Programs & Examples On #Magnetic cards

adding a datatable in a dataset

Just give any name to the DataTable Like:

DataTable dt = new DataTable();
dt = SecondDataTable.Copy();    
dt .TableName = "New Name";
DataSet.Tables.Add(dt );

Celery Received unregistered task of type (run example)

when running the celery with "celery -A conf worker -l info" command all the tasks got listed in log like i was having . conf.celery.debug_task i was getting the error because I was not giving this exact task path. So kindly recheck this by copying and pasting exact task id.

cc1plus: error: unrecognized command line option "-std=c++11" with g++

Seeing from your G++ version, you need to update it badly. C++11 has only been available since G++ 4.3. The most recent version is 4.7.

In versions pre-G++ 4.7, you'll have to use -std=c++0x, for more recent versions you can use -std=c++11.

'Missing contentDescription attribute on image' in XML

This warning tries to improve accessibility of your application.

To disable missing content description warning in the whole project, you can add this to your application module build.gradle

android {


    lintOptions {
        disable 'ContentDescription'

Mounting multiple volumes on a docker container?

You can have Read only or Read and Write only on the volume

docker -v /on/my/host/1:/on/the/container/1:ro \

docker -v /on/my/host/2:/on/the/container/2:rw \

How to access parameters in a RESTful POST method

Your @POST method should be accepting a JSON object instead of a string. Jersey uses JAXB to support marshaling and unmarshaling JSON objects (see the jersey docs for details). Create a class like:

public class MyJaxBean {
    @XmlElement public String param1;
    @XmlElement public String param2;

Then your @POST method would look like the following:

@POST @Consumes("application/json")
public void create(final MyJaxBean input) {
    System.out.println("param1 = " + input.param1);
    System.out.println("param2 = " + input.param2);

This method expects to receive JSON object as the body of the HTTP POST. JAX-RS passes the content body of the HTTP message as an unannotated parameter -- input in this case. The actual message would look something like:

POST /create HTTP/1.1
Content-Type: application/json
Content-Length: 35


Using JSON in this way is quite common for obvious reasons. However, if you are generating or consuming it in something other than JavaScript, then you do have to be careful to properly escape the data. In JAX-RS, you would use a MessageBodyReader and MessageBodyWriter to implement this. I believe that Jersey already has implementations for the required types (e.g., Java primitives and JAXB wrapped classes) as well as for JSON. JAX-RS supports a number of other methods for passing data. These don't require the creation of a new class since the data is passed using simple argument passing.


The parameters would be annotated using @FormParam:

public void create(@FormParam("param1") String param1,
                   @FormParam("param2") String param2) {

The browser will encode the form using "application/x-www-form-urlencoded". The JAX-RS runtime will take care of decoding the body and passing it to the method. Here's what you should see on the wire:

POST /create HTTP/1.1
Content-Type: application/x-www-form-urlencoded;charset=UTF-8
Content-Length: 25


The content is URL encoded in this case.

If you do not know the names of the FormParam's you can do the following:

@POST @Consumes("application/x-www-form-urlencoded")
public void create(final MultivaluedMap<String, String> formParams) {

HTTP Headers

You can using the @HeaderParam annotation if you want to pass parameters via HTTP headers:

public void create(@HeaderParam("param1") String param1,
                   @HeaderParam("param2") String param2) {

Here's what the HTTP message would look like. Note that this POST does not have a body.

POST /create HTTP/1.1
Content-Length: 0
param1: hello
param2: world

I wouldn't use this method for generalized parameter passing. It is really handy if you need to access the value of a particular HTTP header though.

HTTP Query Parameters

This method is primarily used with HTTP GETs but it is equally applicable to POSTs. It uses the @QueryParam annotation.

public void create(@QueryParam("param1") String param1,
                   @QueryParam("param2") String param2) {

Like the previous technique, passing parameters via the query string does not require a message body. Here's the HTTP message:

POST /create?param1=hello&param2=world HTTP/1.1
Content-Length: 0

You do have to be particularly careful to properly encode query parameters on the client side. Using query parameters can be problematic due to URL length restrictions enforced by some proxies as well as problems associated with encoding them.

HTTP Path Parameters

Path parameters are similar to query parameters except that they are embedded in the HTTP resource path. This method seems to be in favor today. There are impacts with respect to HTTP caching since the path is what really defines the HTTP resource. The code looks a little different than the others since the @Path annotation is modified and it uses @PathParam:

public void create(@PathParam("param1") String param1,
                   @PathParam("param2") String param2) {

The message is similar to the query parameter version except that the names of the parameters are not included anywhere in the message.

POST /create/hello/world HTTP/1.1
Content-Length: 0

This method shares the same encoding woes that the query parameter version. Path segments are encoded differently so you do have to be careful there as well.

As you can see, there are pros and cons to each method. The choice is usually decided by your clients. If you are serving FORM-based HTML pages, then use @FormParam. If your clients are JavaScript+HTML5-based, then you will probably want to use JAXB-based serialization and JSON objects. The MessageBodyReader/Writer implementations should take care of the necessary escaping for you so that is one fewer thing that can go wrong. If your client is Java based but does not have a good XML processor (e.g., Android), then I would probably use FORM encoding since a content body is easier to generate and encode properly than URLs are. Hopefully this mini-wiki entry sheds some light on the various methods that JAX-RS supports.

Note: in the interest of full disclosure, I haven't actually used this feature of Jersey yet. We were tinkering with it since we have a number of JAXB+JAX-RS applications deployed and are moving into the mobile client space. JSON is a much better fit that XML on HTML5 or jQuery-based solutions.

Spark: Add column to dataframe conditionally

Try withColumn with the function when as follows:

val sqlContext = new SQLContext(sc)
import sqlContext.implicits._ // for `toDF` and $""
import org.apache.spark.sql.functions._ // for `when`

val df = sc.parallelize(Seq((4, "blah", 2), (2, "", 3), (56, "foo", 3), (100, null, 5)))
    .toDF("A", "B", "C")

val newDf = df.withColumn("D", when($"B".isNull or $"B" === "", 0).otherwise(1)) shows

|  A|   B|  C|  D|
|  4|blah|  2|  1|
|  2|    |  3|  0|
| 56| foo|  3|  1|
|100|null|  5|  0|

I added the (100, null, 5) row for testing the isNull case.

I tried this code with Spark 1.6.0 but as commented in the code of when, it works on the versions after 1.4.0.

How to write a UTF-8 file with Java?

Below sample code can read file line by line and write new file in UTF-8 format. Also, i am explicitly specifying Cp1252 encoding.

    public static void main(String args[]) throws IOException {

    BufferedReader br = new BufferedReader(new InputStreamReader(
            new FileInputStream("c:\\filenonUTF.txt"),
    String line;

    Writer out = new BufferedWriter(
            new OutputStreamWriter(new FileOutputStream(
                    "c:\\fileUTF.txt"), "UTF-8"));

    try {

        while ((line = br.readLine()) != null) {



    } finally {



Correct way to initialize HashMap and can HashMap hold different value types?

In answer to your second question: Yes a HashMap can hold different types of objects. Whether that's a good idea or not depends on the problem you're trying to solve.

That said, your example won't work. The int value is not an Object. You have to use the Integer wrapper class to store an int value in a HashMap

Python way to clone a git repository

With Dulwich tip you should be able to do:

from dulwich.repo import Repo

This is still very basic - it copies across the objects and the refs, but it doesn't yet create the contents of the working tree if you create a non-bare repository.

How to get GMT date in yyyy-mm-dd hh:mm:ss in PHP

You are repeating the y,m,d.

Instead of

gmdate('yyyy-mm-dd hh:mm:ss \G\M\T', time());  

You should use it like

gmdate('Y-m-d h:m:s \G\M\T', time());

php form action php self

You can leave action blank or use this code:

<form name="form1" id="mainForm" method="post" enctype="multipart/form-data" action="<?php echo $_SERVER['REQUEST_URI'];?>">

How to set the color of "placeholder" text?

For giving placeholder a color just use these lines of code:

::-webkit-input-placeholder { color: red; }
::-moz-placeholder {color: red; }
:-ms-input-placeholder { color: red; } 
:-o-input-placeholder { color: red; } 

Get last key-value pair in PHP array

You can use end to advance the internal pointer to the end or array_slice to get an array only containing the last element:

$last = end($arr);
$last = current(array_slice($arr, -1));

Getting pids from ps -ef |grep keyword

You can use pgrep as long as you include the -f options. That makes pgrep match keywords in the whole command (including arguments) instead of just the process name.

pgrep -f keyword

From the man page:

-f       The pattern is normally only matched against the process name. When -f is set, the full command line is used.

If you really want to avoid pgrep, try:

ps -ef | awk '/[k]eyword/{print $2}'

Note the [] around the first letter of the keyword. That's a useful trick to avoid matching the awk command itself.

PHP Checking if the current date is before or after a set date

If you are looking for a generic way of doing this via MySQL, you could simply use a SELECT statement, and add the WHERE clause to it.

This will grab all fields for all rows, where the date stored in field "date" is before "now".


Personally, I found this method to be more gentle on newbies in MySQL, since it uses the standard SELECT statement with WHERE to fetch the results. Obviously, you could grab only the fields relevant if you wanted to, by listing them instead of using a wildcard (*).

How to convert OutputStream to InputStream?

As input and output streams are just start and end point, the solution is to temporary store data in byte array. So you must create intermediate ByteArrayOutputStream, from which you create byte[] that is used as input for new ByteArrayInputStream.

public void doTwoThingsWithStream(InputStream inStream, OutputStream outStream){ 
  //create temporary bayte array output stream
  ByteArrayOutputStream baos = new ByteArrayOutputStream();
  doFirstThing(inStream, baos);
  //create input stream from baos
  InputStream isFromFirstData = new ByteArrayInputStream(baos.toByteArray()); 
  doSecondThing(isFromFirstData, outStream);

Hope it helps.

Iterating through map in template

As Herman pointed out, you can get the index and element from each iteration.

{{range $index, $element := .}}{{$index}}
{{range $element}}{{.Value}}

Working example:

package main

import (

type EntetiesClass struct {
    Name string
    Value int32

// In the template, we use rangeStruct to turn our struct values
// into a slice we can iterate over
var htmlTemplate = `{{range $index, $element := .}}{{$index}}
{{range $element}}{{.Value}}

func main() {
    data := map[string][]EntetiesClass{
        "Yoga": {{"Yoga", 15}, {"Yoga", 51}},
        "Pilates": {{"Pilates", 3}, {"Pilates", 6}, {"Pilates", 9}},

    t := template.New("t")
    t, err := t.Parse(htmlTemplate)
    if err != nil {

    err = t.Execute(os.Stdout, data)
    if err != nil {






How do I commit only some files?

I think you may also use the command line :

git add -p

This allows you to review all your uncommited files, one by one and choose if you want to commit them or not.

Then you have some options that will come up for each modification: I use the "y" for "yes I want to add this file" and the "n" for "no, I will commit this one later".

Stage this hunk [y,n,q,a,d,K,g,/,e,?]?

As for the other options which are ( q,a,d,K,g,/,e,? ), I'm not sure what they do, but I guess the "?" might help you out if you need to go deeper into details.

The great thing about this is that you can then push your work, and create a new branch after and all the uncommited work will follow you on that new branch. Very useful if you have coded many different things and that you actually want to reorganise your work on github before pushing it.

Hope this helps, I have not seen it said previously (if it was mentionned, my bad)

Add new line in text file with Windows batch file

I believe you are using the

echo Text >> Example.txt 


If so the answer would be simply adding a "." (Dot) directly after the echo with nothing else there.


echo Blah
echo Blah 2
echo. #New line is added
echo Next Blah

What is the use of <<<EOD in PHP?

there are four types of strings available in php. They are single quotes ('), double quotes (") and Nowdoc (<<<'EOD') and heredoc(<<<EOD) strings

you can use both single quotes and double quotes inside heredoc string. Variables will be expanded just as double quotes.

nowdoc strings will not expand variables just like single quotes.


How to call function on child component on parent events

Did not like the event-bus approach using $on bindings in the child during create. Why? Subsequent create calls (I'm using vue-router) bind the message handler more than once--leading to multiple responses per message.

The orthodox solution of passing props down from parent to child and putting a property watcher in the child worked a little better. Only problem being that the child can only act on a value transition. Passing the same message multiple times needs some kind of bookkeeping to force a transition so the child can pick up the change.

I've found that if I wrap the message in an array, it will always trigger the child watcher--even if the value remains the same.


   data: function() {
      msgChild: null,
   methods: {
      mMessageDoIt: function() {
         this.msgChild = ['doIt'];


   props: ['msgChild'],
   watch: {
      'msgChild': function(arMsg) {


   <child v-bind="{ 'msgChild': msgChild }"></child>

Matrix Multiplication in pure Python?

The shape of your matrix C is wrong; it's the transpose of what you actually want it to be. (But I agree with ulmangt: the Right Thing is almost certainly to use numpy, really.)

Visual Studio Code pylint: Unable to import 'protorpc'

I've not played around with all possibilities, but at least I had the impression that this could be a python version related issue. No idea why, I just trusted my gut.

Thus I just changed the pythonPath to python3 (default: python):

"python.pythonPath": "python3"

I reinstalled the dependencies (including pylint!!!) with

pip3 install <package> --user

... and after restarting vs code, everything looked fine.


Git error: src refspec master does not match any error: failed to push some refs

It doesn't recognize that you have a master branch, but I found a way to get around it. I found out that there's nothing special about a master branch, you can just create another branch and call it master branch and that's what I did.

To create a master branch:

git checkout -b master

And you can work off of that.

What are good grep tools for Windows?

Git on Windows = grep in cmd.exe

I just found out installing Git will give you some basic Linux commands: cat, grep, scp and all other good ones.

Install then add the Git bin folder to your PATH and then your cmd.exe has basic Linux functionality!

Android draw a Horizontal line between views

A View whose background color you can specify would do (height=a few dpi). Looked in real code and here it is:

            android:background="#000000" />

Note that it may be any kind of View.

Python list / sublist selection -1 weirdness

If you want to get a sub list including the last element, you leave blank after colon:

>>> ll=range(10)
>>> ll
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> ll[5:]
[5, 6, 7, 8, 9]
>>> ll[:]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

www-data permissions?

As stated in an article by Slicehost:

User setup

So let's start by adding the main user to the Apache user group:

sudo usermod -a -G www-data demo

That adds the user 'demo' to the 'www-data' group. Do ensure you use both the -a and the -G options with the usermod command shown above.

You will need to log out and log back in again to enable the group change.

Check the groups now:

# demo www-data

So now I am a member of two groups: My own (demo) and the Apache group (www-data).

Folder setup

Now we need to ensure the public_html folder is owned by the main user (demo) and is part of the Apache group (www-data).

Let's set that up:

sudo chgrp -R www-data /home/demo/public_html

As we are talking about permissions I'll add a quick note regarding the sudo command: It's a good habit to use absolute paths (/home/demo/public_html) as shown above rather than relative paths (~/public_html). It ensures sudo is being used in the correct location.

If you have a public_html folder with symlinks in place then be careful with that command as it will follow the symlinks. In those cases of a working public_html folder, change each folder by hand.


Good so far, but remember the command we just gave only affects existing folders. What about anything new?

We can set the ownership so anything new is also in the 'www-data' group.

The first command will change the permissions for the public_html directory to include the "setgid" bit:

sudo chmod 2750 /home/demo/public_html

That will ensure that any new files are given the group 'www-data'. If you have subdirectories, you'll want to run that command for each subdirectory (this type of permission doesn't work with '-R'). Fortunately new subdirectories will be created with the 'setgid' bit set automatically.

If we need to allow write access to Apache, to an uploads directory for example, then set the permissions for that directory like so:

sudo chmod 2770 /home/demo/public_html/

The permissions only need to be set once as new files will automatically be assigned the correct ownership.

Python: Maximum recursion depth exceeded

You can increment the stack depth allowed - with this, deeper recursive calls will be possible, like this:

import sys
sys.setrecursionlimit(10000) # 10000 is an example, try with different values

... But I'd advise you to first try to optimize your code, for instance, using iteration instead of recursion.

Open soft keyboard programmatically

I have used the following lines to display the soft keyboard manually inside the onclick event.

public void showKeyboard(final EmojiconEditText ettext){
          ettext.postDelayed(new Runnable(){
            @Override public void run(){
              InputMethodManager keyboard=(InputMethodManager)getSystemService(Context.INPUT_METHOD_SERVICE);

CSS Change List Item Background Color with Class

This is an issue of selector specificity. (The selector .selected is less specific than ul.nav li.)

To fix, use as much specificity in the overriding rule as in the original:

ul.nav li {
ul.nav li.selected {

You might also consider nixing the ul, unless there will be other .navs. So:

.nav li {
.nav li.selected {

That's a bit cleaner, less typing, and fewer bits.

Unix: How to delete files listed in a file

This will allow file names to have spaces (reproducible example).

# Select files of interest, here, only text files for ex.
find -type f -exec file {} \; > findresult.txt
grep ": ASCII text$" findresult.txt > textfiles.txt
# leave only the path to the file removing suffix and prefix
sed -i -e 's/:.*$//' textfiles.txt
sed -i -e 's/\.\///' textfiles.txt

#write a script that deletes the files in textfiles.txt
IFS=$(echo "\n\b")
for f in $(cat textfiles.txt); 
rm "$f"; 

# save script as "" and run: sh

CSS Background image not loading

I had the same problem and after reading this found the issue, it was the slash. Windows Path: images\green_cup.png

CSS that worked: images/green_cup.png

images\green_cup.png does not work.


How to make UIButton's text alignment center? Using IB

For swift 4, xcode 9

myButton.contentHorizontalAlignment = .center

React setState not updating state

setState() is usually asynchronous, which means that at the time you console.log the state, it's not updated yet. Try putting the log in the callback of the setState() method. It is executed after the state change is complete:

this.setState({ dealersOverallTotal: total }, () => {
  console.log(this.state.dealersOverallTotal, 'dealersOverallTotal1');

Creating an empty Pandas DataFrame, then filling it?

Initialize empty frame with column names

import pandas as pd

col_names =  ['A', 'B', 'C']
my_df  = pd.DataFrame(columns = col_names)

Add a new record to a frame

my_df.loc[len(my_df)] = [2, 4, 5]

You also might want to pass a dictionary:

my_dic = {'A':2, 'B':4, 'C':5}
my_df.loc[len(my_df)] = my_dic 

Append another frame to your existing frame

col_names =  ['A', 'B', 'C']
my_df2  = pd.DataFrame(columns = col_names)
my_df = my_df.append(my_df2)

Performance considerations

If you are adding rows inside a loop consider performance issues. For around the first 1000 records "my_df.loc" performance is better, but it gradually becomes slower by increasing the number of records in the loop.

If you plan to do thins inside a big loop (say 10M? records or so), you are better off using a mixture of these two; fill a dataframe with iloc until the size gets around 1000, then append it to the original dataframe, and empty the temp dataframe. This would boost your performance by around 10 times.

Where is git.exe located?

I have downloaded stub from After installation of the git from the stub, git.exe is stored in the following location.

C:\Users\**User Name**\AppData\Local\GitHub\PortableGit_****Some No/characters***\cmd\git.exe

In Windows 10 64 bit, I feel the exe file is now stored in cmd folder rather than bin folder.

Format numbers in django templates

Not sure why this has not been mentioned, yet:

{% load l10n %}

{{ value|localize }}

You can also use this in your Django code (outside templates) by calling localize(number).

Integrating the ZXing library directly into my Android application

I tried all possible ways to achieve this and then I discovered Minified version of xZing by JourneyApps. I have ported that for eclipse and shared on GitHub.

If you are using eclipse use this project:-

If you are using Studio use this project :-


  1. Inbuilt Barcode scanner in your App do not required to install third party apps using playstore.

  2. You dont need to get confused between Core,Android client etc jars simply drop this packages and relevent layouts in your project and you are good to go. Only Jar required is which you can download from

  3. No need to add tons of packages see images below for comparison

Before :-

enter image description here

After :-

enter image description here

  1. Most important part is they are highly customizable ie. you can add flash light, use it in fragment and support orientation change.

  2. You can use this Capture activity in Cordova App for barcode scanneing.

your capture activity in app manifest would look like this

            android:windowSoftInputMode="stateAlwaysHidden" >
                <action android:name="" />

                <category android:name="android.intent.category.DEFAULT" />

and plugin will look like this

public class BarcodeScanner extends CordovaPlugin {
    public static final int REQUEST_CODE = 0x0ba7c0de;

    private static final String SCAN = "scan";
    private static final String CANCELLED = "cancelled";
    private static final String FORMAT = "format";
    private static final String TEXT = "text";
    private static final String SCAN_INTENT = "";

    private static final String LOG_TAG = "BarcodeScanner";

    private CallbackContext callbackContext;

     * Constructor.
    public BarcodeScanner() {


     * Executes the request.
     * This method is called from the WebView thread. To do a non-trivial amount of work, use:
     *     cordova.getThreadPool().execute(runnable);
     * To run on the UI thread, use:
     *     cordova.getActivity().runOnUiThread(runnable);
     * @param action          The action to execute.
     * @param args            The exec() arguments.
     * @param callbackContext The callback context used when calling back into JavaScript.
     * @return                Whether the action was valid.
     * @sa
    public boolean execute(String action, JSONArray args, CallbackContext callbackContext) {
        this.callbackContext = callbackContext;
        if (action.equals(SCAN)) {
        } else {
            return false;
        return true;

     * Starts an intent to scan and decode a barcode.
    public void scan(JSONArray args) {
        Intent intentScan = new Intent(SCAN_INTENT);

        // add config as intent extras
        if(args.length() > 0) {

            JSONObject obj;
            JSONArray names;
            String key;
            Object value;

            for(int i=0; i<args.length(); i++) {

                try {
                    obj = args.getJSONObject(i);
                } catch(JSONException e) {
                    Log.i("CordovaLog", e.getLocalizedMessage());

                names = obj.names();
                for(int j=0; j<names.length(); j++) {
                    try {
                        key = names.getString(j);
                        value = obj.get(key);

                        if(value instanceof Integer) {
                            intentScan.putExtra(key, (Integer)value);
                        } else if(value instanceof String) {
                            intentScan.putExtra(key, (String)value);

                    } catch(JSONException e) {
                        Log.i("CordovaLog", e.getLocalizedMessage());


        // avoid calling other phonegap apps

        this.cordova.startActivityForResult((CordovaPlugin) this, intentScan, REQUEST_CODE);

     * Called when the barcode scanner intent completes.
     * @param requestCode The request code originally supplied to startActivityForResult(),
     *                       allowing you to identify who this result came from.
     * @param resultCode  The integer result code returned by the child activity through its setResult().
     * @param intent      An Intent, which can return result data to the caller (various data can be attached to Intent "extras").
    public void onActivityResult(int requestCode, int resultCode, Intent intent) {
        if (requestCode == REQUEST_CODE) {
            if (resultCode == Activity.RESULT_OK) {
                JSONObject obj = new JSONObject();
                try {
                    obj.put(TEXT, intent.getStringExtra("SCAN_RESULT"));
                    obj.put(FORMAT, intent.getStringExtra("SCAN_RESULT_FORMAT"));
                    obj.put(CANCELLED, false);
                } catch (JSONException e) {
                    Log.d(LOG_TAG, "JSONException "+e.getMessage());
            } else if (resultCode == Activity.RESULT_CANCELED) {
            } else {
                this.callbackContext.error("Technical Problem");

Happy Integration !!

What processes are using which ports on unix?

netstat -ln | awk '/^(tcp|udp)/ { split($4, a, /:/); print $1, a[2]}' | sort -u

gives you the active tcp/udp ports. Then you can use the ports with fuser -n tcp or fuser -n udp, as root, and supposing that fuser is GNU fuser or has similar options.

If you need more help, let me know.

JavaScript DOM: Find Element Index In Container

You can use this to find the index of an element:, yourLi)

This for example logs all indices:

var lis = yourList.getElementsByTagName('li');
for(var i = 0; i < lis.length; i++) {
    console.log(, lis[i]));


What should my Objective-C singleton look like?

Shouln't this be threadsafe and avoid the expensive locking after the first call?

+ (MySingleton*)sharedInstance
    if (sharedInstance == nil) {
        @synchronized(self) {
            if (sharedInstance == nil) {
                sharedInstance = [[MySingleton alloc] init];
    return (MySingleton *)sharedInstance;

Is There a Better Way of Checking Nil or Length == 0 of a String in Ruby?

An alternative to jcoby's proposal would be:

class NilClass
  def nil_or_empty?

class String
  def nil_or_empty?

css transition opacity fade background

Please note that the problem is not white color. It is because it is being transparent.

When an element is made transparent, all of its child element's opacity; alpha filter in IE 6 7 etc, is changed to the new value.

So you cannot say that it is white!

You can place an element above it, and change that element's transparency to 1 while changing the image's transparency to .2 or what so ever you want to.

psql: could not connect to server: No such file or directory (Mac OS X)

I've had to look up this post several times to solve this issue. There's another fix, which will also applies to similar issues with other running programs.

I just discovered you can use the following two commands.


This will show all the currently running actions with their pid numbers. When you find postgres and the associated pid

$kill pid_number

dictionary update sequence element #0 has length 3; 2 is required

This error raised up because you trying to update dict object by using a wrong sequence (list or tuple) structure.

cash_id.create(cr, uid, lines,context=None) trying to convert lines into dict object:

(0, 0, {
    'amount': l.amount,
    'type': l.type,
    'ref': l.ref,
    'note': l.note,

Remove the second zero from this tuple to properly convert it into a dict object.

To test it your self, try this into python shell:

>>> l=[(0,0,{'h':88})]
>>> a={}
>>> a.update(l)

Traceback (most recent call last):
  File "<pyshell#11>", line 1, in <module>
ValueError: dictionary update sequence element #0 has length 3; 2 is required

>>> l=[(0,{'h':88})]
>>> a.update(l)

Uninstall all installed gems, in OSX?

I did that not too long ago (same poster-child RVM switcher situation):

gem list | cut -d" " -f1 | sudo xargs gem uninstall -Iax

Takes the list of all gems (incl. version stuff), cuts it to keep only the gem name, then uninstalls all versions of such gems.

The sudo is only useful if you had gems installed system-wide, and should not be included unless necessary.

Most common C# bitwise operations on enums

The idiom is to use the bitwise or-equal operator to set bits:

flags |= 0x04;

To clear a bit, the idiom is to use bitwise and with negation:

flags &= ~0x04;

Sometimes you have an offset that identifies your bit, and then the idiom is to use these combined with left-shift:

flags |= 1 << offset;
flags &= ~(1 << offset);

What does -z mean in Bash?

test -z returns true if the parameter is empty (see man sh or man test).

Is it possible to dynamically compile and execute C# code fragments?

To compile you could just initiate a shell call to the csc compiler. You may have a headache trying to keep your paths and switches straight but it certainly can be done.

C# Corner Shell Examples

EDIT: Or better yet, use the CodeDOM as Noldorin suggested...

PHP foreach with Nested Array?

Both syntaxes are correct. But the result would be Array. You probably want to do something like this:

foreach ($tmpArray[1] as $value) {
  echo $value[0];
  foreach($value[1] as $val){
    echo $val;

This will print out the string "two" ($value[0]) and the integers 4, 5 and 6 from the array ($value[1]).

Android Studio - How to increase Allocated Heap Size

This is how you change the heap size currently in Android Studio 3.6.1

On Windows in your Android Studio:

  1. Select File -> Settings (the popup below will be displayed)

Settings Dialog

  1. Select Appearance & Behavior
  2. Select System Settings
  3. Select Memory Settings

Then change the IDE Heap Size settings to your desired value

On Mac:

  1. Select Android Studio
  2. Select Preferences

The same pop up will appear. However, this time on the Mac its called Preferences.

Follow the same steps as the Windows version of Android Studio to adjust the heap size wants the Preferences dialog has been displayed

When I catch an exception, how do I get the type, file, and line number?

Without any imports, but also incompatible with imported modules:

    raise TypeError("Hello, World!")  # line 2
except Exception as e:
        type(e).__name__,          # TypeError
        __file__,                  # /tmp/
        e.__traceback__.tb_lineno  # 2

$ python3 /tmp/
TypeError /tmp/ 2

To reiterate, this does not work across imports or modules, so if you do import X; try: X.example(); then the filename and line number will point to the line containing X.example() instead of the line where it went wrong within X.example(). If anyone knows how to easily get the file name and line number from the last stack trace line (I expected something like e[-1].filename, but no such luck), please improve this answer.

How to easily duplicate a Windows Form in Visual Studio?

If you're working in VS 2019, take a few minutes to create an item template -- it's a perfect solution. How to: Create item templates

Not sure if it applies to earlier versions of VS.

Copy table without copying data


you will get a create statement for that table, edit the table name, or anything else you like, and then execute it.

This will allow you to copy the indexes and also manually tweak the table creation.

You can also run the query within a program.

SyntaxError: "can't assign to function call"

Syntactically, this line makes no sense:

invest(initial_amount,top_company(5,year,year+1)) = subsequent_amount

You are attempting to assign a value to a function call, as the error says. What are you trying to accomplish? If you're trying set subsequent_amount to the value of the function call, switch the order:

subsequent_amount = invest(initial_amount,top_company(5,year,year+1))

Python: read all text file lines in loop

There are situations where you can't use the (quite convincing) with... for... structure. In that case, do the following:

line =
if len(line) != 0:
     if 'str' in line:

This will work because the the readline() leaves a trailing newline character, where as EOF is just an empty string.

Sending emails in Node.js?

Mature, simple to use and has lots of features if simple isn't enought: Nodemailer: (note correct url!)

How to get name of the computer in VBA?

You can do like this:

Sub Get_Environmental_Variable()

Dim sHostName As String
Dim sUserName As String

' Get Host Name / Get Computer Name    
sHostName = Environ$("computername")

' Get Current User Name    
sUserName = Environ$("username")

End Sub

How to tell which disk Windows Used to Boot


Disable html5 video autoplay

<video class="embed-responsive-item"  controls>_x000D_
   <source src="" autostart="false">_x000D_
   Your browser does not support the video tag._x000D_

Installing PG gem on OS X - failure to build native extension

Same error for me and I didn't experience it until I downloaded OS X 10.9 (Mavericks). Sigh, another OS upgrade headache.

Here's how I fixed it (with homebrew):

  • Install another build of Xcode Tools (typing brew update in the terminal will prompt you to update the Xcode build tools)
  • brew update
  • brew install postgresql

After that gem install pg worked for me.

Why can't decimal numbers be represented exactly in binary?

To repeat what I said in my comment to Mr. Skeet: we can represent 1/3, 1/9, 1/27, or any rational in decimal notation. We do it by adding an extra symbol. For example, a line over the digits that repeat in the decimal expansion of the number. What we need to represent decimal numbers as a sequence of binary numbers are 1) a sequence of binary numbers, 2) a radix point, and 3) some other symbol to indicate the repeating part of the sequence.

Hehner's quote notation is a way of doing this. He uses a quote symbol to represent the repeating part of the sequence. The article: and the Wikipedia entry:

There's nothing that says we can't add a symbol to our representation system, so we can represent decimal rationals exactly using binary quote notation, and vice versa.

DateTime format to SQL format using C#

Using the standard datetime format "s" will also ensure internationalization compatibility (MM/dd versus dd/MM):


=> 2013-12-31T00:00:00

Complete Options: (code: sample result)

d: 6/15/2008 
D: Sunday, June 15, 2008 
f: Sunday, June 15, 2008 9:15 PM 
F: Sunday, June 15, 2008 9:15:07 PM 
g: 6/15/2008 9:15 PM 
G: 6/15/2008 9:15:07 PM 
m: June 15 
o: 2008-06-15T21:15:07.0000000 
R: Sun, 15 Jun 2008 21:15:07 GMT 
s: 2008-06-15T21:15:07 
t: 9:15 PM 
T: 9:15:07 PM 
u: 2008-06-15 21:15:07Z 
U: Monday, June 16, 2008 4:15:07 AM 
y: June, 2008 

'h:mm:ss.ff t': 9:15:07.00 P 
'd MMM yyyy': 15 Jun 2008 
'HH:mm:ss.f': 21:15:07.0 
'dd MMM HH:mm:ss': 15 Jun 21:15:07 
'\Mon\t\h\: M': Month: 6 
'HH:mm:ss.ffffzzz': 21:15:07.0000-07:00

Supported in .NET Framework: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0
Reference: DateTime.ToString Method

Await operator can only be used within an Async method

You can only use await in an async method, and Main cannot be async.

You'll have to use your own async-compatible context, call Wait on the returned Task in the Main method, or just ignore the returned Task and just block on the call to Read. Note that Wait will wrap any exceptions in an AggregateException.

If you want a good intro, see my async/await intro post.

Renaming files in a folder to sequential numbers

I had a similar issue and wrote a shell script for that reason. I've decided to post it regardless that many good answers were already posted because I think it can be helpful for someone. Feel free to improve it!


@Gnutt The behavior you want can be achieved by typing the following:

./ -d <path to directory> -o modtime -L 4 -b <startnumber> -r

If the option -r is left out the reaming will be only simulated (Should be helpful for testing).

The otion L describes the length of the target number (which will be filled with leading zeros) it is also possible to add a prefix/suffix with the options -p <prefix> -s <suffix>.

In case somebody wants the files to be sorted numerically before they get numbered, just remove the -o modtime option.

Copy file remotely with PowerShell

None of the above answers worked for me. I kept getting this error:

Copy-Item : Access is denied
+ CategoryInfo          : PermissionDenied: (\\\Shared\test.txt:String) [Copy-Item], UnauthorizedAccessException>   
+ FullyQualifiedErrorId : ItemExistsUnauthorizedAccessError,Microsoft.PowerShell.Commands.CopyItemCommand

So this did it for me:

netsh advfirewall firewall set rule group="File and Printer Sharing" new enable=yes

Then from my host my machine in the Run box I just did this:

\\{IP address of nanoserver}\C$

How do I set a JLabel's background color?



Otherwise the background is not painted, since the default of opaque is false for JLabel.

From the JavaDocs:

If true the component paints every pixel within its bounds. Otherwise, the component may not paint some or all of its pixels, allowing the underlying pixels to show through.

For more information, read the Java Tutorial How to Use Labels.

Launch an event when checking a checkbox in Angular2

Check Demo:

  CheckBox: use change event to call the function and pass the event.

<label class="container">    
   <input type="checkbox" [(ngModel)]="theCheckbox"  data-md-icheck 
      Checkbox is <span *ngIf="marked">checked</span><span 
     <span class="checkmark"></span>
 <div>And <b>ngModel</b> also works, it's value is <b>{{theCheckbox}}</b></div>

What happens if you don't commit a transaction to a database (say, SQL Server)?

When you open a transaction nothing gets locked by itself. But if you execute some queries inside that transaction, depending on the isolation level, some rows, tables or pages get locked so it will affect other queries that try to access them from other transactions.

Compiling php with curl, where is curl installed?

If you're going to compile a 64bit version(x86_64) of php use: /usr/lib64/

For architectures (i386 ... i686) use /usr/lib/

I recommend compiling php to the same architecture as apache. As you're using a 64bit linux i asume your apache is also compiled for x86_64.

How to install the current version of Go in Ubuntu Precise

For the current release of Go:

The Go Programming Language

Getting Started

Download the Go distribution


Click the link above to visit the Go project's downloads page and select the binary distribution that matches your operating system and processor architecture.

Official binary distributions are available for the FreeBSD, Linux, macOS, and Windows operating systems and the 32-bit (386) and 64-bit (amd64) x86 processor architectures.

If a binary distribution is not available for your combination of operating system and architecture you may want to try installing from source or installing gccgo instead of gc.

Installing Go from source

Gradle: Execution failed for task ':processDebugManifest'

In my case,

I define the activity twice in manifest file


        android:windowSoftInputMode="stateHidden|adjustResize" />

      //Problem here.. same activity twice define

        android:windowSoftInputMode="stateHidden|adjustResize" />


After remove the duplicate error solved.

Pandas DataFrame to List of Lists

"df.values" returns a numpy array. This does not preserve the data types. An integer might be converted to a float.

df.iterrows() returns a series which also does not guarantee to preserve the data types. See:

The code below converts to a list of list and preserves the data types:

rows = [list(row) for row in df.itertuples()]

No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin '...' is therefore not allowed access

The workaround is to use a reverse proxy running on your 'source' host and forwarding to your target server, such as Fiddler:

Link here:

Or an Apache Reverse proxy...

Error to run Android Studio

I ran into this issue when I was referencing

 [drive]:\Program Files\Java\jdk1.8.0_65 

in my JAVA_HOME environment var instead of the Android Studio recommended

[drive]:\Program Files\Java\jdk1.7.0_79. 

I am using the x64 version of the JDK on Windows 10 Pro.

From the Android Studio installation instructions.

Before you set up Android Studio, be sure you have installed JDK 6 or higher (the JRE alone is not sufficient)—JDK 7 is required when developing for Android 5.0 and higher. To check if you have JDK installed (and which version), open a terminal and type javac -version. If the JDK is not available or the version is lower than version 6, download the Java SE Development Kit 7

Vue JS mounted()

Abstract your initialization into a method, and call the method from mounted and wherever else you want.

new Vue({
      //call API
      //Setup game

Then possibly have a button in your template to start over.

<button v-if="playerWon" @click="init">Play Again</button>

In this button, playerWon represents a boolean value in your data that you would set when the player wins the game so the button appears. You would set it back to false in init.

Intellij Cannot resolve symbol on import

Check your module dependencies.

  1. Project Structure (Ctrl+Alt+Shift+S).
  2. Modules
  3. Select your problem module.
  4. Change tab on top of window "Dependencies".
  5. Check what needed library (maybe, you need to add specified library in the tab 'libraries') or module has listed here and it has right scope ('complile' mostly).

How to find a whole word in a String in java

You can use regular expressions. Use Matcher and Pattern methods to get the desired output

Using ORDER BY and GROUP BY together

Why make it so complicated? This worked.

 FROM table_name 
 GROUP BY m_id

The Android emulator is not starting, showing "invalid command-line parameter"

I had the same problem. I made it work with:

"C:\Program Files (x86)\Android\android-sdk\tools\emulator-arm.exe"  @foo

foo is the name of your virtual device.

What is the copy-and-swap idiom?

This answer is more like an addition and a slight modification to the answers above.

In some versions of Visual Studio (and possibly other compilers) there is a bug that is really annoying and doesn't make sense. So if you declare/define your swap function like this:

friend void swap(A& first, A& second) {

    std::swap(first.size, second.size);
    std::swap(first.arr, second.arr);


... the compiler will yell at you when you call the swap function:

enter image description here

This has something to do with a friend function being called and this object being passed as a parameter.

A way around this is to not use friend keyword and redefine the swap function:

void swap(A& other) {

    std::swap(size, other.size);
    std::swap(arr, other.arr);


This time, you can just call swap and pass in other, thus making the compiler happy:

enter image description here

After all, you don't need to use a friend function to swap 2 objects. It makes just as much sense to make swap a member function that has one other object as a parameter.

You already have access to this object, so passing it in as a parameter is technically redundant.

When is it appropriate to use UDP instead of TCP?

It's not always clear cut. However, if you need guaranteed delivery of packets with no loss and in the right sequence then TCP is probably what you want.

On the other hand UDP is appropriate for transmitting short packets of information where the sequence of the information is less important or where the data can fit into a single packet.

It's also appropriate when you want to broadcast the same information to many users.

Other times, it's appropriate when you are sending sequenced data but if some of it goes missing you're not too concerned (e.g. a VOIP application).

Some protocols are more complex because what's needed are some (but not all) of the features of TCP, but more than what UDP provides. That's where the application layer has to implement the additional functionality. In those cases, UDP is also appropriate (e.g. Internet radio, order is important but not every packet needs to get through).

Examples of where it is/could be used 1) A time server broadcasting the correct time to a bunch of machines on a LAN. 2) VOIP protocols 3) DNS lookups 4) Requesting LAN services e.g. where are you? 5) Internet radio 6) and many others...

On unix you can type grep udp /etc/services to get a list of UDP protocols implemented today... there are hundreds.

Assigning default value while creating migration file

You would have to first create your migration for the model basics then you create another migration to modify your previous using the change_column ...

def change
    change_column :widgets, :colour, :string, default: 'red'

Jquery get form field value

var textValue = $("input[type=text]").val()

this will get all values of all text boxes. You can use methods like children, firstchild, etc to hone in. Like by form $('form[name=form1] input[type=text]') Easier to use IDs for targeting elements but if it's purely dynamic you can get all input values then loop through then with JS.

MySQL "Or" Condition

Use brackets to group the OR statements.

mysql_query("SELECT * FROM Drinks WHERE email='$Email' AND (date='$Date_Today' OR date='$Date_Yesterday' OR date='$Date_TwoDaysAgo' OR date='$Date_ThreeDaysAgo' OR date='$Date_FourDaysAgo' OR date='$Date_FiveDaysAgo' OR date='$Date_SixDaysAgo' OR date='$Date_SevenDaysAgo')");

You can also use IN

mysql_query("SELECT * FROM Drinks WHERE email='$Email' AND date IN ('$Date_Today','$Date_Yesterday','$Date_TwoDaysAgo','$Date_ThreeDaysAgo','$Date_FourDaysAgo','$Date_FiveDaysAgo','$Date_SixDaysAgo','$Date_SevenDaysAgo')");

Bootstrap: adding gaps between divs

Adding a padding between the divs to simulate a gap might be a hack, but why not use something Bootstrap provides. It's called offsets. But again, you can define a class in your custom.css (you shouldn't edit the core stylesheet anyway) file and add something like .gap. However, .col-md-offset-* does the job most of the times for me, allowing me to precisely leave a gap between the divs.

As for vertical spacing, unfortunately, there isn't anything set built-in like that in Bootstrap 3, so you will have to invent your own custom class to do that. I'd usually do something like .top-buffer { margin-top:20px; }. This does the trick, and obviously, it doesn't have to be 20px, it can be anything you like.

GCC: array type has incomplete element type

The compiler needs to know the size of the second dimension in your two dimensional array. For example:

void print_graph(g_node graph_node[], double weight[][5], int nodes);

How do you 'redo' changes after 'undo' with Emacs?

I find redo.el extremly handy for doing "normal" undo/redo, and I usually bind it to C-S-z and undo to C-z, like this:

(when (require 'redo nil 'noerror)
    (global-set-key (kbd "C-S-z") 'redo))

(global-set-key (kbd "C-z") 'undo)

Just download the file, put it in your lisp-path and paste the above in your .emacs.

How do I make a div full screen?

<div id="placeholder" style="position:absolute; top:0; right:0; bottom:0; left:0;"></div>

Can I write or modify data on an RFID tag?

RFID tag has more standards. I have developed the RFID tag on Mifare card (ISO 14443A,B) and ISO 15693. Both of them, you can read/write or modify the data in the block data of RFID tag.

How to know a Pod's own IP address from inside a container in the Pod?

The container's IP address should be properly configured inside of its network namespace, so any of the standard linux tools can get it. For example, try ifconfig, ip addr show, hostname -I, etc. from an attached shell within one of your containers to test it out.

This Activity already has an action bar supplied by the window decor

Add this in your values/styles.xml

<style name="YourCustomTheme" parent="Theme.AppCompat.Light.NoActionBar">

<style name="AppBaseTheme" parent="YourCustomTheme">


<style name="AppTheme" parent="AppBaseTheme">


And add the following code in your values-v11/styles.xml and values-v14/styles.xml

<style name="AppBaseTheme" parent="YourCustomTheme">


Thats it. It will work.

Is there 'byte' data type in C++?

There's also byte_lite, compatible with C++98, C++11 and later.

Open a facebook link by native Facebook app on iOS

swift 3

if let url = URL(string: "fb://profile/<id>") {
        if #available(iOS 10, *) {
  , options: [:],completionHandler: { (success) in
                print("Open fb://profile/<id>: \(success)")
        } else {
            let success = UIApplication.shared.openURL(url)
            print("Open fb://profile/<id>: \(success)")

Reverse order of foreach list items

You can use usort function to create own sorting rules

Getting JavaScript object key list

In JavaScript, an object is a standalone entity, with properties and type.

For fetching values from Object in form of array: Object.values(obj) // obj is object name that you used Result -> ["value1", "value2", "value3", "value4"]

For fetching keys from Object in form of array: Object.keys(obj) // obj is object name that you used Result -> ["key1", "key2", "key3", "key4"]

As both functions are returning array you can get the length of keys or value by using length property. For instance - Object.values(obj).length or Object.keys(obj).length

How to implement a custom AlertDialog View

The simplest lines of code that works for me are are follows:

AlertDialog.Builder builder = new AlertDialog.Builder(this);

Whatever the type of layout(LinearLayout, FrameLayout, RelativeLayout) will work by setView and will just differ in the appearance and behavior.

Python date string to date object

For single value the datetime.strptime method is the fastest

import arrow
from datetime import datetime
import pandas as pd

l = ['24052010']

%timeit _ = list(map(lambda x: datetime.strptime(x, '%d%m%Y').date(), l))
6.86 µs ± 56.5 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)

%timeit _ = list(map(lambda x:, pd.to_datetime(l, format='%d%m%Y')))
305 µs ± 6.32 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

%timeit _ = list(map(lambda x: arrow.get(x, 'DMYYYY').date(), l))
46 µs ± 978 ns per loop (mean ± std. dev. of 7 runs, 10000 loops each)

For a list of values the pandas pd.to_datetime is the fastest

l = ['24052010'] * 1000

%timeit _ = list(map(lambda x: datetime.strptime(x, '%d%m%Y').date(), l))
6.32 ms ± 89.6 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)

%timeit _ = list(map(lambda x:, pd.to_datetime(l, format='%d%m%Y')))
1.76 ms ± 27.3 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

%timeit _ = list(map(lambda x: arrow.get(x, 'DMYYYY').date(), l))
44.5 ms ± 522 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)

For ISO8601 datetime format the ciso8601 is a rocket

import ciso8601

l = ['2010-05-24'] * 1000

%timeit _ = list(map(lambda x: ciso8601.parse_datetime(x).date(), l))
241 µs ± 3.24 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

"Cannot allocate an object of abstract type" error

You must have some virtual function declared in one of the parent classes and never implemented in any of the child classes. Make sure that all virtual functions are implemented somewhere in the inheritence chain. If a class's definition includes a pure virtual function that is never implemented, an instance of that class cannot ever be constructed.

How can I hide select options with JavaScript? (Cross browser)

Here's an option that:

  • Works in all browsers
  • Preserves current selection when filtering
  • Preserves order of items when removing / restoring
  • No dirty hacks / invalid HTML


    var $select = $(this);
    $'options', $select.find('option'));

function filter($select, search) {
    var $prev = null;
    var $options = $'options');
    search = search.trim().toLowerCase();
        var $option = $(this);
        var optionText = $option.text();
        if(search == "" || optionText.indexOf(search) >= 0) {
            if ($option.parent().length) {
                    $prev = $option;
            if (!$prev) $select.prepend($option);
            else $prev.after($option);
            $prev = $option;
        else {



Registry Key '...' has value '1.7', but '1.6' is required. Java 1.7 is Installed and the Registry is Pointing to it

I've deleted java files at windows/system32 and I also have removed c:\ProgramData\Oracle\Java\javapath from the PATH variable, because there was 3 symlinks to java 1.8 files.

I had JDK 1.7 in the %JAVA_HOME% variable and java1.7/bin in the PATH.

PS1: My problem was between Java 1.7 and Java 1.8.

PS2: I can't add this as a comment to Victor's answer because I haven't enough points.

Unable to create Genymotion Virtual Device

In case someone is using Mac OSX YOSEMITE or earlier. Follow this post. It worked for me.

Run these two command in Terminal:

sudo chmod 755 /Applications

sudo chmod 755 /Applications/

Took me hours to get it to work!

H2 database error: Database may be already in use: "Locked by another process"

You can also visit the "Preferences" tab from the H2 Console and shutdown all active sessions by pressing the shutdown button.

Sum of two input value by jquery

use parseInt

   var total = parseInt(a) + parseInt(b);


python .replace() regex

No. Regular expressions in Python are handled by the re module.

article = re.sub(r'(?is)</html>.+', '</html>', article)

In general:

text_after = re.sub(regex_search_term, regex_replacement, text_before)

How do I remove time part from JavaScript date?

Split it by space and take first part like below. Hope this will help you.

var d = '12/12/1955 12:00:00 AM';
d = d.split(' ')[0];

Jenkins pipeline how to change to another folder

Use WORKSPACE environment variable to change workspace directory.

If doing using Jenkinsfile, use following code :

    sh "pwd"

SyntaxError: Unexpected token function - Async Await Nodejs

Async functions are not supported by Node versions older than version 7.6.

You'll need to transpile your code (e.g. using Babel) to a version of JS that Node understands if you are using an older version.

That said, the current (2018) LTS version of Node.js is 8.x, so if you are using an earlier version you should very strongly consider upgrading.

ReportViewer Client Print Control "Unable to load client print control"?

I got this working with out removing any patches. The above patch was not working too. Finally what I did was on the IIS server install the following patch and reset / restart the IIS server. This is not for report manager application. This is for any ASP.NET Web application developed in .net3.5 using VS2008

Select the first row by group

(1) SQLite has a built in rowid pseudo-column so this works:

sqldf("select min(rowid) rowid, id, string 
               from test 
               group by id")


  rowid id string
1     1  1      A
2     3  2      B
3     5  3      C
4     7  4      D
5     9  5      E

(2) Also sqldf itself has a row.names= argument:

sqldf("select min(cast(row_names as real)) row_names, id, string 
              from test 
              group by id", row.names = TRUE)


  id string
1  1      A
3  2      B
5  3      C
7  4      D
9  5      E

(3) A third alternative which mixes the elements of the above two might be even better:

sqldf("select min(rowid) row_names, id, string 
               from test 
               group by id", row.names = TRUE)


  id string
1  1      A
3  2      B
5  3      C
7  4      D
9  5      E

Note that all three of these rely on a SQLite extension to SQL where the use of min or max is guaranteed to result in the other columns being chosen from the same row. (In other SQL-based databases that may not be guaranteed.)

A message body writer for Java type, class myPackage.B, and MIME media type, application/octet-stream, was not found

This also happens if you're missing an empty public constructor for the Entity (could be for JSON, XML etc)..

How to create an empty R vector to add new items

vec <- vector()

See also vector help


Why does Lua have no "continue" statement?

Why is there no continue?

Because it's unnecessary¹. There's very few situations where a dev would need it.

A) When you have a very simple loop, say a 1- or 2-liner, then you can just turn the loop condition around and it's still plenty readable.

B) When you're writing simple procedural code (aka. how we wrote code in the last century), you should also be applying structured programming (aka. how we wrote better code in the last century)

C) If you're writing object-oriented code, your loop body should consist of no more than one or two method calls unless it can be expressed in a one- or two-liner (in which case, see A)

D) If you're writing functional code, just return a plain tail-call for the next iteration.

The only case when you'd want to use a continue keyword is if you want to code Lua like it's python, which it just isn't.²

What workarounds are there for it?

Unless A) applies, in which case there's no need for any workarounds, you should be doing Structured, Object-Oriented or Functional programming. Those are the paradigms that Lua was built for, so you'd be fighting against the language if you go out of your way to avoid their patterns.³

Some clarification:

¹ Lua is a very minimalistic language. It tries to have as few features as it can get away with, and a continue statement isn't an essential feature in that sense.

I think this philosophy of minimalism is captured well by Roberto Ierusalimschy in this 2019 interview:

add that and that and that, put that out, and in the end we understand the final conclusion will not satisfy most people and we will not put all the options everybody wants, so we don’t put anything. In the end, strict mode is a reasonable compromise.

² There seems to be a large ammount of programmers coming to Lua from other languages because whatever program they're trying to script for happens to use it, and many of them want don't seem to want to write anything other than their language of choice, which leads to many questions like "Why doesn't Lua have X feature?"

Matz described a similar situation with Ruby in a recent interview:

The most popular question is: "I’m from the language X community; can’t you introduce a feature from the language X to Ruby?", or something like that. And my usual answer to these requests is… "no, I wouldn’t do that", because we have different language design and different language development policies.

³ There's a few ways to hack your way around this; some users have suggested using goto, which is a good enough aproximation in most cases, but gets very ugly very quickly and breaks completely with nested loops. Using gotos also puts you in danger of having a copy of SICP thrown at you whenever you show your code to anybody else.

What does 'COLLATE SQL_Latin1_General_CP1_CI_AS' do?

It sets how the database server sorts (compares pieces of text). in this case:


breaks up into interesting parts:

  1. latin1 makes the server treat strings using charset latin 1, basically ascii
  2. CP1 stands for Code Page 1252
  3. CI case insensitive comparisons so 'ABC' would equal 'abc'
  4. AS accent sensitive, so 'ü' does not equal 'u'

P.S. For more detailed information be sure to read @solomon-rutzky's answer.

Running .sh scripts in Git Bash

I had a similar problem, but I was getting an error message

cannot execute binary file

I discovered that the filename contained non-ASCII characters. When those were fixed, the script ran fine with ./


OPTIONS method returns info about API (methods/content type)

HEAD method returns info about resource (version/length/type)

Server response


HTTP/1.1 200 OK
Content-Type: text/html; charset=UTF-8
Date: Wed, 08 May 2013 10:24:43 GMT
Content-Length: 0


HTTP/1.1 200 OK
Accept-Ranges: bytes
Content-Type: text/html; charset=UTF-8
Date: Wed, 08 May 2013 10:12:29 GMT
ETag: "780602-4f6-4db31b2978ec0"
Last-Modified: Thu, 25 Apr 2013 16:13:23 GMT
Content-Length: 1270
  • OPTIONS Identifying which HTTP methods a resource supports, e.g. can we DELETE it or update it via a PUT?
  • HEAD Checking whether a resource has changed. This is useful when maintaining a cached version of a resource
  • HEAD Retrieving metadata about the resource, e.g. its media type or its size, before making a possibly costly retrieval
  • HEAD, OPTIONS Testing whether a resource exists and is accessible. For example, validating user-submitted links in an application

Here is nice and concise article about how HEAD and OPTIONS fit into RESTful architecture.

How to properly use unit-testing's assertRaises() with NoneType objects?

The usual way to use assertRaises is to call a function:

self.assertRaises(TypeError, test_function, args)

to test that the function call test_function(args) raises a TypeError.

The problem with self.testListNone[:1] is that Python evaluates the expression immediately, before the assertRaises method is called. The whole reason why test_function and args is passed as separate arguments to self.assertRaises is to allow assertRaises to call test_function(args) from within a try...except block, allowing assertRaises to catch the exception.

Since you've defined self.testListNone = None, and you need a function to call, you might use operator.itemgetter like this:

import operator
self.assertRaises(TypeError, operator.itemgetter, (self.testListNone,slice(None,1)))



is a long-winded way of saying self.testListNone[:1], but which separates the function (operator.itemgetter) from the arguments.

What's the difference between SCSS and Sass?

Original sass is ruby syntax-like, similar to ruby, jade etc...

In those syntaxes, we don't use {}, instead we go with white spaces, also no usage of ;...

In scss syntaxes are more like CSS, but with getting more options like: nesting, declaring, etc, similar to less and other pre-processing CSS ...

They basically do the same thing, but I put couple of lines of each to see the syntax difference, look at the {}, ;, and spaces:


$width: 100px
$color: green

  width: $width
  background-color: $color


$width: 100px;
$color: green;

div {
  width: $width;
  background-color: $color;

Passing argument to alias in bash

This is the solution which can avoid using function:

alias addone='{ num=$(cat -); echo "input: $num"; echo "result:$(($num+1))"; }<<<'

test result

addone 200
input: 200

configure: error: C compiler cannot create executables

For me it was a problem with gcc, highlighted by gcc -v. It was down to upgrading Xcode recently this post said to do sudo xcode-select -switch /Applications/ which fixed the issue.

Wpf control size to content?

For most controls, you set its height and width to Auto in the XAML, and it will size to fit its content.

In code, you set the width/height to double.NaN. For details, see FrameworkElement.Width, particularly the "remarks" section.

Receive JSON POST with PHP

I'd like to post an answer that also uses curl to get the contents, and mpdf to save the results to a pdf, so you get all the steps of a tipical use case. It's only raw code (so to be adapted to your needs), but it works.

// import mpdf somewhere
require_once dirname(__FILE__) . '/mpdf/vendor/autoload.php';

// get mpdf instance
$mpdf = new \Mpdf\Mpdf();

// src php file
$mysrcfile = '';
// where we want to save the pdf
$mydestination = '';

// encode $_POST data to json
$json = json_encode($_POST);

// init curl > pass the url of the php file we want to pass 
// data to and then print out to pdf
$ch = curl_init($mysrcfile);

// tell not to echo the results
curl_setopt ($ch, CURLOPT_RETURNTRANSFER, 1 );

// set the proper headers
curl_setopt($ch, CURLOPT_HTTPHEADER, [ 'Content-Type: application/json', 'Content-Length: ' . strlen($json) ]);

// pass the json data to $mysrcfile
curl_setopt($ch, CURLOPT_POSTFIELDS, $json);

// exec curl and save results
$html = curl_exec($ch);


// parse html and then save to a pdf file
$this->mpdf->Output($mydestination, \Mpdf\Output\Destination::FILE);

In $mysrcfile I'll read json data like this (as stated on previous answers):

$data = json_decode(file_get_contents('php://input'));
// (then process it and build the page source)

Difference between Date(dateString) and new Date(dateString)

I was having the same issue using an API call which responded in ISO 8601 format. Working in Chrome this worked: `

// date variable from an api all in ISO 8601 format yyyy-mm-dd hh:mm:ss
  var date = oDate['events']['event'][0]['start_time'];
  var eventDate = new Date();
  var outputDate = eventDate.toDateString();


but this didn't work with firefox.

Above answer helped me format it correctly for firefox:

 // date variable from an api all in ISO 8601 format yyyy-mm-dd hh:mm:ss
 var date = oDate['events']['event'][0]['start_time'];
 var eventDate = new Date(date.replace(/-/g,"/");
 var outputDate = eventDate.toDateString();

How can I print out just the index of a pandas dataframe?

You can use lamba function:

index = df.index[lambda x : for x in df.index() ]

Angular 2 Date Input not binding to date value

Instead of [(ngModel)] you can use:

// view
<input type="date" #myDate [value]=" | date:'yyyy-MM-dd'" (input)="$" />

// controller
parseDate(dateString: string): Date {
    if (dateString) {
        return new Date(dateString);
    return null;

You can also choose not to use parseDate function. In this case the date will be saved as string format like "2016-10-06" instead of Date type (I haven't tried whether this has negative consequences when manipulating the data or saving to database for example).

Merge data frames based on rownames in R

See ?merge:

the name "row.names" or the number 0 specifies the row names.


R> de <- merge(d, e, by=0, all=TRUE)  # merge by row names (by=0 or by="row.names")
R> de[] <- 0                 # replace NA values
R> de
  Row.names   a   b   c   d   e   f   g   h   i  j  k  l  m  n  o  p  q  r  s
1         1 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10 11 12 13 14 15 16 17 18 19
2         2 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9  1  0  0  0  0  0  0  0  0  0
3         3 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0  0 21 22 23 24 25 26 27 28 29
1 20
2  0
3 30

Get value of a merged cell of an excel from its cell address in vba

Even if it is really discouraged to use merge cells in Excel (use Center Across Selection for instance if needed), the cell that "contains" the value is the one on the top left (at least, that's a way to express it).

Hence, you can get the value of merged cells in range B4:B11 in several ways:

  • Range("B4").Value
  • Range("B4:B11").Cells(1).Value
  • Range("B4:B11").Cells(1,1).Value

You can also note that all the other cells have no value in them. While debugging, you can see that the value is empty.

Also note that Range("B4:B11").Value won't work (raises an execution error number 13 if you try to Debug.Print it) because it returns an array.

How to get Latitude and Longitude of the mobile device in android?

Use the LocationManager.

LocationManager lm = (LocationManager)getSystemService(Context.LOCATION_SERVICE); 
Location location = lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
double longitude = location.getLongitude();
double latitude = location.getLatitude();

The call to getLastKnownLocation() doesn't block - which means it will return null if no position is currently available - so you probably want to have a look at passing a LocationListener to the requestLocationUpdates() method instead, which will give you asynchronous updates of your location.

private final LocationListener locationListener = new LocationListener() {
    public void onLocationChanged(Location location) {
        longitude = location.getLongitude();
        latitude = location.getLatitude();

lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 2000, 10, locationListener);

You'll need to give your application the ACCESS_FINE_LOCATION permission if you want to use GPS.

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

You may also want to add the ACCESS_COARSE_LOCATION permission for when GPS isn't available and select your location provider with the getBestProvider() method.

static files with express.js

use below inside your app.js


(folderName is folder which has files) - remember these assets are accessed direct through server path (i.e. http://localhost:3000/abc.png (where as abc.png is inside folderName folder)

How to disable sort in DataGridView?

For extending control functionality like this, I like to use extension methods so that it can be reused easily. Here is a starter extensions file that contains an extension to disable sorting on a datagridview.

To use it, just include it in your project and call like this


In my case, I added this line of code in the DataBindingComplete eventhandler of the DataGridView where I wanted sorting disabled

Imports System.ComponentModel
Imports System.Reflection
Imports System.Runtime.CompilerServices
Imports System.Windows.Forms

Public Module Extensions

Public Sub DisableSorting(datagrid As DataGridView)
    For index = 0 To datagrid.Columns.Count - 1
        datagrid.Columns(index).SortMode = DataGridViewColumnSortMode.NotSortable
End Sub

End Module

How to set an image as a background for Frame in Swing GUI of java?

This is easily done by replacing the frame's content pane with a JPanel which draws your image:

try {
    final Image backgroundImage = File(...));
    setContentPane(new JPanel(new BorderLayout()) {
        @Override public void paintComponent(Graphics g) {
            g.drawImage(backgroundImage, 0, 0, null);
} catch (IOException e) {
    throw new RuntimeException(e);

This example also sets the panel's layout to BorderLayout to match the default content pane layout.

(If you have any trouble seeing the image, you might need to call setOpaque(false) on some other components so that you can see through to the background.)

How to get height of entire document with JavaScript?

The proper answer for 2017 is:


Unlike document.body.scrollHeight this method accounts for body margins. It also gives fractional height value, which can be useful in some cases

How to open SharePoint files in Chrome/Firefox

Installing the Chrome extension IE Tab did the job for me.

It has the ability to auto-detect URLs so whenever I browse to our SharePoint it emulates Internet Explorer. Finally I can open Office documents directly from Chrome.

You can install IETab for FireFox too.

Get Application Name/ Label via ADB Shell or Terminal

If you know the app id of the package (like org.mozilla.firefox), it is easy. First to get the path of actual package file of the appId,

$  adb shell pm list packages -f

Now you can do some grep|sed magic to extract the path : /data/app/

After that aapt tool comes in handy :

$  adb shell aapt dump badging /data/app/

Again some grep magic to get the Label.

How do I force git to checkout the master branch and remove carriage returns after I've normalized files using the "text" attribute?

As others have pointed out one could just delete all the files in the repo and then check them out. I prefer this method and it can be done with the code below

git ls-files -z | xargs -0 rm
git checkout -- .

or one line

git ls-files -z | xargs -0 rm ; git checkout -- .

I use it all the time and haven't found any down sides yet!

For some further explanation, the -z appends a null character onto the end of each entry output by ls-files, and the -0 tells xargs to delimit the output it was receiving by those null characters.

Determining the current foreground application from a background task or service

Try the following code:

ActivityManager activityManager = (ActivityManager) newContext.getSystemService( Context.ACTIVITY_SERVICE );
List<RunningAppProcessInfo> appProcesses = activityManager.getRunningAppProcesses();
for(RunningAppProcessInfo appProcess : appProcesses){
    if(appProcess.importance == RunningAppProcessInfo.IMPORTANCE_FOREGROUND){
        Log.i("Foreground App", appProcess.processName);

Process name is the package name of the app running in foreground. Compare it to the package name of your application. If it is the same then your application is running on foreground.

I hope this answers your question.

how do I use an enum value on a switch statement in C++

Some things to note:

You should always declare your enum inside a namespace as enums are not proper namespaces and you will be tempted to use them like one.

Always have a break at the end of each switch clause execution will continue downwards to the end otherwise.

Always include the default: case in your switch.

Use variables of enum type to hold enum values for clarity.

see here for a discussion of the correct use of enums in C++.

This is what you want to do.

namespace choices
    enum myChoice 
        EASY = 1 ,
        MEDIUM = 2, 
        HARD = 3  

int main(int c, char** argv)
    choices::myChoice enumVar;
    cin >> enumVar;
    switch (enumVar)
        case choices::EASY:
            // do stuff
        case choices::MEDIUM:
            // do stuff

            // is likely to be an error


Load dimension value from res/values/dimension.xml from source code

For those who just need to save some int value in the resources, you can do the following.


<?xml version="1.0" encoding="utf-8"?>
    <integer name="default_value">100</integer>


int defaultValue = getResources().getInteger(R.integer.default_value);

Set default value of an integer column SQLite

A column with default value:

<ColumnName> <Type> DEFAULT <DefaultValue>

<DefaultValue> is a placeholder for a:

  • value literal
  • ( expression )


LastSeen TEXT DEFAULT (datetime('now'))

Why does ++[[]][+[]]+[+[]] return the string "10"?

Step by steps of that, + turn value to a number and if you add to an empty array +[] it's empty and is equal to 0, it will

So from there, now look into your code, it's ++[[]][+[]]+[+[]]...

And there is plus between them ++[[]][+[]] + [+[]]

So these [+[]] will return [0] as they have an empty array which gets converted to 0 inside the other array...

So as imagine, the first value is a 2-dimensional array with one array inside... so [[]][+[]] will be equal to [[]][0] which will return []...

And at the end ++ convert it and increase it to 1...

So you can imagine, 1 + "0" will be "10"...

Why does return the string “10”?

How to set bootstrap navbar active class with Angular JS?

Here's another solution for anyone who might be interested. The advantage of this is it has fewer dependencies. Heck, it works without a web server too. So it's completely client-side.


<nav class="navbar navbar-inverse" ng-controller="topNavBarCtrl"">
<div class="container-fluid">
    <div class="navbar-header">
        <a class="navbar-brand" href="#"><span class="glyphicon glyphicon-home" aria-hidden="true"></span></a>
    <ul class="nav navbar-nav">
        <li ng-click="selectTab()" ng-class="getTabClass()"><a href="#">Home</a></li>
        <li ng-repeat="tab in tabs" ng-click="selectTab(tab)" ng-class="getTabClass(tab)"><a href="#">{{ tab }}</a></li>


Here we are generating the links dynamically from an angularjs model using the directive ng-repeat. Magic happens with the methods selectTab() and getTabClass() defined in the controller for this navbar presented below.


angular.module("app.NavigationControllersModule", [])

// Constant named 'activeTab' holding the value 'active'. We will use this to set the class name of the <li> element that is selected.
.constant("activeTab", "active")

.controller("topNavBarCtrl", function($scope, activeTab){
    // Model used for the ng-repeat directive in the template.
    $scope.tabs = ["Page 1", "Page 2", "Page 3"];

    var selectedTab = null;

    // Sets the selectedTab.
    $scope.selectTab = function(newTab){
       selectedTab = newTab;

    // Sets class of the selectedTab to 'active'.
    $scope.getTabClass = function(tab){
       return selectedTab == tab ? activeTab : "";


selectTab() method is called using ng-click directive. So when the link is clicked, the variable selectedTab is set to the name of this link. In the HTML you can see that this method is called without any argument for Home tab so that it will be highlighted when the page loads.

The getTabClass() method is called via ng-class directive in the HTML. This method checks if the tab it is in is the same as the value of the selectedTab variable. If true, it returns "active" else returns "" which is applied as the class name by ng-class directive. Then whatever css you have applied to class active will be applied to the selected tab.

downcast and upcast

Answer 1 : Yes it called upcasting but the way you do it is not modern way. Upcasting can be performed implicitly you don't need any conversion. So just writing Employee emp = mgr; is enough for upcasting.

Answer 2 : If you create object of Manager class we can say that manager is an employee. Because class Manager : Employee depicts Is-A relationship between Employee Class and Manager Class. So we can say that every manager is an employee.

But if we create object of Employee class we can not say that this employee is manager because class Employee is a class which is not inheriting any other class. So you can not directly downcast that Employee Class object to Manager Class object.

So answer is, if you want to downcast from Employee Class object to Manager Class object, first you must have object of Manager Class first then you can upcast it and then you can downcast it.

Scrollview vertical and horizontal in android

I found a better solution.

XML: (design.xml)

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="" android:layout_width="fill_parent" android:layout_height="fill_parent">
  <FrameLayout android:layout_width="90px" android:layout_height="90px">
    <RelativeLayout android:id="@+id/container" android:layout_width="fill_parent" android:layout_height="fill_parent">        

Java Code:

public class Example extends Activity {
  private RelativeLayout container;
  private int currentX;
  private int currentY;

  protected void onCreate(Bundle savedInstanceState) {

    container = (RelativeLayout)findViewById(;

    int top = 0;
    int left = 0;

    ImageView image1 = ...
    RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
    layoutParams.setMargins(left, top, 0, 0);               
    container.addView(image1, layoutParams);

    ImageView image2 = ...
    left+= 100;
    RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
    layoutParams.setMargins(left, top, 0, 0);               
    container.addView(image2, layoutParams);

    ImageView image3 = ...
    left= 0;
    top+= 100;
    RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
    layoutParams.setMargins(left, top, 0, 0);               
    container.addView(image3, layoutParams);

    ImageView image4 = ...
    left+= 100;     
    RelativeLayout.LayoutParams layoutParams = new RelativeLayout.LayoutParams(RelativeLayout.LayoutParams.WRAP_CONTENT, RelativeLayout.LayoutParams.WRAP_CONTENT);
    layoutParams.setMargins(left, top, 0, 0);               
    container.addView(image4, layoutParams);

  public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN: {
            currentX = (int) event.getRawX();
            currentY = (int) event.getRawY();

        case MotionEvent.ACTION_MOVE: {
            int x2 = (int) event.getRawX();
            int y2 = (int) event.getRawY();
            container.scrollBy(currentX - x2 , currentY - y2);
            currentX = x2;
            currentY = y2;
        case MotionEvent.ACTION_UP: {
      return true; 

That's works!!!

If you want to load other layout or control, the structure is the same.

Converting List<String> to String[] in Java

String[] strarray = strlist.toArray(new String[0]);

if u want List convert to string use StringUtils.join(slist, '\n');

PHPDoc type hinting for array of objects?

In NetBeans 7.0 (may be lower too) you could declare the the return type "array with Text objects " just as @return Text and the code hinting will work:

Edit: updated the example with @Bob Fanger suggestion

 * get all Tests
 * @return Test|Array $tests
public function getAllTexts(){
    return array(new Test(), new Test());

and just use it:

$tests =  $controller->getAllTests();
//$tests->         //codehinting works!
//$tests[0]->      //codehinting works!

foreach($tests as $text){
    //$test->      //codehinting works!

It is not perfect but it is better then just to leave it just "mixed", which brings no value.

CONS is you are allowed to tread the array as Text Object which will throw errors.

Add days Oracle SQL

You can use the plus operator to add days to a date.

order_date + 20

PHP Try and Catch for SQL Insert


I am not sure if there is a mysql version of this but adding this line of code allows throwing mysqli_sql_exception.
I know, passed a lot of time and the question is already checked answered but I got a different answer and it may be helpful.

new DateTime() vs default(DateTime)

The simpliest way to understand it is that DateTime is a struct. When you initialize a struct it's initialize to it's minimum value : DateTime.Min

Therefore there is no difference between default(DateTime) and new DateTime() and DateTime.Min

How to run a makefile in Windows?

Check out GnuWin's make (for windows), which provides a native port for Windows (without requiring a full runtime environment like Cygwin)

If you have winget, you can install via the CLI like this:

winget install GnuWin32.Make

Also, be sure to add the install path to your system PATH:

C:\Program Files (x86)\GnuWin32\bin

Speed comparison with Project Euler: C vs Python vs Erlang vs Haskell

There are some problems with the Erlang implementation. As baseline for the following, my measured execution time for your unmodified Erlang program was 47.6 seconds, compared to 12.7 seconds for the C code.

The first thing you should do if you want to run computationally intensive Erlang code is to use native code. Compiling with erlc +native euler12 got the time down to 41.3 seconds. This is however a much lower speedup (just 15%) than expected from native compilation on this kind of code, and the problem is your use of -compile(export_all). This is useful for experimentation, but the fact that all functions are potentially reachable from the outside causes the native compiler to be very conservative. (The normal BEAM emulator is not that much affected.) Replacing this declaration with -export([solve/0]). gives a much better speedup: 31.5 seconds (almost 35% from the baseline).

But the code itself has a problem: for each iteration in the factorCount loop, you perform this test:

factorCount (_, Sqrt, Candidate, Count) when Candidate == Sqrt -> Count + 1;

The C code doesn't do this. In general, it can be tricky to make a fair comparison between different implementations of the same code, and in particular if the algorithm is numerical, because you need to be sure that they are actually doing the same thing. A slight rounding error in one implementation due to some typecast somewhere may cause it to do many more iterations than the other even though both eventually reach the same result.

To eliminate this possible error source (and get rid of the extra test in each iteration), I rewrote the factorCount function as follows, closely modelled on the C code:

factorCount (N) ->
    Sqrt = math:sqrt (N),
    ISqrt = trunc(Sqrt),
    if ISqrt == Sqrt -> factorCount (N, ISqrt, 1, -1);
       true          -> factorCount (N, ISqrt, 1, 0)

factorCount (_N, ISqrt, Candidate, Count) when Candidate > ISqrt -> Count;
factorCount ( N, ISqrt, Candidate, Count) ->
    case N rem Candidate of
        0 -> factorCount (N, ISqrt, Candidate + 1, Count + 2);
        _ -> factorCount (N, ISqrt, Candidate + 1, Count)

This rewrite, no export_all, and native compilation, gave me the following run time:

$ erlc +native euler12.erl
$ time erl -noshell -s euler12 solve

real    0m19.468s
user    0m19.450s
sys 0m0.010s

which is not too bad compared to the C code:

$ time ./a.out 

real    0m12.755s
user    0m12.730s
sys 0m0.020s

considering that Erlang is not at all geared towards writing numerical code, being only 50% slower than C on a program like this is pretty good.

Finally, regarding your questions:

Question 1: Do erlang, python and haskell loose speed due to using arbitrary length integers or don't they as long as the values are less than MAXINT?

Yes, somewhat. In Erlang, there is no way of saying "use 32/64-bit arithmetic with wrap-around", so unless the compiler can prove some bounds on your integers (and it usually can't), it must check all computations to see if they can fit in a single tagged word or if it has to turn them into heap-allocated bignums. Even if no bignums are ever used in practice at runtime, these checks will have to be performed. On the other hand, that means you know that the algorithm will never fail because of an unexpected integer wraparound if you suddenly give it larger inputs than before.

Question 4: Do my functional implementations permit LCO and hence avoid adding unnecessary frames onto the call stack?

Yes, your Erlang code is correct with respect to last call optimization.

how to change attribute "hidden" in jquery


Note, thanks to tip by A.Wolff, you should use removeAttr instead of setting to false. When set to false, the element will still be hidden. Therefore, removing is more effective.

PostgreSQL, checking date relative to "today"

This should give you the current date minus 1 year:

select now() - interval '1 year';

The type initializer for 'CrystalDecisions.CrystalReports.Engine.ReportDocument' threw an exception

This is because of lack of Capability .... If you see the Inner Exception you will see this message

"Access is denied.
Access to speech functionality requires ID_CAP_SPEECH_RECOGNITION to be defined in the manifest."

So to get rid of this exception. turn on the capability for Speech Recognition from the Manifest file.

I had the same problem, and It solved my Problem. :)

How do I get the dialer to open with phone number displayed?

 android:text="+91 22 2222 2222"

This is how you can open EditText label assigned number on dialer directly.

SSL error : routines:SSL3_GET_SERVER_CERTIFICATE:certificate verify failed

Got this issue today and after wandering for several hours just came to know that my server datetime was wrong.

So first please check your server datetime before going so deep in this issue.

also try doing

>> sudo update-ca-certificates

Improving bulk insert performance in Entity framework

 Use : db.Set<tale>.AddRange(list); 
Ref :
TESTEntities db = new TESTEntities();
List<Person> persons = new List<Person> { 
new  Person{Name="p1",Place="palce"},
new  Person{Name="p2",Place="palce"},
new  Person{Name="p3",Place="palce"},
new  Person{Name="p4",Place="palce"},
new  Person{Name="p5",Place="palce"}

SQL Server String or binary data would be truncated

this can also happen when you dont have adequate permissions

Error: [ng:areq] from angular controller

I experienced this error once. The problem was I had defined angular.module() in two places with different arguments.


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

in other place,

var MyApp2 = angular.module('MyApp', ['ngAnimate']);

Android Emulator sdcard push error: Read-only file system

  1. Give any size to Sdcard in Emulator
  2. unchecked the read only option from c:\\avd -> properties
  3. push a file through file explorer
  4. restart the Emulator

It will definitely works

validation of input text field in html using javascript

For flexibility and other places you might want to validated. You can use the following function.

`function validateOnlyTextField(element) {
    var str = element.value;
    if(!(/^[a-zA-Z, ]+$/.test(str))){
        // console.log('String contain number characters');
        str = str.substr(0,  str.length -1);
        element.value = str;

Then on your html section use the following event.

<input type="text" id="names" onkeyup="validateOnlyTextField(this)" />

You can always reuse the function.

How can I add comments in MySQL?

From here you can use

#  For single line comments
-- Also for single line, must be followed by space/control character
    C-style multiline comment

Android Fragment no view found for ID?

The solution was to use getChildFragmentManager()

instead of getFragmentManager()

when calling from a fragment. If you are calling the method from an activity, then use getFragmentManager().

That will solve the problem.

Using Image control in WPF to display System.Drawing.Bitmap

You can use the Source property of the image. Try this code...

ImageSource imageSource = new BitmapImage(new Uri("C:\\FileName.gif"));

image1.Source = imageSource;

Multiple FROMs - what it means

The first answer is too complex, historic, and uninformative for my tastes.

It's actually rather simple. Docker provides for a functionality called multi-stage builds the basic idea here is to,

  • Free you from having to manually remove what you don't want, by forcing you to whitelist what you do want,
  • Free resources that would otherwise be taken up because of Docker's implementation.

Let's start with the first. Very often with something like Debian you'll see.

RUN apt-get update \ 
  && apt-get dist-upgrade \
  && apt-get install <whatever> \
  && apt-get clean

We can explain all of this in terms of the above. The above command is chained together so it represents a single change with no intermediate Images required. If it was written like this,

RUN apt-get update ;
RUN apt-get dist-upgrade;
RUN apt-get install <whatever>;
RUN apt-get clean;

It would result in 3 more temporary intermediate Images. Having it reduced to one image, there is one remaining problem: apt-get clean doesn't clean up artifacts used in the install. If a Debian maintainer includes in his install a script that modifies the system that modification will also be present in the final solution (see something like pepperflashplugin-nonfree for an example of that).

By using a multi-stage build you get all the benefits of a single changed action, but it will require you to manually whitelist and copy over files that were introduced in the temporary image using the COPY --from syntax documented here. Moreover, it's a great solution where there is no alternative (like an apt-get clean), and you would otherwise have lots of un-needed files in your final image.

See also

Mongodb: Failed to connect to, reason: errno:10061

I was also faced the same issue with mongodb 2.6.

What solved my problem was I just run mongod --repair command

and then start mongod.exe

It's worked for me

How to install Hibernate Tools in Eclipse?

For Eclipse plugins, you just unzip them and drop the folder in the Eclipse\Plugins directory. Simple as that.

Eclipse error: R cannot be resolved to a variable

The R file can't be generated if your layout contains errors. If your res folder is empty, then it's safe to assume that there's no res/layout folder with any layouts in it, but your activity is probably calling setContentView and not finding anything -- that qualifies as a problem with your layout.

Invoke a second script with arguments from a script

You can execute it same as SQL query. first, build your command/Expression and store in a variable and execute/invoke.

$command =  ".\yourExternalScriptFile.ps1" + " -param1 '$paramValue'"

It is pretty forward, I don't think it needs explanations. So all set to execute your command now,

Invoke-Expression $command

I would recommend catching the exception here

Android Failed to install HelloWorld.apk on device (null) Error

I was getting the same error.

I Just left the AVD running even after it says "Failed to install *.apk on device-emulator-5554". It automatically loaded the project afterwards.

I think the error comes due the slow start up of the AVD.

nvarchar(max) vs NText

nvarchar(max) is what you want to be using. The biggest advantage is that you can use all the T-SQL string functions on this data type. This is not possible with ntext. I'm not aware of any real disadvantages.

Stop setInterval

we can easily stop the set interval by calling clear interval

var count = 0 , i = 5;
var vary = function intervalFunc() {
    console.log('hello boy');  
    if (count == 10) {

  setInterval(vary, 1500);

How do I get the position selected in a RecyclerView?

No need to have your ViewHolder implementing View.OnClickListener. You can get directly the clicked position by setting a click listener in the method onCreateViewHolder of RecyclerView.Adapter here is a sample of code :

public class ItemListAdapterRecycler extends RecyclerView.Adapter<ItemViewHolder>

    private final List<Item> items;

    public ItemListAdapterRecycler(List<Item> items)
        this.items = items;

    public ItemViewHolder onCreateViewHolder(final ViewGroup parent, int viewType)
        View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_row, parent, false);

        view.setOnClickListener(new View.OnClickListener()
            public void onClick(View view)
                int currentPosition = getClickedPosition(view);
                Log.d("DEBUG", "" + currentPosition);

        return new ItemViewHolder(view);

    public void onBindViewHolder(ItemViewHolder itemViewHolder, int position)

    public int getItemCount()
        return items.size();

    private int getClickedPosition(View clickedView)
        RecyclerView recyclerView = (RecyclerView) clickedView.getParent();
        ItemViewHolder currentViewHolder = (ItemViewHolder) recyclerView.getChildViewHolder(clickedView);
        return currentViewHolder.getAdapterPosition();


What is the best way to calculate a checksum for a file that is on my machine?

7-Zip can be used to generate hashes for files, folders of files, and trees of folders of files. 7-Zip is small footprint and a very useful compression utility.

How to detect when an Android app goes to the background and come back to the foreground

The android.arch.lifecycle package provides classes and interfaces that let you build lifecycle-aware components

Your application should implement the LifecycleObserver interface:

public class MyApplication extends Application implements LifecycleObserver {

    public void onCreate() {

    private void onAppBackgrounded() {
        Log.d("MyApp", "App in background");

    private void onAppForegrounded() {
        Log.d("MyApp", "App in foreground");

To do that, you need to add this dependency to your build.gradle file:

dependencies {
    implementation "android.arch.lifecycle:extensions:1.1.1"

As recommended by Google, you should minimize the code executed in the lifecycle methods of activities:

A common pattern is to implement the actions of the dependent components in the lifecycle methods of activities and fragments. However, this pattern leads to a poor organization of the code and to the proliferation of errors. By using lifecycle-aware components, you can move the code of dependent components out of the lifecycle methods and into the components themselves.

You can read more here:

Laravel - htmlspecialchars() expects parameter 1 to be string, object given

Laravel - htmlspecialchars() expects parameter 1 to be string, object given.

thank me latter.........................

when you send or get array from contrller or function but try to print as single value or single variable in laravel blade file so it throws an error

->use any think who convert array into string it work.

solution: 1)run the foreach loop and get single single value and print. 2)The implode() function returns a string from the elements of an array. {{ implode($your_variable,',') }}

implode is best way to do it and its 100% work.

Parse JSON object with string and value only

You need to get a list of all the keys, loop over them and add them to your map as shown in the example below:

    String s = "{menu:{\"1\":\"sql\", \"2\":\"android\", \"3\":\"mvc\"}}";
    JSONObject jObject  = new JSONObject(s);
    JSONObject  menu = jObject.getJSONObject("menu");

    Map<String,String> map = new HashMap<String,String>();
    Iterator iter = menu.keys();
        String key = (String);
        String value = menu.getString(key);

@Directive vs @Component in Angular

In Angular 2 and above, “everything is a component.” Components are the main way we build and specify elements and logic on the page, through both custom elements and attributes that add functionality to our existing components.

But what directives do then in Angular2+ ?

Attribute directives attach behaviour to elements.

There are three kinds of directives in Angular:

  1. Components—directives with a template.
  2. Structural directives—change the DOM layout by adding and removing DOM elements.
  3. Attribute directives—change the appearance or behaviour of an element, component, or another directive.

So what's happening in Angular2 and above is Directives are attributes which add functionalities to elements and components.

Look at the sample below from

import { Directive, ElementRef, Input } from '@angular/core';

@Directive({ selector: '[myHighlight]' })
export class HighlightDirective {
    constructor(el: ElementRef) { = 'yellow';

So what it does, it will extends you components and HTML elements with adding yellow background and you can use it as below:

<p myHighlight>Highlight me!</p>

But components will create full elements with all functionalities like below:

import { Component } from '@angular/core';

  selector: 'my-component',
  template: `
    <div>Hello my name is {{name}}. 
      <button (click)="sayMyName()">Say my name</button>
export class MyComponent {
  name: string;
  constructor() { = 'Alireza'
  sayMyName() {
    console.log('My name is',

and you can use it as below:


When we use the tag in the HTML, this component will be created and the constructor get called and rendered.

Register DLL file on Windows Server 2008 R2

This is what has to occur.

You have to copy your DLL that you want to Register to: c:\windows\SysWOW64\

Then in the Run dialog, type this in: C:\Windows\SysWOW64\regsvr32.exe c:\windows\system32\YourDLL.dll

and you will get the message:

DllRegisterServer in c:\windows\system32\YourDLL.dll succeeded.

Draw text in OpenGL ES

For static text:

  • Generate an image with all words used on your PC (For example with GIMP).
  • Load this as a texture and use it as material for a plane.

For long text that needs to be updated once in a while:

  • Let android draw on a bitmap canvas (JVitela's solution).
  • Load this as material for a plane.
  • Use different texture coordinates for each word.

For a number (formatted 00.0):

  • Generate an image with all numbers and a dot.
  • Load this as material for a plane.
  • Use below shader.
  • In your onDraw event only update the value variable sent to the shader.

    precision highp float;
    precision highp sampler2D;
    uniform float uTime;
    uniform float uValue;
    uniform vec3 iResolution;
    varying vec4 v_Color;
    varying vec2 vTextureCoord;
    uniform sampler2D s_texture;
    void main() {
    vec4 fragColor = vec4(1.0, 0.5, 0.2, 0.5);
    vec2 uv = vTextureCoord;
    float devisor = 10.75;
    float digit;
    float i;
    float uCol;
    float uRow;
    if (uv.y < 0.45) {
        if (uv.x > 0.75) {
            digit = floor(uValue*10.0);
            digit = digit - floor(digit/10.0)*10.0;
            i = 48.0 - 32.0 + digit;
            uRow = floor(i / 10.0);
            uCol = i - 10.0 * uRow;
            fragColor = texture2D( s_texture, uv / devisor * 2.0 + vec2((uCol-1.5) / devisor, uRow / devisor) );
        } else if (uv.x > 0.5) {
            uCol = 4.0;
            uRow = 1.0;
            fragColor = texture2D( s_texture, uv / devisor * 2.0 + vec2((uCol-1.0) / devisor, uRow / devisor) );
        } else if (uv.x > 0.25) {
            digit = floor(uValue);
            digit = digit - floor(digit/10.0)*10.0;
            i = 48.0 - 32.0 + digit;
            uRow = floor(i / 10.0);
            uCol = i - 10.0 * uRow;
            fragColor = texture2D( s_texture, uv / devisor * 2.0 + vec2((uCol-0.5) / devisor, uRow / devisor) );
        } else if (uValue >= 10.0) {
            digit = floor(uValue/10.0);
            digit = digit - floor(digit/10.0)*10.0;
            i = 48.0 - 32.0 + digit;
            uRow = floor(i / 10.0);
            uCol = i - 10.0 * uRow;
            fragColor = texture2D( s_texture, uv / devisor * 2.0 + vec2((uCol-0.0) / devisor, uRow / devisor) );
        } else {
            fragColor = vec4(0.0, 0.0, 0.0, 0.0);
    } else {
        fragColor = vec4(0.0, 0.0, 0.0, 0.0);
    gl_FragColor = fragColor;

Above code works for a texture atlas where numbers start from 0 at the 7th column of the 2nd row of the font atlas (texture).

Refer to for demonstration (with wrong texture though)

How to check if a socket is connected/disconnected in C#?

The best way is simply to have your client send a PING every X seconds, and for the server to assume it is disconnected after not having received one for a while.

I encountered the same issue as you when using sockets, and this was the only way I could do it. The socket.connected property was never correct.

In the end though, I switched to using WCF because it was far more reliable than sockets.

Why am I getting "void value not ignored as it ought to be"?

srand doesn't return anything so you can't initialize a with its return value because, well, because it doesn't return a value. Did you mean to call rand as well?

Fitting iframe inside a div

Would this CSS fix it?

iframe {

From this example:

invalid command code ., despite escaping periods, using sed

If you are on a OS X, this probably has nothing to do with the sed command. On the OSX version of sed, the -i option expects an extension argument so your command is actually parsed as the extension argument and the file path is interpreted as the command code.

Try adding the -e argument explicitly and giving '' as argument to -i:

find ./ -type f -exec sed -i '' -e "s/" {} \;

See this.

string to string array conversion in java

String strName = "name";
String[] strArray = new String[] {strName};
System.out.println(strArray[0]); //prints "name"

The second line allocates a String array with the length of 1. Note that you don't need to specify a length yourself, such as:

String[] strArray = new String[1];

instead, the length is determined by the number of elements in the initalizer. Using

String[] strArray = new String[] {strName, "name1", "name2"};

creates an array with a length of 3.

How to align input forms in HTML

You should use a table. As a matter of logical structure the data is tabular: this is why you want it to align, because you want to show that the labels are not related solely to their input boxes but also to each other, in a two-dimensional structure.

[consider what you would do if you had string or numeric values to display instead of input boxes.]

How to get String Array from arrays.xml file

Your XML is not entirely clear, but arrays XML can cause force closes if you make them numbers, and/or put white space in their definition.

Make sure they are defined like No Leading or Trailing Whitespace

Gnuplot line types

Until version 4.6

The dash type of a linestyle is given by the linetype, which does also select the line color unless you explicitely set an other one with linecolor.

However, the support for dashed lines depends on the selected terminal:

  1. Some terminals don't support dashed lines, like png (uses libgd)
  2. Other terminals, like pngcairo, support dashed lines, but it is disables by default. To enable it, use set termoption dashed, or set terminal pngcairo dashed ....
  3. The exact dash patterns differ between terminals. To see the defined linetype, use the test command:


set terminal pngcairo dashed
set output 'test.png'
set output


enter image description here

whereas, the postscript terminal shows different dash patterns:

set terminal postscript eps color colortext
set output 'test.eps'
set output

enter image description here

Version 5.0

Starting with version 5.0 the following changes related to linetypes, dash patterns and line colors are introduced:

  • A new dashtype parameter was introduced:

    To get the predefined dash patterns, use e.g.

    plot x dashtype 2

    You can also specify custom dash patterns like

    plot x dashtype (3,5,10,5),\
         2*x dashtype '.-_'
  • The terminal options dashed and solid are ignored. By default all lines are solid. To change them to dashed, use e.g.

    set for [i=1:8] linetype i dashtype i
  • The default set of line colors was changed. You can select between three different color sets with set colorsequence default|podo|classic:

enter image description here

How to execute a query in ms-access in VBA code?

Take a look at this tutorial for how to use SQL inside VBA:

For a query that won't return results, use (reference here):


For one that will, use (reference here):

Dim dBase As Database

Getting the ID of the element that fired an event

I'm working with

jQuery Autocomplete

I tried looking for an event as described above, but when the request function fires it doesn't seem to be available. I used this.element.attr("id") to get the element's ID instead, and it seems to work fine.

How to draw polygons on an HTML5 canvas?

Here is a function that even supports clockwise/anticlockwise drawing do that you control fills with the non-zero winding rule.

Here is a full article on how it works and more.

// Defines a path for any regular polygon with the specified number of sides and radius, 
// centered on the provide x and y coordinates.
// optional parameters: startAngle and anticlockwise

function polygon(ctx, x, y, radius, sides, startAngle, anticlockwise) {
  if (sides < 3) return;
  var a = (Math.PI * 2)/sides;
  a = anticlockwise?-a:a;;
  for (var i = 1; i < sides; i++) {

// Example using the function.
// Define a path in the shape of a pentagon and then fill and stroke it.

Get size of an Iterable in Java

TL;DR: Use the utility method Iterables.size(Iterable) of the great Guava library.

Of your two code snippets, you should use the first one, because the second one will remove all elements from values, so it is empty afterwards. Changing a data structure for a simple query like its size is very unexpected.

For performance, this depends on your data structure. If it is for example in fact an ArrayList, removing elements from the beginning (what your second method is doing) is very slow (calculating the size becomes O(n*n) instead of O(n) as it should be).

In general, if there is the chance that values is actually a Collection and not only an Iterable, check this and call size() in case:

if (values instanceof Collection<?>) {
  return ((Collection<?>)values).size();
// use Iterator here...

The call to size() will usually be much faster than counting the number of elements, and this trick is exactly what Iterables.size(Iterable) of Guava does for you.

Calculating distance between two points, using latitude longitude?

Note: this solution only works for short distances.

I tried to use dommer's posted formula for an application and found it did well for long distances but in my data I was using all very short distances, and dommer's post did very poorly. I needed speed, and the more complex geo calcs worked well but were too slow. So, in the case that you need speed and all the calculations you're making are short (maybe < 100m or so). I found this little approximation to work great. it assumes the world is flat mind you, so don't use it for long distances, it works by approximating the distance of a single Latitude and Longitude at the given Latitude and returning the Pythagorean distance in meters.

public class FlatEarthDist {
    //returns distance in meters
    public static double distance(double lat1, double lng1, 
                                      double lat2, double lng2){
     double a = (lat1-lat2)*FlatEarthDist.distPerLat(lat1);
     double b = (lng1-lng2)*FlatEarthDist.distPerLng(lat1);
     return Math.sqrt(a*a+b*b);

    private static double distPerLng(double lat){
      return 0.0003121092*Math.pow(lat, 4)
             +0.0101182384*Math.pow(lat, 3)

    private static double distPerLat(double lat){
            return -0.000000487305676*Math.pow(lat, 4)
                -0.0033668574*Math.pow(lat, 3)

How to make a DIV not wrap?

If I don't want to define a minimal width because I don't know the amount of elements the only thing that worked to me was:

display: inline-block;
white-space: nowrap;

But only in Chrome and Safari :/

How to sort a dataframe by multiple column(s)

Alternatively, using the package Deducer

dd<- sortData(dd,c("z","b"),increasing= c(FALSE,TRUE))

Why does the html input with type "number" allow the letter 'e' to be entered in the field?

Using angular, You can do this to restrict to enter e,+,-,E

 <input type="number"  (keypress)="numericOnly($event)"/>

  numericOnly(event): boolean { // restrict e,+,-,E characters in  input type number
    const charCode = (event.which) ? event.which : event.keyCode;
    if (charCode == 101 || charCode == 69 || charCode == 45 || charCode == 43) {
      return false;
    return true;


Is there a way to set background-image as a base64 encoded image?

I tried to do the same as you, but apparently the backgroundImage doesn't work with encoded data. As an alternative, I suggest to use CSS classes and the change between those classes.

If you are generating the data "on the fly" you can load the CSS files dynamically.


.backgroundA {
    background-image: url("data:image/png;base64,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");

.backgroundB {


<div id="test" height="20px" class="backgroundA"> 
  div test 1
<div id="test2" name="test2" height="20px" class="backgroundB">
  div test2
<input type="button" id="btn" />


function change() {
    if (document.getElementById("test").className =="backgroundA") {
    } else {

btn.onclick= change;

I fiddled it here, press the button and it will switch the divs' backgrounds: