Programs & Examples On #File descriptor

Generally, a file descriptor is an index for an entry in a kernel-resident data structure containing the details of all open files. In POSIX this data structure is called a file descriptor table, and each process has its own file descriptor table. In Microsoft Windows terminology and in the context of the C standard I/O library, "file handle" is preferred.

What can lead to "IOError: [Errno 9] Bad file descriptor" during os.system()?

You get this error message if a Python file was closed from "the outside", i.e. not from the file object's close() method:

>>> f = open(".bashrc")
>>> os.close(f.fileno())
>>> del f
close failed in file object destructor:
IOError: [Errno 9] Bad file descriptor

The line del f deletes the last reference to the file object, causing its destructor file.__del__ to be called. The internal state of the file object indicates the file is still open since f.close() was never called, so the destructor tries to close the file. The OS subsequently throws an error because of the attempt to close a file that's not open.

Since the implementation of os.system() does not create any Python file objects, it does not seem likely that the system() call is the origin of the error. Maybe you could show a bit more code?

What is the theoretical maximum number of open TCP connections that a modern Linux box can have

A single listening port can accept more than one connection simultaneously.

There is a '64K' limit that is often cited, but that is per client per server port, and needs clarifying.

Each TCP/IP packet has basically four fields for addressing. These are:

source_ip source_port destination_ip destination_port
<----- client ------> <--------- server ------------>

Inside the TCP stack, these four fields are used as a compound key to match up packets to connections (e.g. file descriptors).

If a client has many connections to the same port on the same destination, then three of those fields will be the same - only source_port varies to differentiate the different connections. Ports are 16-bit numbers, therefore the maximum number of connections any given client can have to any given host port is 64K.

However, multiple clients can each have up to 64K connections to some server's port, and if the server has multiple ports or either is multi-homed then you can multiply that further.

So the real limit is file descriptors. Each individual socket connection is given a file descriptor, so the limit is really the number of file descriptors that the system has been configured to allow and resources to handle. The maximum limit is typically up over 300K, but is configurable e.g. with sysctl.

The realistic limits being boasted about for normal boxes are around 80K for example single threaded Jabber messaging servers.

What are file descriptors, explained in simple terms?

File descriptors

  • To Kernel all open files are referred to by file descriptors.
  • A file descriptor is a non - negative integer.
  • When we open an existing or create a new file, the kernel returns a file descriptor to a process.
  • When we want to read or write on a file, we identify the file with file descriptor that was retuned by open or create, as an argument to either read or write.
  • Each UNIX process has 20 file descriptors and it disposal, numbered 0 through 19 but it was extended to 63 by many systems.
  • The first three are already opened when the process begins 0: The standard input 1: The standard output 2: The standard error output
  • When the parent process forks a process, the child process inherits the file descriptors of the parent

IOException: Too many open files

Don't know the nature of your app, but I have seen this error manifested multiple times because of a connection pool leak, so that would be worth checking out. On Linux, socket connections consume file descriptors as well as file system files. Just a thought.

Bad File Descriptor with Linux Socket write() Bad File Descriptor C

The value you have passed as the file descriptor is not valid. It is either negative or does not represent a currently open file or socket.

So you have either closed the socket before calling write() or you have corrupted the value of 'sockfd' somewhere in your code.

It would be useful to trace all calls to close(), and the value of 'sockfd' prior to the write() calls.

Your technique of only printing error messages in debug mode seems to me complete madness, and in any case calling another function between a system call and perror() is invalid, as it may disturb the value of errno. Indeed it may have done so in this case, and the real underlying error may be different.

Retrieve filename from file descriptor in C

I had this problem on Mac OS X. We don't have a /proc virtual file system, so the accepted solution cannot work.

We do, instead, have a F_GETPATH command for fcntl:

 F_GETPATH          Get the path of the file descriptor Fildes.  The argu-
                    ment must be a buffer of size MAXPATHLEN or greater.

So to get the file associated to a file descriptor, you can use this snippet:

#include <sys/syslimits.h>
#include <fcntl.h>

char filePath[PATH_MAX];
if (fcntl(fd, F_GETPATH, filePath) != -1)
    // do something with the file path

Since I never remember where MAXPATHLEN is defined, I thought PATH_MAX from syslimits would be fine.

draw diagonal lines in div background with CSS

You can do it something like this:

    .background {
        background-color: #BCBCBC;
        width: 100px;
        height: 50px;
        padding: 0; 
        margin: 0
    .line1 {
        width: 112px;
        height: 47px;
        border-bottom: 1px solid red;
        position: absolute;
        /* top: -20px; */
    .line2 {
        width: 112px;
        height: 47px;
        border-bottom: 1px solid green;
        position: absolute;
        top: -33px;
        left: -13px;
<div class="background">
    <div class="line1"></div>
    <div class="line2"></div>

Here is a jsfiddle.

Improved version of answer for your purpose.

How to top, left justify text in a <td> cell that spans multiple rows

try this

<!DOCTYPE html>_x000D_
table, th, td {_x000D_
    border: 1px solid black;_x000D_
<table style="width:50%;">_x000D_
    <tr style="height:100px">_x000D_
      <td valign="top">January</td>_x000D_
      <td valign="bottom">$100</td>_x000D_
<p><b>Note:</b> The valign attribute is not supported in HTML5. Use CSS instead.</p>_x000D_

use valign="top" for td style

C# Interfaces. Implicit implementation versus Explicit implementation

The previous answers explain why implementing an interface explicitly in C# may be preferrable (for mostly formal reasons). However, there is one situation where explicit implementation is mandatory: In order to avoid leaking the encapsulation when the interface is non-public, but the implementing class is public.

// Given:
internal interface I { void M(); }

// Then explicit implementation correctly observes encapsulation of I:
// Both ((I)CExplicit).M and CExplicit.M are accessible only internally.
public class CExplicit: I { void I.M() { } }

// However, implicit implementation breaks encapsulation of I, because
// ((I)CImplicit).M is only accessible internally, while CImplicit.M is accessible publicly.
public class CImplicit: I { public void M() { } }

The above leakage is unavoidable because, according to the C# specification, "All interface members implicitly have public access." As a consequence, implicit implementations must also give public access, even if the interface itself is e.g. internal.

Implicit interface implementation in C# is a great convenience. In practice, many programmers use it all the time/everywhere without further consideration. This leads to messy type surfaces at best and leaked encapsulation at worst. Other languages, such as F#, don't even allow it.

Batch script to find and replace a string in text file without creating an extra output file for storing the modified file

@echo off 
    setlocal enableextensions disabledelayedexpansion

    set "search=%1"
    set "replace=%2"

    set "textFile=Input.txt"

    for /f "delims=" %%i in ('type "%textFile%" ^& break ^> "%textFile%" ') do (
        set "line=%%i"
        setlocal enabledelayedexpansion
        >>"%textFile%" echo(!line:%search%=%replace%!

for /f will read all the data (generated by the type comamnd) before starting to process it. In the subprocess started to execute the type, we include a redirection overwritting the file (so it is emptied). Once the do clause starts to execute (the content of the file is in memory to be processed) the output is appended to the file.

Remove duplicates from an array of objects in JavaScript

This is a generic way of doing this: you pass in a function that tests whether two elements of an array are considered equal. In this case, it compares the values of the name and place properties of the two objects being compared.

ES5 answer

function removeDuplicates(arr, equals) {_x000D_
    var originalArr = arr.slice(0);_x000D_
    var i, len, val;_x000D_
    arr.length = 0;_x000D_
    for (i = 0, len = originalArr.length; i < len; ++i) {_x000D_
        val = originalArr[i];_x000D_
        if (!arr.some(function(item) { return equals(item, val); })) {_x000D_
function thingsEqual(thing1, thing2) {_x000D_
    return === thing2.place_x000D_
        && ===;_x000D_
var things = [_x000D_
removeDuplicates(things, thingsEqual);_x000D_

Original ES3 answer

function arrayContains(arr, val, equals) {
    var i = arr.length;
    while (i--) {
        if ( equals(arr[i], val) ) {
            return true;
    return false;

function removeDuplicates(arr, equals) {
    var originalArr = arr.slice(0);
    var i, len, j, val;
    arr.length = 0;

    for (i = 0, len = originalArr.length; i < len; ++i) {
        val = originalArr[i];
        if (!arrayContains(arr, val, equals)) {

function thingsEqual(thing1, thing2) {
    return ===
        && ===;

removeDuplicates(things.thing, thingsEqual);

javascript regex for password containing at least 8 characters, 1 number, 1 upper and 1 lowercase

Your regular expression should look like:


Here is an explanation:

  (?=.*\d)          // should contain at least one digit
  (?=.*[a-z])       // should contain at least one lower case
  (?=.*[A-Z])       // should contain at least one upper case
  [a-zA-Z0-9]{8,}   // should contain at least 8 from the mentioned characters

Select NOT IN multiple columns

I'm not sure whether you think about:

select * from friend f
where not exists (
    select 1 from likes l where f.id1 = and f.id2 = l.id2

it works only if id1 is related with id1 and id2 with id2 not both.

How do you convert an entire directory with ffmpeg?

Getting a bit like code golf here, but since nearly all the answers so far are bash (barring one lonely cmd one), here's a windows cross-platform command that uses powershell (because awesome):

ls *.avi|%{ ffmpeg -i $_ <ffmpeg options here> $$_.extension, ".mp4")}

You can change *.avi to whatever matches your source footage.

Removing nan values from an array

If you're using numpy for your arrays, you can also use

x = x[numpy.logical_not(numpy.isnan(x))]


x = x[~numpy.isnan(x)]

[Thanks to chbrown for the added shorthand]


The inner function, numpy.isnan returns a boolean/logical array which has the value True everywhere that x is not-a-number. As we want the opposite, we use the logical-not operator, ~ to get an array with Trues everywhere that x is a valid number.

Lastly we use this logical array to index into the original array x, to retrieve just the non-NaN values.

How to execute an Oracle stored procedure via a database link

for me, this worked

exec utl_mail.send@myotherdb(
  sender => '[email protected]',recipients => '[email protected], 
  cc => null, subject => 'my subject', message => 'my message'

Adding header to all request with Retrofit 2

Try this type header for Retrofit 1.9 and 2.0. For Json Content Type.

@Headers({"Accept: application/json"})
Call<playlist> addToPlaylist(@Body PlaylistParm parm);

You can add many more headers i.e

        "Accept: application/json",
        "User-Agent: Your-App-Name",
        "Cache-Control: max-age=640000"

Dynamically Add to headers:

Call<ResponseModel> addToPlaylist(@Header("Content-Type") String content_type, @Body RequestModel req);

Call you method i.e

mAPI.addToPlayList("application/json", playListParam);


Want to pass everytime then Create HttpClient object with http Interceptor:

OkHttpClient httpClient = new OkHttpClient();
        httpClient.networkInterceptors().add(new Interceptor() {
            public com.squareup.okhttp.Response intercept(Chain chain) throws IOException {
                Request.Builder requestBuilder = chain.request().newBuilder();
                requestBuilder.header("Content-Type", "application/json");
                return chain.proceed(;

Then add to retrofit object

Retrofit retrofit = new Retrofit.Builder().baseUrl(BASE_URL).client(httpClient).build();

UPDATE if you are using Kotlin remove the { } else it will not work

How can I match multiple occurrences with a regex in JavaScript similar to PHP's preg_match_all()?

If someone (like me) needs Tomalak's method with array support (ie. multiple select), here it is:

function getUrlParams(url) {
  var re = /(?:\?|&(?:amp;)?)([^=&#]+)(?:=?([^&#]*))/g,
      match, params = {},
      decode = function (s) {return decodeURIComponent(s.replace(/\+/g, " "));};

  if (typeof url == "undefined") url = document.location.href;

  while (match = re.exec(url)) {
    if( params[decode(match[1])] ) {
        if( typeof params[decode(match[1])] != 'object' ) {
            params[decode(match[1])] = new Array( params[decode(match[1])], decode(match[2]) );
        } else {
        params[decode(match[1])] = decode(match[2]);
  return params;
var urlParams = getUrlParams(;

input ?my=1&my=2&my=things

result 1,2,things (earlier returned only: things)

Array.sort() doesn't sort numbers correctly

The default sort for arrays in Javascript is an alphabetical search. If you want a numerical sort, try something like this:

var a = [ 1, 100, 50, 2, 5];
a.sort(function(a,b) { return a - b; });

Converting NumPy array into Python List structure?

The numpy .tolist method produces nested lists if the numpy array shape is 2D.

if flat lists are desired, the method below works.

import numpy as np
from itertools import chain

a = [1,2,3,4,5,6,7,8,9]
print type(a), len(a), a
npa = np.asarray(a)
print type(npa), npa.shape, "\n", npa
npa = npa.reshape((3, 3))
print type(npa), npa.shape, "\n", npa
a = list(chain.from_iterable(npa))
print type(a), len(a), a`

The model backing the <Database> context has changed since the database was created

I had the same problem when we used one database for two applications. Setting disableDatabaseInitialization="true" in context type section works for me.

  <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
  <context type="PreferencesContext, Preferences" disableDatabaseInitialization="true">
    <databaseInitializer type="System.Data.Entity.MigrateDatabaseToLatestVersion`2[[PreferencesContext, Preferences], [Migrations.Configuration, Preferences]], EntityFramework" />

See more details

Calling virtual functions inside constructors

Other answers have already explained why virtual function calls don't work as expected when called from a constructor. I'd like to instead propose another possible work around for getting polymorphic-like behavior from a base type's constructor.

By adding a template constructor to the base type such that the template argument is always deduced to be the derived type it's possible to be aware of the derived type's concrete type. From there, you can call static member functions for that derived type.

This solution does not allow non-static member functions to be called. While execution is in the base type's constructor, the derived type's constructor hasn't even had time to go through it's member initialization list. The derived type portion of the instance being created hasn't begun being initialized it. And since non-static member functions almost certainly interact with data members it would be unusual to want to call the derived type's non-static member functions from the base type's constructor.

Here is a sample implementation :

#include <iostream>
#include <string>

struct Base {
    template<class T>
    explicit Base(const T*) : class_name(T::Name())
        std::cout << class_name << " created\n";

    Base() : class_name(Name())
        std::cout << class_name << " created\n";

    virtual ~Base() {
        std::cout << class_name << " destroyed\n";

    static std::string Name() {
        return "Base";

    std::string class_name;

struct Derived : public Base
    Derived() : Base(this) {} // `this` is used to allow Base::Base<T> to deduce T

    static std::string Name() {
        return "Derived";

int main(int argc, const char *argv[]) {

    Derived{};  // Create and destroy a Derived
    Base{};     // Create and destroy a Base

    return 0;

This example should print

Derived created
Derived destroyed
Base created
Base destroyed

When a Derived is constructed, the Base constructor's behavior depends on the actual dynamic type of the object being constructed.

In-place type conversion of a NumPy array

You can make a view with a different dtype, and then copy in-place into the view:

import numpy as np
x = np.arange(10, dtype='int32')
y = x.view('float32')
y[:] = x



array([ 0.,  1.,  2.,  3.,  4.,  5.,  6.,  7.,  8.,  9.], dtype=float32)

To show the conversion was in-place, note that copying from x to y altered x:



array([         0, 1065353216, 1073741824, 1077936128, 1082130432,
       1084227584, 1086324736, 1088421888, 1090519040, 1091567616])

Center align "span" text inside a div

You are giving the span a 100% width resulting in it expanding to the size of the parent. This means you can’t center-align it, as there is no room to move it.

You could give the span a set width, then add the margin:0 auto again. This would center-align it.

   background-color: #999999;
   height: 50px;
   width: 24.5%;
   height: 100%;
   margin: 0 auto;

Fragment onCreateView and onActivityCreated called twice

I was scratching my head about this for a while too, and since Dave's explanation is a little hard to understand I'll post my (apparently working) code:

private class TabListener<T extends Fragment> implements ActionBar.TabListener {
    private Fragment mFragment;
    private Activity mActivity;
    private final String mTag;
    private final Class<T> mClass;

    public TabListener(Activity activity, String tag, Class<T> clz) {
        mActivity = activity;
        mTag = tag;
        mClass = clz;

    public void onTabSelected(Tab tab, FragmentTransaction ft) {
        if (mFragment == null) {
            mFragment = Fragment.instantiate(mActivity, mClass.getName());
            ft.replace(, mFragment, mTag);
        } else {
            if (mFragment.isDetached()) {

    public void onTabUnselected(Tab tab, FragmentTransaction ft) {
        if (mFragment != null) {

    public void onTabReselected(Tab tab, FragmentTransaction ft) {

As you can see it's pretty much like the Android sample, apart from not detaching in the constructor, and using replace instead of add.

After much headscratching and trial-and-error I found that finding the fragment in the constructor seems to make the double onCreateView problem magically go away (I assume it just ends up being null for onTabSelected when called through the ActionBar.setSelectedNavigationItem() path when saving/restoring state).

Combining (concatenating) date and time into a datetime

The simple solution

SELECT CAST(CollectionDate as DATETIME) + CAST(CollectionTime as DATETIME)
FROM field

Getting rid of bullet points from <ul>

I had the same problem, and the way I ended up fixing it was like this:

ul, li{

Maybe it's a little extreme, but when I did that, it worked for me.

Hope this helped

How to read single Excel cell value

 //THIS IS WORKING CODE                        
 Microsoft.Office.Interop.Excel.Range Range_Number,r2;
 Range_Number = wsheet.UsedRange.Find("smth");
 string f_number="";

 r2 = wsheet.Cells;

 int n_c = Range_Number.Column;
 int n_r = Range_Number.Row;
 var number = ((Range)r2[n_r + 1, n_c]).Value;

 f_number = (string)number;

Show data on mouseover of circle

This concise example demonstrates common way how to create custom tooltip in d3.

var w = 500;_x000D_
var h = 150;_x000D_
var dataset = [5, 10, 15, 20, 25];_x000D_
// firstly we create div element that we can use as_x000D_
// tooltip container, it have absolute position and_x000D_
// visibility: hidden by default_x000D_
var tooltip ="body")_x000D_
  .attr('class', 'tooltip');_x000D_
var svg ="body")_x000D_
  .attr("width", w)_x000D_
  .attr("height", h);_x000D_
// here we add some circles on the page_x000D_
var circles = svg.selectAll("circle")_x000D_
circles.attr("cx", function(d, i) {_x000D_
    return (i * 50) + 25;_x000D_
  .attr("cy", h / 2)_x000D_
  .attr("r", function(d) {_x000D_
    return d;_x000D_
  // we define "mouseover" handler, here we change tooltip_x000D_
  // visibility to "visible" and add appropriate test_x000D_
  .on("mouseover", function(d) {_x000D_
    return"visibility", "visible").text('radius = ' + d);_x000D_
  // we move tooltip during of "mousemove"_x000D_
  .on("mousemove", function() {_x000D_
    return"top", (event.pageY - 30) + "px")_x000D_
      .style("left", event.pageX + "px");_x000D_
  // we hide our tooltip on "mouseout"_x000D_
  .on("mouseout", function() {_x000D_
    return"visibility", "hidden");_x000D_
.tooltip {_x000D_
    position: absolute;_x000D_
    z-index: 10;_x000D_
    visibility: hidden;_x000D_
    background-color: lightblue;_x000D_
    text-align: center;_x000D_
    padding: 4px;_x000D_
    border-radius: 4px;_x000D_
    font-weight: bold;_x000D_
    color: orange;_x000D_
<script src=""></script>

How do I get the project basepath in CodeIgniter

Following are the build-in constants you can use as per your requirements for getting the paths in Codeigniter:

EXT: The PHP file extension

FCPATH: Path to the front controller (this file) (root of CI)

SELF: The name of THIS file (index.php)

BASEPATH: Path to the system folder

APPPATH: The path to the “application” folder


How do I determine the dependencies of a .NET application?

I find the small utility AsmSpy an invaluable tool to for resolving issues with loading assemblies. It lists all assembly references of managed assemblies including assembly versions.

Run it in a command prompt in the directory of the .dll with the following arguments:

asmspy . all

asmspy output screenshot

Install it quickly with Chocolatey:

choco install asmspy

How to download source in ZIP format from GitHub?

I was facing same problem but accidentlty I sorted this problem. 1) Login in github 2) Click on Fork Button at Top Right. 3) After above step you can see Clone or download in Green color under <> Code Tab.

How to free memory in Java?

To extend upon the answer and comment by Yiannis Xanthopoulos and Hot Licks (sorry, I cannot comment yet!), you can set VM options like this example:

-XX:+UseG1GC -XX:MinHeapFreeRatio=15 -XX:MaxHeapFreeRatio=30

In my jdk 7 this will then release unused VM memory if more than 30% of the heap becomes free after GC when the VM is idle. You will probably need to tune these parameters.

While I didn't see it emphasized in the link below, note that some garbage collectors may not obey these parameters and by default java may pick one of these for you, should you happen to have more than one core (hence the UseG1GC argument above).

VM arguments

Update: For java 1.8.0_73 I have seen the JVM occasionally release small amounts with the default settings. Appears to only do it if ~70% of the heap is unused though.. don't know if it would be more aggressive releasing if the OS was low on physical memory.

App.Config file in console application C#

use this


How to draw polygons on an HTML5 canvas?

You can use the lineTo() method same as: var objctx = canvas.getContext('2d');

        objctx.moveTo(75, 50);
        objctx.lineTo(175, 50);
        objctx.lineTo(200, 75);
        objctx.lineTo(175, 100);
        objctx.lineTo(75, 100);
        objctx.lineTo(50, 75);
        objctx.fillStyle = "rgb(200,0,0)";

if you not want to fill the polygon use the stroke() method in the place of fill()

You can also check the following:


What is the difference between json.load() and json.loads() functions

QUICK ANSWER (very simplified!)

json.load() takes a FILE

json.load() expects a file (file object) - e.g. a file you opened before given by filepath like 'files/example.json'.

json.loads() takes a STRING

json.loads() expects a (valid) JSON string - i.e. {"foo": "bar"}


Assuming you have a file example.json with this content: { "key_1": 1, "key_2": "foo", "Key_3": null }

>>> import json
>>> file = open("example.json")

>>> type(file)
<class '_io.TextIOWrapper'>

>>> file
<_io.TextIOWrapper name='example.json' mode='r' encoding='UTF-8'>

>>> json.load(file)
{'key_1': 1, 'key_2': 'foo', 'Key_3': None}

>>> json.loads(file)
Traceback (most recent call last):
  File "/usr/local/python/Versions/3.7/lib/python3.7/json/", line 341, in loads
TypeError: the JSON object must be str, bytes or bytearray, not TextIOWrapper

>>> string = '{"foo": "bar"}'

>>> type(string)
<class 'str'>

>>> string
'{"foo": "bar"}'

>>> json.loads(string)
{'foo': 'bar'}

>>> json.load(string)
Traceback (most recent call last):
  File "/usr/local/python/Versions/3.7/lib/python3.7/json/", line 293, in load
    return loads(,
AttributeError: 'str' object has no attribute 'read'

Iterate all files in a directory using a 'for' loop

%1 refers to the first argument passed in and can't be used in an iterator.

Try this:

@echo off
for %%i in (*.*) do echo %%i

Getting datarow values into a string?

You can get a columns value by doing this


You will also have to cast to the appropriate type.

 output += (string)rows["ColumnName"]

How to delete a workspace in Perforce (using p4v)?

If you have successfully deleted from workspace tab but still it is showing in drop down menu. Then also you can successfully remove that by following these steps:

  1. Go to C:/Users/user_name/.p4qt

user_name will be your username of your computer

  1. Inside 001Clients folder WorkspaceSettings.xml file will be there.

There will be two tag

  1. varName = "RecentlyUsedWorkspaces" remove the deleted workspace tag

  2. A propertyList tag will be there with varName=deleted_workspace_name delete that tag.

from drop down menu workspace name will be deleted

Creating JSON on the fly with JObject

Simple way of creating newtonsoft JObject from Properties.

This is a Sample User Properties

public class User
    public string Name;
    public string MobileNo;
    public string Address;

and i want this property in newtonsoft JObject is:

JObject obj = JObject.FromObject(new User()
    Name = "Manjunath",
    MobileNo = "9876543210",
    Address = "Mumbai, Maharashtra, India",

Output will be like this:

{"Name":"Manjunath","MobileNo":"9876543210","Address":"Mumbai, Maharashtra, India"}

Select all columns except one in MySQL?

Based on @Mahomedalid answer, I have done some improvements to support "select all columns except some in mysql"

SET @database    = 'database_name';
SET @tablename   = 'table_name';
SET @cols2delete = 'col1,col2,col3';

SET @sql = CONCAT(
' FROM ',

SELECT @sql;

If you do have a lots of cols, use this sql to change group_concat_max_len

SET @@group_concat_max_len = 2048;

Simple if else onclick then do?

The preferred modern method is to use addEventListener either by adding the event listener direct to the element or to a parent of the elements (delegated).

An example, using delegated events, might be

var box = document.getElementById('box');_x000D_
document.getElementById('buttons').addEventListener('click', function(evt) {_x000D_
  var target =;_x000D_
  if ( === 'yes') {_x000D_ = 'red';_x000D_
  } else if ( === 'no') {_x000D_ = 'green';_x000D_
  } else {_x000D_ = 'purple';_x000D_
}, false);
#box {_x000D_
  width: 200px;_x000D_
  height: 200px;_x000D_
  background-color: red;_x000D_
#buttons {_x000D_
  margin-top: 50px;_x000D_
<div id='box'></div>_x000D_
<div id='buttons'>_x000D_
  <button id='yes'>yes</button>_x000D_
  <button id='no'>no</button>_x000D_
  <p>Click one of the buttons above.</p>_x000D_

How to return the current timestamp with Moment.js?

I would like to add that you can have the whole data information in an object with:

const today = moment().toObject();

You should obtain an object with this properties:

today: {
    date: 15,
    hours: 1,
    milliseconds: 927,
    minutes: 59,
    months: 4,
    seconds: 43,
    years: 2019

It is very useful when you have to calculate dates.

Matlab: Running an m-file from command-line

Thanks to malat. Your comment helped me. But I want to add my try-catch block, as I found the MExeption method getReport() that returns the whole error message and prints it to the matlab console.

Additionally I printed the filename as this compilation is part of a batch script that calls matlab.

catch message
    display(['ERROR in file: ' message.stack.file])
    display(['ERROR: ' getReport(message)])

For a false model name passed to legacy code generation method, the output would look like:

ERROR in file: C:\..\..\..
ERROR: Undefined function or variable 'modelname'.

Error in sub-m-file (line 63)
legacy_code( 'slblock_generate', specs, modelname);

Error in m-file (line 11)

Error in run (line 63)
evalin('caller', [script ';']);

Finally, to display the output at the windows command prompt window, just log the matlab console to a file with -logfile logfile.txt (use additionally -wait) and call the batch command type logfile.txt

What does ENABLE_BITCODE do in xcode 7?

Bitcode (iOS, watchOS)

Bitcode is an intermediate representation of a compiled program. Apps you upload to iTunes Connect that contain bitcode will be compiled and linked on the App Store. Including bitcode will allow Apple to re-optimize your app binary in the future without the need to submit a new version of your app to the store.

Basically this concept is somewhat similar to java where byte code is run on different JVM's and in this case the bitcode is placed on iTune store and instead of giving the intermediate code to different platforms(devices) it provides the compiled code which don't need any virtual machine to run.

Thus we need to create the bitcode once and it will be available for existing or coming devices. It's the Apple's headache to compile an make it compatible with each platform they have.

Devs don't have to make changes and submit the app again to support new platforms.

Let's take the example of iPhone 5s when apple introduced x64 chip in it. Although x86 apps were totally compatible with x64 architecture but to fully utilise the x64 platform the developer has to change the architecture or some code. Once s/he's done the app is submitted to the app store for the review.

If this bitcode concept was launched earlier then we the developers doesn't have to make any changes to support the x64 bit architecture.

to_string not declared in scope

This error, as correctly identified above, is due to the compiler not using c++11 or above standard. This answer is for Windows 10.

For c++11 and above standard support in codeblocks version 17:

  1. Click settings in the toolbar.

  2. A drop-down menu appears. Select compiler option.

  3. Choose Global Compiler Settings.

  4. In the toolbar in this new window in second section, choose compiler settings.

  5. Then choose compiler flags option in below toolbar.

  6. Unfold general tab. Check the C++ standard that you want your compiler to follow.

  7. Click OK.

For those who are trying to get C++11 support in Sublime text.

  1. Download mingw compiler version 7 or above. In versions below this, the default c++ standard used is c++98 whereas in versions higher than 7, the default standard used is c++11.

  2. Copy the folder in main C drive. It should not be inside any other folder in C drive.

  3. Rename the folder as MinGW. This name is case insensitive, so it should any variation of mingw and must not include any other characters in the name.

  4. Then go to environment variables and edit the path variable. Add this "C:\mingw\bin" and click OK.

  5. You can check the version of g++ in cmd by typing g++ -v.

  6. This should be sufficient to enable c++11 in sublime text.

If you want to take inputs and outputs as well from input files for competitive programming purposes, then follow this link.

Maven Run Project

1. Edit POM.xml

Add the following property in pom.xml. Make sure you use the fully qualified class name (i.e. with package name) which contains the main method:


2. Run Command

Now from the terminal, trigger the following command:

mvn clean compile exec:java

NOTE You can pass further arguments via -Dexec.args="xxx" flag.

npm ERR! network getaddrinfo ENOTFOUND

does your proxy require you to authenticate? because if it does, you might want you configure your proxy like this.

placeholder names. username is a placeholder for your actual username. password is a placeholder for your actual password. is a placeholder for your actualy proxy *port" is your actualy port the proxy goes through. its usualy 8080

npm config set proxy "http://username:[email protected]:port"
npm config set https-proxy "http://username:[email protected]:port"

C# SQL Server - Passing a list to a stored procedure

No, arrays/lists can't be passed to SQL Server directly.

The following options are available:

  1. Passing a comma-delimited list and then having a function in SQL split the list. The comma delimited list will most likely be passed as an Nvarchar()
  2. Pass xml and have a function in SQL Server parse the XML for each value in the list
  3. Use the new defined User Defined table type (SQL 2008)
  4. Dynamically build the SQL and pass in the raw list as "1,2,3,4" and build the SQL statement. This is prone to SQL injection attacks, but it will work.

How to set the timeout for a TcpClient?

As Simon Mourier mentioned, it's possible to use ConnectAsync TcpClient's method with Task in addition and stop operation as soon as possible.
For example:

// ...
client = new TcpClient(); // Initialization of TcpClient
CancellationToken ct = new CancellationToken(); // Required for "*.Task()" method
if (client.ConnectAsync(this.ip, this.port).Wait(1000, ct)) // Connect with timeout of 1 second

    // ... transfer

    if (client != null) {
        client.Close(); // Close the connection and dispose a TcpClient object
        ct.ThrowIfCancellationRequested(); // Stop asynchronous operation after successull connection(...and transfer(in needed))
    Console.WriteLine("Connetion timed out");
// ...

Also, I would recommended checking the AsyncTcpClient C# library with some examples provided like Server <> Client.

How to create a sub array from another array in Java?

Use copyOfRange method from java.util.Arrays class:

int[] newArray = Arrays.copyOfRange(oldArray, startIndex, endIndex);

For more details:

Link to similar question

How to find elements by class

Update: 2016 In the latest version of beautifulsoup, the method 'findAll' has been renamed to 'find_all'. Link to official documentation

List of method names changed

Hence the answer will be

soup.find_all("html_element", class_="your_class_name")

What's the idiomatic syntax for prepending to a short python list?

In my opinion, the most elegant and idiomatic way of prepending an element or list to another list, in Python, is using the expansion operator * (also called unpacking operator),

# Initial list
l = [4, 5, 6]

# Modification
l = [1, 2, 3, *l]

Where the resulting list after the modification is [1, 2, 3, 4, 5, 6]

I also like simply combining two lists with the operator +, as shown,

# Prepends [1, 2, 3] to l
l = [1, 2, 3] + l

# Prepends element 42 to l
l = [42] + l

I don't like the other common approach, l.insert(0, value), as it requires a magic number. Moreover, insert() only allows prepending a single element, however the approach above has the same syntax for prepending a single element or multiple elements.

How can I add shadow to the widget in flutter?

The given answers do the trick for outer shadow i.e. around the widget. I wanted a shadow on the widget which is inside the boundaries and according to the github issue there is no inset attribute in ShadowBox yet. My workaround was to add a layer of widget with a gradient using the stack widget so that it looks like the widget itself has the shadows. You must use the mediaQuery for dimensions otherwise the layout will be messed up on different devices. Here's a sample of code for better understanding:

            children: <Widget>[
                decoration: BoxDecoration(
                  image: DecorationImage(
                    fit: BoxFit.cover,
                    image: AssetImage("assets/sampleFaces/makeup.jpeg"),
                    // fit: BoxFit.cover,
                height: 350.0,
                decoration: BoxDecoration(
                  gradient: LinearGradient(
                    begin: FractionalOffset.topCenter,
                    end: FractionalOffset.bottomCenter,
                    colors: [
                    stops: [0.95, 5.0],

Best way to check that element is not present using Selenium WebDriver with java

Use findElements instead of findElement.

findElements will return an empty list if no matching elements are found instead of an exception. Also, we can make sure that the element is present or not.

Ex: List elements = driver.findElements(By.yourlocatorstrategy);

    do this..
 } else {
    do that..

The endpoint reference (EPR) for the Operation not found is

try removing the extra '/' after the operation name (authentication) when invoking through the client


How to keep footer at bottom of screen

use this style


Difference between except: and except Exception as e: in Python

There are differences with some exceptions, e.g. KeyboardInterrupt.

Reading PEP8:

A bare except: clause will catch SystemExit and KeyboardInterrupt exceptions, making it harder to interrupt a program with Control-C, and can disguise other problems. If you want to catch all exceptions that signal program errors, use except Exception: (bare except is equivalent to except BaseException:).

Random String Generator Returning Same String

This solution is an extension for a Random class.


class Program
    private static Random random = new Random(); 

    static void Main(string[] args)
        random.NextString(10); // "cH*%I\fUWH0"
        random.NextString(10); // "Cw&N%27+EM"
        random.NextString(10); // "0LZ}nEJ}_-"
        random.NextString();   // "kFmeget80LZ}nEJ}_-"


public static class RandomEx
    /// <summary>
    /// Generates random string of printable ASCII symbols of a given length
    /// </summary>
    /// <param name="r">instance of the Random class</param>
    /// <param name="length">length of a random string</param>
    /// <returns>Random string of a given length</returns>
    public static string NextString(this Random r, int length)
        var data = new byte[length];
        for (int i = 0; i < data.Length; i++)
            // All ASCII symbols: printable and non-printable
            // data[i] = (byte)r.Next(0, 128);
            // Only printable ASCII
            data[i] = (byte)r.Next(32, 127);
        var encoding = new ASCIIEncoding();
        return encoding.GetString(data);

    /// <summary>
    /// Generates random string of printable ASCII symbols
    /// with random length of 10 to 20 chars
    /// </summary>
    /// <param name="r">instance of the Random class</param>
    /// <returns>Random string of a random length between 10 and 20 chars</returns>
    public static string NextString(this Random r)
        int length  = r.Next(10, 21);
        return NextString(r, length);

Checking if a character is a special character in Java

This method checks if a String contains a special character (based on your definition).

 *  Returns true if s contains any character other than 
 *  letters, numbers, or spaces.  Returns false otherwise.

public boolean containsSpecialCharacter(String s) {
    return (s == null) ? false : s.matches("[^A-Za-z0-9 ]");

You can use the same logic to count special characters in a string like this:

 *  Counts the number of special characters in s.

 public int getSpecialCharacterCount(String s) {
     if (s == null || s.trim().isEmpty()) {
         return 0;
     int theCount = 0;
     for (int i = 0; i < s.length(); i++) {
         if (s.substring(i, 1).matches("[^A-Za-z0-9 ]")) {
     return theCount;

Another approach is to put all the special chars in a String and use String.contains:

 *  Counts the number of special characters in s.

 public int getSpecialCharacterCount(String s) {
     if (s == null || s.trim().isEmpty()) {
         return 0;
     int theCount = 0;
     String specialChars = "/*!@#$%^&*()\"{}_[]|\\?/<>,.";
     for (int i = 0; i < s.length(); i++) {
         if (specialChars.contains(s.substring(i, 1))) {
     return theCount;

NOTE: You must escape the backslash and " character with a backslashes.

The above are examples of how to approach this problem in general.

For your exact problem as stated in the question, the answer by @LanguagesNamedAfterCoffee is the most efficient approach.

How to get all the AD groups for a particular user?

The following example is from the Code Project article, (Almost) Everything In Active Directory via C#:

// userDn is a Distinguished Name such as:
// "LDAP://CN=Joe Smith,OU=Sales,OU=domain,OU=com"
public ArrayList Groups(string userDn, bool recursive)
    ArrayList groupMemberships = new ArrayList();
    return AttributeValuesMultiString("memberOf", userDn,
        groupMemberships, recursive);

public ArrayList AttributeValuesMultiString(string attributeName,
     string objectDn, ArrayList valuesCollection, bool recursive)
    DirectoryEntry ent = new DirectoryEntry(objectDn);
    PropertyValueCollection ValueCollection = ent.Properties[attributeName];
    IEnumerator en = ValueCollection.GetEnumerator();

    while (en.MoveNext())
        if (en.Current != null)
            if (!valuesCollection.Contains(en.Current.ToString()))
                if (recursive)
                    AttributeValuesMultiString(attributeName, "LDAP://" +
                    en.Current.ToString(), valuesCollection, true);
    return valuesCollection;

Just call the Groups method with the Distinguished Name for the user, and pass in the bool flag to indicate if you want to include nested / child groups memberships in your resulting ArrayList:

ArrayList groups = Groups("LDAP://CN=Joe Smith,OU=Sales,OU=domain,OU=com", true);
foreach (string groupName in groups)

If you need to do any serious level of Active Directory programming in .NET I highly recommend bookmarking & reviewing the Code Project article I mentioned above.

How to find the 'sizeof' (a pointer pointing to an array)?

There is a clean solution with C++ templates, without using sizeof(). The following getSize() function returns the size of any static array:

#include <cstddef>

template<typename T, size_t SIZE>
size_t getSize(T (&)[SIZE]) {
    return SIZE;

Here is an example with a foo_t structure:

#include <cstddef>

template<typename T, size_t SIZE>
size_t getSize(T (&)[SIZE]) {
    return SIZE;

struct foo_t {
    int ball;

int main()
    foo_t foos3[] = {{1},{2},{3}};
    foo_t foos5[] = {{1},{2},{3},{4},{5}};
    printf("%u\n", getSize(foos3));
    printf("%u\n", getSize(foos5));

    return 0;



Getting current unixtimestamp using Moment.js

for UNIX time-stamp in milliseconds

moment().format('x') // lowerCase x

for UNIX time-stamp in seconds moment().format('X') // capital X

Difference between BYTE and CHAR in column datatypes

Depending on the system configuration, size of CHAR mesured in BYTES can vary. In your examples:

  1. Limits field to 11 BYTE
  2. Limits field to 11 CHARacters

Conclusion: 1 CHAR is not equal to 1 BYTE.

Creating a simple login form

Check it - You can try this code for your login form design as you ask thank you.

Explain css -

First, we define property font style and width And after that I have defined form id to set background image and the border And after that I have to define the header text in tag and after that I have added new and define by.New to set background properties and width. Thanks

Create a file index.html

<!DOCTYPE html>
      <link rel="stylesheet" href="style.css">
      <div id="login_form">
         <div class="new"><span>enter login details</span></div>
         <!-- This is your header text-->
         <form name="f1" method="post" action="login.php" id="f1">
                  <td class="f1_label">User Name :</td>
                  <!-- This is your first Input Box Label-->
                     <input type="text" name="username" value="" /><!-- This is your first Input Box-->
                  <td class="f1_label">Password  :</td>
                  <!-- This is your Second Input Box Label-->
                     <input type="password" name="password" value=""  /><!-- This is your Second Input Box -->
                     <input type="submit" name="login" value="Log In" style="font-size:18px; " /><!-- This is your submit button -->

Create css file style.css

body {
    font-style: italic;
    width: 50%;
    margin: 0px auto;

#login_form {}

#f1 {
    background-color: #FFF;
    border-style: solid;
    border-width: 1px;
    padding: 23px 1px 20px 114px;

.f1_label {
    white-space: nowrap;

span {
    color: white;

.new {
    background: black;
    text-align: center;

How to save an image to localStorage and display it on the next page?

I wrote a little 2,2kb library of saving image in localStorage JQueryImageCaching Usage:

<img data-src="path/to/image">

Import local function from a module housed in another directory with relative imports in Jupyter Notebook using Python 3

I have found that python-dotenv helps solve this issue pretty effectively. Your project structure ends up changing slightly, but the code in your notebook is a bit simpler and consistent across notebooks.

For your project, do a little install.

pipenv install python-dotenv

Then, project changes to:

+-- .env (this can be empty)
+-- ipynb
¦   +-- 20170609-Examine_Database_Requirements.ipynb
¦   +-- 20170609-Initial_Database_Connection.ipynb
+-- lib

And finally, your import changes to:

import os
import sys

from dotenv import find_dotenv


A +1 for this package is that your notebooks can be several directories deep. python-dotenv will find the closest one in a parent directory and use it. A +2 for this approach is that jupyter will load environment variables from the .env file on startup. Double whammy.

curl: (60) SSL certificate problem: unable to get local issuer certificate

Had this problem after install Git Extensions v3.48. Tried to install mysysgit again but same problem. At the end, had to disable (please consider security implications!) Git SSL verification with:

git config --global http.sslVerify false

but if you have a domain certificate better add it to (Win7)

C:\Program Files (x86)\Git\bin\curl-ca-bundle.crt

Move column by name to front of table in pandas

We can use ix to reorder by passing a list:

In [27]:
# get a list of columns
cols = list(df)
# move the column to head of list using index, pop and insert
cols.insert(0, cols.pop(cols.index('Mid')))
['Mid', 'Net', 'Upper', 'Lower', 'Zsore']
In [28]:
# use ix to reorder
df = df.ix[:, cols]
                      Mid Net  Upper   Lower  Zsore
More_than_once_a_day    2  0%  0.22%  -0.12%     65
Once_a_day              3  0%  0.32%  -0.19%     45
Several_times_a_week    4  2%  2.45%   1.10%     78
Once_a_week             6  1%  1.63%  -0.40%     65

Another method is to take a reference to the column and reinsert it at the front:

In [39]:
mid = df['Mid']
df.drop(labels=['Mid'], axis=1,inplace = True)
df.insert(0, 'Mid', mid)
                      Mid Net  Upper   Lower  Zsore
More_than_once_a_day    2  0%  0.22%  -0.12%     65
Once_a_day              3  0%  0.32%  -0.19%     45
Several_times_a_week    4  2%  2.45%   1.10%     78
Once_a_week             6  1%  1.63%  -0.40%     65

You can also use loc to achieve the same result as ix will be deprecated in a future version of pandas from 0.20.0 onwards:

df = df.loc[:, cols]

Docker - Cannot remove dead container

I got the same issue and both answers did not help.

What helped for me is just creating the directories that are missing and them remove them:

mkdir /var/lib/docker/devicemapper/mnt/656cfd09aee399c8ae8c8d3e735fe48d70be6672773616e15579c8de18e2a3b3
mkdir /var/lib/docker/devicemapper/mnt/656cfd09aee399c8ae8c8d3e735fe48d70be6672773616e15579c8de18e2a3b3-init
docker rm 656cfd09aee399c8ae8c8d3e735fe48d70be6672773616e15579c8de18e2a3b3

Could not establish secure channel for SSL/TLS with authority '*'

Yes an Untrusted certificate can cause this. Look at the certificate path for the webservice by opening the websservice in a browser and use the browser tools to look at the certificate path. You may need to install one or more intermediate certificates onto the computer calling the webservice. In the browser you may see "Certificate errors" with an option to "Install Certificate" when you investigate further - this could be the certificate you missing.

My particular problem was a Geotrust Geotrust DV SSL CA intermediate certificate missing following an upgrade to their root server in July 2010

(2020 update deadlink preserved here: )

UnicodeDecodeError, invalid continuation byte

In this case, I tried to execute a .py which active a path/file.sql.

My solution was to modify the codification of the file.sql to "UTF-8 without BOM" and it works!

You can do it with Notepad++.

i will leave a part of my code.


con=psycopg2.connect(host = sys.argv[1], port = sys.argv[2],dbname = sys.argv[3],user = sys.argv[4], password = sys.argv[5])

cursor = con.cursor() sqlfile = open(path, 'r')

How to scroll to top of page with JavaScript/jQuery?

Why don't you just use some reference element at the very beginning of your html file, like

<div id="top"></div>

and then, when the page loads, simply do


    top.location.href = '#top';


If the browser scrolls after this function fires, you simply do


    top.location.href = '#top';


Does adding a duplicate value to a HashSet/HashMap replace the previous value

The docs are pretty clear on this: HashSet.add doesn't replace:

Adds the specified element to this set if it is not already present. More formally, adds the specified element e to this set if this set contains no element e2 such that (e==null ? e2==null : e.equals(e2)). If this set already contains the element, the call leaves the set unchanged and returns false.

But HashMap.put will replace:

If the map previously contained a mapping for the key, the old value is replaced.

Simple Vim commands you wish you'd known earlier

:shell to launch a shell console from Vim. Useful when for example you want to test a script without quitting Vim. Simply hit ^d when you done with the shell console, and then you come back to Vim and your edited file.

Issue with virtualenv - cannot activate

If you are using windows OS then in Gitbash terminal use the following command $source venv/Scripts/activate. This will help you to enter the virtual environment.

jQuery: checking if the value of a field is null (empty)


var val = $('#person_data[document_type]').value();

you have these cases:

val === 'NULL';  // actual value is a string with content "NULL"
val === '';      // actual value is an empty string
val === null;    // actual value is null (absence of any value)

So, use what you need.

Hibernate Criteria Join with 3 Tables

The fetch mode only says that the association must be fetched. If you want to add restrictions on an associated entity, you must create an alias, or a subcriteria. I generally prefer using aliases, but YMMV:

Criteria c = session.createCriteria(Dokument.class, "dokument");
c.createAlias("dokument.role", "role"); // inner join by default
c.createAlias("", "contact");
c.add(Restrictions.eq("contact.lastName", "Test"));
return c.list();

This is of course well explained in the Hibernate reference manual, and the javadoc for Criteria even has examples. Read the documentation: it has plenty of useful information.

Plugin execution not covered by lifecycle configuration (JBossas 7 EAR archetype)

I tried to execute specific plugging right after clean up i.e. post-clean (default is clean phase). This worked for me with eclipse indigo. Just added post-clean resolved the problem for me.


Find indices of elements equal to zero in a NumPy array

import numpy as np

x = np.array([1,0,2,3,6])
non_zero_arr = np.extract(x>0,x)

min_index = np.amin(non_zero_arr)
min_value = np.argmin(non_zero_arr)

Efficient Algorithm for Bit Reversal (from MSB->LSB to LSB->MSB) in C

This thread caught my attention since it deals with a simple problem that requires a lot of work (CPU cycles) even for a modern CPU. And one day I also stood there with the same ¤#%"#" problem. I had to flip millions of bytes. However I know all my target systems are modern Intel-based so let's start optimizing to the extreme!!!

So I used Matt J's lookup code as the base. the system I'm benchmarking on is a i7 haswell 4700eq.

Matt J's lookup bitflipping 400 000 000 bytes: Around 0.272 seconds.

I then went ahead and tried to see if Intel's ISPC compiler could vectorise the arithmetics in the reverse.c.

I'm not going to bore you with my findings here since I tried a lot to help the compiler find stuff, anyhow I ended up with performance of around 0.15 seconds to bitflip 400 000 000 bytes. It's a great reduction but for my application that's still way way too slow..

So people let me present the fastest Intel based bitflipper in the world. Clocked at:

Time to bitflip 400000000 bytes: 0.050082 seconds !!!!!

// Bitflip using AVX2 - The fastest Intel based bitflip in the world!!
// Made by Anders Cedronius 2014 (anders.cedronius (you know what)

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

using namespace std;

#define DISPLAY_WIDTH   32
#define NUM_DATA_BYTES  400000000

// Constants (first we got the mask, then the high order nibble look up table and last we got the low order nibble lookup table)
__attribute__ ((aligned(32))) static unsigned char k1[32*3]={

// The data to be bitflipped (+32 to avoid the quantization out of memory problem)
__attribute__ ((aligned(32))) static unsigned char data[NUM_DATA_BYTES+32]={};

extern "C" {
void bitflipbyte(unsigned char[],unsigned int,unsigned char[]);

int main()

    for(unsigned int i = 0; i < NUM_DATA_BYTES; i++)
        data[i] = rand();

    printf ("\r\nData in(start):\r\n");
    for (unsigned int j = 0; j < 4; j++)
        for (unsigned int i = 0; i < DISPLAY_WIDTH; i++)
            printf ("0x%02x,",data[i+(j*DISPLAY_WIDTH)]);
        printf ("\r\n");

    printf ("\r\nNumber of 32-byte chunks to convert: %d\r\n",(unsigned int)ceil(NUM_DATA_BYTES/32.0));

    double start_time = omp_get_wtime();
    bitflipbyte(data,(unsigned int)ceil(NUM_DATA_BYTES/32.0),k1);
    double end_time = omp_get_wtime();

    printf ("\r\nData out:\r\n");
    for (unsigned int j = 0; j < 4; j++)
        for (unsigned int i = 0; i < DISPLAY_WIDTH; i++)
            printf ("0x%02x,",data[i+(j*DISPLAY_WIDTH)]);
        printf ("\r\n");
    printf("\r\n\r\nTime to bitflip %d bytes: %f seconds\r\n\r\n",NUM_DATA_BYTES, end_time-start_time);

    // return with no errors
    return 0;

The printf's are for debugging..

Here is the workhorse:

bits 64
global bitflipbyte

        vmovdqa     ymm2, [rdx]
        add         rdx, 20h
        vmovdqa     ymm3, [rdx]
        add         rdx, 20h
        vmovdqa     ymm4, [rdx]
        vmovdqa     ymm0, [rdi] 
        vpand       ymm1, ymm2, ymm0 
        vpandn      ymm0, ymm2, ymm0 
        vpsrld      ymm0, ymm0, 4h 
        vpshufb     ymm1, ymm4, ymm1 
        vpshufb     ymm0, ymm3, ymm0         
        vpor        ymm0, ymm0, ymm1
        vmovdqa     [rdi], ymm0
        add     rdi, 20h
        dec     rsi
        jnz     bitflipp_loop

The code takes 32 bytes then masks out the nibbles. The high nibble gets shifted right by 4. Then I use vpshufb and ymm4 / ymm3 as lookup tables. I could use a single lookup table but then I would have to shift left before ORing the nibbles together again.

There are even faster ways of flipping the bits. But I'm bound to single thread and CPU so this was the fastest I could achieve. Can you make a faster version?

Please make no comments about using the Intel C/C++ Compiler Intrinsic Equivalent commands...

OCI runtime exec failed: exec failed: (...) executable file not found in $PATH": unknown

Get rid of your quotes around your command. When you quote it, docker tries to run the full string "lsb_release -a" as a command, which doesn't exist. Instead, you want to run the command lsb_release with an argument -a, and no quotes.

sudo docker exec -it c44f29d30753 lsb_release -a

Note, everything after the container name is the command and arguments to run inside the container, docker will not process any of that as options to the docker command.

Python multiprocessing PicklingError: Can't pickle <type 'function'>

I'd use pathos.multiprocesssing, instead of multiprocessing. pathos.multiprocessing is a fork of multiprocessing that uses dill. dill can serialize almost anything in python, so you are able to send a lot more around in parallel. The pathos fork also has the ability to work directly with multiple argument functions, as you need for class methods.

>>> from pathos.multiprocessing import ProcessingPool as Pool
>>> p = Pool(4)
>>> class Test(object):
...   def plus(self, x, y): 
...     return x+y
>>> t = Test()
>>>, x, y)
[4, 6, 8, 10]
>>> class Foo(object):
...   @staticmethod
...   def work(self, x):
...     return x+1
>>> f = Foo()
>>> p.apipe(, f, 100)
<processing.pool.ApplyResult object at 0x10504f8d0>
>>> res = _
>>> res.get()

Get pathos (and if you like, dill) here:

Get clicked item and its position in RecyclerView

//simply check if the adapter position you get not less than zero

holder.btnDelItem.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {

/bin/sh: pushd: not found

Your shell (/bin/sh) is trying to find 'pushd'. But it can't find it because 'pushd','popd' and other commands like that are build in bash.

Launch you script using Bash (/bin/bash) instead of Sh like you are doing now, and it will work

RegEx for matching "A-Z, a-z, 0-9, _" and "."


From beginning until the end of the string, match one or more of these characters.


Note that ^ and $ match the beginning and the end of a line. When multiline is enabled, this can mean that one line matches, but not the complete string.

Use \A for the beginning of the string, and \z for the end.

See for example:

Find files in a folder using Java

Consider Apache Commons IO, it has a class called FileUtils that has a listFiles method that might be very useful in your case.

Split code over multiple lines in an R script

I know this post is old, but I had a Situation like this and just want to share my solution. All the answers above work fine. But if you have a Code such as those in data.table chaining Syntax it becomes abit challenging. e.g. I had a Problem like this.

mass <- files[, Veg:=tstrsplit(files$file, "/")[1:4][[1]]][, Rain:=tstrsplit(files$file, "/")[1:4][[2]]][, Roughness:=tstrsplit(files$file, "/")[1:4][[3]]][, Geom:=tstrsplit(files$file, "/")[1:4][[4]]][time_[s]<=12000]

I tried most of the suggestions above and they didn´t work. but I figured out that they can be split after the comma within []. Splitting at ][ doesn´t work.

mass <- files[, Veg:=tstrsplit(files$file, "/")[1:4][[1]]][, 
    Rain:=tstrsplit(files$file, "/")[1:4][[2]]][, 
    Roughness:=tstrsplit(files$file, "/")[1:4][[3]]][, 
    Geom:=tstrsplit(files$file, "/")[1:4][[4]]][`time_[s]`<=12000]

Android: Tabs at the BOTTOM

This may not be exactly what you're looking for (it's not an "easy" solution to send your Tabs to the bottom of the screen) but is nevertheless an interesting alternative solution I would like to flag to you :

ScrollableTabHost is designed to behave like TabHost, but with an additional scrollview to fit more items ...

maybe digging into this open-source project you'll find an answer to your question. If I see anything easier I'll come back to you.

MySQL create stored procedure syntax with delimiter

Here is the sample MYSQL Stored Procedure with delimiter and how to call..


DROP PROCEDURE IF EXISTS `sp_user_login` $$
CREATE DEFINER=`root`@`%` PROCEDURE `sp_user_login`(
  IN loc_username VARCHAR(255),
  IN loc_password VARCHAR(255)

  SELECT user_id,
    FROM tbl_user
   WHERE user_name = loc_username
     AND password = loc_password
     AND status = 1;

END $$


and call by, mysql_connection specification and

$loginCheck="call sp_user_login('".$username."','".$password."');";

it will return the result from the procedure.

How to change current working directory using a batch file

Try this

chdir /d D:\Work\Root

Enjoy rooting ;)

Winforms issue - Error creating window handle

The windows handle limit for your application is 10,000 handles. You're getting the error because your program is creating too many handles. You'll need to find the memory leak. As other users have suggested, use a Memory Profiler. I use the .Net Memory Profiler as well. Also, make sure you're calling the dispose method on controls if you're removing them from a form before the form closes (otherwise the controls won't dispose). You'll also have to make sure that there are no events registered with the control. I myself have the same issue, and despite what I already know, I still have some memory leaks that continue to elude me..

Java: Check the date format of current string is according to required format or not

For your case, you may use regex:

boolean checkFormat;

if (input.matches("([0-9]{2})/([0-9]{2})/([0-9]{4})"))

For a larger scope or if you want a flexible solution, refer to MadProgrammer's answer.


Almost 5 years after posting this answer, I realize that this is a stupid way to validate a date format. But i'll just leave this here to tell people that using regex to validate a date is unacceptable

Entity framework self referencing loop detected

Self-referencing as example

public class Employee {
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Email { get; set; }
    public int ManagerId { get; set; }
    public virtual Employee Manager { get; set; }

    public virtual ICollection<Employee> Employees { get; set; }

    public Employee() {
        Employees = new HashSet<Employee>();
HasMany(e => e.Employees)
    .WithRequired(e => e.Manager)
    .HasForeignKey(e => e.ManagerId)

Looping from 1 to infinity in Python

def to_infinity():
    index = 0
    while True:
        yield index
        index += 1

for i in to_infinity():
    if i > 10:

Can I make a <button> not submit a form?

Without setting the type attribute, you could also return false from your OnClick handler, and declare the onclick attribute as onclick="return onBtnClick(event)".

How to set environment variables from within package.json?

Note : In order to set multiple environment variable, script should goes like this

  "scripts": {
    "start": "set NODE_ENV=production&& set MONGO_USER=your_DB_USER_NAME&& set MONGO_PASSWORD=DB_PASSWORD&& set MONGO_DEFAULT_DATABASE=DB_NAME&& node app.js",

Recommended SQL database design for tags or tagging

Use a single formatted text column[1] for storing the tags and use a capable full text search engine to index this. Else you will run into scaling problems when trying to implement boolean queries.

If you need details about the tags you have, you can either keep track of it in a incrementally maintained table or run a batch job to extract the information.

[1] Some RDBMS even provide a native array type which might be even better suited for storage by not needing a parsing step, but might cause problems with the full text search.

How to merge a transparent png image with another image using PIL

from PIL import Image

background ="test1.png")
foreground ="test2.png")

background.paste(foreground, (0, 0), foreground)

First parameter to .paste() is the image to paste. Second are coordinates, and the secret sauce is the third parameter. It indicates a mask that will be used to paste the image. If you pass a image with transparency, then the alpha channel is used as mask.

Check the docs.

What is the point of WORKDIR on Dockerfile?

Beware of using vars as the target directory name for WORKDIR - doing that appears to result in a "cannot normalize nothing" fatal error. IMO, it's also worth pointing out that WORKDIR behaves in the same way as mkdir -p <path> i.e. all elements of the path are created if they don't exist already.

UPDATE: I encountered the variable related problem (mentioned above) whilst running a multi-stage build - it now appears that using a variable is fine - if it (the variable) is "in scope" e.g. in the following, the 2nd WORKDIR reference fails ...

FROM <some image>
ENV varname varval
WORKDIR $varname

FROM <some other image>
WORKDIR $varname

whereas, it succeeds in this ...

FROM <some image>
ENV varname varval
WORKDIR $varname

FROM <some other image>
ENV varname varval
WORKDIR $varname

.oO(Maybe it's in the docs & I've missed it)

HTTP Error 401.2 - Unauthorized You are not authorized to view this page due to invalid authentication headers

Open Project properties by selecting project then go to

View>Properties Windows

and make sure Anonymous Authentication is Enabled

enter image description here

Return multiple values to a method caller

Here are basic Two methods:

1) Use of 'out' as parameter You can use 'out' for both 4.0 and minor versions too.

Example of 'out':

using System;

namespace out_parameter
  class Program
     //Accept two input parameter and returns two out value
     public static void rect(int len, int width, out int area, out int perimeter)
        area = len * width;
        perimeter = 2 * (len + width);
     static void Main(string[] args)
        int area, perimeter;
        // passing two parameter and getting two returning value
        Program.rect(5, 4, out area, out perimeter);
        Console.WriteLine("Area of Rectangle is {0}\t",area);
        Console.WriteLine("Perimeter of Rectangle is {0}\t", perimeter);


Area of Rectangle is 20

Perimeter of Rectangle is 18

*Note:*The out-keyword describes parameters whose actual variable locations are copied onto the stack of the called method, where those same locations can be rewritten. This means that the calling method will access the changed parameter.

2) Tuple<T>

Example of Tuple:

Returning Multiple DataType values using Tuple<T>

using System;

class Program
    static void Main()
    // Create four-item tuple; use var implicit type.
    var tuple = new Tuple<string, string[], int, int[]>("perl",
        new string[] { "java", "c#" },
        new int[] { 2, 3 });
    // Pass tuple as argument.

    static void M(Tuple<string, string[], int, int[]> tuple)
    // Evaluate the tuple's items.
    foreach (string value in tuple.Item2)
    foreach (int value in tuple.Item4)



NOTE: Use of Tuple is valid from Framework 4.0 and above.Tuple type is a class. It will be allocated in a separate location on the managed heap in memory. Once you create the Tuple, you cannot change the values of its fields. This makes the Tuple more like a struct.

CSS background image to fit width, height should auto-scale in proportion

Based on tips from I end up with the following recipe that worked for me

body {
        overflow-y: hidden ! important;
        overflow-x: hidden ! important;
        background-color: #f8f8f8;
        background-image: url('index.png');
        /*background-size: cover;*/
        background-size: contain;
        background-repeat: no-repeat;
        background-position: right;

How to get multiple select box values using jQuery?

Get selected values in comma separator

var Accessids = "";
$(".multi_select .btn-group>ul>li input:checked").each(function(i,obj)
Accessids = Accessids.substring(0,Accessids.length - 1);

Get difference between two lists

def diffList(list1, list2):     # returns the difference between two lists.
    if len(list1) > len(list2):
        return (list(set(list1) - set(list2)))
        return (list(set(list2) - set(list1)))

e.g. if list1 = [10, 15, 20, 25, 30, 35, 40] and list2 = [25, 40, 35] then the returned list will be output = [10, 20, 30, 15]

js then print()

Turgut gave the right solution. Just for clarity, you need to add close after writing.

function openWin()
    myWindow.document.write("<p>This is 'myWindow'</p>");

    myWindow.document.close(); //missing code


relative path to CSS file

You have to move the css folder into your web folder. It seems that your web folder on the hard drive equals the /ServletApp folder as seen from the www. Other content than inside your web folder cannot be accessed from the browsers.

The url of the CSS link is then

 <link rel="stylesheet" type="text/css" href="/ServletApp/css/styles.css"/>

Key Presses in Python

PyAutoGui also lets you press a button multiple times:'tab', presses=5)   # press TAB five times in a row'A', presses=1000)   # press A a thousand times in a row

regex match any whitespace

The reason I used a + instead of a '*' is because a plus is defined as one or more of the preceding element, where an asterisk is zero or more. In this case we want a delimiter that's a little more concrete, so "one or more" spaces.


will match:

wordA wordB     wordC
worda wordb wordc
wordA   wordb   wordC

The words, in this expression, will have to be specific, and also in order (a, b, then c)

How do I use DrawerLayout to display over the ActionBar/Toolbar and under the status bar?

EDIT: The new Design Support Library supports this and the previous method is no longer required.

This can now be achieved using the new Android Design Support Library.

You can see the Cheesesquare sample app by Chris Banes which demos all the new features.

Previous method:

Since there is no complete solution posted, here is the way I achieved the desired result.

First include a ScrimInsetsFrameLayout in your project.

* Copyright 2014 Google Inc.
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.

* A layout that draws something in the insets passed to 
* {@link #fitSystemWindows(Rect)}, i.e. the area above UI chrome
* (status and navigation bars, overlay action bars).
public class ScrimInsetsFrameLayout extends FrameLayout {
    private Drawable mInsetForeground;

    private Rect mInsets;
    private Rect mTempRect = new Rect();
    private OnInsetsCallback mOnInsetsCallback;

    public ScrimInsetsFrameLayout(Context context) {
        init(context, null, 0);

    public ScrimInsetsFrameLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context, attrs, 0);

    public ScrimInsetsFrameLayout(
        Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init(context, attrs, defStyle);

    private void init(Context context, AttributeSet attrs, int defStyle) {
        final TypedArray a = context.obtainStyledAttributes(attrs,
                R.styleable.ScrimInsetsView, defStyle, 0);
        if (a == null) {
        mInsetForeground = a.getDrawable(


    protected boolean fitSystemWindows(Rect insets) {
        mInsets = new Rect(insets);
        setWillNotDraw(mInsetForeground == null);
        if (mOnInsetsCallback != null) {
        return true; // consume insets

    public void draw(Canvas canvas) {

        int width = getWidth();
        int height = getHeight();
        if (mInsets != null && mInsetForeground != null) {
            int sc =;
            canvas.translate(getScrollX(), getScrollY());

            // Top
            mTempRect.set(0, 0, width,;

            // Bottom
            mTempRect.set(0, height - mInsets.bottom, width, height);

            // Left
                height - mInsets.bottom);

            // Right
                width - mInsets.right, 
      , width, 
                height - mInsets.bottom);


    protected void onAttachedToWindow() {
        if (mInsetForeground != null) {

    protected void onDetachedFromWindow() {
        if (mInsetForeground != null) {

     * Allows the calling container to specify a callback for custom 
     * processing when insets change (i.e. when {@link #fitSystemWindows(Rect)}
     * is called. This is useful for setting padding on UI elements 
     * based on UI chrome insets (e.g. a Google Map or a ListView). 
     * When using with ListView or GridView, remember to set
     * clipToPadding to false.
    public void setOnInsetsCallback(OnInsetsCallback onInsetsCallback) {
        mOnInsetsCallback = onInsetsCallback;

    public static interface OnInsetsCallback {
        public void onInsetsChanged(Rect insets);

Then create a styleable so that the insetForeground can be set.


<declare-styleable name="ScrimInsetsView">
    <attr name="insetForeground" format="reference|color" />

Update your activity's xml file and make sure android:fitsSystemWindows is set to true on both the DrawerLayout as well as the ScrimInsetsFrameLayout.



    <!-- The main content view -->

        <!-- Your main content -->


    <!-- The navigation drawer -->

        <!-- Your drawer content -->



Inside the onCreate method of your activity set the status bar background color on the drawer layout.

protected void onCreate(Bundle savedInstanceState) {

    // ...

    mDrawerLayout = (DrawerLayout) findViewById(;

Finally update your app's theme so that the DrawerLayout is behind the status bar.


<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <item name="android:windowDrawsSystemBarBackgrounds">true</item>
    <item name="android:statusBarColor">@android:color/transparent</item>


What is difference between CrudRepository and JpaRepository interfaces in Spring Data JPA?

JpaRepository extends PagingAndSortingRepository which in turn extends CrudRepository.

Their main functions are:

Because of the inheritance mentioned above, JpaRepository will have all the functions of CrudRepository and PagingAndSortingRepository. So if you don't need the repository to have the functions provided by JpaRepository and PagingAndSortingRepository , use CrudRepository.

How to validate numeric values which may contain dots or commas?


EDIT: update to meet the new requirements (comments) ;)
EDIT: remove unnecesary qtfier as per Bryan


Which data structures and algorithms book should I buy?

Introduction to Algorithms by Cormen et. al. is a standard introductory algorithms book, and is used by many universities, including my own. It has pretty good coverage and is very approachable.

And anything by Robert Sedgewick is good too.

Can I run a 64-bit VMware image on a 32-bit machine?

VMware? No. However, QEMU has an x86_64 system target that you can use. You likely won't be able to use a VMware image directly (IIRC, there's no conversion tool), but you can install the OS and such yourself and work inside it. QEMU can be a bit of a PITA to get up and running, but it tends to work quite nicely.

How to change collation of database, table, column?

You can run a php script.

                   $con = mysql_connect('localhost','user','password');
                   if(!$con) { echo "Cannot connect to the database ";die();}
                   $result=mysql_query('show tables');
                   while($tables = mysql_fetch_array($result)) {
                            foreach ($tables as $key => $value) {
                             mysql_query("ALTER TABLE $value CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci");
                   echo "The collation of your database has been successfully changed!";

Disable Buttons in jQuery Mobile

For disabling a button add css class disabled to it . write


PostgreSQL CASE ... END with multiple conditions

This kind of code perhaps should work for You

  WHEN (pvc IS NULL OR pvc = '') AND (datepose < 1980) THEN '01'
  WHEN (pvc IS NULL OR pvc = '') AND (datepose >= 1980) THEN '02'
  WHEN (pvc IS NULL OR pvc = '') AND (datepose IS NULL OR datepose = 0) THEN '03'
  ELSE '00'
 END AS modifiedpvc
FROM my_table;

 gid | datepose | pvc | modifiedpvc 
   1 |     1961 | 01  | 00
   2 |     1949 |     | 01
   3 |     1990 | 02  | 00
   1 |     1981 |     | 02
   1 |          | 03  | 00
   1 |          |     | 03
(6 rows)

C# Create New T()

Just for completion, the best solution here is often to require a factory function argument:

T GetObject<T>(Func<T> factory)
{  return factory(); }

and call it something like this:

string s = GetObject(() => "result");

You can use that to require or make use of available parameters, if needed.

Can you split/explode a field in a MySQL query?

I've resolved this kind of problem with a regular expression pattern. They tend to be slower than regular queries but it's an easy way to retrieve data in a comma-delimited query column


the greedy question mark helps to search at the beggining or the end of the string.

Hope that helps for anyone in the future

css ellipsis on second line

a pure css method base on -webkit-line-clamp, which works on webkit:

@-webkit-keyframes ellipsis {/*for test*/_x000D_
    0% { width: 622px }_x000D_
    50% { width: 311px }_x000D_
    100% { width: 622px }_x000D_
.ellipsis {_x000D_
    max-height: 40px;/* h*n */_x000D_
    overflow: hidden;_x000D_
    background: #eee;_x000D_
    -webkit-animation: ellipsis ease 5s infinite;/*for test*/_x000D_
    overflow: visible;_x000D_
.ellipsis .content {_x000D_
    position: relative;_x000D_
    display: -webkit-box;_x000D_
    -webkit-box-orient: vertical;_x000D_
    -webkit-box-pack: center;_x000D_
    font-size: 50px;/* w */_x000D_
    line-height: 20px;/* line-height h */_x000D_
    color: transparent;_x000D_
    -webkit-line-clamp: 2;/* max row number n */_x000D_
    vertical-align: top;_x000D_
.ellipsis .text {_x000D_
    display: inline;_x000D_
    vertical-align: top;_x000D_
    font-size: 14px;_x000D_
    color: #000;_x000D_
.ellipsis .overlay {_x000D_
    position: absolute;_x000D_
    top: 0;_x000D_
    left: 50%;_x000D_
    width: 100%;_x000D_
    height: 100%;_x000D_
    overflow: hidden;_x000D_
    overflow: visible;_x000D_
    left: 0;_x000D_
    background: rgba(0,0,0,.5);_x000D_
.ellipsis .overlay:before {_x000D_
    content: "";_x000D_
    display: block;_x000D_
    float: left;_x000D_
    width: 50%;_x000D_
    height: 100%;_x000D_
    background: lightgreen;_x000D_
.ellipsis .placeholder {_x000D_
    float: left;_x000D_
    width: 50%;_x000D_
    height: 40px;/* h*n */_x000D_
    background: lightblue;_x000D_
.ellipsis .more {_x000D_
    position: relative;_x000D_
    top: -20px;/* -h */_x000D_
    left: -50px;/* -w */_x000D_
    float: left;_x000D_
    color: #000;_x000D_
    width: 50px;/* width of the .more w */_x000D_
    height: 20px;/* h */_x000D_
    font-size: 14px;_x000D_
    top: 0;_x000D_
    left: 0;_x000D_
    background: orange;_x000D_
<div class='ellipsis'>_x000D_
    <div class='content'>_x000D_
        <div class='text'>text text text text text text text text text text text text text text text text text text text text text </div>_x000D_
        <div class='overlay'>_x000D_
            <div class='placeholder'></div>_x000D_
            <div class='more'>...more</div>_x000D_

How to solve the memory error in Python

Simplest solution: You're probably running out of virtual address space (any other form of error usually means running really slowly for a long time before you finally get a MemoryError). This is because a 32 bit application on Windows (and most OSes) is limited to 2 GB of user mode address space (Windows can be tweaked to make it 3 GB, but that's still a low cap). You've got 8 GB of RAM, but your program can't use (at least) 3/4 of it. Python has a fair amount of per-object overhead (object header, allocation alignment, etc.), odds are the strings alone are using close to a GB of RAM, and that's before you deal with the overhead of the dictionary, the rest of your program, the rest of Python, etc. If memory space fragments enough, and the dictionary needs to grow, it may not have enough contiguous space to reallocate, and you'll get a MemoryError.

Install a 64 bit version of Python (if you can, I'd recommend upgrading to Python 3 for other reasons); it will use more memory, but then, it will have access to a lot more memory space (and more physical RAM as well).

If that's not enough, consider converting to a sqlite3 database (or some other DB), so it naturally spills to disk when the data gets too large for main memory, while still having fairly efficient lookup.

splitting a string into an array in C++ without using vector

#define MAXSPACE 25

string line =  "test one two three.";
string arr[MAXSPACE];
string search = " ";
int spacePos;
int currPos = 0;
int k = 0;
int prevPos = 0;


    spacePos = line.find(search,currPos);

    if(spacePos >= 0)

        currPos = spacePos;
        arr[k] = line.substr(prevPos, currPos - prevPos);
        prevPos = currPos;

}while( spacePos >= 0);

arr[k] = line.substr(prevPos,line.length());

for(int i = 0; i < k; i++)
   cout << arr[i] << endl;

Foreach in a Foreach in MVC View

You have:

foreach (var category in Model.Categories)

and then

@foreach (var product in Model)

Based on that view and model it seems that Model is of type Product if yes then the second foreach is not valid. Actually the first one could be the one that is invalid if you return a collection of Product.


You are right, I am returning the model of type Product. Also, I do understand what is wrong now that you've pointed it out. How am I supposed to do what I'm trying to do then if I can't do it this way?

I'm surprised your code compiles when you said you are returning a model of Product type. Here's how you can do it:

@foreach (var category in Model)

            @foreach (var product in category.Products)
                    put the rest of your code

That suggest that instead of returning a Product, you return a collection of Category with Products. Something like this in EF:

// I am typing it here directly 
// so I'm not sure if this is the correct syntax.
// I assume you know how to do this,
// anyway this should give you an idea.

Material UI and Grid system

From the description of material design specs:

Grid Lists are an alternative to standard list views. Grid lists are distinct from grids used for layouts and other visual presentations.

If you are looking for a much lightweight Grid component library, I'm using React-Flexbox-Grid, the implementation of flexboxgrid.css in React.

On top of that, React-Flexbox-Grid played nicely with both material-ui, and react-toolbox (the alternative material design implementation).

iOS: Convert UTC NSDate to local Timezone

You can try this one:

NSDate *currentDate = [[NSDate alloc] init];
NSTimeZone *timeZone = [NSTimeZone defaultTimeZone];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateStyle:NSDateFormatterLongStyle];
[dateFormatter setTimeStyle:NSDateFormatterLongStyle];
[dateFormatter setTimeZone:timeZone];
[dateFormatter setDateFormat:@"ZZZ"];
NSString *localDateString = [dateFormatter stringFromDate:currentDate];
NSMutableString *mu = [NSMutableString stringWithString:localDateString];
[mu insertString:@":" atIndex:3];
 NSString *strTimeZone = [NSString stringWithFormat:@"(GMT%@)%@",mu,];

React Native Error: ENOSPC: System limit for number of file watchers reached

The meaning of this error is that the number of files monitored by the system has reached the limit!!

Result: The command executed failed! Or throw a warning (such as executing a react-native start VSCode)


Modify the number of system monitoring files


sudo gedit /etc/sysctl.conf

Add a line at the bottom


Then save and exit!

sudo sysctl -p

to check it

Then it is solved!

How to find char in string and get all the indexes?

You could try this

def find(ch,string1):
    for i in range(len(string1)):
        if ch == string1[i]:

How to use lifecycle method getDerivedStateFromProps as opposed to componentWillReceiveProps

getDerivedStateFromProps is used whenever you want to update state before render and update with the condition of props

GetDerivedStateFromPropd updating the stats value with the help of props value


Use index in pandas to plot data

Marius's answer worked perfectly for me:

df.reset_index() sets the index as the first column, with the column label "index." You can now use the index as an axis for plotting, as described in his answer:

monthly_mean.reset_index().plot(x='index', y='A')

However, this does not change the original dataframe. The original dataframe will be unchanged unless it is set using df = df.reset_index().


        COF    TSF    PSF
3.0   0.946  0.914  0.966
4.0   0.963  0.940  0.976
6.0   0.978  0.965  0.987
8.0   0.989  0.984  0.995
10.0  1.000  1.000  1.000
12.0  1.004  1.013  1.009
15.0  1.013  1.026  1.012
17.0  1.019  1.037  1.017
20.0  1.024  1.045  1.020
25.0  1.030  1.057  1.026
30.0  1.034  1.065  1.030
35.0  1.037  1.069  1.031
40.0  1.037  1.068  1.030
60.0  1.037  1.068  1.030
df = df.reset_index()
    index    COF    TSF    PSF
0     3.0  0.946  0.914  0.966
1     4.0  0.963  0.940  0.976
2     6.0  0.978  0.965  0.987
3     8.0  0.989  0.984  0.995
4    10.0  1.000  1.000  1.000
5    12.0  1.004  1.013  1.009
6    15.0  1.013  1.026  1.012
7    17.0  1.019  1.037  1.017
8    20.0  1.024  1.045  1.020
9    25.0  1.030  1.057  1.026
10   30.0  1.034  1.065  1.030
11   35.0  1.037  1.069  1.031
12   40.0  1.037  1.068  1.030
13   60.0  1.037  1.068  1.030

See: DataFrame.reset_index and DataFrame.set_index

How to remove all null elements from a ArrayList or String Array?

As of 2015, this is the best way (Java 8):


Note: This code will throw java.lang.UnsupportedOperationException for fixed-size lists (such as created with Arrays.asList), including immutable lists.

How to sort a data frame by alphabetic order of a character variable in R?

Well, I've got no problem here :

df <- data.frame(v=1:5, x=sample(LETTERS[1:5],5))

#   v x
# 1 1 D
# 2 2 A
# 3 3 B
# 4 4 C
# 5 5 E

df <- df[order(df$x),]

#   v x
# 2 2 A
# 3 3 B
# 4 4 C
# 1 1 D
# 5 5 E

Access index of last element in data frame

You want .iloc with double brackets.

import pandas as pd
df = pd.DataFrame({"date": range(10, 64, 8), "not_date": "fools"})
df.index += 17

You give .iloc a list of indexes - specifically the first and last, [0, -1]. That returns a dataframe from which you ask for the 'date' column. ['date'] will give you a series (yuck), and [['date']] will give you a dataframe.

Clear image on picturebox

I assume you want to clear the Images drawn via PictureBox.

This you would be achieved via a Bitmap object and using Graphics object. you might be doing something like

Graphics graphic = Graphics.FromImage(pictbox.Image);
graphic.Clear(Color.Red) //Color to fill the background and reset the box

Is this what you were looking out?


Since you are using the paint method this would cause it to be redrawn every time, I would suggest you to set a flag at the formlevel indicating whether it should or not paint the Picturebox

private bool _shouldDraw = true;
public bool ShouldDraw
    get { return _shouldDraw; }
    set { _shouldDraw = value; }

In your paint just use

  //do your stuff

When you click the button set this property to false and you should be fine.

Cannot bulk load because the file could not be opened. Operating System Error Code 3

To keep this simple, I just changed the directory from which I was importing the data to a local folder on the server.

I had the file located on a shared folder, I just copied my files to "c:\TEMP\Reports" on my server (updated the query to BULK INSERT from the new folder). The Agent task completed successfully :)

Finally after a long time I'm able to BULK Insert automatically via agent job.

Best regards.

Java 8: How do I work with exception throwing methods in streams?

You can wrap and unwrap exceptions this way.

class A {
    void foo() throws Exception {
        throw new Exception();

interface Task {
    void run() throws Exception;

static class TaskException extends RuntimeException {
    private static final long serialVersionUID = 1L;
    public TaskException(Exception e) {

void bar() throws Exception {
      Stream<A> as = Stream.generate(()->new A());
      try {
        as.forEach(a -> wrapException(() ->; // or a::foo instead of () ->
    } catch (TaskException e) {
        throw (Exception)e.getCause();

static void wrapException(Task task) {
    try {;
    } catch (Exception e) {
        throw new TaskException(e);

Writing an mp4 video using python opencv

This worked for me.

self._name = name + '.mp4'
self._cap = VideoCapture(0)
self._fourcc = VideoWriter_fourcc(*'MP4V')
self._out = VideoWriter(self._name, self._fourcc, 20.0, (640,480))

How can I submit form on button click when using preventDefault()?

Trigger the submit event on the DOM Node, not a jQuery Object.






This bypasses the jQuery bound event allowing the form to submit normally.

how to read System environment variable in Spring applicationContext

You can mention your variable attributes in a property file and define environment specific property files like, production.propertied etc.

Now based on the environment, one of these property file can be read in one the listeners invoked at startup, like the ServletContextListener.

The property file will contain the the environment specific values for various keys.

Sample "local.propeties"



Sample ""



For using these properties file, you can make use of REsource as mentioned below

        PropertyPlaceholderConfigurer configurer = new PropertyPlaceholderConfigurer();
        ResourceLoader resourceLoader = new DefaultResourceLoader();

        Resource resource = resourceLoader.getResource("classpath:"+System.getenv("SERVER_TYPE")+"");

SERVER_TYPE can be defined as the environment variable with appropriate values for local and production environment.

With these changes the appplicationContext.xml will have the following changes

<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">
 <property name="driverClassName" value="com.mysql.jdbc.Driver" />
  <property name="url" value="${db.dataSource.url}" />
  <property name="username" value="${db.dataSource.username}" />
  <property name="password" value="${db.dataSource.password}" />

Hope this helps .

How do you determine what technology a website is built on?

In Linux/OSX I often use simple command curl -sI

Understanding passport serialize deserialize

For anyone using Koa and koa-passport:

Know that the key for the user set in the serializeUser method (often a unique id for that user) will be stored in:


When you set in done(null, user) in deserializeUser where 'user' is some user object from your database:

this.req.user OR this.passport.user

for some reason this.user Koa context never gets set when you call done(null, user) in your deserializeUser method.

So you can write your own middleware after the call to app.use(passport.session()) to put it in this.user like so:

app.use(function * setUserInContext (next) {
  this.user = this.req.user
  yield next

If you're unclear on how serializeUser and deserializeUser work, just hit me up on twitter. @yvanscher

PHP Accessing Parent Class Variable

all the properties and methods of the parent class is inherited in the child class so theoretically you can access them in the child class but beware using the protected keyword in your class because it throws a fatal error when used in the child class.
as mentioned in

The visibility of a property or method can be defined by prefixing the declaration with the keywords public, protected or private. Class members declared public can be accessed everywhere. Members declared protected can be accessed only within the class itself and by inherited and parent classes. Members declared as private may only be accessed by the class that defines the member.

Converting List<Integer> to List<String>

I think using Object.toString() for any purpose other than debugging is probably a really bad idea, even though in this case the two are functionally equivalent (assuming the list has no nulls). Developers are free to change the behavior of any toString() method without any warning, including the toString() methods of any classes in the standard library.

Don't even worry about the performance problems caused by the boxing/unboxing process. If performance is critical, just use an array. If it's really critical, don't use Java. Trying to outsmart the JVM will only lead to heartache.

How to add chmod permissions to file in Git?

Antwane's answer is correct, and this should be a comment but comments don't have enough space and do not allow formatting. :-) I just want to add that in Git, file permissions are recorded only1 as either 644 or 755 (spelled (100644 and 100755; the 100 part means "regular file"):

diff --git a/path b/path
new file mode 100644

The former—644—means that the file should not be executable, and the latter means that it should be executable. How that turns into actual file modes within your file system is somewhat OS-dependent. On Unix-like systems, the bits are passed through your umask setting, which would normally be 022 to remove write permission from "group" and "other", or 002 to remove write permission only from "other". It might also be 077 if you are especially concerned about privacy and wish to remove read, write, and execute permission from both "group" and "other".

1Extremely-early versions of Git saved group permissions, so that some repositories have tree entries with mode 664 in them. Modern Git does not, but since no part of any object can ever be changed, those old permissions bits still persist in old tree objects.

The change to store only 0644 or 0755 was in commit e44794706eeb57f2, which is before Git v0.99 and dated 16 April 2005.

Using Javascript's atob to decode base64 doesn't properly decode utf-8 strings

Small correction, unescape and escape are deprecated, so:

function utf8_to_b64( str ) {
    return window.btoa(decodeURIComponent(encodeURIComponent(str)));

function b64_to_utf8( str ) {
     return decodeURIComponent(encodeURIComponent(window.atob(str)));

function b64_to_utf8( str ) {
    str = str.replace(/\s/g, '');    
    return decodeURIComponent(encodeURIComponent(window.atob(str)));

jQuery - adding elements into an array

Try this, at the end of the each loop, ids array will contain all the hexcodes.

var ids = [];

    $(document).ready(function($) {
    var $div = $("<div id='hexCodes'></div>").appendTo(document.body), code;
    $(".color_cell").each(function() {
        code = $(this).attr('id');
        $div.append(code + "<br />");


Firing a Keyboard Event in Safari, using JavaScript

I am not very good with this but KeyboardEvent => see KeyboardEvent is initialized with initKeyEvent .
Here is an example for emitting event on <input type="text" /> element

document.getElementById("txbox").addEventListener("keypress", function(e) {_x000D_
  alert("Event " + e.type + " emitted!\nKey / Char Code: " + e.keyCode + " / " + e.charCode);_x000D_
}, false);_x000D_
document.getElementById("btn").addEventListener("click", function(e) {_x000D_
  var doc = document.getElementById("txbox");_x000D_
  var kEvent = document.createEvent("KeyboardEvent");_x000D_
  kEvent.initKeyEvent("keypress", true, true, null, false, false, false, false, 74, 74);_x000D_
}, false);
<input id="txbox" type="text" value="" />_x000D_
<input id="btn" type="button" value="CLICK TO EMIT KEYPRESS ON TEXTBOX" />

Get Date in YYYYMMDD format in windows batch file

You can try this ! This should work on windows machines.

for /F "usebackq tokens=1,2,3 delims=-" %%I IN (`echo %date%`) do echo "%%I" "%%J" "%%K"

Is "&#160;" a replacement of "&nbsp;"?

  • &nbsp; is the character entity reference (meant to be easily parseable by humans).
  • &#160; is the numeric entity reference (meant to be easily parseable by machines).

They are the same except for the fact that the latter does not need another lookup table to find its actual value. The lookup table is called a DTD, by the way.

You can read more about character entity references in the offical W3C documents.

Java Inheritance - calling superclass method

Whenever you create child class object then that object has all the features of parent class. Here Super() is the facilty for accession parent.

If you write super() at that time parents's default constructor is called. same if you write super.

this keyword refers the current object same as super key word facilty for accessing parents.

Add one year in current date PYTHON

convert it into python datetime object if it isn't already. then add deltatime

one_years_later = Your_date + datetime.timedelta(days=(years*days_per_year)) 

for your case days=365.

you can have condition to check if the year is leap or no and adjust days accordingly

you can add as many years as you want

How to specify the current directory as path in VBA?

If the path you want is the one to the workbook running the macro, and that workbook has been saved, then


is what you would use.

Why does GitHub recommend HTTPS over SSH?

I assume HTTPS is recommended by GitHub for several reasons

  1. It's simpler to access a repository from anywhere as you only need your account details (no SSH keys required) to write to the repository.

  2. HTTPS Is a port that is open in all firewalls. SSH is not always open as a port for communication to external networks

A GitHub repository is therefore more universally accessible using HTTPS than SSH.

In my view SSH keys are worth the little extra work in creating them

  1. SSH Keys do not provide access to your GitHub account, so your account cannot be hijacked if your key is stolen.

  2. Using a strong keyphrase with your SSH key limits any misuse, even if your key gets stolen (after first breaking access protection to your computer account)

If your GitHub account credentials (username/password) are stolen, your GitHub password can be changed to block you from access and all your shared repositories can be quickly deleted.

If a private key is stolen, someone can do a force push of an empty repository and wipe out all change history for each repository you own, but cannot change anything in your GitHub account. It will be much easier to try recovery from this breach of you have access to your GitHub account.

My preference is to use SSH with a passphrase protected key. I have a different SSH key for each computer, so if that machine gets stolen or key compromised, I can quickly login to GitHub and delete that key to prevent unwanted access.

SSH can be tunneled over HTTPS if the network you are on blocks the SSH port.

If you use HTTPS, I would recommend adding two-factor authentication, to protect your account as well as your repositories.

If you use HTTPS with a tool (e.g an editor), you should use a developer token from your GitHub account rather than cache username and password in that tools configuration. A token would mitigate the some of the potential risk of using HTTPS, as tokens can be configured for very specific access privileges and easily be revoked if that token is compromised.

How to interpolate variables in strings in JavaScript, without concatenation?

If you're trying to do interpolation for microtemplating, I like Mustache.js for that purpose.

filter out multiple criteria using excel vba

Alternative using VBA's Filter function

As an innovative alternative to @schlebe 's recent answer, I tried to use the Filter function integrated in VBA, which allows to filter out a given search string setting the third argument to False. All "negative" search strings (e.g. A, B, C) are defined in an array. I read the criteria in column A to a datafield array and basicly execute a subsequent filtering (A - C) to filter these items out.


Sub FilterOut()
Dim ws  As Worksheet
Dim rng As Range, i As Integer, n As Long, v As Variant
' 1) define strings to be filtered out in array
  Dim a()                    ' declare as array
  a = Array("A", "B", "C")   ' << filter out values
' 2) define your sheetname and range (e.g. criteria in column A)
  Set ws = ThisWorkbook.Worksheets("FilterOut")
  n = ws.Range("A" & ws.Rows.Count).End(xlUp).row
  Set rng = ws.Range("A2:A" & n)
' 3) hide complete range rows temporarily
  rng.EntireRow.Hidden = True
' 4) set range to a variant 2-dim datafield array
  v = rng
' 5) code array items by appending row numbers
  For i = 1 To UBound(v): v(i, 1) = v(i, 1) & "#" & i + 1: Next i
' 6) transform to 1-dim array and FILTER OUT the first search string, e.g. "A"
  v = Filter(Application.Transpose(Application.Index(v, 0, 1)), a(0), False, False)
' 7) filter out each subsequent search string, i.e. "B" and "C"
  For i = 1 To UBound(a): v = Filter(v, a(i), False, False): Next i
' 8) get coded row numbers via split function and unhide valid rows
  For i = LBound(v) To UBound(v)
      ws.Range("A" & Split(v(i) & "#", "#")(1)).EntireRow.Hidden = False
  Next i
End Sub

How can I make my own event in C#?

Here's an example of creating and using an event with C#

using System;

namespace Event_Example
    //First we have to define a delegate that acts as a signature for the
    //function that is ultimately called when the event is triggered.
    //You will notice that the second parameter is of MyEventArgs type.
    //This object will contain information about the triggered event.
    public delegate void MyEventHandler(object source, MyEventArgs e);

    //This is a class which describes the event to the class that recieves it.
    //An EventArgs class must always derive from System.EventArgs.
    public class MyEventArgs : EventArgs
        private string EventInfo;
        public MyEventArgs(string Text)
            EventInfo = Text;
        public string GetInfo()
            return EventInfo;

    //This next class is the one which contains an event and triggers it
    //once an action is performed. For example, lets trigger this event
    //once a variable is incremented over a particular value. Notice the
    //event uses the MyEventHandler delegate to create a signature
    //for the called function.
    public class MyClass
        public event MyEventHandler OnMaximum;
        private int i;
        private int Maximum = 10;
        public int MyValue
                return i;
                if(value <= Maximum)
                    i = value;
                    //To make sure we only trigger the event if a handler is present
                    //we check the event to make sure it's not null.
                    if(OnMaximum != null)
                        OnMaximum(this, new MyEventArgs("You've entered " +
                            value.ToString() +
                            ", but the maximum is " +

    class Program
        //This is the actual method that will be assigned to the event handler
        //within the above class. This is where we perform an action once the
        //event has been triggered.
        static void MaximumReached(object source, MyEventArgs e)

        static void Main(string[] args)
            //Now lets test the event contained in the above class.
            MyClass MyObject = new MyClass();
            MyObject.OnMaximum += new MyEventHandler(MaximumReached);

            for(int x = 0; x <= 15; x++)
                MyObject.MyValue = x;


Splitting applicationContext to multiple files

I find the following setup the easiest.

Use the default config file loading mechanism of DispatcherServlet:

The framework will, on initialization of a DispatcherServlet, look for a file named [servlet-name]-servlet.xml in the WEB-INF directory of your web application and create the beans defined there (overriding the definitions of any beans defined with the same name in the global scope).

In your case, simply create a file intrafest-servlet.xml in the WEB-INF dir and don't need to specify anything specific information in web.xml.

In intrafest-servlet.xml file you can use import to compose your XML configuration.

  <bean id="bean1" class="..."/>
  <bean id="bean2" class="..."/>

  <import resource="foo-services.xml"/>
  <import resource="foo-persistence.xml"/>

Note that the Spring team actually prefers to load multiple config files when creating the (Web)ApplicationContext. If you still want to do it this way, I think you don't need to specify both context parameters (context-param) and servlet initialization parameters (init-param). One of the two will do. You can also use commas to specify multiple config locations.

Java List.contains(Object with field value equal to x)

This is how to do it using Java 8+ :

boolean isJohnAlive = -> o.getName().equals("John"));

python mpl_toolkits installation issue

It is not on PyPI and you should not be installing it via pip. If you have matplotlib installed, you should be able to import mpl_toolkits directly:

$ pip install --upgrade matplotlib

$ python
>>> import mpl_toolkits

JAX-RS / Jersey how to customize error handling?

This is the correct behavior actually. Jersey will try to find a handler for your input and will try to construct an object from the provided input. In this case it will try to create a new Date object with the value X provided to the constructor. Since this is an invalid date, by convention Jersey will return 404.

What you can do is rewrite and put birth date as a String, then try to parse and if you don't get what you want, you're free to throw any exception you want by any of the exception mapping mechanisms (there are several).

How do I commit case-sensitive only filename changes in Git?

You can use git mv:

git mv -f OldFileNameCase newfilenamecase

How can I roll back my last delete command in MySQL?

I also had deleted some values from my development database, but I had the same copy in QA database, so I did a generate script and selected option "type of data to script" to "data only" and selected my table.

Then I got the insert statements with same data, and then I run the script on my development database.

Why do you have to link the math library in C?

Because time() and some other functions are builtin defined in the C library (libc) itself and GCC always links to libc unless you use the -ffreestanding compile option. However math functions live in libm which is not implicitly linked by gcc.

Java Code for calculating Leap Year

Pseudo code from Wikipedia translated into the most compact Java

(year % 400 == 0) || ((year % 4 == 0) && (year % 100 != 0))

How to get client IP address using jQuery

A simple AJAX call to your server, and then the serverside logic to get the ip address should do the trick.

$.getJSON('getip.php', function(data){
  alert('Your ip is: ' +  data.ip);

Then in php you might do:

/* getip.php */
header('Cache-Control: no-cache, must-revalidate');
header('Expires: Mon, 26 Jul 1997 05:00:00 GMT');
header('Content-type: application/json');

if (!empty($_SERVER['HTTP_CLIENT_IP']))
elseif (!empty($_SERVER['HTTP_X_FORWARDED_FOR']))
print json_encode(array('ip' => $ip));

How do I get Month and Date of JavaScript in 2 digit format?

I would suggest you use a different library called Moment

This way you are able to format the date directly without having to do extra work

const date = moment().format('YYYY-MM-DD')
// date: '2020-01-04'

Make sure you import moment as well to be able to use it.

yarn add moment 
# to add the dependency
import moment from 'moment' 
// import this at the top of the file you want to use it in

Hope this helps :D

Send mail via Gmail with PowerShell V2's Send-MailMessage

On a Windows 8.1 machine I got Send-MailMessage to send an email with an attachment through Gmail using the following script:

$EmFrom = "[email protected]"
$username = "[email protected]"
$EmTo = "[email protected]"
$Server = ""
$port = 587
$Subj = "Test"
$Bod = "Test 123"
$Att = "c:\Filename.FileType"
$securepwd = ConvertTo-SecureString $pwd -AsPlainText -Force
$cred = New-Object -TypeName System.Management.Automation.PSCredential -ArgumentList $username, $securepwd
Send-MailMessage -To $EmTo -From $EmFrom -Body $Bod -Subject $Subj -Attachments $Att -SmtpServer $Server -port $port -UseSsl  -Credential $cred

How can I add numbers in a Bash script?

You should declare metab as integer and then use arithmetic evaluation

declare -i metab num

For more information see

Go to beginning of line without opening new line in VI

0 Takes you to the beginning of the line

Shift 0 Takes you to the end of the line

What is (functional) reactive programming?

OK, from background knowledge and from reading the Wikipedia page to which you pointed, it appears that reactive programming is something like dataflow computing but with specific external "stimuli" triggering a set of nodes to fire and perform their computations.

This is pretty well suited to UI design, for example, in which touching a user interface control (say, the volume control on a music playing application) might need to update various display items and the actual volume of audio output. When you modify the volume (a slider, let's say) that would correspond to modifying the value associated with a node in a directed graph.

Various nodes having edges from that "volume value" node would automatically be triggered and any necessary computations and updates would naturally ripple through the application. The application "reacts" to the user stimulus. Functional reactive programming would just be the implementation of this idea in a functional language, or generally within a functional programming paradigm.

For more on "dataflow computing", search for those two words on Wikipedia or using your favorite search engine. The general idea is this: the program is a directed graph of nodes, each performing some simple computation. These nodes are connected to each other by graph links that provide the outputs of some nodes to the inputs of others.

When a node fires or performs its calculation, the nodes connected to its outputs have their corresponding inputs "triggered" or "marked". Any node having all inputs triggered/marked/available automatically fires. The graph might be implicit or explicit depending on exactly how reactive programming is implemented.

Nodes can be looked at as firing in parallel, but often they are executed serially or with limited parallelism (for example, there may be a few threads executing them). A famous example was the Manchester Dataflow Machine, which (IIRC) used a tagged data architecture to schedule execution of nodes in the graph through one or more execution units. Dataflow computing is fairly well suited to situations in which triggering computations asynchronously giving rise to cascades of computations works better than trying to have execution be governed by a clock (or clocks).

Reactive programming imports this "cascade of execution" idea and seems to think of the program in a dataflow-like fashion but with the proviso that some of the nodes are hooked to the "outside world" and the cascades of execution are triggered when these sensory-like nodes change. Program execution would then look like something analogous to a complex reflex arc. The program may or may not be basically sessile between stimuli or may settle into a basically sessile state between stimuli.

"non-reactive" programming would be programming with a very different view of the flow of execution and relationship to external inputs. It's likely to be somewhat subjective, since people will likely be tempted to say anything that responds to external inputs "reacts" to them. But looking at the spirit of the thing, a program that polls an event queue at a fixed interval and dispatches any events found to functions (or threads) is less reactive (because it only attends to user input at a fixed interval). Again, it's the spirit of the thing here: one can imagine putting a polling implementation with a fast polling interval into a system at a very low level and program in a reactive fashion on top of it.

How to position a div in the middle of the screen when the page is bigger than the screen

For this you would have to detect screen size. That is not possible with CSS or HTML; you need JavaScript. Here is the Mozilla Developer Center entry on window properties

Detect the available height and position accordingly.

Looping Over Result Sets in MySQL

Something like this should do the trick (However, read after the snippet for more info)


  DECLARE var1 CHAR(16);    -- or approriate type

  DECLARE curs CURSOR FOR  SELECT something FROM somewhere WHERE some stuff;

    --Fld1 type,
    --Fld2 type,

  OPEN curs;

  SET bDone = 0;
    FETCH curs INTO var1,, b;

    IF whatever_filtering_desired
       -- here for whatever_transformation_may_be_desired
       INSERT INTO tblResults VALUES (var1, var2, var3 ...);
    END IF;

  CLOSE curs;
  SELECT * FROM tblResults;

A few things to consider...

Concerning the snippet above:

  • may want to pass part of the query to the Stored Procedure, maybe particularly the search criteria, to make it more generic.
  • If this method is to be called by multiple sessions etc. may want to pass a Session ID of sort to create a unique temporary table name (actually unnecessary concern since different sessions do not share the same temporary file namespace; see comment by Gruber, below)
  • A few parts such as the variable declarations, the SELECT query etc. need to be properly specified

More generally: trying to avoid needing a cursor.

I purposely named the cursor variable curs[e], because cursors are a mixed blessing. They can help us implement complicated business rules that may be difficult to express in the declarative form of SQL, but it then brings us to use the procedural (imperative) form of SQL, which is a general feature of SQL which is neither very friendly/expressive, programming-wise, and often less efficient performance-wise.

Maybe you can look into expressing the transformation and filtering desired in the context of a "plain" (declarative) SQL query.

How to read .pem file to get private and public key

Well, my code is like yours, with little diferences...

public static X509Certificate loadPublicX509(String fileName) 
        throws GeneralSecurityException {
    InputStream is = null;
    X509Certificate crt = null;
    try {
        is = fileName.getClass().getResourceAsStream("/" + fileName);
        CertificateFactory cf = CertificateFactory.getInstance("X.509");
        crt = (X509Certificate)cf.generateCertificate(is);
    } finally {
    return crt;

public static PrivateKey loadPrivateKey(String fileName) 
        throws IOException, GeneralSecurityException {
    PrivateKey key = null;
    InputStream is = null;
    try {
        is = fileName.getClass().getResourceAsStream("/" + fileName);
        BufferedReader br = new BufferedReader(new InputStreamReader(is));
        StringBuilder builder = new StringBuilder();
        boolean inKey = false;
        for (String line = br.readLine(); line != null; line = br.readLine()) {
            if (!inKey) {
                if (line.startsWith("-----BEGIN ") && 
                        line.endsWith(" PRIVATE KEY-----")) {
                    inKey = true;
            else {
                if (line.startsWith("-----END ") && 
                        line.endsWith(" PRIVATE KEY-----")) {
                    inKey = false;
        byte[] encoded = DatatypeConverter.parseBase64Binary(builder.toString());
        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(encoded);
        KeyFactory kf = KeyFactory.getInstance("RSA");
        key = kf.generatePrivate(keySpec);
    } finally {
    return key;

public static void closeSilent(final InputStream is) {
    if (is == null) return;
    try { is.close(); } catch (Exception ign) {}

Generating a Random Number between 1 and 10 Java

The standard way to do this is as follows:


  • min Minimum value
  • max Maximum value

and get in return a Integer between min and max, inclusive.

Random rand = new Random();

// nextInt as provided by Random is exclusive of the top value so you need to add 1 

int randomNum = rand.nextInt((max - min) + 1) + min;

See the relevant JavaDoc.

As explained by Aurund, Random objects created within a short time of each other will tend to produce similar output, so it would be a good idea to keep the created Random object as a field, rather than in a method.

How do I register a .NET DLL file in the GAC?

From Wikipedia:

gacutil.exe is the .NET utility used to work with the GAC.

One can check the availability of a shared assembly in GAC by using the command:

gacutil.exe /l "assemblyName"

One can register a shared assembly in the GAC by using the command:

gacutil.exe /i "assemblyName"

Or by dropping an assembly file into the following location using the GUI:


Other options for this utility will be briefly described if you use the /? flag, that is:

gacutil.exe /?

How to make a text box have rounded corners?

You could use CSS to do that, but it wouldn't be supported in IE8-. You can use some site like to come up with actual CSS you'd use, which would look something like this (again, depending on how many browsers you're trying to support):

-webkit-border-radius: 5px;
-moz-border-radius: 5px;
border-radius: 5px;

Calculate last day of month in JavaScript

In computer terms, new Date() and regular expression solutions are slow! If you want a super-fast (and super-cryptic) one-liner, try this one (assuming m is in Jan=1 format). I keep trying different code changes to get the best performance.

My current fastest version:

After looking at this related question Leap year check using bitwise operators (amazing speed) and discovering what the 25 & 15 magic number represented, I have come up with this optimized hybrid of answers:

function getDaysInMonth(m, y) {
    return m===2 ? y & 3 || !(y%25) && y & 15 ? 28 : 29 : 30 + (m+(m>>3)&1);

Given the bit-shifting this obviously assumes that your m & y parameters are both integers, as passing numbers as strings would result in weird results.


JSPerf results:

For some reason, (m+(m>>3)&1) is more efficient than (5546>>m&1) on almost all browsers.

The only real competition for speed is from @GitaarLab, so I have created a head-to-head JSPerf for us to test on:

It works based on my leap year answer here: javascript to find leap year this answer here Leap year check using bitwise operators (amazing speed) as well as the following binary logic.

A quick lesson in binary months:

If you interpret the index of the desired months (Jan = 1) in binary you will notice that months with 31 days either have bit 3 clear and bit 0 set, or bit 3 set and bit 0 clear.

Jan = 1  = 0001 : 31 days
Feb = 2  = 0010
Mar = 3  = 0011 : 31 days
Apr = 4  = 0100
May = 5  = 0101 : 31 days
Jun = 6  = 0110
Jul = 7  = 0111 : 31 days
Aug = 8  = 1000 : 31 days
Sep = 9  = 1001
Oct = 10 = 1010 : 31 days
Nov = 11 = 1011
Dec = 12 = 1100 : 31 days

That means you can shift the value 3 places with >> 3, XOR the bits with the original ^ m and see if the result is 1 or 0 in bit position 0 using & 1. Note: It turns out + is slightly faster than XOR (^) and (m >> 3) + m gives the same result in bit 0.

JSPerf results:

What is an example of the Liskov Substitution Principle?

Long story short, let's leave rectangles rectangles and squares squares, practical example when extending a parent class, you have to either PRESERVE the exact parent API or to EXTEND IT.

Let's say you have a base ItemsRepository.

class ItemsRepository
    * @return int Returns number of deleted rows
    public function delete()
        // perform a delete query
        $numberOfDeletedRows = 10;

        return $numberOfDeletedRows;

And a sub class extending it:

class BadlyExtendedItemsRepository extends ItemsRepository
     * @return void Was suppose to return an INT like parent, but did not, breaks LSP
    public function delete()
        // perform a delete query
        $numberOfDeletedRows = 10;

        // we broke the behaviour of the parent class

Then you could have a Client working with the Base ItemsRepository API and relying on it.

 * Class ItemsService is a client for public ItemsRepository "API" (the public delete method).
 * Technically, I am able to pass into a constructor a sub-class of the ItemsRepository
 * but if the sub-class won't abide the base class API, the client will get broken.
class ItemsService
     * @var ItemsRepository
    private $itemsRepository;

     * @param ItemsRepository $itemsRepository
    public function __construct(ItemsRepository $itemsRepository)
        $this->itemsRepository = $itemsRepository;

     * !!! Notice how this is suppose to return an int. My clients expect it based on the
     * ItemsRepository API in the constructor !!!
     * @return int
    public function delete()
        return $this->itemsRepository->delete();

The LSP is broken when substituting parent class with a sub class breaks the API's contract.

class ItemsController
     * Valid delete action when using the base class.
    public function validDeleteAction()
        $itemsService = new ItemsService(new ItemsRepository());
        $numberOfDeletedItems = $itemsService->delete();

        // $numberOfDeletedItems is an INT :)

     * Invalid delete action when using a subclass.
    public function brokenDeleteAction()
        $itemsService = new ItemsService(new BadlyExtendedItemsRepository());
        $numberOfDeletedItems = $itemsService->delete();

        // $numberOfDeletedItems is a NULL :(

You can learn more about writing maintainable software in my course:

Minimum 6 characters regex expression

Something along the lines of this?

<asp:TextBox id="txtUsername" runat="server" />

    ErrorMessage="Field not valid!"
    ValidationExpression="[0-9a-zA-Z]{6,}" />

How to make a div 100% height of the browser window

There are a couple of CSS 3 measurement units called:

Viewport-Percentage (or Viewport-Relative) Lengths

What are Viewport-Percentage Lengths?

From the linked W3 Candidate Recommendation above:

The viewport-percentage lengths are relative to the size of the initial containing block. When the height or width of the initial containing block is changed, they are scaled accordingly.

These units are vh (viewport height), vw (viewport width), vmin (viewport minimum length) and vmax (viewport maximum length).

How can this be used to make a divider fill the height of the browser?

For this question, we can make use of vh: 1vh is equal to 1% of the viewport's height. That is to say, 100vh is equal to the height of the browser window, regardless of where the element is situated in the DOM tree:




div {
    height: 100vh;

This is literally all that's needed. Here is a JSFiddle example of this in use.

What browsers support these new units?

This is currently supported on all up-to-date major browsers apart from Opera Mini. Check out Can I use... for further support.

How can this be used with multiple columns?

In the case of the question at hand, featuring a left and a right divider, here is a JSFiddle example showing a two-column layout involving both vh and vw.

How is 100vh different to 100%?

Take this layout for example:

<body style="height:100%">
    <div style="height:200px">
        <p style="height:100%; display:block;">Hello, world!</p>

The p tag here is set to 100% height, but because its containing div has 200 pixels height, 100% of 200 pixels becomes 200 pixels, not 100% of the body height. Using 100vh instead means that the p tag will be 100% height of the body regardless of the div height. Take a look at this accompanying JSFiddle to easily see the difference!

Maven parent pom vs modules pom

There is one little catch with the third approach. Since aggregate POMs (myproject/pom.xml) usually don't have parent at all, they do not share configuration. That means all those aggregate POMs will have only default repositories.

That is not a problem if you only use plugins from Central, however, this will fail if you run plugin using the plugin:goal format from your internal repository. For example, you can have foo-maven-plugin with the groupId of org.example providing goal generate-foo. If you try to run it from the project root using command like mvn org.example:foo-maven-plugin:generate-foo, it will fail to run on the aggregate modules (see compatibility note).

Several solutions are possible:

  1. Deploy plugin to the Maven Central (not always possible).
  2. Specify repository section in all of your aggregate POMs (breaks DRY principle).
  3. Have this internal repository configured in the settings.xml (either in local settings at ~/.m2/settings.xml or in the global settings at /conf/settings.xml). Will make build fail without those settings.xml (could be OK for large in-house projects that are never supposed to be built outside of the company).
  4. Use the parent with repositories settings in your aggregate POMs (could be too many parent POMs?).

Does file_get_contents() have a timeout setting?

Yes! By passing a stream context in the third parameter:

Here with a timeout of 1s:

file_get_contents("", 0, stream_context_create(["http"=>["timeout"=>1]]));

Source in comment section of

HTTP context options:


Other contexts:

How do I change the figure size with subplots?

Alternatively, create a figure() object using the figsize argument and then use add_subplot to add your subplots. E.g.

import matplotlib.pyplot as plt
import numpy as np

f = plt.figure(figsize=(10,3))
ax = f.add_subplot(121)
ax2 = f.add_subplot(122)
x = np.linspace(0,4,1000)
ax.plot(x, np.sin(x))
ax2.plot(x, np.cos(x), 'r:')

Simple Example

Benefits of this method are that the syntax is closer to calls of subplot() instead of subplots(). E.g. subplots doesn't seem to support using a GridSpec for controlling the spacing of the subplots, but both subplot() and add_subplot() do.

How update the _id of one MongoDB Document?

To do it for your whole collection you can also use a loop (based on Niels example):

    doc._id=doc.UserId; db.status_new.insert(doc);
db.status_new.renameCollection("status", true);

In this case UserId was the new ID I wanted to use

How can I get Docker Linux container information from within the container itself?

WARNING: You should understand the security risks of this method before you consider it. John's summary of the risk:

By giving the container access to /var/run/docker.sock, it is [trivially easy] to break out of the containment provided by docker and gain access to the host machine. Obviously this is potentially dangerous.

Inside the container, the dockerId is your hostname. So, you could:

  • install the docker-io package in your container with the same version as the host
  • start it with --volume /var/run/docker.sock:/var/run/docker.sock --privileged
  • finally, run: docker inspect $(hostname) inside the container

Avoid this. Only do it if you understand the risks and have a clear mitigation for the risks.

LaTeX table positioning

Not necessary to use \restylefloat and destroys other options, like caption placement. just use [H] or [!h] after \begin{table}.

Not class selector in jQuery

You need the :not() selector:


or, alternatively, the .not() method:


GitLab git user password

I am using a mac.gitlab is installed in a centos server.

I have tried all the methods above and found the final answer for me:


ssh-keygen -t rsa


 ssh-keygen -t rsa -C "[email protected]" -b 4096

PHP - Notice: Undefined index:

You're getting errors because you're attempting to read post variables that haven't been set, they only get set on form submission. Wrap your php code at the bottom in an

if ($_SERVER['REQUEST_METHOD'] === 'POST') { ... }

Also, your code is ripe for SQL injection. At the very least use mysql_real_escape_string on the post vars before using them in SQL queries. mysql_real_escape_string is not good enough for a production site, but should score you extra points in class.

What does body-parser do with express?

It parses the HTTP request body. This is usually necessary when you need to know more than just the URL you hit, particular in the context of a POST or PUT PATCH HTTP request where the information you want is contains in the body.

Basically its a middleware for parsing JSON, plain text, or just returning a raw Buffer object for you to deal with as you require.

How ViewBag in ASP.NET MVC works

public dynamic ViewBag
        if (_viewBag == null)
            _viewBag = new DynamicViewData(() => ViewData);

        return _viewBag;

Python Pandas: Get index of rows which column matches certain value

Can be done using numpy where() function:

import pandas as pd
import numpy as np

In [716]: df = pd.DataFrame({"gene_name": ['SLC45A1', 'NECAP2', 'CLIC4', 'ADC', 'AGBL4'] , "BoolCol": [False, True, False, True, True] },

In [717]: df
  BoolCol gene_name
a   False   SLC45A1
b    True    NECAP2
c   False     CLIC4
d    True       ADC
e    True     AGBL4

In [718]: np.where(df["BoolCol"] == True)
Out[718]: (array([1, 3, 4]),)

In [719]: select_indices = list(np.where(df["BoolCol"] == True)[0])

In [720]: df.iloc[select_indices]
  BoolCol gene_name
b    True    NECAP2
d    True       ADC
e    True     AGBL4

Though you don't always need index for a match, but incase if you need:

In [796]: df.iloc[select_indices].index
Out[796]: Index([u'b', u'd', u'e'], dtype='object')

In [797]: df.iloc[select_indices].index.tolist()
Out[797]: ['b', 'd', 'e']

How does GPS in a mobile phone work exactly?

There's 3 satellites at least that you must be able to receive from of the 24-32 out there, and they each broadcast a time from a synchronized atomic clock. The differences in those times that you receive at any one time tell you how long the broadcast took to reach you, and thus where you are in relation to the satellites. So, it sort of reads from something, but it doesn't connect to that thing. Note that this doesn't tell you your orientation, many GPSes fake that (and speed) by interpolating data points.

If you don't count the cost of the receiver, it's a free service. Apparently there's higher resolution services out there that are restricted to military use. Those are likely a fixed cost for a license to decrypt the signals along with a confidentiality agreement.

Now your device may support GPS tracking, in which case it might communicate, say via GPRS, to a database which will store the location the device has found itself to be at, so that multiple devices may be tracked. That would require some kind of connection.

Maps are either stored on the device or received over a connection. Navigation is computed based on those maps' databases. These likely are a licensed item with a cost associated, though if you use a service like Google Maps they have the license with NAVTEQ and others.

How to print out more than 20 items (documents) in MongoDB's shell?

Could always do:{print(tojson(f, '', true));});

To get that compact view.

Also, I find it very useful to limit the fields returned by the find so:{},{name:1}).forEach(function(f){print(tojson(f, '', true));});

which would return only the _id and name field from foo.

Assign multiple values to array in C

Although in your case, just plain initialization will do, there's a trick to wrap the array into a struct (which can be initialized after declaration).

For example:

struct foo {
  GLfloat arr[10];
struct foo foo;
foo = (struct foo) { .arr = {1.0, ... } };

Send Mail to multiple Recipients in java

Hi every one this code is workin for me please try with this for sending mail to multiple recepients

private String recipient = "[email protected] ,[email protected] ";
String[] recipientList = recipient.split(",");
InternetAddress[] recipientAddress = new InternetAddress[recipientList.length];
int counter = 0;
for (String recipient : recipientList) {
    recipientAddress[counter] = new InternetAddress(recipient.trim());
message.setRecipients(Message.RecipientType.TO, recipientAddress);

How to find and return a duplicate value in array

find_all() returns an array containing all elements of enum for which block is not false.

To get duplicate elements

>> arr = ["A", "B", "C", "B", "A"]
>> arr.find_all { |x| arr.count(x) > 1 }

=> ["A", "B", "B", "A"]

Or duplicate uniq elements

>> arr.find_all { |x| arr.count(x) > 1 }.uniq
=> ["A", "B"] 

How to pass data from 2nd activity to 1st activity when pressed back? - android

this is your first Activity1.

public class Activity1 extends Activity{
private int mRequestCode = 100;

protected void onCreate(Bundle savedInstanceState) {

    Intent intent = new Intent(this, Activity2.class);
    startActivityForResult(intent, mRequestCode);

protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if(requestCode == mRequestCode && resultCode == RESULT_OK){
        String editTextString = data.getStringExtra("editText");

From here you are starting your Activity2.class by using startActivityForResult(mRequestCode, Activity2.class);

Now this is your second Activity, name is Activity2

public class Activity2 extends Activity {
private EditText mEditText;

protected void onCreate(Bundle savedInstanceState) {

    //mEditText = (EditText)findViewById(;

    Intent intent = new Intent();
    intent.putExtra("editText", mEditText.getText().toString());
    setResult(RESULT_OK, intent);


Now when you done with your second Activity then you call setResult() method, from onBackPress() or from any button click when your Activity2 will destroy then your Activity1's call back method onActivityResult() will call from there you can get your data from intent..

Hope it will help to you...:)

How to set cornerRadius for only top-left and top-right corner of a UIView?

And finally… there is CACornerMask in iOS11! With CACornerMask it can be done pretty easy:

let view = UIView()
view.clipsToBounds = true
view.layer.cornerRadius = 10
view.layer.maskedCorners = [.layerMaxXMinYCorner, .layerMinXMinYCorner] // Top right corner, Top left corner respectively

How to pass props to {this.props.children}

Cleaner way considering one or more children

   {, child => React.cloneElement(child, {...this.props}))}

Creating a new directory in C

I want to write a program that (...) creates the directory and a (...) file inside of it

because this is a very common question, here is the code to create multiple levels of directories and than call fopen. I'm using a gnu extension to print the error message with printf.

void rek_mkdir(char *path) {
    char *sep = strrchr(path, '/');
    if(sep != NULL) {
        *sep = 0;
        *sep = '/';
    if(mkdir(path, 0777) && errno != EEXIST)
        printf("error while trying to create '%s'\n%m\n", path); 

FILE *fopen_mkdir(char *path, char *mode) {
    char *sep = strrchr(path, '/');
    if(sep) { 
        char *path0 = strdup(path);
        path0[ sep - path ] = 0;
    return fopen(path,mode);

JavaScript: Create and save file

For latest browser, like Chrome, you can use the File API as in this tutorial:

window.requestFileSystem  = window.requestFileSystem || window.webkitRequestFileSystem;
window.requestFileSystem(window.PERSISTENT, 5*1024*1024 /*5MB*/, saveFile, errorHandler);

Add item to Listview control

The first column actually refers to Text Field:

  // Add the pet to our listview
    ListViewItem lvi = new ListViewItem();
    lvi.text = pet.Name;


Or you can use the Constructor

 ListViewItem lvi = new ListViewItem(pet.Name);

How do I force a favicon refresh?

I know this is a really old question but it is also one that is still relevant, though these days applies only to mozilla. (I have no idea what explorer does coz we don't code for non standard browsers).

Chrome is well behaved if one includes an icon tag in the header.

Although mozilla are well aware of the issue, as usual, they never fix the annoying small stuff. Even 6 years later.

So, there are two ways of forcing an icon refresh with firefox.

  1. Have all your clients uninstall firefox. Then re-install.

  2. Manually type just the domain in the url bar - do not use http or www just the domain (

This assumes of course that your ns records include resolution for the domain name only.

XPath test if node value is number

I've been dealing with 01 - which is a numeric.

string(number($v)) != string($v) makes the segregation

How do I make a JAR from a .java file?

This can be done without terminal, directly from IDE. Netbeans, for example.

  1. Create a separate project with packages (Create Project - Java - Java Class Library).
  2. Put your .java classes there.
  3. Build this project.
  4. Go to your project folder and find build and dist folders there.
  5. Find .jar file in your dist folder.
  6. Get your other project and add this .jar file to project libraries.
  7. You can now reference classes from this library and its methods directly from code, if import is automatically done for you.