}

Checking Value of Radio Button Group via JavaScript?

function myFunction() {_x000D_
 document.getElementById("myCheck_2").checked = false;_x000D_
  var checkBox = document.getElementById("myCheck");_x000D_
  var text = document.getElementById("text");_x000D_
  if (checkBox.checked == true){_x000D_ = "block";_x000D_
  } else {_x000D_ = "none";_x000D_
function myFunction_2() {_x000D_
 document.getElementById("myCheck").checked = false;_x000D_
  var checkBox = document.getElementById("myCheck_2");_x000D_
  var text = document.getElementById("text");_x000D_
  if (checkBox.checked == true){_x000D_ = "block";_x000D_
  } else {_x000D_ = "none";_x000D_
Male: <input type="checkbox" id="myCheck"  onclick="myFunction()">_x000D_
Female: <input type="checkbox" id="myCheck_2"  onclick="myFunction_2()">_x000D_
<input type="text" id="text" placeholder="Name">

Python datetime strptime() and strftime(): how to preserve the timezone information

Here is my answer in Python 2.7

Print current time with timezone

from datetime import datetime
import tzlocal  # pip install tzlocal

print"%Y-%m-%d %H:%M:%S %z")

Print current time with specific timezone

from datetime import datetime
import pytz # pip install pytz

print'Asia/Taipei')).strftime("%Y-%m-%d %H:%M:%S %z")

It will print something like

2017-08-10 20:46:24 +0800

How do I avoid the specification of the username and password at every git push?

Appears that, at least when using TortoiseGIT on Windows, it is possible to create the SSH keys and transfer these to the GIT server using simply:

> ssh-keygen.exe
> ssh-copy-id [username]@[GIT_server]

Algorithm to calculate the number of divisors of a given number

This is an efficient solution:

#include <iostream>
int main() {
  int num = 20; 
  int numberOfDivisors = 1;

  for (int i = 2; i <= num; i++)
    int exponent = 0;
    while (num % i == 0) {
        num /= i;
    numberOfDivisors *= (exponent+1);

  std::cout << numberOfDivisors << std::endl;
  return 0;

HTML - Change\Update page contents without refreshing\reloading the page

jQuery will do the job. You can use either jQuery.ajax function, which is general one for performing ajax calls, or its wrappers: jQuery.get, for getting/posting data. Its very easy to use, for example, check out this tutorial, which shows how to use jQuery with PHP.

How to insert TIMESTAMP into my MySQL table?

You do not need to insert the current timestamp manually as MySQL provides this facility to store it automatically. When the MySQL table is created, simply do this:

  • select TIMESTAMP as your column type
  • set the Default value to CURRENT_TIMESTAMP
  • then just insert any rows into the table without inserting any values for the time column

You'll see the current timestamp is automatically inserted when you insert a row. Please see the attached picture. enter image description here

How to use DISTINCT and ORDER BY in same SELECT statement?

Try next, but it's not useful for huge data...

  SELECT Category as Cat FROM MonitoringJob ORDER BY CreationDate DESC

Java Class that implements Map and keeps insertion order?

You can maintain a Map (for fast lookup) and List (for order) but a LinkedHashMap may be the simplest. You can also try a SortedMap e.g. TreeMap, which an have any order you specify.

How to solve "The specified service has been marked for deletion" error

Most probably deleting service fails because

protected override void OnStop()

throw error when stopping a service. wrapping things inside a try catch will prevent mark for deletion error

protected override void OnStop()
                //things to do
            catch (Exception)


How do I iterate through each element in an n-dimensional matrix in MATLAB?

these solutions are more faster (about 11%) than using numel;)

for idx = reshape(array,1,[]),
     element = element + idx;


for idx = array(:)',
    element = element + idx;

UPD. tnx @rayryeng for detected error in last answer


The timing information that this post has referenced is incorrect and inaccurate due to a fundamental typo that was made (see comments stream below as well as the edit history - specifically look at the first version of this answer). Caveat Emptor.

What is the best way to return different types of ResponseEntity in Spring MVC or Spring-Boot

I recommend using Spring's @ControllerAdvice to handle errors. Read this guide for a good introduction, starting at the section named "Spring Boot Error Handling". For an in-depth discussion, there's an article in the blog that was updated on April, 2018.

A brief summary on how this works:

  • Your controller method should only return ResponseEntity<Success>. It will not be responsible for returning error or exception responses.
  • You will implement a class that handles exceptions for all controllers. This class will be annotated with @ControllerAdvice
  • This controller advice class will contain methods annotated with @ExceptionHandler
  • Each exception handler method will be configured to handle one or more exception types. These methods are where you specify the response type for errors
  • For your example, you would declare (in the controller advice class) an exception handler method for the validation error. The return type would be ResponseEntity<Error>

With this approach, you only need to implement your controller exception handling in one place for all endpoints in your API. It also makes it easy for your API to have a uniform exception response structure across all endpoints. This simplifies exception handling for your clients.

Transparent background in JPEG image

You can't make a JPEG image transparent. You should use a format that allows transparency, like GIF or PNG.

Paint will open these files, but AFAIK it'll erase transparency if you edit the file. Use some other application like Paint.NET (it's free).

Edit: since other people have mentioned it: you can convert JPEG images into PNG, in any editor that's capable of working with both types.

SQL Server Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >=

The select statement in the cost part of your select is returning more than one value. You need to add more where clauses, or use an aggregation.

Passing parameter to controller action from a Html.ActionLink

You are using the incorrect overload of ActionLink. Try this

<%= Html.ActionLink("Create New Part", "CreateParts", "PartList", new { parentPartId = 0 }, null)%>

How can I quickly sum all numbers in a file?

Running R scripts

I've written an R script to take arguments of a file name and sum the lines.

#! /usr/local/bin/R

This can be sped up with the "data.table" or "vroom" package as follows:

#! /usr/local/bin/R
#! /usr/local/bin/R


Same benchmarking data as @glenn jackman.

for ((i=0; i<1000000; i++)) ; do echo $RANDOM; done > random_numbers

In comparison to the R call above, running R 3.5.0 as a script is comparable to other methods (on the same Linux Debian server).

$ time R -e 'sum(scan("random_numbers"))'  
 0.37s user
 0.04s system
 86% cpu
 0.478 total

R script with readLines

$ time Rscript sum.R random_numbers
  0.53s user
  0.04s system
  84% cpu
  0.679 total

R script with data.table

$ time Rscript sum.R random_numbers     
 0.30s user
 0.05s system
 77% cpu
 0.453 total

R script with vroom

$ time Rscript sum.R random_numbers     
  0.54s user 
  0.11s system
  93% cpu
  0.696 total

Comparison with other languages

For reference here as some other methods suggested on the same hardware

Python 2 (2.7.13)

$ time python2 -c "import sys; print sum((float(l) for l in sys.stdin))" < random_numbers 
 0.27s user 0.00s system 89% cpu 0.298 total

Python 3 (3.6.8)

$ time python3 -c "import sys; print(sum((float(l) for l in sys.stdin)))" < random_number
0.37s user 0.02s system 98% cpu 0.393 total

Ruby (2.3.3)

$  time ruby -e 'sum = 0; File.foreach(ARGV.shift) {|line| sum+=line.to_i}; puts sum' random_numbers
 0.42s user
 0.03s system
 72% cpu
 0.625 total

Perl (5.24.1)

$ time perl -nle '$sum += $_ } END { print $sum' random_numbers
 0.24s user
 0.01s system
 99% cpu
 0.249 total

Awk (4.1.4)

$ time awk '{ sum += $0 } END { print sum }' random_numbers
 0.26s user
 0.01s system
 99% cpu
 0.265 total
$ time awk '{ sum += $1 } END { print sum }' random_numbers
 0.34s user
 0.01s system
 99% cpu
 0.354 total

C (clang version 3.3; gcc (Debian 6.3.0-18) 6.3.0 )

 $ gcc sum.c -o sum && time ./sum < random_numbers   
 0.10s user
 0.00s system
 96% cpu
 0.108 total

Update with additional languages

Lua (5.3.5)

$ time lua -e 'sum=0; for line in io.lines() do sum=sum+line end; print(sum)' < random_numbers 
 0.30s user 
 0.01s system
 98% cpu
 0.312 total

tr (8.26) must be timed in bash, not compatible with zsh

$time { { tr "\n" + < random_numbers ; echo 0; } | bc; }
real    0m0.494s
user    0m0.488s
sys 0m0.044s

sed (4.4) must be timed in bash, not compatible with zsh

$  time { head -n 10000 random_numbers | sed ':a;N;s/\n/+/;ta' |bc; }
real    0m0.631s
user    0m0.628s
sys     0m0.008s
$  time { head -n 100000 random_numbers | sed ':a;N;s/\n/+/;ta' |bc; }
real    1m2.593s
user    1m2.588s
sys     0m0.012s

note: sed calls seem to work faster on systems with more memory available (note smaller datasets used for benchmarking sed)

Julia (0.5.0)

$ time julia -e 'print(sum(readdlm("random_numbers")))'
 3.00s user 
 1.39s system 
 136% cpu 
 3.204 total
$  time julia -e 'print(sum(readtable("random_numbers")))'
 0.63s user 
 0.96s system 
 248% cpu 
 0.638 total

Notice that as in R, file I/O methods have different performance.

How to color the Git console?

Well, if you are not satisfied with the default setting, you can use ANSI escape code to help you set the color, and if you want to modify some text, you can write bash to help you. see as below:


# .gitconfig

    st-color = "!f() { \
        echo -n -e '\\033[38;2;255;0;01m\\033[4m' ;\
        git status -s | grep ' D' | \
        sed -e 's/^ ./DELETE:/' ; \
        echo -n -e '\\033[m' ;\
        echo -n -e '\\033[48;2;128;128;128m' ;\
        echo -n -e '\\033[38;2;0;255;01m' ;\
        git status -s | grep ' [AM]' | \
        sed -e 's/^ ./NEW OR MODIFY:/' ; \
        echo -n -e '\\033[m' ;\
        echo -n -e '\\033[38;2;255;0;255m' ;\
        echo Rename ;\
        git status -s | grep 'R ' | \
        sed -e 's/^..//' ; \
        echo -n -e '\\033[m' ;\
    }; f"


enter image description here


  1. you can write the long script on .gitconfig use the syntax as below:

        your-cmd = !f() { \
        }; f"
  2. echo -n -e (see more echo)

    • -n = Do not output a trailing newline.
    • -e Enable interpretation of the following backslash-escaped
  3. \\033[38;2;255;0;0m\\033[4m (see more SGR parameters)

    • \\033[38;2;255;0;0m : 38 mean fore color. 255;0;0 = Red | r;g;b
    • \\033[4m : underline
  4. grep : The grep command is used to search text.

  5. sed -e 's/be_replace_string/new_string/' replace string to new string.

Very Long If Statement in Python

According to PEP8, long lines should be placed in parentheses. When using parentheses, the lines can be broken up without using backslashes. You should also try to put the line break after boolean operators.

Further to this, if you're using a code style check such as pycodestyle, the next logical line needs to have different indentation to your code block.

For example:

if (abcdefghijklmnopqrstuvwxyz > some_other_long_identifier and
        here_is_another_long_identifier != and_finally_another_long_name):
    # ... your code here ...

Quicker way to get all unique values of a column in VBA?

PowerShell is a very powerful and efficient tool. This is cheating a little, but shelling PowerShell via VBA opens up lots of options

The bulk of the code below is simply to save the current sheet as a csv file. The output is another csv file with just the unique values

Sub AnotherWay()
Dim strPath As String
Dim strPath2 As String

Application.DisplayAlerts = False
strPath = "C:\Temp\test.csv"
strPath2 = "C:\Temp\testout.csv"
ActiveWorkbook.SaveAs strPath, xlCSV
x = Shell("powershell.exe $csv = import-csv -Path """ & strPath & """ -Header A | Select-Object -Unique A | Export-Csv """ & strPath2 & """ -NoTypeInformation", 0)
Application.DisplayAlerts = True

End Sub

SEVERE: ContainerBase.addChild: start:org.apache.catalina.LifecycleException: Failed to start error

Weird error, you can try methods given by james goooseling and also I have done it by following ways:

  • Remove all jars or libraries from build path and lib folders and add them again in lib folder or build path as you wish.

  • Check if you have servlet annotation @WebServlet for given servlet and if it has mapping in web.xml as well .. this is most common error due to which tomcat gets confused , that what url pattern must he use.

Node.js setting up environment specific configs to be used with everyauth

My solution,

load the app using

NODE_ENV=production node app.js

Then setup config.js as a function rather than an object

module.exports = function(){
        case 'development':
            return {dev setting};

        case 'production':
            return {prod settings};

            return {error or other settings};

Then as per Jans solution load the file and create a new instance which we could pass in a value if needed, in this case process.env.NODE_ENV is global so not needed.

var Config = require('./conf'),
    conf = new Config();

Then we can access the config object properties exactly as before


Where does PHP's error log reside in XAMPP?

As said above you can find PHP error log in windows. In c:\xampp\apache\logs\error.log. You can easily display the last logs by tail -f .\error.log

Write values in app.config file

Try the following:

Configuration config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);            
config.AppSettings.Settings[key].Value = value;

How to redirect to an external URL in Angular2?

An Angular approach to the methods previously described is to import DOCUMENT from @angular/common (or @angular/platform-browser in Angular < 4) and use

document.location.href = '';

inside a function.


import { DOCUMENT } from '@angular/common';
constructor(@Inject(DOCUMENT) private document: Document) { }

goToUrl(): void {
    this.document.location.href = '';


<button type="button" (click)="goToUrl()">Click me!</button>

Check out the plateformBrowser repo for more info.

How to set value to variable using 'execute' in t-sql?

The dynamic SQL is a different scope to the outer, calling SQL: so @siteid is not recognised

You'll have to use a temp table/table variable outside of the dynamic SQL:

DECLARE @dbName nvarchar(128) = 'myDb'
DECLARE @siteId TABLE (siteid int)

INSERT @siteId
exec ('SELECT TOP 1 Id FROM ' + @dbName + '..myTbl')  

select * FROM @siteId

Note: TOP without an ORDER BY is meaningless. There is no natural, implied or intrinsic ordering to a table. Any order is only guaranteed by the outermost ORDER BY

Singleton design pattern vs Singleton beans in Spring container

All the answers, so far at least, concentrate on explaining the difference between the design pattern and Spring singleton and do not address your actual question: Should a Singleton design pattern be used or a Spring singleton bean? what is better?

Before I answer let me just state that you can do both. You can implement the bean as a Singleton design pattern and use Spring to inject it into the client classes as a Spring singleton bean.

Now, the answer to the question is simple: Do not use the Singleton design pattern!
Use Spring's singleton bean implemented as a class with public constructor.
Why? Because the Singleton design pattern is considered an anti-pattern. Mostly because it complicates testing. (And if you don't use Spring to inject it then all classes that use the singleton are now tightly bound to it), and you can't replace or extend it. One can google "Singleton anti-pattern" to get more info on this, e.g. Singleton anti-pattern

Using Spring singleton is the way to go (with a the singleton bean implemented NOT as a Singleton design pattern, but rather with a public constructor) so that the Spring singleton bean can easily be tested and classes that use it are not tightly coupled to it, but rather, Spring injects the singleton (as an interface) into all the beans that need it, and the singleton bean can be replaced any time with another implementation without affecting the client classes that use it.

How to detect running app using ADB command

Alternatively, you could go with pgrep or Process Grep. (Busybox is needed)

You could do a adb shell pgrep and it would display just the process Id.

As a suggestion, since Android is Linux, you can use most basic Linux commands with adb shell to navigate/control around. :D

How to Right-align flex item?

For those using Angular and Flex-Layout, use the following on the flex-item container:

<div fxLayout="row" fxLayoutAlign="flex-end">

See fxLayoutAlign docs here and the full fxLayout docs here.

Linking to a specific part of a web page

In case the target page is on the same domain (i.e. shares the same origin with your page) and you don't mind creation of new tabs (1), you can (ab)use some JavaScript:

<a href="javascript:void('./target.html').onload=function(){this.document.querySelector('p:nth-child(10)').scrollIntoView()})">see tenth paragraph on another page</a>


var w ='some URL of the same origin');
w.onload = function(){
  // do whatever you want with `this.document`, like

Working example of such 'exploit' you can try right now could be:


If you enter this into location bar (mind that Chrome removes javascript: prefix when pasted from clipboard) or make it a href value of any link on this page (using Developer Tools) and click it, you will get another (duplicate) SO question page scrolled to the footer and footer painted red. (Delay added as a workaround for ajax-loaded content pushing footer down after load.)


  • Tested in current Chrome and Firefox, generally should work since it is based on defined standard behaviour.
  • Cannot be illustrated in interactive snippet here at SO, because they are isolated from the page origin-wise.
  • MDN:
  • (1),'_self') seems to be breaking the load event; basically makes the behave like a normal a href="" click navigation; haven't researched more yet.

ConcurrentHashMap vs Synchronized HashMap

ConcurrentHashMap allows concurrent access to data. Whole map is divided into segments.

Read operation ie. get(Object key) is not synchronized even at segment level.

But write operations ie. remove(Object key), get(Object key) acquire lock at segment level. Only part of whole map is locked, other threads still can read values from various segments except locked one.

SynchronizedMap on the other hand, acquire lock at object level. All threads should wait for current thread irrespective of operation(Read/Write).

How to set default text for a Tkinter Entry widget

Use Entry.insert. For example:

    from tkinter import *  # Python 3.x
except Import Error:
    from Tkinter import *  # Python 2.x

root = Tk()
e = Entry(root)
e.insert(END, 'default text')

Or use textvariable option:

    from tkinter import *  # Python 3.x
except Import Error:
    from Tkinter import *  # Python 2.x

root = Tk()
v = StringVar(root, value='default text')
e = Entry(root, textvariable=v)

What does $_ mean in PowerShell?

$_ is an variable which iterates over each object/element passed from the previous | (pipe).

Android: Background Image Size (in Pixel) which Support All Devices

Check this. This image will show for all icon size for different screen sizes


error: invalid type argument of ‘unary *’ (have ‘int’)

Since c is holding the address of an integer pointer, its type should be int**:

int **c;
c = &a;

The entire program becomes:

#include <stdio.h>                                                              
int main(){
    int b=10;
    int *a;
    int **c;
    printf("%d",(**c));   //successfully prints 10
    return 0;

How can I alias a default import in JavaScript?

defaultMember already is an alias - it doesn't need to be the name of the exported function/thing. Just do

import alias from 'my-module';

Alternatively you can do

import {default as alias} from 'my-module';

but that's rather esoteric.

Read file line by line in PowerShell

The almighty switch works well here:

three' > file

$regex = '^t'

switch -regex -file file { 
  $regex { "line is $_" } 


line is two
line is three

Python Socket Receive Large Amount of Data

Modifying Adam Rosenfield's code:

import sys

def send_msg(sock, msg):
    size_of_package = sys.getsizeof(msg)
    package = str(size_of_package)+":"+ msg #Create our package size,":",message

def recv_msg(sock):
        header = sock.recv(2)#Magic, small number to begin with.
        while ":" not in header:
            header += sock.recv(2) #Keep looping, picking up two bytes each time

        size_of_package, separator, message_fragment = header.partition(":")
        message = sock.recv(int(size_of_package))
        full_message = message_fragment + message
        return full_message

    except OverflowError:
        return "OverflowError."
        print "Unexpected error:", sys.exc_info()[0]

I would, however, heavily encourage using the original approach.

How to change indentation in Visual Studio Code?

Adding on: yes, you can use the bottom-right UI to configure the space settings. But if you have existing code that's not formatted to the new spacing, then you can right-click anywhere within the file and click Format Document. Took me a while to figure this out until I stumbled on this issue.

Format Document menu

Adding an img element to a div with javascript

It should be:


And place your div before your javascript, because if you don't, the javascript executes before the div exists. Or wait for it to load. So your code looks like this:


<script type="text/javascript">
var elem = document.createElement("img");
elem.setAttribute("src", "");
elem.setAttribute("height", "768");
elem.setAttribute("width", "1024");
elem.setAttribute("alt", "Flower");
<div id="placehere">



To prove my point, see this with the onload and this without the onload. Fire up the console and you'll find an error stating that the div doesn't exist or cannot find appendChild method of null.

jQuery Clone table row

Here you go:

$( table ).delegate( '.tr_clone_add', 'click', function () {
    var thisRow = $( this ).closest( 'tr' )[0];
    $( thisRow ).clone().insertAfter( thisRow ).find( 'input:text' ).val( '' );

Live demo:

Update: The new way of delegating events in jQuery is

$(table).on('click', '.tr_clone_add', function () { … });

Allowed memory size of 33554432 bytes exhausted (tried to allocate 43148176 bytes) in php

I had the same issue which running php in command line. Recently, I had changes the php.ini file and did a mistake while changing the php.ini

This is for php7.0

path to php.ini where I made mistake: /etc/php/7.0/cli/php.ini

I had set memory_limit = 256 (which means 256 bytes)
instead of memory_limit = 256M (which means 256 Mega bytes).

; Maximum amount of memory a script may consume (128MB)
memory_limit = 128M

Once I corrected it, my process started running fine.

How to add a RequiredFieldValidator to DropDownList control?

For the most part you treat it as if you are validating any other kind of control but use the InitialValue property of the required field validator.

<asp:RequiredFieldValidator ID="rfv1" runat="server" ControlToValidate="your-dropdownlist" InitialValue="Please select" ErrorMessage="Please select something" />

Basically what it's saying is that validation will succeed if any other value than the 1 set in InitialValue is selected in the dropdownlist.

If databinding you will need to insert the "Please select" value afterwards as follows

this.ddl1.Items.Insert(0, "Please select");

How to get current user in core

It would appear that as of now (April of 2017) that the following works:

public string LoggedInUser => User.Identity.Name;

At least while within a Controller

Absolute position of an element on the screen using jQuery

BTW, if anyone want to get coordinates of element on screen without jQuery, please try this:

function getOffsetTop (el) {
    if (el.offsetParent) return el.offsetTop + getOffsetTop(el.offsetParent)
    return el.offsetTop || 0
function getOffsetLeft (el) {
    if (el.offsetParent) return el.offsetLeft + getOffsetLeft(el.offsetParent)
    return el.offsetleft || 0
function coordinates(el) {
    var y1 = getOffsetTop(el) - window.scrollY;
    var x1 = getOffsetLeft(el) - window.scrollX; 
    var y2 = y1 + el.offsetHeight;
    var x2 = x1 + el.offsetWidth;
    return {
        x1: x1, x2: x2, y1: y1, y2: y2

Convert the values in a column into row names in an existing data frame

It looks like the one-liner got even simpler along the line (currently using R 3.5.3):

# generate original data.frame
df <- data.frame(a = letters[1:10], b = 1:10, c = LETTERS[1:10])
# use first column for row names
df <- data.frame(df, row.names = 1)

The column used for row names is removed automatically.


i found i had to do something akin to

=(countifs (A1:A196,"yes", j1:j196, "agree") + (countifs (A1:A196,"no", j1:j196, "agree"))

How do I set path while saving a cookie value in JavaScript?

For access cookie in whole app (use path=/):

function createCookie(name,value,days) {
    if (days) {
        var date = new Date();
        var expires = "; expires="+date.toGMTString();
    else var expires = "";
    document.cookie = name+"="+value+expires+"; path=/"; 


If you set path=/,
Now the cookie is available for whole application/domain. If you not specify the path then current cookie is save just for the current page you can't access it on another page(s).

For more info read- (Domain and path part)

If you use cookies in jquery by plugin jquery-cookie:

$.cookie('name', 'value', { expires: 7, path: '/' });
$.cookie('name', 'value', { path: '/' });

how to set default method argument values?

You can accomplish this via method overloading.

public int doSomething(int arg1, int arg2)
        return 0;

public int doSomething()
        return doSomething(defaultValue0, defaultValue1);

By creating this parameterless method you are allowing the user to call the parameterfull method with the default arguments you supply within the implementation of the parameterless method. This is known as overloading the method.

How to get week numbers from dates?

if you try with lubridate:

lubridate::week(ymd("2014-03-16", "2014-03-17","2014-03-18", '2014-01-01'))

[1] 11 11 12  1

The pattern is the same. Try isoweek

lubridate::isoweek(ymd("2014-03-16", "2014-03-17","2014-03-18", '2014-01-01'))
[1] 11 12 12  1

HTML - Alert Box when loading page

If you use jqueryui (or another toolset) this is the way you do it


<div id="hw" title="Empty the recycle bin?">The new way</div>


        alert('the old way')

UPDATE : how to include jqueryui by pointing to cdn

<link rel="stylesheet" type="text/css" href="">
<script src=""></script>
<script src=""></script>

Add/remove HTML inside div using JavaScript

To remove node you can try this solution it helped me.

var rslt = (nodee=document.getElementById(id)).parentNode.removeChild(nodee);

Using prepared statements with JDBCTemplate

I've tried a select statement now with a PreparedStatement, but it turned out that it was not faster than the Jdbc template. Maybe, as mezmo suggested, it automatically creates prepared statements.

Anyway, the reason for my sql SELECTs being so slow was another one. In the WHERE clause I always used the operator LIKE, when all I wanted to do was finding an exact match. As I've found out LIKE searches for a pattern and therefore is pretty slow.

I'm using the operator = now and it's much faster.

Replacing spaces with underscores in JavaScript?

const updateKey = key => console.log(key.split(' ').join('_'));
updateKey('Hello World');

How to avoid soft keyboard pushing up my layout?

Solved it by setting the naughty EditText:

etSearch = (EditText) view.findViewById(;


etSearch.setOnTouchListener(new OnTouchListener() {
    public boolean onTouch(View v, MotionEvent event) {
        return false;

How do I call REST API from an android app?

  1. If you want to integrate Retrofit (all steps defined here):

Goto my blog : retrofit with kotlin

  1. Please use android-async-http library.

the link below explains everything step by step.

Here are sample apps:



Create a class :

public class HttpUtils {
  private static final String BASE_URL = "";
  private static AsyncHttpClient client = new AsyncHttpClient();

  public static void get(String url, RequestParams params, AsyncHttpResponseHandler responseHandler) {
      client.get(getAbsoluteUrl(url), params, responseHandler);

  public static void post(String url, RequestParams params, AsyncHttpResponseHandler responseHandler) {, params, responseHandler);
  public static void getByUrl(String url, RequestParams params, AsyncHttpResponseHandler responseHandler) {
      client.get(url, params, responseHandler);

  public static void postByUrl(String url, RequestParams params, AsyncHttpResponseHandler responseHandler) {, params, responseHandler);

  private static String getAbsoluteUrl(String relativeUrl) {
      return BASE_URL + relativeUrl;

Call Method :

    RequestParams rp = new RequestParams();
    rp.add("username", "aaa"); rp.add("password", "aaa@123");
               , rp, new JsonHttpResponseHandler() {
        public void onSuccess(int statusCode, Header[] headers, JSONObject response) {
            // If the response is JSONObject instead of expected JSONArray
            Log.d("asd", "---------------- this is response : " + response);
            try {
                JSONObject serverResp = new JSONObject(response.toString());                                                
            } catch (JSONException e) {
                // TODO Auto-generated catch block
        public void onSuccess(int statusCode, Header[] headers, JSONArray timeline) {
            // Pull out the first event on the public timeline

Please grant internet permission in your manifest file.

 <uses-permission android:name="android.permission.INTERNET" />

you can add compile '' for Header[] and compile 'org.json:json:20160212' for JSONObject in build.gradle file if required.

How to run a SQL query on an Excel table?

There are many fine ways to get this done, which others have already suggestioned. Following along the "get Excel data via SQL track", here are some pointers.

  1. Excel has the "Data Connection Wizard" which allows you to import or link from another data source or even within the very same Excel file.

  2. As part of Microsoft Office (and OS's) are two providers of interest: the old "Microsoft.Jet.OLEDB", and the latest "Microsoft.ACE.OLEDB". Look for them when setting up a connection (such as with the Data Connection Wizard).

  3. Once connected to an Excel workbook, a worksheet or range is the equivalent of a table or view. The table name of a worksheet is the name of the worksheet with a dollar sign ("$") appended to it, and surrounded with square brackets ("[" and "]"); of a range, it is simply the name of the range. To specify an unnamed range of cells as your recordsource, append standard Excel row/column notation to the end of the sheet name in the square brackets.

  4. The native SQL will (more or less be) the SQL of Microsoft Access. (In the past, it was called JET SQL; however Access SQL has evolved, and I believe JET is deprecated old tech.)

  5. Example, reading a worksheet: SELECT * FROM [Sheet1$]

  6. Example, reading a range: SELECT * FROM MyRange

  7. Example, reading an unnamed range of cells: SELECT * FROM [Sheet1$A1:B10]

  8. There are many many many books and web sites available to help you work through the particulars.

=== Further notes ===

By default, it is assumed that the first row of your Excel data source contains column headings that can be used as field names. If this is not the case, you must turn this setting off, or your first row of data "disappears" to be used as field names. This is done by adding the optional HDR= setting to the Extended Properties of the connection string. The default, which does not need to be specified, is HDR=Yes. If you do not have column headings, you need to specify HDR=No; the provider names your fields F1, F2, etc.

A caution about specifying worksheets: The provider assumes that your table of data begins with the upper-most, left-most, non-blank cell on the specified worksheet. In other words, your table of data can begin in Row 3, Column C without a problem. However, you cannot, for example, type a worksheeet title above and to the left of the data in cell A1.

A caution about specifying ranges: When you specify a worksheet as your recordsource, the provider adds new records below existing records in the worksheet as space allows. When you specify a range (named or unnamed), Jet also adds new records below the existing records in the range as space allows. However, if you requery on the original range, the resulting recordset does not include the newly added records outside the range.

Data types (worth trying) for CREATE TABLE: Short, Long, Single, Double, Currency, DateTime, Bit, Byte, GUID, BigBinary, LongBinary, VarBinary, LongText, VarChar, Decimal.

Connecting to "old tech" Excel (files with the xls extention): Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\MyFolder\MyWorkbook.xls;Extended Properties=Excel 8.0;. Use the Excel 5.0 source database type for Microsoft Excel 5.0 and 7.0 (95) workbooks and use the Excel 8.0 source database type for Microsoft Excel 8.0 (97), 9.0 (2000) and 10.0 (2002) workbooks.

Connecting to "latest" Excel (files with the xlsx file extension): Provider=Microsoft.ACE.OLEDB.12.0;Data Source=Excel2007file.xlsx;Extended Properties="Excel 12.0 Xml;HDR=YES;"

Treating data as text: IMEX setting treats all data as text. Provider=Microsoft.ACE.OLEDB.12.0;Data Source=Excel2007file.xlsx;Extended Properties="Excel 12.0 Xml;HDR=YES;IMEX=1";

(More details at

More information at, and at

Connecting to Excel via ADODB via VBA detailed at

Microsoft JET 4 details at

What is the default scope of a method in Java?

If you are not giving any modifier to your method then as default it will be Default modifier which has scope within package.
for more info you can refer

Using getResources() in non-activity class

this can be done by using


Reference to a non-shared member requires an object reference occurs when calling public sub

You either have to make the method Shared or use an instance of the class General:

Dim gen = New General()



Public Shared Sub updateDynamics(dynID As Int32)
    ' ... '
End Sub


How to synchronize a static variable among threads running different instances of a class in Java?

There are several ways to synchronize access to a static variable.

  1. Use a synchronized static method. This synchronizes on the class object.

    public class Test {
        private static int count = 0;
        public static synchronized void incrementCount() {
  2. Explicitly synchronize on the class object.

    public class Test {
        private static int count = 0;
        public void incrementCount() {
            synchronized (Test.class) {
  3. Synchronize on some other static object.

    public class Test {
        private static int count = 0;
        private static final Object countLock = new Object();
        public void incrementCount() {
            synchronized (countLock) {

Method 3 is the best in many cases because the lock object is not exposed outside of your class.

Git push/clone to new server

remote server> cd /home/ec2-user
remote server> git init --bare --shared  test
add ssh pub key to remote server
local> git remote add aws ssh://ec2-user@<hostorip>:/home/ec2-user/dev/test
local> git push aws master

Import Excel Spreadsheet Data to an EXISTING sql table?

If you would like a software tool to do this, you might like to check out this step-by-step guide:

"How to Validate and Import Excel spreadsheet to SQL Server database"

Running powershell script within python script, how to make python print the powershell output while it is running

I don't have Python 2.7 installed, but in Python 3.3 calling Popen with stdout set to sys.stdout worked just fine. Not before I had escaped the backslashes in the path, though.

>>> import subprocess
>>> import sys
>>> p = subprocess.Popen(['powershell.exe', 'C:\\Temp\\test.ps1'], stdout=sys.stdout)
>>> Hello World

Should I always use a parallel stream when possible?

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

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

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

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

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

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

(B) that it will actually deliver increased performance.

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

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

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

Running the new Intel emulator for Android

You might need to turn on virtualization in your BIOS, most manufacturers disable it by default. Intel HAX requires CPU virtualization to be enabled.

What is secret key for JWT based authentication and how to generate it?

What is the secret key

The secret key is combined with the header and the payload to create a unique hash. You are only able to verify this hash if you have the secret key.

How to generate the key

You can choose a good, long password. Or you can generate it from a site like this.

Example (but don't use this one now):


Creating temporary files in bash

Yes, use mktemp.

It will create a temporary file inside a folder that is designed for storing temporary files, and it will guarantee you a unique name. It outputs the name of that file:

> mktemp

How do you kill a Thread in Java?

Thread.stop is deprecated so how do we stop a thread in java ?

Always use interrupt method and future to request cancellation

  1. When the task responds to interrupt signal, for example, blocking queue take method.
Callable < String > callable = new Callable < String > () {
    public String call() throws Exception {
        String result = "";
        try {
            //assume below take method is blocked as no work is produced.
            result = queue.take();
        } catch (InterruptedException e) {
        return result;
Future future = executor.submit(callable);
try {
    String result = future.get(5, TimeUnit.SECONDS);
} catch (TimeoutException e) {
    logger.error("Thread timedout!");
    return "";
} finally {
    //this will call interrupt on queue which will abort the operation.
    //if it completes before time out, it has no side effects

  1. When the task does not respond to interrupt signal.Suppose the task performs socket I/O which does not respond to interrupt signal and thus using above approach will not abort the task, future would time out but the cancel in finally block will have no effect, thread will keep on listening to socket. We can close the socket or call close method on connection if implemented by pool.
public interface CustomCallable < T > extends Callable < T > {
    void cancel();
    RunnableFuture < T > newTask();

public class CustomExecutorPool extends ThreadPoolExecutor {
    protected < T > RunnableFuture < T > newTaskFor(Callable < T > callable) {
        if (callable instanceof CancellableTask)
            return ((CancellableTask < T > ) callable).newTask();
            return super.newTaskFor(callable);

public abstract class UnblockingIOTask < T > implements CustomCallable < T > {
    public synchronized void cancel() {
        try {
        } catch (IOException e) {
            logger.error("io exception", e);

    public RunnableFuture < T > newTask() {
        return new FutureTask < T > (this) {
            public boolean cancel(boolean mayInterruptIfRunning) {
                try {
                } finally {
                    return super.cancel(mayInterruptIfRunning);


rails 3 validation on uniqueness on multiple attributes

Dont work for me, need to put scope in plural

validates_uniqueness_of :teacher_id, :scopes => [:semester_id, :class_id]

RegEx: Grabbing values between quotation marks

For me worked this one:


I've used in a sentence like this one:

preg_match_all('|([\'"])(.*?)\1|i', $cont, $matches);

and it worked great.

HTML input - name vs. id

Adding some actual references to W3 docs that authoritatively explain the role of the 'name' attribute on form elements. (For what it's worth, I arrived here while exploring exactly how Stripe.js works to implement safe interaction with payment gateway Stripe. In particular, what causes a form input element to get submitted back to the server, or prevents it from being submitted?)

The following W3 docs are relevent:

HTML 4: Section 17.2 Controls

HTML 5: and Section Constructing the form data set.

As explained therein, an input element will be submitted by the browser if and only if it has a valid 'name' attribute.

As others have noted, the 'id' attribute uniquely identifies DOM elements, but is not involved in normal form submission. (Though 'id' or other attributes can of course be used by javascript to obtain form values, which javascript could then use for AJAX submissions and so on.)

One oddity regarding previous answers/commenters concern about id's values and name's values being in the same namespace. So far as I can tell from the specs, this applied to some deprecated uses of the name attribute (not on form elements). For example

"Authors should not specify the name attribute on a elements. If the attribute is present, its value must not be the empty string and must neither be equal to the value of any of the IDs in the element's home subtree other than the element's own ID, if any, nor be equal to the value of any of the other name attributes on a elements in the element's home subtree. If this attribute is present and the element has an ID, then the attribute's value must be equal to the element's ID. In earlier versions of the language, this attribute was intended as a way to specify possible targets for fragment identifiers in URLs. The id attribute should be used instead."

Clearly in this special case there's some overlap between id and name values for 'a' tags. But this seems to be a peculiarity of processing for fragment ids, not due to general sharing of namespace of ids and names.

How to iterate over associative arrays in Bash

Use this higher order function to prevent the pyramid of doom

  arr="$(declare -p $1)" ; eval "declare -A f="${arr#*=}; 
  for i in ${!f[@]}; do $2 "$i" "${f[$i]}"; done


$ bar(){ echo "$1 -> $2"; }
$ declare -A foo["flap"]="three four" foo["flop"]="one two"
$ foreach foo bar
flap -> three four
flop -> one two

How to get the element clicked (for the whole document)?

Use delegate and delegate takes advantage of the event bubbling by letting one element listen for, and handle, events on child elements. target is the jQ-normalized property of the event object representing the object from which the event originated.

$(document).delegate('*', 'click', function (event) {
    // is the element
    // $( gets its text


Disable submit button on form submit

This should take care of it in your app.

    $(':submit').attr('disabled', 'disabled');

Android Studio doesn't see device

For Samsung Galaxy s4 i resolved issue by instaling Kies software, after that everything works like a charm.

Memcached vs. Redis?

It would not be wrong, if we say that redis is combination of (cache + data structure) while memcached is just a cache.

Converting Stream to String and back...what are we missing?

I want to serialize objects to strings, and back.

Different from the other answers, but the most straightforward way to do exactly that for most object types is XmlSerializer:

        Subject subject = new Subject();
        XmlSerializer serializer = new XmlSerializer(typeof(Subject));
        using (Stream stream = new MemoryStream())
            serializer.Serialize(stream, subject);
            // do something with stream
            Subject subject2 = (Subject)serializer.Deserialize(stream);
            // do something with subject2

All your public properties of supported types will be serialized. Even some collection structures are supported, and will tunnel down to sub-object properties. You can control how the serialization works with attributes on your properties.

This does not work with all object types, some data types are not supported for serialization, but overall it is pretty powerful, and you don't have to worry about encoding.

Why is MySQL InnoDB insert so slow?

things that speed up the inserts:

  • i had removed all keys from a table before large insert into empty table
  • then found i had a problem that the index did not fit in memory.
  • also found i had sync_binlog=0 (should be 1) even if binlog is not used.
  • also found i did not set innodb_buffer_pool_instances

How do I rename a file using VBScript?

Rename File using VB SCript.

  1. Create Folder Source and Archive in D : Drive. [You can choose other drive but make change in code from D:\Source to C:\Source in case you create folder in C: Drive]
  2. Save files in Source folder to be renamed.
  3. Save below code and save it as .vbs e.g ChangeFileName.vbs
  4. Run file and the file will be renamed with existing file name and current date

    Option Explicit

    Dim fso,sfolder,fs,f1,CFileName,strRename,NewFilename,GFileName,CFolderName,CFolderName1,Dfolder,afolder

    Dim myDate

    myDate =Date

    Function pd(n, totalDigits)

        if totalDigits > len(n) then 
            pd = String(totalDigits-len(n),"0") & n 
            pd = n 
        end if 

    End Function

    myDate= Pd(DAY(date()),2) & _

    Pd(Month(date()),2) & _


    'MsgBox ("Create Folders 'Source' 'Destination ' and 'Archive' in D drive. Save PDF files into Source Folder ")




    Set fso= CreateObject("Scripting.FileSystemObject")

    Set fs= fso.GetFolder(sfolder)

    For each f1 in fs.files

            CFileName=sfolder &
            CFolderName=Replace(CFolderName1,"." & fso.GetExtensionName(f1.Path),"")
            'Msgbox CFileName 
            'MsgBox CFolderName 
            'MsgBox myDate
            'strRename="DA009B_"& CFolderName &"_20032019"
            strRename= "DA009B_"& CFolderName &"_"& myDate &""
            'fso.CopyFile CFolderName1 , afolder
            fso.MoveFile CFileName , NewFilename
            'fso.CopyFile CFolderName, Dfolder


    MsgBox "File Renamed Successfully !!! "

    Set fso= Nothing

    Set fs=Nothing

CSS change button style after click

It is possible to do with CSS only by selecting active and focus pseudo element of the button.



See codepen:

You could also write a simple jQuery click function which changes the background color.


<button class="js-click">Click me!</button>


button {
  background: none;


  $( ".js-click" ).click(function() {
    $( ".js-click" ).css('background', 'green');

Check out this codepen:

How to pass a value from Vue data to href?

Or you can do that with ES6 template literal:

<a :href="`/job/${}`"

how to display none through code behind

Since this is a login div, shouldn't the default be to NOT display it. I am going to go ahead and assume then you want to display it then via javascript.

<div id="login" style="display:none;">Content</div>

Then using jQuery:

<script type="javascript">$('#login').show();</script>

Another method you might consider is something like this:

<div id="login" style="display:<%=SetDisplay() %>">Content</div>

And the SetDisplay() method output "none" or "block"

Is there a Google Keep API?

No there's not and developers still don't know why google doesn't pay attention to this request!

As you can see in this link it's one of the most popular issues with many stars in google code but still no response from google! You can also add stars to this issue, maybe google hears that!

ORA-00932: inconsistent datatypes: expected - got CLOB

I found that selecting a clob column in CTE caused this explosion. ie

with cte as (
    from mytable1
    join mytable2 on ...
select myIntCol, myClobCol
from cte
where ...

presumably because oracle can't handle a clob in a temporary table.

Because my values were longer than 4K, I couldn't use to_char().
My work around was to select it from the final select, ie

with cte as (
    from mytable1
select myIntCol, myClobCol
from cte
join mytable2 on ...
where ...

Too bad if this causes a performance problem.

JavaScript window resize event

Solution for 2018+:

You should use ResizeObserver. It is a browser-native solution that has a much better performance than to use the resize event. In addition, it not only supports the event on the document but also on arbitrary elements.

var ro = new ResizeObserver( entries => {
  for (let entry of entries) {
    const cr = entry.contentRect;
    console.log(`Element size: ${cr.width}px x ${cr.height}px`);
    console.log(`Element padding: ${}px ; ${cr.left}px`);

// Observe one or multiple elements

Currently, Firefox, Chrome, Safari, and Edge support it. For other (and older) browsers you have to use a polyfill.

What is the dual table in Oracle?

More Facts about the DUAL....

Thrilling experiments done here, and more thrilling explanations by Tom

Understanding generators in Python

I put up this piece of code which explains 3 key concepts about generators:

def numbers():
    for i in range(10):
            yield i

gen = numbers() #this line only returns a generator object, it does not run the code defined inside numbers

for i in gen: #we iterate over the generator and the values are printed

#the generator is now empty

for i in gen: #so this for block does not print anything

Get Unix timestamp with C++

Windows uses a different epoch and time units: see Convert Windows Filetime to second in Unix/Linux

What std::time() returns on Windows is (as yet) unknown to me (;-))

When is the init() function run?

mutil init function in one package execute order:

  1. const and variable defined file init() function execute

  2. init function execute order by the filename asc

CMake: How to build external projects and include their targets

This post has a reasonable answer:

cmake_minimum_required(VERSION 2.8.2)

project(googletest-download NONE)

  GIT_TAG           master
  SOURCE_DIR        "${CMAKE_BINARY_DIR}/googletest-src"
  BINARY_DIR        "${CMAKE_BINARY_DIR}/googletest-build"
  TEST_COMMAND      ""


# Download and unpack googletest at configure time
  WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/googletest-download )
execute_process(COMMAND ${CMAKE_COMMAND} --build .
  WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/googletest-download )

# Prevent GoogleTest from overriding our compiler/linker options
# when building with Visual Studio
set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)

# Add googletest directly to our build. This adds
# the following targets: gtest, gtest_main, gmock
# and gmock_main

# The gtest/gmock targets carry header search path
# dependencies automatically when using CMake 2.8.11 or
# later. Otherwise we have to add them here ourselves.

# Now simply link your own targets against gtest, gmock,
# etc. as appropriate

However it does seem quite hacky. I'd like to propose an alternative solution - use Git submodules.

cd MyProject/dependencies/gtest
git submodule add
cd googletest
git checkout release-1.8.0
cd ../../..
git add *
git commit -m "Add googletest"

Then in MyProject/dependencies/gtest/CMakeList.txt you can do something like:

cmake_minimum_required(VERSION 3.3)

if(TARGET gtest) # To avoid diamond dependencies; may not be necessary depending on you project.


I haven't tried this extensively yet but it seems cleaner.

Edit: There is a downside to this approach: The subdirectory might run install() commands that you don't want. This post has an approach to disable them but it was buggy and didn't work for me.

Edit 2: If you use add_subdirectory("googletest" EXCLUDE_FROM_ALL) it seems means the install() commands in the subdirectory aren't used by default.

Can a foreign key be NULL and/or duplicate?

I think foreign key of one table also primary key to some other table.So it won't allows nulls.So there is no question of having null value in foreign key.

Stopping Excel Macro executution when pressing Esc won't work

I forgot to comment out a line with a MsgBox before executing my macro. Meaning I'd have to click OK over a hundred thousand times. The ESC key was just escaping the message box but not stopping the execution of the macro. Holding the ESC key continuously for a few seconds helped me stop the execution of the code.

[Vue warn]: Property or method is not defined on the instance but referenced during render


[Vue warn]: Property or method "changeSetting" is not defined on the instance but referenced during render. Make sure to declare reactive data properties in the data option. (found in <MainTable>)

The error is occurring because the changeSetting method is being referenced in the MainTable component here:

    "<button @click='changeSetting(index)'> Info </button>" +

However the changeSetting method is not defined in the MainTable component. It is being defined in the root component here:

var app = new Vue({
  el: "#settings",
  data: data,
  methods: {
    changeSetting: function(index) {
      data.settingsSelected = data.settings[index];

What needs to be remembered is that properties and methods can only be referenced in the scope where they are defined.

Everything in the parent template is compiled in parent scope; everything in the child template is compiled in child scope.

You can read more about component compilation scope in Vue's documentation.

What can I do about it?

So far there has been a lot of talk about defining things in the correct scope so the fix is just to move the changeSetting definition into the MainTable component?

It seems that simple but here's what I recommend.

You'd probably want your MainTable component to be a dumb/presentational component. (Here is something to read if you don't know what it is but a tl;dr is that the component is just responsible for rendering something – no logic). The smart/container element is responsible for the logic – in the example given in your question the root component would be the smart/container component. With this architecture you can use Vue's parent-child communication methods for the components to interact. You pass down the data for MainTable via props and emit user actions from MainTable to its parent via events. It might look something like this:

Vue.component('main-table', {
  template: "<ul>" +
    "<li v-for='(set, index) in settings'>" +
    "{{index}}) " +
    "{{set.title}}" +
    "<button @click='changeSetting(index)'> Info </button>" +
    "</li>" +
  props: ['settings'],
  methods: {
    changeSetting(value) {
      this.$emit('change', value);

var app = new Vue({
  el: '#settings',
  template: '<main-table :settings="data.settings" @change="changeSetting"></main-table>',
  data: data,
  methods: {
    changeSetting(value) {
      // Handle changeSetting

The above should be enough to give you a good idea of what to do and kickstart resolving your issue.

How to output MySQL query results in CSV format?

The following bash script works for me. It optionally also gets the schema for the requested tables.

# export mysql data to CSV

#ansi colors
green='\033[0;32m' # '\e[1;32m' is too bright for white bg.

# a colored message 
#   params:
#     1: l_color - the color of the message
#     2: l_msg - the message to display
color_msg() {
  local l_color="$1"
  local l_msg="$2"
  echo -e "${l_color}$l_msg${endColor}"

# error
# show the given error message on stderr and exit
#   params:
#     1: l_msg - the error message to display
error() {
  local l_msg="$1"
  # use ansi red for error
  color_msg $red "Error:" 1>&2
  color_msg $red "\t$l_msg" 1>&2

# display usage 
usage() {
  echo "usage: $0 [-h|--help]" 1>&2
  echo "               -o  | --output      csvdirectory"    1>&2
  echo "               -d  | --database    database"   1>&2
  echo "               -t  | --tables      tables"     1>&2
  echo "               -p  | --password    password"   1>&2
  echo "               -u  | --user        user"       1>&2
  echo "               -hs | --host        host"       1>&2
  echo "               -gs | --get-schema"             1>&2
  echo "" 1>&2
  echo "     output: output csv directory to export mysql data into" 1>&2
  echo "" 1>&2
  echo "         user: mysql user" 1>&2
  echo "     password: mysql password" 1>&2
  echo "" 1>&2
  echo "     database: target database" 1>&2
  echo "       tables: tables to export" 1>&2
  echo "         host: host of target database" 1>&2
  echo "" 1>&2
  echo "  -h|--help: show help" 1>&2
  exit 1

# show help 
help() {
  echo "$0 Help" 1>&2
  echo "===========" 1>&2
  echo "$0 exports a csv file from a mysql database optionally limiting to a list of tables" 1>&2
  echo "   example: $0 --database=cms --user=scott --password=tiger  --tables=person --output person.csv" 1>&2
  echo "" 1>&2

domysql() {
  mysql --host $host -u$user --password=$password $database

getcolumns() {
  local l_table="$1"
  echo "describe $l_table" | domysql | cut -f1 | grep -v "Field" | grep -v "Warning" | paste -sd "," - 2>/dev/null


# parse command line options
while true; do
  #echo "option $1"
  case "$1" in
    # options without arguments
    -h|--help) usage;;
    -d|--database)     database="$2" ; shift ;;
    -t|--tables)       tables="$2" ; shift ;;
    -o|--output)       csvoutput="$2" ; shift ;;
    -u|--user)         user="$2" ; shift ;;
    -hs|--host)        host="$2" ; shift ;;
    -p|--password)     password="$2" ; shift ;;
    -gs|--get-schema)  option="getschema";; 
    (--) shift; break;;
    (-*) echo "$0: error - unrecognized option $1" 1>&2; usage;;
    (*) break;;

# checks
if [ "$csvoutput" == "" ]
  error "ouput csv directory not set"
if [ "$database" == "" ]
  error "mysql database not set"
if [ "$user" == "" ]
  error "mysql user not set"
if [ "$password" == "" ]
  error "mysql password not set"

color_msg $blue "exporting tables of database $database"
if [ "$tables" = "" ]
tables=$(echo "show tables" | domysql)

case $option in
   rm $csvoutput$database.schema
   for table in $tables
     color_msg $blue "getting schema for $table"
     echo -n "$table:" >> $csvoutput$database.schema
     getcolumns $table >> $csvoutput$database.schema
for table in $tables
  color_msg $blue "exporting table $table"
  cols=$(grep "$table:" $csvoutput$database.schema | cut -f2 -d:)
  if [  "$cols" = "" ]
    cols=$(getcolumns $table)
  ssh $host rm $mysqlfiles/$table.csv
cat <<EOF | mysql --host $host -u$user --password=$password $database 
SELECT $cols FROM $table INTO OUTFILE '$mysqlfiles$table.csv'
  scp $host:$mysqlfiles/$table.csv $csvoutput$table.csv.raw
  (echo "$cols"; cat $csvoutput$table.csv.raw) > $csvoutput$table.csv
  rm $csvoutput$table.csv.raw

Add a row number to result set of a SQL query

So before MySQL 8.0 there is no ROW_NUMBER() function. Accpted answer rewritten to support older versions of MySQL:

SET @row_number = 0;
SELECT t.A, t.B, t.C, (@row_number:=@row_number + 1) AS number
FROM dbo.tableZ AS t ORDER BY t.A;

How to convert string to IP address and vice versa

This example shows how to convert from string to ip, and viceversa:

struct sockaddr_in sa;
char ip_saver[INET_ADDRSTRLEN];

// store this IP address in sa:
inet_pton(AF_INET, "", &(sa.sin_addr));

// now get it back 
sprintf(ip_saver, "%s", sa.sin_addr));

// prints ""
printf("%s\n", ip_saver); 

HTML text input allow only numeric input

You can use pattern for this:

<input id="numbers" pattern="[0-9.]+" type="number">

Here you can see the complete mobile website interface tips.

Eclipse will not open due to environment variables

very easy, you just copy the folder 'jre' to the folder that you put eclipse. That'all. Jre is the environment, normally it's location in the C:/Programing Files/Java/jre :D

Fix GitLab error: "you are not allowed to push code to protected branches on this project"?

I was on Windows when this problem appeared.

The error is strange because it happens before I could enter my username and my password. What if there was a cache or something like this? I dig it online and found this answer on gitlab's support forum:

I open "Control Panel => User Accounts => Manage your credentials => Windows Credentials" I found two for and one was the wrong user. I deleted it and on the next "git push" I was reprompted and provided the correct credentials and it worked! Some other notes - this could have happened with any git remote.

In the Windows Credentials, I found two GitLab entries for an old account. I remove both and now it works!

The panel:

enter image description here

How to Set Active Tab in jQuery Ui

just trigger a click, it's work for me:


How to use pip with Python 3.x alongside Python 2.x

First, install Python 3 pip using:

sudo apt-get install python3-pip

Then, to use Python 3 pip use:

pip3 install <module-name>

For Python 2 pip use:

pip install <module-name>

Multi-dimensional arraylist or list in C#?

Depending on your exact requirements, you may do best with a jagged array of sorts with:

List<string>[] results = new { new List<string>(), new List<string>() };

Or you may do well with a list of lists or some other such construct.

Android Fastboot devices not returning device

You must run fastboot as root. Try sudo fastboot

Amazon Linux: apt-get: command not found

You need to manually download the apt deb package. Then run dpkg and it should install.

Passing headers with axios POST request


I had the same issue and the reason was that I hadn't returned the response in the interceptor. Javascript thought, rightfully so, that I wanted to return undefined for the promise:

// Add a request interceptor
axios.interceptors.request.use(function (config) {
    // Do something before request is sent
    return config;
  }, function (error) {
    // Do something with request error
    return Promise.reject(error);

CSS: how do I create a gap between rows in a table?

You could also just modify the height for each row using CSS.

 tr {


<tr> <td>One</td> <td>Two</td> </tr>
<tr> <td>Three</td> <td>Four</td> </tr>
<tr> <td>Five</td> <td>Six</td> </tr>


You could also modify the height of the <td> element, it should give you the same result.

Converting EditText to int? (Android)

Try this,

EditText x = (EditText) findViewById(;
int n = Integer.parseInt(x.getText().toString());

JWT (Json Web Token) Audience "aud" versus Client_Id - What's the difference?

If you came here searching OpenID Connect (OIDC): OAuth 2.0 != OIDC

I recognize that this is tagged for oauth 2.0 and NOT OIDC, however there is frequently a conflation between the 2 standards since both standards can use JWTs and the aud claim. And one (OIDC) is basically an extension of the other (OAUTH 2.0). (I stumbled across this question looking for OIDC myself.)

OAuth 2.0 Access Tokens##

For OAuth 2.0 Access tokens, existing answers pretty well cover it. Additionally here is one relevant section from OAuth 2.0 Framework (RFC 6749)

For public clients using implicit flows, this specification does not provide any method for the client to determine what client an access token was issued to.
Authenticating resource owners to clients is out of scope for this specification. Any specification that uses the authorization process as a form of delegated end-user authentication to the client (e.g., third-party sign-in service) MUST NOT use the implicit flow without additional security mechanisms that would enable the client to determine if the access token was issued for its use (e.g., audience- restricting the access token).

OIDC ID Tokens##

OIDC has ID Tokens in addition to Access tokens. The OIDC spec is explicit on the use of the aud claim in ID Tokens. (openid-connect-core-1.0)

REQUIRED. Audience(s) that this ID Token is intended for. It MUST contain the OAuth 2.0 client_id of the Relying Party as an audience value. It MAY also contain identifiers for other audiences. In the general case, the aud value is an array of case sensitive strings. In the common special case when there is one audience, the aud value MAY be a single case sensitive string.

furthermore OIDC specifies the azp claim that is used in conjunction with aud when aud has more than one value.

OPTIONAL. Authorized party - the party to which the ID Token was issued. If present, it MUST contain the OAuth 2.0 Client ID of this party. This Claim is only needed when the ID Token has a single audience value and that audience is different than the authorized party. It MAY be included even when the authorized party is the same as the sole audience. The azp value is a case sensitive string containing a StringOrURI value.

How to select an option from drop down using Selenium WebDriver C#?

To Select an Option Via Text;

(new SelectElement(driver.FindElement(By.XPath(""))).SelectByText("");

To Select an Option via Value:

 (new SelectElement(driver.FindElement(By.XPath(""))).SelectByValue("");

Downloading a file from spring controllers

You should be able to write the file on the response directly. Something like

response.setHeader("Content-Disposition", "attachment; filename=\"somefile.pdf\""); 

and then write the file as a binary stream on response.getOutputStream(). Remember to do response.flush() at the end and that should do it. (Access is denied)

Here's a gotcha that I just discovered - perhaps it might help someone else. If using windows the classes folder must not have encryption enabled! Tomcat doesn't seem to like that. Right click on the classes folder, select "Properties" and then click the "Advanced..." button. Make sure the "Encrypt contents to secure data" checkbox is cleared. Restart Tomcat.

It worked for me so here's hoping it helps someone else, too.

True/False vs 0/1 in MySQL

Some "front ends", with the "Use Booleans" option enabled, will treat all TINYINT(1) columns as Boolean, and vice versa.

This allows you to, in the application, use TRUE and FALSE rather than 1 and 0.

This doesn't affect the database at all, since it's implemented in the application.

There is not really a BOOLEAN type in MySQL. BOOLEAN is just a synonym for TINYINT(1), and TRUE and FALSE are synonyms for 1 and 0.

If the conversion is done in the compiler, there will be no difference in performance in the application. Otherwise, the difference still won't be noticeable.

You should use whichever method allows you to code more efficiently, though not using the feature may reduce dependency on that particular "front end" vendor.

How to check if a DateTime field is not null or empty?

DateTime is not standard nullable type. If you want assign null to DateTime type of variable, you have to use DateTime? type which supports null value.

If you only want test your variable to be set (e.g. variable holds other than default value), you can use keyword "default" like in following code:

if (dateTimeVariable == default(DateTime))
    //do work for dateTimeVariable == null situation

SASS - use variables across multiple files

This question was asked a long time ago so I thought I'd post an updated answer.

You should now avoid using @import. Taken from the docs:

Sass will gradually phase it out over the next few years, and eventually remove it from the language entirely. Prefer the @use rule instead.

A full list of reasons can be found here

You should now use @use as shown below:


$text-colour: #262626;


@use 'variables'; // Path to _variables.scss Notice how we don't include the underscore or file extension

body {
  // namespace.$variable-name
  // namespace is just the last component of its URL without a file extension
  color: variables.$text-colour;

You can also create an alias for the namespace:


@use 'variables' as v;

body {
  // alias.$variable-name
  color: v.$text-colour;

EDIT As pointed out by @und3rdg at the time of writing (November 2020) @use is currently only available for Dart Sass and not LibSass (now deprecated) or Ruby Sass. See for the latest compatibility

Get current user id in ASP.NET Identity 2.0

In order to get CurrentUserId in Identity 2.0, at first import Microsoft.AspNet.Identity:


using Microsoft.AspNet.Identity;


Imports Microsoft.AspNet.Identity

And then call User.Identity.GetUserId() everywhere you want:

strCurrentUserId = User.Identity.GetUserId()

This method returns current user id as defined datatype for userid in database (the default is String).

Android: How to handle right to left swipe gestures

If you also need to process click events here some modifications:

public class OnSwipeTouchListener implements OnTouchListener {

    private final GestureDetector gestureDetector = new GestureDetector(new GestureListener());

    public boolean onTouch(final View v, final MotionEvent event) {
        return gestureDetector.onTouchEvent(event);

    private final class GestureListener extends SimpleOnGestureListener {

        private static final int SWIPE_THRESHOLD = 100;
        private static final int SWIPE_VELOCITY_THRESHOLD = 100;

        public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
            boolean result = false;
            try {
                float diffY = e2.getY() - e1.getY();
                float diffX = e2.getX() - e1.getX();
                if (Math.abs(diffX) > Math.abs(diffY)) {
                    if (Math.abs(diffX) > SWIPE_THRESHOLD && Math.abs(velocityX) > SWIPE_VELOCITY_THRESHOLD) {
                        if (diffX > 0) {
                            result = onSwipeRight();
                        } else {
                            result = onSwipeLeft();
                } else {
                    if (Math.abs(diffY) > SWIPE_THRESHOLD && Math.abs(velocityY) > SWIPE_VELOCITY_THRESHOLD) {
                        if (diffY > 0) {
                            result = onSwipeBottom();
                        } else {
                            result = onSwipeTop();
            } catch (Exception exception) {
            return result;

    public boolean onSwipeRight() {
        return false;

    public boolean onSwipeLeft() {
        return false;

    public boolean onSwipeTop() {
        return false;

    public boolean onSwipeBottom() {
        return false;

And sample usage:

    background.setOnClickListener(new View.OnClickListener() {
        public void onClick(View arg0) {
    background.setOnTouchListener(new OnSwipeTouchListener() {
        public boolean onSwipeTop() {
            Toast.makeText(MainActivity.this, "top", Toast.LENGTH_SHORT).show();
            return true;
        public boolean onSwipeRight() {
            Toast.makeText(MainActivity.this, "right", Toast.LENGTH_SHORT).show();
            return true;
        public boolean onSwipeLeft() {
            Toast.makeText(MainActivity.this, "left", Toast.LENGTH_SHORT).show();
            return true;
        public boolean onSwipeBottom() {
            Toast.makeText(MainActivity.this, "bottom", Toast.LENGTH_SHORT).show();
            return true;

Difference between "module.exports" and "exports" in the CommonJs Module System

module is a plain JavaScript object with an exports property. exports is a plain JavaScript variable that happens to be set to module.exports. At the end of your file, node.js will basically 'return' module.exports to the require function. A simplified way to view a JS file in Node could be this:

var module = { exports: {} };
var exports = module.exports;

// your code

return module.exports;

If you set a property on exports, like exports.a = 9;, that will set module.exports.a as well because objects are passed around as references in JavaScript, which means that if you set multiple variables to the same object, they are all the same object; so then exports and module.exports are the same object.
But if you set exports to something new, it will no longer be set to module.exports, so exports and module.exports are no longer the same object.

Detect click outside Angular component

u can call event function like (focusout) or (blur) then u put your code

<div tabindex=0 (blur)="outsideClick()">raw data </div>

 outsideClick() {
  alert('put your condition here');

C++ convert string to hexadecimal and vice versa

You can try this. It's Working...

#include <algorithm>
#include <sstream>
#include <iostream>
#include <iterator>
#include <iomanip>

namespace {
   const std::string test="hello world";

int main() {
   std::ostringstream result;
   result << std::setw(2) << std::setfill('0') << std::hex << std::uppercase;
   std::copy(test.begin(), test.end(), std::ostream_iterator<unsigned int>(result, " "));
   std::cout << test << ":" << result.str() << std::endl;

What's the Use of '\r' escape sequence?

As amaud576875 said, the \r escape sequence signifies a carriage-return, similar to pressing the Enter key. However, I'm not sure how you get "o world"; you should (and I do) get "my first hello world" and then a new line. Depending on what operating system you're using (I'm using Mac) you might want to use a \n instead of a \r.

How can I use custom fonts on a website?

Yes, there is a way. Its called custom fonts in CSS.Your CSS needs to be modified, and you need to upload those fonts to your website.

The CSS required for this is:

@font-face {
     font-family: Thonburi-Bold;
     src: url('pathway/Thonburi-Bold.otf'); 

How to underline a UILabel in swift?

Same Answer in Swift 4.2

For UILable

extension UILabel {
    func underline() {
        if let textString = self.text {
            let attributedString = NSMutableAttributedString(string: textString)
                                          value: NSUnderlineStyle.single.rawValue,
                                          range: NSRange(location: 0, length: textString.count))
            self.attributedText = attributedString

Call for UILabel like below


For UIButton

extension UIButton {
    func underline() {
        if let textString = self.titleLabel?.text {

            let attributedString = NSMutableAttributedString(string: textString)
                                          value: NSUnderlineStyle.single.rawValue,
                                          range: NSRange(location: 0, length: textString.count))
            self.setAttributedTitle(attributedString, for: .normal)


Call for UIButton like below


I looked into above answers and some of them are force unwrapping text value. I will suggest to get value by safely unwrapping. This will avoid crash in case of nil value. Hope This helps :)

Calculate a MD5 hash from a string

I'd like to offer an alternative that appears to perform at least 10% faster than craigdfrench's answer in my tests (.NET 4.7.2):

public static string GetMD5Hash(string text)
    using ( var md5 = MD5.Create() )
        byte[] computedHash = md5.ComputeHash( Encoding.UTF8.GetBytes(text) );
        return new System.Runtime.Remoting.Metadata.W3cXsd2001.SoapHexBinary(computedHash).ToString();

If you prefer to have using System.Runtime.Remoting.Metadata.W3cXsd2001; at the top, the method body can be made an easier to read one-liner:

using ( var md5 = MD5.Create() )
    return new SoapHexBinary( md5.ComputeHash( Encoding.UTF8.GetBytes(text) ) ).ToString();

Obvious enough, but for completeness, in OP's context it would be used as:

sSourceData = "MySourceData";
tmpHash = GetMD5Hash(sSourceData);

Why is this HTTP request not working on AWS Lambda?

enter image description here

Add above code in API gateway under GET-Integration Request> mapping section.

Difference between the Apache HTTP Server and Apache Tomcat?

an apache server is an http server which can serve any simple http requests, where tomcat server is actually a servlet container which can serve java servlet requests.

Web server [apache] process web client (web browsers) requests and forwards it to servlet container [tomcat] and container process the requests and sends response which gets forwarded by web server to the web client [browser].

Also you can check this link for more clarification:-

Also check this answer for further researching :-

What are invalid characters in XML

For Java folks, Apache has a utility class (StringEscapeUtils) that has a helper method escapeXml which can be used for escaping characters in a string using XML entities.

It says that TypeError: document.getElementById(...) is null

I got the same error. In my case I had multiple div with same id in a page. I renamed the another id of the div used and fixed the issue.

So confirm whether the element:

  • exists with id
  • doesn't have duplicate with id
  • confirm whether the script is called

How to get all selected values from <select multiple=multiple>?

If you need to respond to changes, you can try this:

document.getElementById('select-meal-type').addEventListener('change', function(e) {
    let values = [] => a.value));

The [] is needed because returns a HTMLCollection, not an Array. That call converts it to Array so that we can then apply the map function, which extract the values.

Call to undefined function App\Http\Controllers\ [ function name ]

If they are in the same controller class, it would be:

foreach ( $characters as $character) {
    $num += $this->getFactorial($index) * $index;
    $index ++;

Otherwise you need to create a new instance of the class, and call the method, ie:

$controller = new MyController();
foreach ( $characters as $character) {
    $num += $controller->getFactorial($index) * $index;
    $index ++;

How to not wrap contents of a div?

I don't know the reasoning behind this, but I set my parent container to display:flex and the child containers to display:inline-block and they stayed inline despite the combined width of the children exceeding the parent.

Didn't need to toy with max-width, max-height, white-space, or anything else.

Hope that helps someone.

XSD - how to allow elements in any order any number of times?

But from what I understand xs:choice still only allows single element selection. Hence setting the MaxOccurs to unbounded like this should only mean that "any one" of the child elements can appear multiple times. Is this accurate?

No. The choice happens individually for every "repetition" of xs:choice that occurs due to maxOccurs="unbounded". Therefore, the code that you have posted is correct, and will actually do what you want as written.

How to add a browser tab icon (favicon) for a website?

I have created an online Favicon Generator with which you can create favicons from Font Awesome Icons. You can preview the created favicon live in the browser.

enter image description here

If you want additional features please feel free to submit an issue or a pull request here :).

Proper way to handle multiple forms on one page in Django

You have a few options:

  1. Put different URLs in the action for the two forms. Then you'll have two different view functions to deal with the two different forms.

  2. Read the submit button values from the POST data. You can tell which submit button was clicked: How can I build multiple submit buttons django form?

How do I disable the security certificate check in Python requests

If you want to send exactly post request with verify=False option, fastest way is to use this code:

import requests

requests.api.request('post', url, data={'bar':'baz'}, json=None, verify=False)

SQL Server loop - how do I loop through a set of records

Small change to sam yi's answer (for better readability):

select top 1000 TableID
into #ControlTable 
from dbo.table
where StatusID = 7

declare @TableID int

while exists (select * from #ControlTable)

    select @TableID = (select top 1 TableID
                       from #ControlTable
                       order by TableID asc)

    -- Do something with your TableID

    delete #ControlTable
    where TableID = @TableID


drop table #ControlTable

How to do join on multiple criteria, returning all combinations of both criteria

create table a1
(weddingTable INT(3),
 tableSeat INT(3),
 tableSeatID INT(6),
 Name varchar(10));

insert into a1
 (weddingTable, tableSeat, tableSeatID, Name)
 values (001,001,001001,'Bob'),

create table a2
 (weddingTable int(3),
 tableSeat int(3),
 Meal varchar(10));

insert into a2
(weddingTable, tableSeat, Meal)

select x.*, y.Meal

from a1 as x
JOIN a2 as y ON (x.weddingTable = y.weddingTable) AND (x.tableSeat = y. tableSeat);

How to convert binary string value to decimal

According to this : 1 we can write this help function :

    public static int convertBinaryToDecimal(String str) {
        int result = 0;
        for (int i = 0; i < str.length(); i++) {
            int value = Character.getNumericValue(str.charAt(i));
            result = result * 2 + value;
        return result;

Does reading an entire file leave the file handle open?

Well, if you have to read file line by line to work with each line, you can use

with open('Path/to/file', 'r') as f:
    s = f.readline()
    while s:
        # do whatever you want to
        s = f.readline()

Or even better way:

with open('Path/to/file') as f:
    for line in f:
        # do whatever you want to

Initializing entire 2D array with one value

Note that GCC has an extension to the designated initializer notation which is very useful for the context. It is also allowed by clang without comment (in part because it tries to be compatible with GCC).

The extension notation allows you to use ... to designate a range of elements to be initialized with the following value. For example:

#include <stdio.h>

enum { ROW = 5, COLUMN = 10 };

int array[ROW][COLUMN] = { [0 ... ROW-1] = { [0 ... COLUMN-1] = 1 } };

int main(void)
    for (int i = 0; i < ROW; i++)
        for (int j = 0; j < COLUMN; j++)
            printf("%2d", array[i][j]);
    return 0;

The output is, unsurprisingly:

 1 1 1 1 1 1 1 1 1 1
 1 1 1 1 1 1 1 1 1 1
 1 1 1 1 1 1 1 1 1 1
 1 1 1 1 1 1 1 1 1 1
 1 1 1 1 1 1 1 1 1 1

Note that Fortran 66 (Fortran IV) had repeat counts for initializers for arrays; it's always struck me as odd that C didn't get them when designated initializers were added to the language. And Pascal uses the 0..9 notation to designate the range from 0 to 9 inclusive, but C doesn't use .. as a token, so it is not surprising that was not used.

Note that the spaces around the ... notation are essentially mandatory; if they're attached to numbers, then the number is interpreted as a floating point number. For example, 0...9 would be tokenized as 0., ., .9, and floating point numbers aren't allowed as array subscripts. With the named constants, ...ROW-1 would not cause trouble, but it is better to get into the safe habits.


I note in passing that GCC 7.3.0 rejects:

int array[ROW][COLUMN] = { [0 ... ROW-1] = { [0 ... COLUMN-1] = { 1 } } };

where there's an extra set of braces around the scalar initializer 1 (error: braces around scalar initializer [-Werror]). I'm not sure that's correct given that you can normally specify braces around a scalar in int a = { 1 };, which is explicitly allowed by the standard. I'm not certain it's incorrect, either.

I also wonder if a better notation would be [0]...[9] — that is unambiguous, cannot be confused with any other valid syntax, and avoids confusion with floating point numbers.

int array[ROW][COLUMN] = { [0]...[4] = { [0]...[9] = 1 } };

Maybe the standards committee would consider that?

Displaying better error message than "No JSON object could be decoded"

Just hit the same issue and in my case the problem was related to BOM (byte order mark) at the beginning of the file.

json.tool would refuse to process even empty file (just curly braces) until i removed the UTF BOM mark.

What I have done is:

  • opened my json file with vim,
  • removed byte order mark (set nobomb)
  • save file

This resolved the problem with json.tool. Hope this helps!

How to format date and time in Android?

This code work for me!

Date d = new Date();
    CharSequence s = android.text.format.DateFormat.format("MM-dd-yy hh-mm-ss",d.getTime());

error LNK2038: mismatch detected for '_MSC_VER': value '1600' doesn't match value '1700' in CppFile1.obj

I was importing also some projects from VS2010 to VS 2012. I had the same errors. The errors disappeared when I set back Properties > Config. Properties > General > Platform Toolset to v100 (VS2010). That might not be the correct approach, however.

On delete cascade with doctrine2

Here is simple example. A contact has one to many associated phone numbers. When a contact is deleted, I want all its associated phone numbers to also be deleted, so I use ON DELETE CASCADE. The one-to-many/many-to-one relationship is implemented with by the foreign key in the phone_numbers.

 PRIMARY KEY(contact_id)) ENGINE = InnoDB;

CREATE TABLE phone_numbers
  phone_number CHAR(10) NOT NULL,
 contact_id BIGINT NOT NULL,
 PRIMARY KEY(phone_id),
 UNIQUE(phone_number)) ENGINE = InnoDB;

ALTER TABLE phone_numbers ADD FOREIGN KEY (contact_id) REFERENCES \
contacts(contact_id) ) ON DELETE CASCADE;

By adding "ON DELETE CASCADE" to the foreign key constraint, phone_numbers will automatically be deleted when their associated contact is deleted.

INSERT INTO table contacts(name) VALUES('Robert Smith');
INSERT INTO table phone_numbers(phone_number, contact_id) VALUES('8963333333', 1);
INSERT INTO table phone_numbers(phone_number, contact_id) VALUES('8964444444', 1);

Now when a row in the contacts table is deleted, all its associated phone_numbers rows will automatically be deleted.

DELETE TABLE contacts as c WHERE; /* delete cascades to phone_numbers */

To achieve the same thing in Doctrine, to get the same DB-level "ON DELETE CASCADE" behavoir, you configure the @JoinColumn with the onDelete="CASCADE" option.

namespace Entities;

use Doctrine\Common\Collections\ArrayCollection;

 * @Entity
 * @Table(name="contacts")
class Contact 

     *  @Id
     *  @Column(type="integer", name="contact_id") 
     *  @GeneratedValue
    protected $id;  

     * @Column(type="string", length="75", unique="true") 
    protected $name; 

     * @OneToMany(targetEntity="Phonenumber", mappedBy="contact")
    protected $phonenumbers; 

    public function __construct($name=null)
        $this->phonenumbers = new ArrayCollection();

        if (!is_null($name)) {

            $this->name = $name;

    public function getId()
        return $this->id;

    public function setName($name)
        $this->name = $name;

    public function addPhonenumber(Phonenumber $p)
        if (!$this->phonenumbers->contains($p)) {

            $this->phonenumbers[] = $p;

    public function removePhonenumber(Phonenumber $p)

namespace Entities;

 * @Entity
 * @Table(name="phonenumbers")
class Phonenumber 

    * @Id
    * @Column(type="integer", name="phone_id") 
    * @GeneratedValue
    protected $id; 

     * @Column(type="string", length="10", unique="true") 
    protected $number;

     * @ManyToOne(targetEntity="Contact", inversedBy="phonenumbers")
     * @JoinColumn(name="contact_id", referencedColumnName="contact_id", onDelete="CASCADE")
    protected $contact; 

    public function __construct($number=null)
        if (!is_null($number)) {

            $this->number = $number;

    public function setPhonenumber($number)
        $this->number = $number;

    public function setContact(Contact $c)
        $this->contact = $c;


$em = \Doctrine\ORM\EntityManager::create($connectionOptions, $config);

$contact = new Contact("John Doe"); 

$phone1 = new Phonenumber("8173333333");
$phone2 = new Phonenumber("8174444444");

try {

} catch(Exception $e) {

    $m = $e->getMessage();
    echo $m . "<br />\n";

If you now do

# doctrine orm:schema-tool:create --dump-sql

you will see that the same SQL will be generated as in the first, raw-SQL example

SQLite in Android How to update a specific row

you can try this...


Change "on" color of a Switch

To change Switch style without using style.xml or Java code, you can customize switch into layout XML :

        android:layout_height="wrap_content" />

It's attribute android:thumbTint and android:trackTint that allowed you to customize color

This is the visual result for this XML :

enter image description here

Getting next element while cycling through a list

A rather different way to solve this:

   li = [0,1,2,3]

   for i in range(len(li)):

       if i < len(li)-1:

           # until end is reached
           print 'this', li[i]
           print 'next', li[i+1]


           # end
           print 'this', li[i]

How organize uploaded media in WP?

The plugin Media File Manager advanced is amazing and allow you to create folders and subfolders very easily and move files with a simple drag & drop.

Check it at:

Declare global variables in Visual Studio 2010 and VB.NET

small remark: I am using modules in webbased application ( I need to remember that everything I store in the variables on the module are seen by everyone in the application, read website. Not only in my session. If i try to add up a calculation in my session I need to make an array to filter the numbers for my session and for others. Modules is a great way to work but need concentration on how to use it.

To help against mistakes: classes are send to the


when the page is finished. My modules stay alive (as long as the application is not ended or restarted) and I can reuse the data in it. I use this to save data that sometimes is lost because of the sessionhandling by IIS.

IIS Form auth



are not in sync, and with my module I pull back data that went over de cliff.

Removing the remembered login and password list in SQL Server Management Studio

For SQL Server Management Studio 2008

  1. You need to go C:\Documents and Settings\%username%\Application Data\Microsoft\Microsoft SQL Server\100\Tools\Shell

  2. Delete SqlStudio.bin

npm install hangs

*Try doing sudo npm install.

*If you're using github then it could be you don't have permission and need to generated a public SSH key and add it to your settings account: (

How to format column to number format in Excel sheet?

This will format column A as text, B as General, C as a number.

Sub formatColumns()
 Columns(1).NumberFormat = "@"
 Columns(2).NumberFormat = "General"
 Columns(3).NumberFormat = "0"
End Sub

Export data from Chrome developer tool

I had same issue for which I came here. With some trials, I figured out for copying multiple pages of chrome data as in the question I zoomed out till I got all the data in one page, that is, without scroll, with very small font size. Now copy and paste that in excel which copies all the records and in normal font. This is good for few pages of data I think.

How to get `DOM Element` in Angular 2?

Update (using renderer):

Note that the original Renderer service has now been deprecated in favor of Renderer2

as on Renderer2 official doc.

Furthermore, as pointed out by @GünterZöchbauer:

Actually using ElementRef is just fine. Also using ElementRef.nativeElement with Renderer2 is fine. What is discouraged is accessing properties of directly.

You can achieve this by using elementRef as well as by ViewChild. however it's not recommendable to use elementRef due to:

  • security issue
  • tight coupling

as pointed out by official ng2 documentation.

1. Using elementRef (Direct Access):

export class MyComponent {    
constructor (private _elementRef : ElementRef) {

2. Using ViewChild (better approach):

<textarea  #tasknote name="tasknote" [(ngModel)]="taskNote" placeholder="{{ notePlaceholder }}" 
style="background-color: pink" (blur)="updateNote() ; noteEditMode = false " (click)="noteEditMode = false"> {{ todo.note }} </textarea> // <-- changes id to local var

export class MyComponent implements AfterViewInit {
  @ViewChild('tasknote') input: ElementRef;

   ngAfterViewInit() {


3. Using renderer:

export class MyComponent implements AfterViewInit {
      @ViewChild('tasknote') input: ElementRef;
         constructor(private renderer: Renderer2){           

       ngAfterViewInit() {
       //using selectRootElement instead of depreaced invokeElementMethod


Is there any advantage of using map over unordered_map in case of trivial keys?

I was intrigued by the answer from @Jerry Coffin, which suggested that the ordered map would exhibit performance increases on long strings, after some experimentation (which can be downloaded from pastebin), I've found that this seems to hold true only for collections of random strings, when the map is initialised with a sorted dictionary (which contain words with considerable amounts of prefix-overlap), this rule breaks down, presumably because of the increased tree depth necessary to retrieve value. The results are shown below, the 1st number column is insert time, 2nd is fetch time.

g++ -g -O3 --std=c++0x   -c -o stdtests.o stdtests.cpp
g++ -o stdtests stdtests.o
gmurphy@interloper:HashTests$ ./stdtests
# 1st number column is insert time, 2nd is fetch time
 ** Integer Keys ** 
 unordered:      137      15
   ordered:      168      81
 ** Random String Keys ** 
 unordered:       55      50
   ordered:       33      31
 ** Real Words Keys ** 
 unordered:      278      76
   ordered:      516     298

Custom HTTP headers : naming conventions

The recommendation is was to start their name with "X-". E.g. X-Forwarded-For, X-Requested-With. This is also mentioned in a.o. section 5 of RFC 2047.

Update 1: On June 2011, the first IETF draft was posted to deprecate the recommendation of using the "X-" prefix for non-standard headers. The reason is that when non-standard headers prefixed with "X-" become standard, removing the "X-" prefix breaks backwards compatibility, forcing application protocols to support both names (E.g, x-gzip & gzip are now equivalent). So, the official recommendation is to just name them sensibly without the "X-" prefix.

Update 2: On June 2012, the deprecation of recommendation to use the "X-" prefix has become official as RFC 6648. Below are cites of relevance:

3. Recommendations for Creators of New Parameters


  1. SHOULD NOT prefix their parameter names with "X-" or similar constructs.

4. Recommendations for Protocol Designers


  1. SHOULD NOT prohibit parameters with an "X-" prefix or similar constructs from being registered.

  2. MUST NOT stipulate that a parameter with an "X-" prefix or similar constructs needs to be understood as unstandardized.

  3. MUST NOT stipulate that a parameter without an "X-" prefix or similar constructs needs to be understood as standardized.

Note that "SHOULD NOT" ("discouraged") is not the same as "MUST NOT" ("forbidden"), see also RFC 2119 for another spec on those keywords. In other words, you can keep using "X-" prefixed headers, but it's not officially recommended anymore and you may definitely not document them as if they are public standard.


  • the official recommendation is to just name them sensibly without the "X-" prefix
  • you can keep using "X-" prefixed headers, but it's not officially recommended anymore and you may definitely not document them as if they are public standard

IE11 meta element Breaks SVG

I was having the same problem with 3 of 4 inline svgs I was using, and they only disappeared (in one case, partially) on IE11.

I had <meta http-equiv="x-ua-compatible" content="ie=edge"> on the page.

In the end, the problem was extra clipping paths on the svg file. I opened the files on Illustrator, removed the clipping path (normally at the bottom of the layers) and now they're all working.

Wrap text in <td> tag

This works really well:

<td><div style = "width:80px; word-wrap: break-word"> your text </div></td> 

You can use the same width for all your <div's, or adjust the width in each case to break your text wherever you like.

This way you do not have to fool around with fixed table widths, or complex css.

Using JQuery hover with HTML image map

You should check out this plugin:

and the demo:

if anything, you might be able to borrow some code from it to fix yours.

How do I find out which DOM element has the focus?

If you want to get a object that is instance of Element, you must use document.activeElement, but if you want to get a object that is instance of Text, you must to use document.getSelection().focusNode.

I hope helps.

MySql Table Insert if not exist otherwise update

Jai is correct that you should use INSERT ... ON DUPLICATE KEY UPDATE.

Note that you do not need to include datenum in the update clause since it's the unique key, so it should not change. You do need to include all of the other columns from your table. You can use the VALUES() function to make sure the proper values are used when updating the other columns.

Here is your update re-written using the proper INSERT ... ON DUPLICATE KEY UPDATE syntax for MySQL:

INSERT INTO AggregatedData (datenum,Timestamp)
VALUES ("734152.979166667","2010-01-14 23:30:00.000")

How to create a byte array in C++?

Byte is not a standard type in C/C++, so it is represented by char.

An advantage of this is that you can treat a basic_string as a byte array allowing for safe storage and function passing. This will help you avoid the memory leaks and segmentation faults you might encounter when using the various forms of char[] and char*.

For example, this creates a string as a byte array of null values:

typedef basic_string<unsigned char> u_string;

u_string bytes = u_string(16,'\0');

This allows for standard bitwise operations with other char values, including those stored in other string variables. For example, to XOR the char values of another u_string across bytes:

u_string otherBytes = "some more chars, which are just bytes";
for(int i = 0; i < otherBytes.length(); i++)
    bytes[i%16] ^= (int)otherBytes[i];

Spring MVC: Error 400 The request sent by the client was syntactically incorrect

Please keep your

<form method="POST" action="XYZ">

@RequestMapping(value="/XYZ", method=RequestMethod.POST)
    public void handleSave(@RequestParam String action){

Your form action attribute value must match to value of @RequestMapping, So that Spring MVC can resolve it.

Also, as you told it is giving 404 after changing, for this, can you please check whether control is entering inside handleSave() method.

I think, as you are not returning any thing from handleSave() method, you have to look at it.

if it still not work, can you please post your spring logs.

Also, make sure that your request should come like


if there is anything between like PORTAL/jsp/save the mention in @RequestMapping(value="/jsp/save")

Graphical DIFF programs for linux

Subclipse for Eclipse has an excellent graphical diff plugin if you are using SVN (subversion) source control.

Save and load MemoryStream to/from a file

For anyone looking for the short versions:

var memoryStream = new MemoryStream(File.ReadAllBytes("1.dat"));

File.WriteAllBytes("1.dat", memoryStream.ToArray()); 

Unable to update the EntitySet - because it has a DefiningQuery and no <UpdateFunction> element exist

Open Your .edmx file in XML editor and then remove tag from Tag and also change store:Schema="dbo" to Schema="dbo" and rebuild the solution now error will resolve and you will be able to save the data.

pip issue installing almost any library

If it is only about nltk, I once faced similar problem. Try following guide for installation. Install NLTK

If you are sure it doesn't work with any other module, you may have problem with different versions of Python installed.

Or Give It a Try to see if it says pip is already installed.:

sudo apt-get install python-pip python-dev build-essential 

and see if it works.

Full Screen Theme for AppCompat

Based on the answer by @nebyan, I found that the action bar is still not hiding.

The following code works for me:

<style name="AppFullScreenTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <item name="android:windowNoTitle">true</item>
    <item name="android:windowActionBar">false</item>
    <item name="android:windowFullscreen">true</item>
    <item name="android:windowContentOverlay">@null</item>

and of course dont forgot to edit your AndroidManifest file.


JPA 2.0, Criteria API, Subqueries, In Expressions

Below is the pseudo-code for using sub-query using Criteria API.

CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
CriteriaQuery<Object> criteriaQuery = criteriaBuilder.createQuery();
Root<EMPLOYEE> from = criteriaQuery.from(EMPLOYEE.class);
Path<Object> path = from.get("compare_field"); // field to map with sub-query
CriteriaQuery<Object> select =;

Subquery<PROJECT> subquery = criteriaQuery.subquery(PROJECT.class);
Root fromProject = subquery.from(PROJECT.class);"requiredColumnName")); // field to map with main-query


TypedQuery<Object> typedQuery = entityManager.createQuery(select);
List<Object> resultList = typedQuery.getResultList();

Also it definitely needs some modification as I have tried to map it according to your query. Here is a link which explains concept nicely.

HRESULT: 0x80131040: The located assembly's manifest definition does not match the assembly reference

If you got this error trying to add a component to Visual Studio,- Microsoft.VisualStudio.TemplateWizardInterface - (after trying to install weird development tools)

consider this solution(courtesy of larocha (thanks, whoever you are)):

  1. Open C:\Program Files\Microsoft Visual Studio 9.0\Common7\IDE\devenv.exe.config in a text editor
  2. Find this string: "Microsoft.VisualStudio.TemplateWizardInterface"
  3. Comment out the element so it looks like this:

<!-- assemblyIdentity name="Microsoft.VisualStudio.TemplateWizardInterface" publicKeyToken="b03f5f7f11d50a3a" culture="neutral" / -->
<bindingRedirect oldVersion="" newVersion="" />


duplicate 'row.names' are not allowed error

In my case was a comma at the end of every line. By removing that worked

How to know which is running in Jupyter notebook?

import sys

Seen below :- output when i run JupyterNotebook outside a CONDA venv

2.7.12 |Anaconda 4.2.0 (64-bit)| (default, Jul  2 2016, 17:42:40) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-1)]
sys.version_info(major=2, minor=7, micro=12, releaselevel='final', serial=0)

Seen below when i run same JupyterNoteBook within a CONDA Venv created with command --

conda create -n py35 python=3.5 ## Here - py35 , is name of my VENV

in my Jupyter Notebook it prints :-

3.5.2 |Continuum Analytics, Inc.| (default, Jul  2 2016, 17:53:06) 
[GCC 4.4.7 20120313 (Red Hat 4.4.7-1)]
sys.version_info(major=3, minor=5, micro=2, releaselevel='final', serial=0)

also if you already have various VENV's created with different versions of Python you switch to the desired Kernel by choosing KERNEL >> CHANGE KERNEL from within the JupyterNotebook menu... JupyterNotebookScreencapture

Also to install ipykernel within an existing CONDA Virtual Environment -

Source ---

 $ /path/to/python -m  ipykernel install --help
 usage: ipython-kernel-install [-h] [--user] [--name NAME]
                          [--display-name DISPLAY_NAME]
                          [--profile PROFILE] [--prefix PREFIX]

Install the IPython kernel spec.

optional arguments: -h, --help show this help message and exit --user Install for the current user instead of system-wide --name NAME Specify a name for the kernelspec. This is needed to have multiple IPython kernels at the same time. --display-name DISPLAY_NAME Specify the display name for the kernelspec. This is helpful when you have multiple IPython kernels. --profile PROFILE Specify an IPython profile to load. This can be used to create custom versions of the kernel. --prefix PREFIX Specify an install prefix for the kernelspec. This is needed to install into a non-default location, such as a conda/virtual-env. --sys-prefix Install to Python's sys.prefix. Shorthand for --prefix='/Users/bussonniermatthias/anaconda'. For use in conda/virtual-envs.

Replacing few values in a pandas dataframe column with another value

loc function can be used to replace multiple values, Documentation for it : loc

df.loc[df['BrandName'].isin(['ABC', 'AB'])]='A'

How to create custom exceptions in Java?

For a checked exception:

public class MyCustomException extends Exception { }

Technically, anything that extends Throwable can be an thrown, but exceptions are generally extensions of the Exception class so that they're checked exceptions (except RuntimeException or classes based on it, which are not checked), as opposed to the other common type of throwable, Errors which usually are not something designed to be gracefully handled beyond the JVM internals.

You can also make exceptions non-public, but then you can only use them in the package that defines them, as opposed to across packages.

As far as throwing/catching custom exceptions, it works just like the built-in ones - throw via

throw new MyCustomException()

and catch via

catch (MyCustomException e) { }

How to vertically align into the center of the content of a div with defined width/height?

I found this solution in this article

.parent-element {
  -webkit-transform-style: preserve-3d;
  -moz-transform-style: preserve-3d;
  transform-style: preserve-3d;

.element {
  position: relative;
  top: 50%;
  transform: translateY(-50%);

It work like a charm if the height of element is not fixed.

Row count where data exists

I found this method on

This computes the number of non-blank cells in column A of worksheet named "Data"

With Worksheets("Data")
  Ndt =Application.Range("A:A").Cells.SpecialCells(xlCellTypeConstants).Count
  debug.print Ndt
End With

The result is printed to the immediate window. You need to subtract 1 (or more) if column A has a header line (or lines) you do not wish to count.

Iteration over std::vector: unsigned vs signed index variable

Regarding Johannes Schaub's answer:

for(std::vector<T*>::iterator it = v.begin(); it != v.end(); ++it) { 

That may work with some compilers but not with gcc. The problem here is the question if std::vector::iterator is a type, a variable (member) or a function (method). We get the following error with gcc:

In member function ‘void MyClass<T>::myMethod()’:
error: expected `;' before ‘it’
error: ‘it’ was not declared in this scope
In member function ‘void MyClass<T>::sort() [with T = MyClass]’:
instantiated from ‘void MyClass<T>::run() [with T = MyClass]’
instantiated from here
dependent-name ‘std::vector<T*,std::allocator<T*> >::iterator’ is parsed as a non-type, but instantiation yields a type
note: say ‘typename std::vector<T*,std::allocator<T*> >::iterator’ if a type is meant

The solution is using the keyword 'typename' as told:

typename std::vector<T*>::iterator it = v.begin();
for( ; it != v.end(); ++it) {

How to trigger Jenkins builds remotely and to pass parameters

In your Jenkins job configuration, tick the box named "This build is parameterized", click the "Add Parameter" button and select the "String Parameter" drop down value.

Now define your parameter - example:

Enter image description here

Now you can use your parameter in your job / build pipeline, example:

Enter image description here

Next to trigger the build with own/custom parameter, invoke the following URL (using either POST or GET):