Programs & Examples On #Smack

Smack is an XMPP (Jabber) client library written in Java for Android and Java SE. It provides a simple API allowing developers to write clients for XMPP services.

Error:Execution failed for task ':app:compileDebugKotlin'. > Compilation error. See log for more details

upgraded Android Studio from 3.2.1 to 3.3 and the problem disappeared

Gradle DSL method not found: 'runProguard'

enter image description hereIf you are using version 0.14.0 or higher of the gradle plugin, you should replace "runProguard" with "minifyEnabled" in your build.gradle files.

runProguard was renamed to minifyEnabled in version 0.14.0. For more info, See Android Build System

Delayed function calls

I've been looking for something like this myself - I came up with the following, although it does use a timer, it uses it only once for the initial delay, and doesn't require any Sleep calls ...

public void foo()
    System.Threading.Timer timer = null; 
    timer = new System.Threading.Timer((obj) =>
                null, 1000, System.Threading.Timeout.Infinite);

public void bar()
    // do stuff

(thanks to Fred Deschenes for the idea of disposing the timer within the callback)

Default string initialization: NULL or Empty?

Strings aren't value types, and never will be ;-)

Is there a “not in” operator in JavaScript for checking object properties?

It seems wrong to me to set up an if/else statement just to use the else portion...

Just negate your condition, and you'll get the else logic inside the if:

if (!(id in tutorTimes)) { ... }

String.strip() in Python

strip does nothing but, removes the the whitespace in your string. If you want to remove the extra whitepace from front and back of your string, you can use strip.

The example string which can illustrate that is this:

In [2]: x = "something \t like     \t this"
In [4]: x.split('\t')
Out[4]: ['something ', ' like     ', ' this']

See, even after splitting with \t there is extra whitespace in first and second items which can be removed using strip in your code.

How to execute a remote command over ssh with arguments?

Do it this way instead:

function mycommand {
    ssh [email protected] "cd testdir;./ \"$1\""

You still have to pass the whole command as a single string, yet in that single string you need to have $1 expanded before it is sent to ssh so you need to use "" for it.


Another proper way to do this actually is to use printf %q to properly quote the argument. This would make the argument safe to parse even if it has spaces, single quotes, double quotes, or any other character that may have a special meaning to the shell:

function mycommand {
    printf -v __ %q "$1"
    ssh [email protected] "cd testdir;./ $__"
  • When declaring a function with function, () is not necessary.
  • Don't comment back about it just because you're a POSIXist.

What's the foolproof way to tell which version(s) of .NET are installed on a production Windows Server?

OneTouch deployment will do all the detection and installation of pre-requisites. It's probably best to go with a pre-made solution than trying to roll your own. Trying to roll your own may lead to problems because whatever thing you key on may change with a hotfix or service pack. Likely Microsoft has some heuristic for determining what version is running.

how to fix groovy.lang.MissingMethodException: No signature of method:

This may also be because you might have given classname with all letters in lowercase something which groovy (know of version 2.5.0) does not support.

class name - User is accepted but user is not.

How to make the Facebook Like Box responsive?

The answer you're looking for as of June, 2013 can be found here:

It's accomplished using jQuery to rewrite the inner HTML of the parent container that holds the facebook widget.

Hope this helps!

Default Xmxsize in Java 8 (max heap size)

On my Ubuntu VM, with 1048 MB total RAM, java -XX:+PrintFlagsFinal -version | grep HeapSize printed : uintx MaxHeapSize := 266338304, which is approx 266MB and is 1/4th of my total RAM.

React Hook Warnings for async function in useEffect: useEffect function must return a cleanup function or nothing

When you use an async function like

async () => {
    try {
        const response = await fetch(`${subreddit}.json`);
        const json = await response.json();
        setPosts( =>;
    } catch (e) {

it returns a promise and useEffect doesn't expect the callback function to return Promise, rather it expects that nothing is returned or a function is returned.

As a workaround for the warning you can use a self invoking async function.

useEffect(() => {
    (async function() {
        try {
            const response = await fetch(
            const json = await response.json();
            setPosts( =>;
        } catch (e) {
}, []);

or to make it more cleaner you could define a function and then call it

useEffect(() => {
    async function fetchData() {
        try {
            const response = await fetch(
            const json = await response.json();
            setPosts( =>;
        } catch (e) {
}, []);

the second solution will make it easier to read and will help you write code to cancel previous requests if a new one is fired or save the latest request response in state

Working codesandbox


Each statement has a distinct use case. They are not interchangeable.

SELECT...INTO MyTable... creates a new MyTable where one did not exist before.

INSERT INTO MyTable...SELECT... is used when MyTable already exists.

Creating and playing a sound in swift

Couldn't you just import AVFoundation, select the audio player (var audioPlayer : AVAudioPlayer!), and play the sound? (let soundURL = Bundle.main.url(forResource: "sound", withExtension: "wav")

How to write super-fast file-streaming code in C#?

The fastest way to do file I/O from C# is to use the Windows ReadFile and WriteFile functions. I have written a C# class that encapsulates this capability as well as a benchmarking program that looks at differnet I/O methods, including BinaryReader and BinaryWriter. See my blog post at:

Can a local variable's memory be accessed outside its scope?

This behavior is undefined, as Alex pointed out--in fact, most compilers will warn against doing this, because it's an easy way to get crashes.

For an example of the kind of spooky behavior you are likely to get, try this sample:

int *a()
   int x = 5;
   return &x;

void b( int *c )
   int y = 29;
   *c = 123;
   cout << "y=" << y << endl;

int main()
   b( a() );
   return 0;

This prints out "y=123", but your results may vary (really!). Your pointer is clobbering other, unrelated local variables.

Capture screenshot of active window?

I suggest next solution for capturing any current active window (not only our C# application) or entire screen with cursor position determination relative to left-top corner of window or screen respectively:

public enum enmScreenCaptureMode

class ScreenCapturer
    private static extern IntPtr GetForegroundWindow();

    private static extern IntPtr GetWindowRect(IntPtr hWnd, ref Rect rect);

    private struct Rect
        public int Left;
        public int Top;
        public int Right;
        public int Bottom;

    public Bitmap Capture(enmScreenCaptureMode screenCaptureMode = enmScreenCaptureMode.Window)
        Rectangle bounds;

        if (screenCaptureMode == enmScreenCaptureMode.Screen)
            bounds = Screen.GetBounds(Point.Empty);
            CursorPosition = Cursor.Position;
            var foregroundWindowsHandle = GetForegroundWindow();
            var rect = new Rect();
            GetWindowRect(foregroundWindowsHandle, ref rect);
            bounds = new Rectangle(rect.Left, rect.Top, rect.Right - rect.Left, rect.Bottom - rect.Top);
            CursorPosition = new Point(Cursor.Position.X - rect.Left, Cursor.Position.Y - rect.Top);

        var result = new Bitmap(bounds.Width, bounds.Height);

        using (var g = Graphics.FromImage(result))
            g.CopyFromScreen(new Point(bounds.Left, bounds.Top), Point.Empty, bounds.Size);

        return result;

    public Point CursorPosition
        protected set;

How to move from one fragment to another fragment on click of an ImageView in Android?

inside your onClickListener.onClick, put

getFragmentManager().beginTransaction().replace(, new tasks()).commit();

In another word, in your mycontacts.class

public class mycontacts extends Fragment {

    public mycontacts() {

    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        final View v = super.getView(position, convertView, parent);
        ImageView purple = (ImageView) v.findViewById(;
        purple.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {
                // TODO Auto-generated method stub
                        .replace(, new tasks())
        return view;


now, remember is the container (FrameLayout or other layouts) for the activity that calls the fragment

Find value in an array

I'm guessing that you're trying to find if a certain value exists inside the array, and if that's the case, you can use Array#include?(value):

a = [1,2,3,4,5]
a.include?(3)   # => true
a.include?(9)   # => false

If you mean something else, check the Ruby Array API

T-sql - determine if value is integer

In his article Can I convert this string to an integer?, Itzik Ben-Gan provides a solution in pure T-SQL and another that uses the CLR.

Which solution should you choose?

Is the T-SQL or CLR Solution Better? The advantage of using the T-SQL solution is that you don’t need to go outside the domain of T-SQL programming. However, the CLR solution has two important advantages: It's simpler and faster. When I tested both solutions against a table that had 1,000,000 rows, the CLR solution took two seconds, rather than seven seconds (for the T-SQL solution), to run on my laptop. So the next time you need to check whether a given string can be converted to an integer, you can include the T-SQL or CLR solution that I provided in this article.

If you only want to maintain T-SQL, then use the pure T-SQL solution. If performance is more important than convenience, then use the CLR solution.

The pure T-SQL Solution is tricky. It combines the built-in ISNUMERIC function with pattern-matching and casting to check if the string represents an int.

SELECT keycol, string, ISNUMERIC(string) AS is_numeric,
    WHEN ISNUMERIC(string) = 0     THEN 0
    WHEN string LIKE '%[^-+ 0-9]%' THEN 0
    WHEN CAST(string AS NUMERIC(38, 0))
      NOT BETWEEN -2147483648. AND 2147483647. THEN 0
    ELSE 1
  END AS is_int
FROM dbo.T1;

The T-SQL part of the CLR solution is simpler. You call the fn_IsInt function just like you would call ISNUMERIC.

SELECT keycol, string, ISNUMERIC(string) AS is_numeric,
  dbo.fn_IsInt(string) AS is_int
FROM dbo.T1;

The C# part is simply a wrapper for the .NET's parsing function Int32.TryParse. This works because the SQL Server int and the .NET Int32 are both 32-bit signed integers.

using System;
using System.Data.SqlTypes;

public partial class UserDefinedFunctions
    public static SqlBoolean fn_IsInt(SqlString s)
        if (s.IsNull)
            return SqlBoolean.False;
            Int32 i = 0;
            return Int32.TryParse(s.Value, out i);

Please read Itzik's article for a full explanation of these code samples.

TortoiseSVN icons not showing up under Windows 7

A combination of solutions worked for me. I tried to kill and restart explorer.exe as suggested by @LeighRiffel. Did not work. I uninstalled dropbox because I rarely use it. Then, I tried the explorer thing again and it worked. Maybe you can reinstall dropbox after this and see if things are okay ? I don't care though.

Here are the steps: Run taskmgr.exe or task manager > processes tab > select explorer.exe > kill. Then click file option > new task > enter explorer.exe > ok.

In Python, what is the difference between ".append()" and "+= []"?

The rebinding behaviour mentioned in other answers does matter in certain circumstances:

>>> a = ([],[])
>>> a[0].append(1)
>>> a
([1], [])
>>> a[1] += [1]
Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment

That's because augmented assignment always rebinds, even if the object was mutated in-place. The rebinding here happens to be a[1] = *mutated list*, which doesn't work for tuples.

docker build with --build-arg with multiple arguments

If you want to use environment variable during build. Lets say setting username and password.

username= Ubuntu
password= swed24sw


FROM ubuntu:16.04
# Creates a new User
RUN useradd -ms /bin/bash $SMB_USER
# Enters the password twice.
RUN echo "$SMB_PASS\n$SMB_PASS" | smbpasswd -a $SMB_USER

Terminal Command

docker build --build-arg SMB_PASS=swed24sw --build-arg SMB_USER=Ubuntu . -t IMAGE_TAG

Get first element from a dictionary

Dictionary<string, Dictionary<string, string>> like = new Dictionary<string, Dictionary<string, string>>();
Dictionary<string, string> first = like.Values.First();

Searching for Text within Oracle Stored Procedures

I allways use UPPER(text) like UPPER('%blah%')

Should I use "camel case" or underscores in python?

PEP 8 advises the first form for readability. You can find it here.

Function names should be lowercase, with words separated by underscores as necessary to improve readability.

What is null in Java?

Short and precise answer which answers all your questions formally from JLS:

3.10.7. The Null Literal

The null type has one value, the null reference, represented by the null literal null, which is formed from ASCII characters.

A null literal is always of the null type.

Only a reference of type which is assigned to null is allocated. You don't assign any value (object) to the reference. Such allocation is specific to JVM how much reference will take and in which memory area it will be allocated.

How can one develop iPhone apps in Java?

I think Google Open Sources Java To Objective-C Translator will make it possiblöe to develop in Java for iOS

css overflow - only 1 line of text

the best code for UX and UI is

white-space: nowrap;
text-overflow: ellipsis;
overflow: hidden;
display: inherit;

SELECT INTO a table variable in T-SQL

First create a temp table :

Step 1:

create table #tblOm_Temp (

    Name varchar(100),
    Age Int ,
    RollNumber bigint

**Step 2: ** Insert Some value in Temp table .

insert into #tblom_temp values('Om Pandey',102,1347)

Step 3: Declare a table Variable to hold temp table data.

declare   @tblOm_Variable table(

    Name Varchar(100),
    Age int,
    RollNumber bigint

Step 4: select value from temp table and insert into table variable.

insert into @tblOm_Variable select * from #tblom_temp

Finally value is inserted from a temp table to Table variable

Step 5: Can Check inserted value in table variable.

select * from @tblOm_Variable

Round double value to 2 decimal places

You can use the below code to format it to two decimal places

NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];

[formatter setNumberStyle:NSNumberFormatterDecimalStyle];
[formatter setMaximumFractionDigits:2];
[formatter setRoundingMode: NSNumberFormatterRoundUp];

NSString *numberString = [formatter stringFromNumber:[NSNumber numberWithFloat:22.368511]];

NSLog(@"Result...%@",numberString);//Result 22.37

Swift 4:

let formatter = NumberFormatter()
formatter.numberStyle = .decimal
formatter.maximumFractionDigits = 2
formatter.roundingMode = .up

let str = String(describing: formatter.string(from: 12.2345)!)


How to set a cron job to run every 3 hours

Change Minute to be 0. That's it :)

Note: you can check your "crons" in


How to input matrix (2D list) in Python?

row=list(map(int,input().split())) #input no. of row and column
for i in range(0,row[0]):
    print('value of i: ',i)


2 3

value of i:0
1 2 4 5
[1, 2, 4, 5]
value of i:  1
2 4 5 6
[2, 4, 5, 6]
[[1, 2, 4, 5], [2, 4, 5, 6]]
[2, 3]

Note: this code in case of only control no. Of rows but we can enter any number of column we want i.e row[0]=2 so be careful. This is not the code where you can control no of columns.

use mysql SUM() in a WHERE clause

In general, a condition in the WHERE clause of an SQL query can reference only a single row. The context of a WHERE clause is evaluated before any order has been defined by an ORDER BY clause, and there is no implicit order to an RDBMS table.

You can use a derived table to join each row to the group of rows with a lesser id value, and produce the sum of each sum group. Then test where the sum meets your criterion.


INSERT INTO MyTable (id, cash) VALUES
  (1, 200), (2, 301), (3, 101), (4, 700);

  SELECT, SUM( AS cash_sum
  FROM MyTable t JOIN MyTable prev ON ( >
WHERE s.cash_sum >= 500


| id | cash_sum |
|  3 |      501 |

What is the JavaScript version of sleep()?

I got Promise is not a constructor using the top answer. If you import bluebird you can do this. Simplest solution imo.

import * as Promise from 'bluebird';

  await Promise.delay(5000)

'"SDL.h" no such file or directory found' when compiling

Having a similar case and I couldn't use StackAttacks solution as he's referring to SDL2 which is for the legacy code I'm using too new.

Fortunately our friends from askUbuntu had something similar:

Download SDL

tar xvf SDL-1.2.tar.gz
cd SDL-1.2
sudo make install

Decorators with parameters?

This is a template for a function decorator that does not require () if no parameters are to be given:

import functools

def decorator(x_or_func=None, *decorator_args, **decorator_kws):
    def _decorator(func):
        def wrapper(*args, **kws):
            if 'x_or_func' not in locals() \
                    or callable(x_or_func) \
                    or x_or_func is None:
                x = ...  # <-- default `x` value
                x = x_or_func
            return func(*args, **kws)

        return wrapper

    return _decorator(x_or_func) if callable(x_or_func) else _decorator

an example of this is given below:

def multiplying(factor_or_func=None):
    def _decorator(func):
        def wrapper(*args, **kwargs):
            if 'factor_or_func' not in locals() \
                    or callable(factor_or_func) \
                    or factor_or_func is None:
                factor = 1
                factor = factor_or_func
            return factor * func(*args, **kwargs)
        return wrapper
    return _decorator(factor_or_func) if callable(factor_or_func) else _decorator

def summing(x): return sum(x)

# 45

def summing(x): return sum(x)

# 45

def summing(x): return sum(x)

# 450

Create a CSS rule / class with jQuery at runtime

if you don' t want to assign a display:none to a css class, the right approach in to append to style, jQuery.Rule do the job.

I some cases you want to apply stiles before the append event of ajax content and fade content after append and this is it!

Unique device identification

You can use the fingerprintJS2 library, it helps a lot with calculating a browser fingerprint.

By the way, on Panopticlick you can see how unique this usually is.

.htaccess File Options -Indexes on Subdirectories

htaccess files affect the directory they are placed in and all sub-directories, that is an htaccess file located in your root directory ( would affect,, etc.

Laravel - Eloquent "Has", "With", "WhereHas" - What do they mean?


with() is for eager loading. That basically means, along the main model, Laravel will preload the relationship(s) you specify. This is especially helpful if you have a collection of models and you want to load a relation for all of them. Because with eager loading you run only one additional DB query instead of one for every model in the collection.


User > hasMany > Post

$users = User::with('posts')->get();
foreach($users as $user){
    $users->posts; // posts is already loaded and no additional DB query is run


has() is to filter the selecting model based on a relationship. So it acts very similarly to a normal WHERE condition. If you just use has('relation') that means you only want to get the models that have at least one related model in this relation.


User > hasMany > Post

$users = User::has('posts')->get();
// only users that have at least one post are contained in the collection


whereHas() works basically the same as has() but allows you to specify additional filters for the related model to check.


User > hasMany > Post

$users = User::whereHas('posts', function($q){
    $q->where('created_at', '>=', '2015-01-01 00:00:00');
// only users that have posts from 2015 on forward are returned

Using wire or reg with input or output in Verilog

seeing it in digital circuit domain

  1. A Wire will create a wire output which can only be assigned any input by using assign statement as assign statement creates a port/pin connection and wire can be joined to the port/pin
  2. A reg will create a register(D FLIP FLOP ) which gets or recieve inputs on basis of sensitivity list either it can be clock (rising or falling ) or combinational edge .

so it completely depends on your use whether you need to create a register and tick it according to sensitivity list or you want to create a port/pin assignment

Difference between Big-O and Little-O Notation

Big-O is to little-o as = is to <. Big-O is an inclusive upper bound, while little-o is a strict upper bound.

For example, the function f(n) = 3n is:

  • in O(n²), o(n²), and O(n)
  • not in O(lg n), o(lg n), or o(n)

Analogously, the number 1 is:

  • = 2, < 2, and = 1
  • not = 0, < 0, or < 1

Here's a table, showing the general idea:

Big o table

(Note: the table is a good guide but its limit definition should be in terms of the superior limit instead of the normal limit. For example, 3 + (n mod 2) oscillates between 3 and 4 forever. It's in O(1) despite not having a normal limit, because it still has a lim sup: 4.)

I recommend memorizing how the Big-O notation converts to asymptotic comparisons. The comparisons are easier to remember, but less flexible because you can't say things like nO(1) = P.

Add views in UIStackView programmatically

In my case the thing that was messing with I would expect was that I was missing this line:

stackView.translatesAutoresizingMaskIntoConstraints = false;

After that no need to set constraints to my arranged subviews whatsoever, the stackview is taking care of that.

Pandas DataFrame Groupby two columns and get counts

Followed by @Andy's answer, you can do following to solve your second question:

In [56]: df.groupby(['col5','col2']).size().reset_index().groupby('col2')[[0]].max()
A     3
B     2
C     1
D     3

convert pfx format to p12

.p12 and .pfx are both PKCS #12 files. Am I missing something?

Have you tried renaming the exported .pfx file to have a .p12 extension?

Iterate over object in Angular

try to use this pipe

import { Pipe, PipeTransform } from '@angular/core';

@Pipe({ name: 'values',  pure: false })
export class ValuesPipe implements PipeTransform {
  transform(value: any, args: any[] = null): any {
    return Object.keys(value).map(key => value[key]);

<div *ngFor="#value of object | values"> </div>

Trim spaces from end of a NSString

To remove whitespace from only the beginning and end of a string in Swift:

Swift 3

string.trimmingCharacters(in: .whitespacesAndNewlines)

Previous Swift Versions


Use grep --exclude/--include syntax to not grep through certain files

find and xargs are your friends. Use them to filter the file list rather than grep's --exclude

Try something like

find . -not -name '*.png' -o -type f -print | xargs grep -icl "foo="

The advantage of getting used to this, is that it is expandable to other use cases, for example to count the lines in all non-png files:

find . -not -name '*.png' -o -type f -print | xargs wc -l

To remove all non-png files:

find . -not -name '*.png' -o -type f -print | xargs rm


As pointed out in the comments, if some files may have spaces in their names, use -print0 and xargs -0 instead.

What is a elegant way in Ruby to tell if a variable is a Hash or an Array?

You can use instance_of?



SQL Joins Vs SQL Subqueries (Performance)?

I know this is an old post, but I think this is a very important topic, especially nowadays where we have 10M+ records and talk about terabytes of data.

I will also weight in with the following observations. I have about 45M records in my table ([data]), and about 300 records in my [cats] table. I have extensive indexing for all of the queries I am about to talk about.

Consider Example 1:

UPDATE d set category = c.categoryname
FROM [data] d
JOIN [cats] c on = d.catid

versus Example 2:

UPDATE d set category = (SELECT TOP(1) c.categoryname FROM [cats] c where = d.catid)
FROM [data] d

Example 1 took about 23 mins to run. Example 2 took around 5 mins.

So I would conclude that sub-query in this case is much faster. Of course keep in mind that I am using M.2 SSD drives capable of i/o @ 1GB/sec (thats bytes not bits), so my indexes are really fast too. So this may affect the speeds too in your circumstance

If its a one-off data cleansing, probably best to just leave it run and finish. I use TOP(10000) and see how long it takes and multiply by number of records before I hit the big query.

If you are optimizing production databases, I would strongly suggest pre-processing data, i.e. use triggers or job-broker to async update records, so that real-time access retrieves static data.

How to change the commit author for one specific commit?

You can change author of last commit using the command below.

git commit --amend --author="Author Name <[email protected]>"

However, if you want to change more than one commits author name, it's a bit tricky. You need to start an interactive rebase then mark commits as edit then amend them one by one and finish.

Start rebasing with git rebase -i. It will show you something like this.

Change the pick keyword to edit for the commits you want to change the author name.

Then close the editor. For the beginners, hit Escape then type :wq and hit Enter.

Then you will see your terminal like nothing happened. Actually you are in the middle of an interactive rebase. Now it's time to amend your commit's author name using the command above. It will open the editor again. Quit and continue rebase with git rebase --continue. Repeat the same for the commit count you want to edit. You can make sure that interactive rebase finished when you get the No rebase in progress? message.

Headers and client library minor version mismatch

I have this problems when use Percona/MySQL 5.6 and the php driver was compiled with 5.5 and php5-mysql is required for some apps, so I write a script to rebuild the drivers.

XmlSerializer: remove unnecessary xsi and xsd namespaces

I'm using:

public class Person
    public string FirstName { get; set; }
    public string LastName { get; set; }

class Program
    static void Main(string[] args)
        const string DEFAULT_NAMESPACE = "";
        var serializer = new XmlSerializer(typeof(Person), DEFAULT_NAMESPACE);
        var namespaces = new XmlSerializerNamespaces();
        namespaces.Add("", DEFAULT_NAMESPACE);

        using (var stream = new MemoryStream())
            var someone = new Person
                FirstName = "Donald",
                LastName = "Duck"
            serializer.Serialize(stream, someone, namespaces);
            stream.Position = 0;
            using (var reader = new StreamReader(stream))

To get the following XML:

<?xml version="1.0"?>
<Person xmlns="">

If you don't want the namespace, just set DEFAULT_NAMESPACE to "".

Easiest way to open a download window without navigating away from the page

Modifying the location of window might cause some issue especially when you have a persistent connection like websocket. So I always resort to good old iframe solution.


<input type="button" onclick="downloadButtonClicked()" value="Download"/>
<iframe style="display:none;" name="hiddenIframe" id="hiddenIframe"></iframe>


function downloadButtonClicked() {
    // Simulate a link click
    var url = 'your_download_url_here';
    var elem = document.createElement('a');
    elem.href = url; = 'hiddenIframe';;

Load jQuery with Javascript and use jQuery

From the DevTools console, you can run:

document.getElementsByTagName("head")[0].innerHTML += '<script type="text/javascript" src="//"><\/script>';

Check the available jQuery version at

To check whether it's loaded, see: Checking if jquery is loaded using Javascript.

How to change a single value in a NumPy array?

Is this what you are after? Just index the element and assign a new value.


array([[ 1,  2,  3,  4],
       [ 5,  6,  7,  8],
       [ 9, 150, 11, 12],
       [13, 14, 15, 16]])

Rails 4: how to use $(document).ready() with turbo-links

NOTE: See @SDP's answer for a clean, built-in solution

I fixed it as follows:

make sure you include application.js before the other app dependent js files get included by changing the include order as follows:

// in application.js - make sure `require_self` comes before `require_tree .`
//= require_self
//= require_tree .

Define a global function that handles the binding in application.js

// application.js
window.onLoad = function(callback) {
  // binds ready event and turbolink page:load event

Now you can bind stuff like:

// in coffee script:
onLoad ->
  $('a.clickable').click => 
    alert('link clicked!');

// equivalent in javascript:
onLoad(function() {
  $('a.clickable').click(function() {
    alert('link clicked');

anaconda/conda - install a specific package version

There is no version 1.3.0 for rope. 1.3.0 refers to the package cached-property. The highest available version of rope is 0.9.4.

You can install different versions with conda install package=version. But in this case there is only one version of rope so you don't need that.

The reason you see the cached-property in this listing is because it contains the string "rope": "cached-p rope erty"

py35_0 means that you need python version 3.5 for this specific version. If you only have python3.4 and the package is only for version 3.5 you cannot install it with conda.

I am not quite sure on the defaults either. It should be an indication that this package is inside the default conda channel.

Extract source code from .jar file

Steps to get sources of a jar file as a zip :

  1. Download JD-GUI from and save it at any location on your system.

  2. Drag and drop the jar or open .jar file for which you want the sources on the JD.

  3. Java Decompiler will open with all the package structure in a tree format.

  4. Click on File menu and select save jar sources. It will save the sources as a zip with the same name as the jar.


enter image description here

We can use Eclipse IDE for Java EE Developers as well for update/extract code if require.

From eclipse chose Import Jar and then select jar which you need. Follow instruction as per image below

enter image description here

enter image description here

How do I filter ForeignKey choices in a Django ModelForm?

ForeignKey is represented by django.forms.ModelChoiceField, which is a ChoiceField whose choices are a model QuerySet. See the reference for ModelChoiceField.

So, provide a QuerySet to the field's queryset attribute. Depends on how your form is built. If you build an explicit form, you'll have fields named directly.

form.rate.queryset = Rate.objects.filter(

If you take the default ModelForm object, form.fields["rate"].queryset = ...

This is done explicitly in the view. No hacking around.

WCF Service, the type provided as the service attribute values…could not be found

Right click on the .svc file in Solution Explorer and click View Markup

 <%@ ServiceHost Language="C#" Debug="true" 
     CodeBehind="GetHistoryInfo.svc.cs" %>

Update the service reference where you are referring to.

how to get docker-compose to use the latest image from repository

I spent half a day with this problem. The reason was that be sure to check where the volume was recorded.

volumes: - api-data:/src/patterns

But the fact is that in this place was the code that we changed. But when updating the docker, the code did not change.

Therefore, if you are checking someone else's code and for some reason you are not updating, check this.

And so in general this approach works:

docker-compose down

docker-compose build

docker-compose up -d

How to Specify Eclipse Proxy Authentication Credentials?

If you have still problems, try deactivating ("Clear") SOCKS

see: "I believe the reason for this is because it uses the SOCKS proxy instead of the HTTP proxy if SOCKS is configured."

Div Height in Percentage

It doesn't take the 50% of the whole page is because the "whole page" is only how tall your contents are. Change the enclosing html and body to 100% height and it will work.

html, body{
    height: 100%;
    height: 50%;

enter image description here

^ Your document is only 20px high. 50% of 20px is 10px, and it is not what you expected.

enter image description here

^ Now if you change the height of the document to the height of the whole page (150px), 50% of 150px is 75px, then it will work.

Calculate relative time in C#

In PHP, I do it this way:

function timesince($original) {
    // array of time period chunks
    $chunks = array(
        array(60 * 60 * 24 * 365 , 'year'),
        array(60 * 60 * 24 * 30 , 'month'),
        array(60 * 60 * 24 * 7, 'week'),
        array(60 * 60 * 24 , 'day'),
        array(60 * 60 , 'hour'),
        array(60 , 'minute'),

    $today = time(); /* Current unix time  */
    $since = $today - $original;

    if($since > 604800) {
    $print = date("M jS", $original);

    if($since > 31536000) {
        $print .= ", " . date("Y", $original);

    return $print;

// $j saves performing the count function each time around the loop
for ($i = 0, $j = count($chunks); $i < $j; $i++) {

    $seconds = $chunks[$i][0];
    $name = $chunks[$i][1];

    // finding the biggest chunk (if the chunk fits, break)
    if (($count = floor($since / $seconds)) != 0) {

$print = ($count == 1) ? '1 '.$name : "$count {$name}s";

return $print . " ago";

} ?>

Video format or MIME type is not supported

Firefox does not support the MPEG H.264 (mp4) format at this time, due to a philosophical disagreement with the closed-source nature of the format.

To play videos in all browsers without using plugins, you will need to host multiple copies of each video, in different formats. You will also need to use an alternate form of the video tag, as seen in the JSFiddle from @TimHayes above, reproduced below. Mozilla claims that only mp4 and WebM are necessary to ensure complete coverage of all major browsers, but you may wish to consult the Video Formats and Browser Support heading on W3C's HTML5 Video page to see which browser supports what formats.

Additionally, it's worth checking out the HTML5 Video page on Wikipedia for a basic comparison of the major file formats.

Below is the appropriate video tag (you will need to re-encode your video in WebM or OGG formats as well as your existing mp4):

<video id="video" controls='controls'>
  <source src="videos/clip.mp4" type="video/mp4"/>
  <source src="videos/clip.webm" type="video/webm"/>
  <source src="videos/clip.ogv" type="video/ogg"/>
  Your browser doesn't seem to support the video tag.

Updated Nov. 8, 2013

Network infrastructure giant Cisco has announced plans to open-source an implementation of the H.264 codec, removing the licensing fees that have so far proved a barrier to use by Mozilla. Without getting too deep into the politics of it (see following link for that) this will allow Firefox to support H.264 starting in "early 2014". However, as noted in that link, this still comes with a caveat. The H.264 codec is merely for video, and in the MPEG-4 container it is most commonly paired with the closed-source AAC audio codec. Because of this, playback of H.264 video will work, but audio will depend on whether the end-user has the AAC codec already present on their machine.

The long and short of this is that progress is being made, but you still can't avoid using multiple encodings without using a plugin.

How to get the path of running java program




You can also split it into it's elements easily

String classpath = System.getProperty("java.class.path");
String[] classpathEntries = classpath.split(File.pathSeparator);

Android Facebook style slide

I've had a play with this myself, and the best way I could find was to use a FrameLayout and lay a custom HorizontalScrollView (HSV) on top of the menu. Inside the HSV are your application Views, but there is a transparent View as the first child. This means, when the HSV has zero scroll offset, the menu will show through (and still be clickable surprisingly).

When the app starts up, we scroll the HSV to the offset of the first visible application View, and when we want to show the menu we scroll back to reveal the menu through the transparent View.

The code is here, and the bottom two buttons (called HorzScrollWithListMenu and HorzScrollWithImageMenu) in the Launch activity show the best menus I could come up with:

Android sliding menu demo

Screenshot from emulator (mid-scroll):

Screenshot from emulator (mid-scroll)

Screenshot from device (full-scroll). Note my icon is not as wide as the Facebook menu icon, so the menu view and 'app' view are not aligned.

Screenshot from device (full-scroll)

Get HTML5 localStorage keys

For those mentioning using Object.keys(localStorage)... don't because it won't work in Firefox (ironically because Firefox is faithful to the spec). Consider this:

localStorage.setItem("key", "value1")
localStorage.setItem("key2", "value2")
localStorage.setItem("getItem", "value3")
localStorage.setItem("setItem", "value4")

Because key, getItem and setItem are prototypal methods Object.keys(localStorage) will only return ["key2"].

You are best to do something like this:

let t = [];
for (let i = 0; i < localStorage.length; i++) {

What's the best way to parse command line arguments?

I prefer optparse to getopt. It's very declarative: you tell it the names of the options and the effects they should have (e.g., setting a boolean field), and it hands you back a dictionary populated according to your specifications.

How do you display a Toast from a background thread on Android?

You can do it by calling an Activity's runOnUiThread method from your thread:

activity.runOnUiThread(new Runnable() {
    public void run() {
        Toast.makeText(activity, "Hello", Toast.LENGTH_SHORT).show();

Error: [ng:areq] from angular controller

I have made a stupid mistake and wasted lot of time so adding this answer over here so that it helps someone

I was incorrectly adding the $scope variable(dependency)(was adding it without single quotes)

for example what i was doing was something like this


where the desired syntax is like this


Stop handler.postDelayed()

You can use:

 Handler handler = new Handler()
 handler.postDelayed(new Runnable())

Or you can use:



public final void removeCallbacksAndMessages (Object token)

Added in API level 1 Remove any pending posts of callbacks and sent messages whose obj is token. If token is null, all callbacks and messages will be removed.

Or you could also do like the following:

Handler handler =  new Handler()
Runnable myRunnable = new Runnable() {
public void run() {
    // do something




public final void removeCallbacks (Runnable r)

Added in API level 1 Remove any pending posts of Runnable r that are in the message queue.

public final void removeCallbacks (Runnable r, Object token)


Change this:

public void onClick(View v) {
    Handler handler =  new Handler();
    Runnable myRunnable = new Runnable() {


public void onClick(View v) {
    handler = new Handler();
    myRunnable = new Runnable() { /* ... */}

Because you have the below. Declared before onCreate but you re-declared and then initialized it in onClick leading to a NPE.

Handler handler; // declared before onCreate
Runnable myRunnable;

How To Include CSS and jQuery in my WordPress plugin?

Accepted answer is incomplete. You should use the right hook: wp_enqueue_scripts


    function add_my_css_and_my_js_files(){
        wp_enqueue_script('your-script-name', $this->urlpath  . '/your-script-filename.js', array('jquery'), '1.2.3', true);
        wp_enqueue_style( 'your-stylesheet-name', plugins_url('/css/new-style.css', __FILE__), false, '1.0.0', 'all');
    add_action('wp_enqueue_scripts', "add_my_css_and_my_js_files");

How do I select and store columns greater than a number in pandas?

Sample DF:

In [79]: df = pd.DataFrame(np.random.randint(5, 15, (10, 3)), columns=list('abc'))

In [80]: df
    a   b   c
0   6  11  11
1  14   7   8
2  13   5  11
3  13   7  11
4  13   5   9
5   5  11   9
6   9   8   6
7   5  11  10
8   8  10  14
9   7  14  13

present only those rows where b > 10

In [81]: df[df.b > 10]
   a   b   c
0  6  11  11
5  5  11   9
7  5  11  10
9  7  14  13

Minimums (for all columns) for the rows satisfying b > 10 condition

In [82]: df[df.b > 10].min()
a     5
b    11
c     9
dtype: int32

Minimum (for the b column) for the rows satisfying b > 10 condition

In [84]: df.loc[df.b > 10, 'b'].min()
Out[84]: 11

UPDATE: starting from Pandas 0.20.1 the .ix indexer is deprecated, in favor of the more strict .iloc and .loc indexers.

SSL: error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch

SL_CTX_use_PrivateKey("/etc/nginx/ssl/file") failed (SSL: error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch)

This error can happen, when the certificate private key (ssl_certificate_key, e.g. .key or .pem file) does not match the public certificate file (ssl_certificate) in your Nginx configuration (check nginx.conf or in sites-enabled/). Make sure both files are matching.

Check Nginx error logs for further details (e.g. /var/log/nginx/error.log).

Fade In Fade Out Android Animation in Java

You can also use animationListener, something like this:

fadeIn.setAnimationListener(new AnimationListener() {
    public void onAnimationEnd(Animation animation) {

Excel VBA - Delete empty rows

How about

sub foo()
  dim r As Range, rows As Long, i As Long
  Set r = ActiveSheet.Range("A1:Z50")
  rows = r.rows.Count
  For i = rows To 1 Step (-1)
    If WorksheetFunction.CountA(r.rows(i)) = 0 Then r.rows(i).Delete
End Sub

Try this

Option Explicit

Sub Sample()
    Dim i As Long
    Dim DelRange As Range

    On Error GoTo Whoa

    Application.ScreenUpdating = False

    For i = 1 To 50
        If Application.WorksheetFunction.CountA(Range("A" & i & ":" & "Z" & i)) = 0 Then
            If DelRange Is Nothing Then
                Set DelRange = Range("A" & i & ":" & "Z" & i)
                Set DelRange = Union(DelRange, Range("A" & i & ":" & "Z" & i))
            End If
        End If
    Next i

    If Not DelRange Is Nothing Then DelRange.Delete shift:=xlUp
    Application.ScreenUpdating = True

    Exit Sub
    MsgBox Err.Description
    Resume LetsContinue
End Sub

IF you want to delete the entire row then use this code

Option Explicit

Sub Sample()
    Dim i As Long
    Dim DelRange As Range

    On Error GoTo Whoa

    Application.ScreenUpdating = False

    For i = 1 To 50
        If Application.WorksheetFunction.CountA(Range("A" & i & ":" & "Z" & i)) = 0 Then
            If DelRange Is Nothing Then
                Set DelRange = Rows(i)
                Set DelRange = Union(DelRange, Rows(i))
            End If
        End If
    Next i

    If Not DelRange Is Nothing Then DelRange.Delete shift:=xlUp
    Application.ScreenUpdating = True

    Exit Sub
    MsgBox Err.Description
    Resume LetsContinue
End Sub

How to save a data.frame in R?

Let us say you have a data frame you created and named "Data_output", you can simply export it to same directory by using the following syntax.

write.csv(Data_output, "output.csv", row.names = F, quote = F)

credit to Peter and Ilja, UMCG, the Netherlands

Android Studio suddenly cannot resolve symbols

There is a far easier solution built into Android Studio, and it usually works for me without needing any brute force solution mentioned in other answers - so you should try this first: enter image description here

click on the "gradle" symbol on the right side of Android Studio, and then on the "Refresh all Gradle projects" tool.

In Python, how do I index a list with another list?

A functional approach:

a = [1,"A", 34, -123, "Hello", 12]
b = [0, 2, 5]

from operator import itemgetter

[1, 34, 12]

hadoop No FileSystem for scheme: file

thanks david_p,scala

conf.set("fs.hdfs.impl", classOf[org.apache.hadoop.hdfs.DistributedFileSystem].getName);
conf.set("fs.file.impl", classOf[org.apache.hadoop.fs.LocalFileSystem].getName);



Remove '\' char from string c#

to remove all '\' from a string, simply do the following:

myString = myString.Replace("\\", "");

Python sys.argv lists and indexes

So if I wanted to return a first name and last name like: Hello Fred Gerbig I would use the code below, this code works but is it actually the most correct way to do it?

import sys
def main():
  if len(sys.argv) >= 2:
    fname = sys.argv[1]
    lname = sys.argv[2]
    name = 'World'
  print 'Hello', fname, lname
if __name__ == '__main__':

Edit: Found that the above code works with 2 arguments but crashes with 1. Tried to set len to 3 but that did nothing, still crashes (re-read the other answers and now understand why the 3 did nothing). How do I bypass the arguments if only one is entered? Or how would error checking look that returned "You must enter 2 arguments"?

Edit 2: Got it figured out:

import sys
def main():
  if len(sys.argv) >= 2:
    name = sys.argv[1] + " " + sys.argv[2]
    name = 'World'
  print 'Hello', name
if __name__ == '__main__':

What are the complexity guarantees of the standard containers?

I found the nice resource Standard C++ Containers. Probably this is what you all looking for.



vector<T> v;              Make an empty vector.                                     O(1)
vector<T> v(n);           Make a vector with N elements.                            O(n)
vector<T> v(n, value);    Make a vector with N elements, initialized to value.      O(n)
vector<T> v(begin, end);  Make a vector and copy the elements from begin to end.    O(n)


v[i]          Return (or set) the I'th element.                        O(1)       Return (or set) the I'th element, with bounds checking.  O(1)
v.size()      Return current number of elements.                       O(1)
v.empty()     Return true if vector is empty.                          O(1)
v.begin()     Return random access iterator to start.                  O(1)
v.end()       Return random access iterator to end.                    O(1)
v.front()     Return the first element.                                O(1)
v.back()      Return the last element.                                 O(1)
v.capacity()  Return maximum number of elements.                       O(1)


v.push_back(value)         Add value to end.                                                O(1) (amortized)
v.insert(iterator, value)  Insert value at the position indexed by iterator.                O(n)
v.pop_back()               Remove value from end.                                           O(1)
v.assign(begin, end)       Clear the container and copy in the elements from begin to end.  O(n)
v.erase(iterator)          Erase value indexed by iterator.                                 O(n)
v.erase(begin, end)        Erase the elements from begin to end.                            O(n)

For other containers, refer to the page.

How do I write output in same place on the console?

For Python 3xx:

import time
for i in range(10):
    print ("\r Loading... {}".format(i)+str(i), end="")

Select multiple images from android gallery

A lot of these answers have similarities but are all missing the most important part which is in onActivityResult, check if data.getClipData is null before checking data.getData

The code to call the file chooser:

Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
intent.setType("image/*"); //allows any image file type. Change * to specific extension to limit it
//**The following line is the important one!
intent.putExtra(Intent.EXTRA_ALLOW_MULTIPLE, true);
startActivityForResult(Intent.createChooser(intent, "Select Picture"), SELECT_PICTURES); //SELECT_PICTURES is simply a global int used to check the calling intent in onActivityResult

The code to get all of the images selected:

public void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if(requestCode == SELECT_PICTURES) {
        if(resultCode == Activity.RESULT_OK) {
            if(data.getClipData() != null) {
                int count = data.getClipData().getItemCount(); //evaluate the count before the for loop --- otherwise, the count is evaluated every loop.
                for(int i = 0; i < count; i++)  
                    Uri imageUri = data.getClipData().getItemAt(i).getUri();
                    //do something with the image (save it to some directory or whatever you need to do with it here) 
            } else if(data.getData() != null) {
                String imagePath = data.getData().getPath();
                //do something with the image (save it to some directory or whatever you need to do with it here)

Note that Android's chooser has Photos and Gallery available on some devices. Photos allows multiple images to be selected. Gallery allows just one at a time.

How can I download a file from a URL and save it in Rails?

I think this is the clearest way:

require 'open-uri'

File.write 'image.png', open('').read

Gaussian fit for Python

After losing hours trying to find my error, the problem is your formula:

sigma = sum(y*(x-mean)**2)/n

This previous formula is wrong, the correct formula is the square root of this!;


Hope this helps

html text input onchange event

Use the oninput event

<input type="text" oninput="myFunction();" />

How do I tell if an object is a Promise?

Update: This is no longer the best answer. Please vote up my other answer instead.

obj instanceof Promise

should do it. Note that this may only work reliably with native es6 promises.

If you're using a shim, a promise library or anything else pretending to be promise-like, then it may be more appropriate to test for a "thenable" (anything with a .then method), as shown in other answers here.

Java replace issues with ' (apostrophe/single quote) and \ (backslash) together

Example :

String teste = " 'Bauru '";

teste = teste.replaceAll("  '  ","");

SQL Stored Procedure set variables using SELECT

One advantage your current approach does have is that it will raise an error if multiple rows are returned by the predicate. To reproduce that you can use.

SELECT @currentTerm = currentterm,
       @termID = termid,
       @endDate = enddate
FROM   table1
WHERE  iscurrent = 1

IF( @@ROWCOUNT <> 1 )
      RAISERROR ('Unexpected number of matching rows',


Function pointer as a member of a C struct

You can use also "void*" (void pointer) to send an address to the function.

typedef struct pstring_t {
    char * chars;
} PString;

int length(void* self) {
    return strlen(((PString*)self)->chars);

PString initializeString() {
    PString str;
    str.length = &length;
    return str;

int main()
    PString p = initializeString();

    p.chars = "Hello";

    printf("Length: %i\n", p.length(&p));

    return 0;


Length: 5

javascript function wait until another function to finish

Following answer can help in this and other similar situations like synchronous AJAX call -

Working example

  console.log('Finally, I can execute!!!');
  console.log('This is error message.');

function waitForMe(){
    // Returns promise
    console.log('Inside waitForMe');
    return new Promise(function(resolve, reject){
        if(true){ // Try changing to 'false'
                console.log('waitForMe\'s function succeeded');
            }, 2500);
                console.log('waitForMe\'s else block failed');
            }, 2500);

jQuery SVG vs. Raphael

For posterity, I'd like to note that I ended up choosing Raphael, because of the clean API and "free" IE support, and also because the active development looks promising (event support was just added in 0.7, for instance). However, I'll leave the question unanswered, and I'd still be interested to hear about others' experiences using Javascript + SVG libraries.

jQuery - Appending a div to body, the body is the object?

$('</div>').attr('id', 'holdy').appendTo('body');

SQL Server® 2016, 2017 and 2019 Express full download

Once you start the web installer there's an option to download media, that being the full installation package. There's even download options for what kind of package to download.

Show ImageView programmatically

If you add to RelativeLayout, don't forget to set imageView's position. For instance:

RelativeLayout.LayoutParams lp = new RelativeLayout.LayoutParams(200, 200);
lp.addRule(RelativeLayout.CENTER_IN_PARENT); // A position in layout.
ImageView imageView = new ImageView(this); // initialize ImageView
// imageView.setScaleType(ImageView.ScaleType.FIT_CENTER);
RelativeLayout layout = (RelativeLayout) findViewById(;

Differences between and websockets

Even if modern browsers support WebSockets now, I think there is no need to throw SocketIO away and it still has its place in any nowadays project. It's easy to understand, and personally, I learned how WebSockets work thanks to SocketIO.

As said in this topic, there's a plenty of integration libraries for Angular, React, etc. and definition types for TypeScript and other programming languages.

The other point I would add to the differences between and WebSockets is that clustering with is not a big deal. offers Adapters that can be used to link it with Redis to enhance scalability. You have ioredis and for example.

Yes I know, SocketCluster exists, but that's off-topic.

What does the colon (:) operator do?

In your specific case,

String cardString = "";
for (PlayingCard c : this.list)  // <--
    cardString = cardString + c + "\n";

this.list is a collection (list, set, or array), and that code assigns c to each element of the collection.

So, if this.list were a collection {"2S", "3H", "4S"} then the cardString on the end would be this string:


Restarting cron after changing crontab file?

On CentOS (my version is 6.5) when editing crontab you must close the editor to reflect your changes in CRON.

crontab -e

After that command You can see that new entry appears in /var/log/cron

Sep 24 10:44:26 ***** crontab[17216]: (*****) BEGIN EDIT (*****)

But only saving crontab editor after making some changes does not work. You must leave the editor to reflect changes in cron. After exiting new entry appears in the log:

Sep 24 10:47:58 ***** crontab[17216]: (*****) END EDIT (*****)

From this point changes you made are visible to CRON.

Passing parameter via url to sql server reporting service

Try changing "Reports" to "ReportServer" in your url

Java: Multiple class declarations in one file

1.Is there a tidy name for this technique (analogous to inner, nested, anonymous)?

Multi-class single-file demo.

2.The JLS says the system may enforce the restriction that these secondary classes can't be referred to by code in other compilation units of the package, e.g., they can't be treated as package-private. Is that really something that changes between Java implementations?

I'm not aware of any which don't have that restriction - all the file based compilers won't allow you to refer to source code classes in files which are not named the same as the class name. ( if you compile a multi-class file, and put the classes on the class path, then any compiler will find them )

How to output (to a log) a multi-level array in a format that is human-readable?

You should be able to use a var_dump() within a pre tag. Otherwise you could look into using a library like dump_r.php:

My solution is incorrect. OP was looking for a solution formatted with spaces to store in a log file.

A solution might be to use output buffering with var_dump, then str_replace() all the tabs with spaces to format it in the log file.

How to format date string in java?

If you are looking for a solution to your particular case, it would be:

Date date = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'").parse("2012-05-20T09:00:00.000Z");
String formattedDate = new SimpleDateFormat("dd/MM/yyyy, Ka").format(date);

Flushing footer to bottom of the page, twitter bootstrap

Here's a solution for the newest version of Bootstrap (4.3 at time of writing) using Flexbox.


<div class="wrapper">
  <div class="content">
    <p>Content goes here</p>
<footer class="footer"></footer>


html, body {
  height: 100%;

body {
  display: flex;
  flex-direction: column;

.wrapper {
  flex-grow: 1;

And a codepen example:

Bootstrap navbar Active State not working

For bootstrap mobile menu un-collapse after clicking a item you can use this

$("ul.nav.navbar-nav li a").click(function() {    


Load HTML file into WebView

The easiest way would probably be to put your web resources into the assets folder then call:


For Complete Communication between Java and Webview See This

Update: The assets folder is usually the following folder: <project>/src/main/assets This can be changed in the asset folder configuration setting in your <app>.iml file as:

<option name=”ASSETS_FOLDER_RELATIVE_PATH” value=”/src/main/assets” /> See Article Where to place the assets folder in Android Studio

Animated GIF in IE stopping

Here's what I did. All you have to to is to break up your GIF to say 10 images (in this case i started with 01.gif and ended with 10.gif) and specify the directory where you keep them.


<div id="tester"></div>


function pad2(number) {   
    return (number < 10 ? '0' : '') + number 
    dirURL = 'path/to/your/images/folder',
    ajaxLoader = document.createElement('img');
ajaxLoader.className = 'ajax-image-loader';
function set(i) {
    if (i > 10) i = 1;    
    img.src = dirURL + pad2(i) + '.gif';
    setTimeout(function() {
    }, 100);    

This method works with IE7, IE8 and IE9 (althought for IE9 you could use spin.js). NOTE: I have not tested this in IE6 since I have no machine running a browser from the 60s, although the method is so simple it probably works even in IE6 and lower.

Perform curl request in javascript?

You can use JavaScripts Fetch API (available in your browser) to make network requests.

If using node, you will need to install the node-fetch package.

const url = "";

const options = {
  headers: {
    Authorization: "Bearer 6Q************"

fetch(url, options)
  .then( res => res.json() )
  .then( data => console.log(data) );

Javascript: 'window' is not defined

Trying to access an undefined variable will throw you a ReferenceError.

A solution to this is to use typeof:

if (typeof window === "undefined") {
  console.log("Oops, `window` is not defined")

or a try catch:

try { window } catch (err) {
  console.log("Oops, `window` is not defined")

While typeof window is probably the cleanest of the two, the try catch can still be useful in some cases.

Can I position an element fixed relative to parent?

I know this is super old but after not finding the (pure CSS) answer I was looking for I came up with this solution (partially abstracted from and thought it might help others looking to do the same thing.

If you combine @DuckMaestro's answers you can position an element fixed relative to a parent (actually grandparent). Use position: absolute; to position an element inside a parent with position: relative; and then position: fixed; on an element inside the absolute positioned element like so:


<div class="relative">
  <div class="absolute">
    <a class="fixed-feedback">This element will be fixed</a>


.relative {
  margin: 0 auto;
  position: relative;
  width: 300px;

.absolute {
  position: absolute;
  right: 0;
  top: 0;
  width: 50px;

.fixed-feedback {
  position: fixed;
  top: 120px;
  width: 50px;


Like @JonAdams said, the definition of position: fixed requires the element to be positioned relative to the viewport but you can get around the horizontal aspect of that using this solution.

Note: This is different than just setting a right or left value on the fixed element because that would cause it to move horizontally when a window is resized.

Create a user with all privileges in Oracle

My issue was, i am unable to create a view with my "scott" user in oracle 11g edition. So here is my solution for this

Error in my case

SQL>create view v1 as select * from books where id=10;

insufficient privileges.


1)open your cmd and change your directory to where you install your oracle database. in my case i was downloaded in E drive so my location is E:\app\B_Amar\product\11.2.0\dbhome_1\BIN> after reaching in the position you have to type sqlplus sys as sysdba

E:\app\B_Amar\product\11.2.0\dbhome_1\BIN>sqlplus sys as sysdba

2) Enter password: here you have to type that password that you give at the time of installation of oracle software.

3) Here in this step if you want create a new user then you can create otherwise give all the privileges to existing user.

for creating new user

SQL> create user abc identified by xyz;

here abc is user and xyz is password.

giving all the privileges to abc user

SQL> grant all privileges to abc;

 grant succeeded. 

if you are seen this message then all the privileges are giving to the abc user.

4) Now exit from cmd, go to your SQL PLUS and connect to the user i.e enter your username & password.Now you can happily create view.

In My case

in cmd E:\app\B_Amar\product\11.2.0\dbhome_1\BIN>sqlplus sys as sysdba

SQL> grant all privileges to SCOTT;

grant succeeded.

Now I can create views.

size of struct in C

The compiler may add padding for alignment requirements. Note that this applies not only to padding between the fields of a struct, but also may apply to the end of the struct (so that arrays of the structure type will have each element properly aligned).

For example:

struct foo_t {
    int x;
    char c;

Even though the c field doesn't need padding, the struct will generally have a sizeof(struct foo_t) == 8 (on a 32-bit system - rather a system with a 32-bit int type) because there will need to be 3 bytes of padding after the c field.

Note that the padding might not be required by the system (like x86 or Cortex M3) but compilers might still add it for performance reasons.

How to write specific CSS for mozilla, chrome and IE

Since you also have PHP in the tag, I'm going to suggest some server side options.

The easiest solution is the one most people suggest here. The problem I generally have with this, is that it can causes your CSS files or <style> tags to be up to 20 times bigger than your html documents and can cause browser slowdowns for parsing and processing tags that it can't understand -moz-border-radius vs -webkit-border-radius

The second best solution(i've found) is to have php output your actual css file i.e.

<link rel="stylesheet" type="text/css" href="mycss.php">


header("Content-Type: text/css");
if( preg_match("/chrome/", $_SERVER['HTTP_USER_AGENT']) ) {
  // output chrome specific css style
} else {
  // output default css style

This allows you to create smaller easier to process files for the browser.

The best method I've found, is specific to Apache though. The method is to use mod_rewrite or mod_perl's PerlMapToStorageHandler to remap the URL to a file on the system based on the rendering engine.

say your website is and it points to /srv/www/html. For chrome, if you ask for main.css, instead of loading /srv/www/html/main.css it checks to see if there is a /srv/www/html/main.webkit.css and if it exists, it dump that, else it'll output the main.css. For IE, it tries main.trident.css, for firefox it tries main.gecko.css. Like above, it allows me to create smaller, more targeted, css files, but it also allows me to use caching better, as the browser will attempt to redownload the file, and the web server will present the browser with proper 304's to tell it, you don't need to redownload it. It also allows my web developers a bit more freedom without for them having to write backend code to target platforms. I also have .js files being redirected to javascript engines as well, for main.js, in chrome it tries main.v8.js, in safari, main.nitro.js, in firefox, main.gecko.js. This allows for outputting of specific javascript that will be faster(less browser testing code/feature testing). Granted the developers don't have to target specific and can write a main.js and not make main.<js engine>.js and it'll load that normally. i.e. having a main.js and a main.jscript.js file means that IE gets the jscript one, and everyone else gets the default js, same with the css files.

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

In Java all the variables you declare are actually "references" to the objects (or primitives) and not the objects themselves.

When you attempt to execute one object method, the reference asks the living object to execute that method. But if the reference is referencing NULL (nothing, zero, void, nada) then there is no way the method gets executed. Then the runtime let you know this by throwing a NullPointerException.

Your reference is "pointing" to null, thus "Null -> Pointer".

The object lives in the VM memory space and the only way to access it is using this references. Take this example:

public class Some {
    private int id;
    public int getId(){
    public setId( int newId ) { = newId;

And on another place in your code:

Some reference = new Some();    // Point to a new object of type Some()
Some otherReference = null;     // Initiallly this points to NULL

reference.setId( 1 );           // Execute setId method, now private var id is 1

System.out.println( reference.getId() ); // Prints 1 to the console

otherReference = reference      // Now they both point to the only object.

reference = null;               // "reference" now point to null.

// But "otherReference" still point to the "real" object so this print 1 too...
System.out.println( otherReference.getId() );

// Guess what will happen
System.out.println( reference.getId() ); // :S Throws NullPointerException because "reference" is pointing to NULL remember...

This an important thing to know - when there are no more references to an object (in the example above when reference and otherReference both point to null) then the object is "unreachable". There is no way we can work with it, so this object is ready to be garbage collected, and at some point, the VM will free the memory used by this object and will allocate another.

Call one constructor from another

Yeah, you can call other method before of the call base or this!

public class MyException : Exception
    public MyException(int number) : base(ConvertToString(number)) 

    private static string ConvertToString(int number) 
      return number.toString()


What does "Changes not staged for commit" mean

when you change a file which is already in the repository, you have to git add it again if you want it to be staged.

This allows you to commit only a subset of the changes you made since the last commit. For example, let's say you have file a, file b and file c. You modify file a and file b but the changes are very different in nature and you don't want all of them to be in one single commit. You issue

git add a
git commit a -m "bugfix, in a"
git add b
git commit b -m "new feature, in b"

As a side note, if you want to commit everything you can just type

git commit -a

Hope it helps.

Could not reserve enough space for object heap to start JVM

I had the same problem when using a 32 bit version of java in a 64 bit environment. When using 64 java in a 64 OS it was ok.

Sort Pandas Dataframe by Date

The data containing the date column can be read by using the below code:

data = pd.csv(file_path,parse_dates=[date_column])

Once the data is read by using the above line of code, the column containing the information about the date can be accessed using pd.date_time() like:

pd.date_time(data[date_column], format = '%d/%m/%y')

to change the format of date as per the requirement.

Hadoop cluster setup - Connection refused

Hi Edit your conf/core-site.xml and change localhost to Use the conf below. That should work.


How to remove underline from a link in HTML?

This will remove all underlines from all links:

a {text-decoration: none; }

If you have specific links that you want to apply this to, give them a class name, like nounderline and do this:

a.nounderline {text-decoration: none; }

That will apply only to those links and leave all others unaffected.

This code belongs in the <head> of your document or in a stylesheet:

    <style type="text/css">
        a.nounderline {text-decoration: none; }

And in the body:

<a href="#" class="nounderline">Link</a>

On logout, clear Activity history stack, preventing "back" button from opening logged-in-only Activities

This worked for me:

     // After logout redirect user to Loing Activity
    Intent i = new Intent(_context, MainActivity.class);
    // Closing all the Activities

    // Add new Flag to start new Activity

    // Staring Login Activity

Validate Dynamically Added Input fields

In case you have a form you can add a class name as such:

<form id="my-form">
  <input class="js-input" type="text" name="samplename" />
  <input class="js-input" type="text" name="samplename" />
  <input class="submit" type="submit" value="Submit" />

you can then use the addClassRules method of validator to add your rules like this and this will apply to all the dynamically added inputs:

$(document).ready(function() {
  $.validator.addClassRules('js-input', {
    required: true,
  //validate the form

Convert Json string to Json object in Swift 4

Using JSONSerialization always felt unSwifty and unwieldy, but it is even more so with the arrival of Codable in Swift 4. If you wield a [String:Any] in front of a simple struct it will ... hurt. Check out this in a Playground:

import Cocoa

let data = "[{\"form_id\":3465,\"canonical_name\":\"df_SAWERQ\",\"form_name\":\"Activity 4 with Images\",\"form_desc\":null}]".data(using: .utf8)!

struct Form: Codable {
    let id: Int
    let name: String
    let description: String?

    private enum CodingKeys: String, CodingKey {
        case id = "form_id"
        case name = "form_name"
        case description = "form_desc"

do {
    let f = try JSONDecoder().decode([Form].self, from: data)
} catch {

With minimal effort handling this will feel a whole lot more comfortable. And you are given a lot more information if your JSON does not parse properly.

Auto refresh page every 30 seconds

If you want refresh the page you could use like this, but refreshing the page is usually not the best method, it better to try just update the content that you need to be updated.


<script language="javascript">
}, 30000);

How large should my recv buffer be when calling recv in the socket library

For streaming protocols such as TCP, you can pretty much set your buffer to any size. That said, common values that are powers of 2 such as 4096 or 8192 are recommended.

If there is more data then what your buffer, it will simply be saved in the kernel for your next call to recv.

Yes, you can keep growing your buffer. You can do a recv into the middle of the buffer starting at offset idx, you would do:

recv(socket, recv_buffer + idx, recv_buffer_size - idx, 0);

Rename Files and Directories (Add Prefix)

Thanks to Peter van der Heijden, here's one that'll work for filenames with spaces in them:

for f in * ; do mv -- "$f" "PRE_$f" ; done

("--" is needed to succeed with files that begin with dashes, whose names would otherwise be interpreted as switches for the mv command)

Convert double to float in Java

Use dataType casting. For example:

// converting from double to float:
double someValue;
// cast someValue to float!
float newValue = (float)someValue;



Integers are whole numbers, e.g. 10, 400, or -5.

Floating point numbers (floats) have decimal points and decimal places, for example 12.5, and 56.7786543.

Doubles are a specific type of floating point number that have greater precision than standard floating point numbers (meaning that they are accurate to a greater number of decimal places).

How can I uninstall an application using PowerShell?

For Most of my programs the scripts in this Post did the job. But I had to face a legacy program that I couldn't remove using msiexec.exe or Win32_Product class. (from some reason I got exit 0 but the program was still there)

My solution was to use Win32_Process class:

with the help from nickdnk this command is to get the uninstall exe file path:


[array]$unInstallPathReg= gci "HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall" | foreach { gp $_.PSPath } | ? { $_ -match $programName } | select UninstallString


 [array]$unInstallPathReg= gci "HKLM:\SOFTWARE\Wow6432Node\Microsoft\Windows\CurrentVersion\Uninstall" | foreach { gp $_.PSPath } | ? { $_ -match $programName } | select UninstallString

you will have to clean the the result string:

$uninstallPath = $unInstallPathReg[0].UninstallString
$uninstallPath = $uninstallPath -Replace "msiexec.exe","" -Replace "/I","" -Replace "/X",""
$uninstallPath = $uninstallPath .Trim()

now when you have the relevant program uninstall exe file path you can use this command:

$uninstallResult = (Get-WMIObject -List -Verbose | Where-Object {$_.Name -eq "Win32_Process"}).InvokeMethod("Create","$unInstallPath")

$uninstallResult - will have the exit code. 0 is success

the above commands can also run remotely - I did it using invoke command but I believe that adding the argument -computername can work

Resizing image in Java

Resize image with high quality:

private static InputStream resizeImage(InputStream uploadedInputStream, String fileName, int width, int height) {

        try {
            BufferedImage image =;
            Image originalImage= image.getScaledInstance(width, height, Image.SCALE_DEFAULT);

            int type = ((image.getType() == 0) ? BufferedImage.TYPE_INT_ARGB : image.getType());
            BufferedImage resizedImage = new BufferedImage(width, height, type);

            Graphics2D g2d = resizedImage.createGraphics();
            g2d.drawImage(originalImage, 0, 0, width, height, null);

            ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();

            ImageIO.write(resizedImage, fileName.split("\\.")[1], byteArrayOutputStream);
            return new ByteArrayInputStream(byteArrayOutputStream.toByteArray());
        } catch (IOException e) {
            // Something is going wrong while resizing image
            return uploadedInputStream;

Angular ngClass and click event for toggling class

We can also use ngClass to assign multiple CSS classes based on multiple conditions as below:

  'class-name': trueCondition,
  'other-class': !trueCondition

How to change the color of an svg element?

Actually, there is a quite more flexible solution to this problem: writing a Web Component which will patch SVG as text in runtime. Also published in gist with a link to JSFiddle

filter: invert(42%) sepia(93%) saturate(1352%) hue-rotate(87deg) brightness(119%) contrast(119%);


  <title>SVG with color</title>

    (function () {
      const createSvg = (color = '#ff9933') => `
          <svg xmlns="" xmlns:xlink="" version="1.1" width="76px" height="22px" viewBox="-0.5 -0.5 76 22">
                <ellipse cx="5" cy="10" rx="5" ry="5" fill="#ff9933" stroke="none" pointer-events="all"/>
                <ellipse cx="70" cy="10" rx="5" ry="5" fill="#ff9933" stroke="none" pointer-events="all"/>
                <path d="M 9.47 12.24 L 17.24 16.12 Q 25 20 30 13 L 32.5 9.5 Q 35 6 40 9 L 42.5 10.5 Q 45 12 50 6 L 52.5 3 Q 55 0 60.73 3.23 L 66.46 6.46" fill="none" stroke="#ff9933" stroke-miterlimit="10" pointer-events="stroke"/>

      function SvgWithColor() {
        const div = Reflect.construct(HTMLElement, [], SvgWithColor);
        const color = div.hasAttribute('color') ? div.getAttribute('color') : 'cyan';
        div.innerHTML = createSvg(color);
        return div;

      SvgWithColor.prototype = Object.create(HTMLElement.prototype);
      customElements.define('svg-with-color', SvgWithColor);

      document.body.innerHTML += `<svg-with-color




error: could not create '/usr/local/lib/python2.7/dist-packages/virtualenv_support': Permission denied

In the case of permission denied error, you just need to go with this command.

sudo pip install virtualenv

sudo before the command will throw away the current user permissions error.

Note: For security risks, You should read piotr comment.

How to install pip in CentOS 7?

There is a easy way of doing this by just using easy_install (A Setuptools to package python librarie).

  • Assumption. Before doing this check whether you have python installed into your Centos machine (at least 2.x).

  • Steps to install pip.

    1. So lets do install easy_install,

      sudo yum install python-setuptools python-setuptools-devel

    2. Now lets do pip with easy_install,

      sudo easy_install pip

That's Great. Now you have pip :)

Installing a dependency with Bower from URL and specify version

Use a git endpoint instead of a package name:

bower install

how to reset <input type = "file">

I miss an other Solution here (2021): I use FileList to interact with file input.

Since there is no way to create a FileList object, I use DataTransfer, that brings clean FilleList with it.

I reset it with:

  file_input.files=new DataTransfer().files  

In my case this perfectly fits, since I interact only via FileList with my encapsulated file input element.

Ansible playbook shell output

ANSIBLE_STDOUT_CALLBACK=debug ansible-playbook /tmp/foo.yml -vvv

Tasks with STDOUT will then have a section:


What ever was in STDOUT

Decode Base64 data in Java

Given a test encode/decode example of javax.xml.bind.DatatypeConverter using methods parseBase64Binary() and printBase64Binary() referring to @jeremy-ross and @nightfirecat answer.

public void EncodeDecode() {
    String hello = "Hello World";
    byte[] helloBytes = hello.getBytes(StandardCharsets.UTF_8);
    String encodedHello = DatatypeConverter.printBase64Binary(helloBytes); + " encoded=> " + encodedHello);

    byte[] encodedHelloBytes = DatatypeConverter.parseBase64Binary(encodedHello);
    String helloAgain = new String(encodedHelloBytes, StandardCharsets.UTF_8) ; + " decoded=> " + helloAgain);

    Assert.assertEquals(hello, helloAgain);


INFO - Hello World encoded=> SGVsbG8gV29ybGQ=
INFO - SGVsbG8gV29ybGQ= decoded=> Hello World

How to get the nth element of a python list or a default if not available

l[index] if index < len(l) else default

To support negative indices we can use:

l[index] if -len(l) <= index < len(l) else default

Unresponsive KeyListener for JFrame

You must add your keyListener to every component that you need. Only the component with the focus will send these events. For instance, if you have only one TextBox in your JFrame, that TextBox has the focus. So you must add a KeyListener to this component as well.

The process is the same:

myComponent.addKeyListener(new KeyListener ...);

Note: Some components aren't focusable like JLabel.

For setting them to focusable you need to:


Where does linux store my syslog?

syslog() generates a log message, which will be distributed by syslogd.

The file to configure syslogd is /etc/syslog.conf. This file will tell your where the messages are logged.

How to change options in this file ? Here you go

Difference between Node object and Element object?

Element inherits from Node, in the same way that Dog inherits from Animal.

An Element object "is-a" Node object, in the same way that a Dog object "is-a" Animal object.

Node is for implementing a tree structure, so its methods are for firstChild, lastChild, childNodes, etc. It is more of a class for a generic tree structure.

And then, some Node objects are also Element objects. Element inherits from Node. Element objects actually represents the objects as specified in the HTML file by the tags such as <div id="content"></div>. The Element class define properties and methods such as attributes, id, innerHTML, clientWidth, blur(), and focus().

Some Node objects are text nodes and they are not Element objects. Each Node object has a nodeType property that indicates what type of node it is, for HTML documents:

1: Element node
3: Text node
8: Comment node
9: the top level node, which is document

We can see some examples in the console:

> document instanceof Node

> document instanceof Element

> document.firstChild

> document.firstChild instanceof Node

> document.firstChild instanceof Element

> document.firstChild.firstChild.nextElementSibling

> document.firstChild.firstChild.nextElementSibling === document.body

> document.firstChild.firstChild.nextSibling

> document.firstChild.firstChild.nextSibling instanceof Node

> document.firstChild.firstChild.nextSibling instanceof Element

> Element.prototype.__proto__ === Node.prototype

The last line above shows that Element inherits from Node. (that line won't work in IE due to __proto__. Will need to use Chrome, Firefox, or Safari).

By the way, the document object is the top of the node tree, and document is a Document object, and Document inherits from Node as well:

> Document.prototype.__proto__ === Node.prototype

Here are some docs for the Node and Element classes:

Unable to install packages in latest version of RStudio and R Version.3.1.1

My solution that worked was to open R studio options and select global miror (the field was empty before) and the error went away.

Adding text to a cell in Excel using VBA

Range("$A$1").Value = "'01/01/13 00:00" will do it.

Note the single quote; this will defeat automatic conversion to a number type. But is that what you really want? An alternative would be to format the cell to take a date-time value. Then drop the single quote from the string.

How to measure elapsed time in Python?

import time

def getElapsedTime(startTime, units):
    elapsedInSeconds = time.time() - startTime
    if units == 'sec':
        return elapsedInSeconds
    if units == 'min':
        return elapsedInSeconds/60
    if units == 'hour':
        return elapsedInSeconds/(60*60)

How to make blinking/flashing text with CSS 3

Late but wanted to add a new one with more keyframes ... here is an example on CodePen since there was an issue with the built-in code snippets:

  padding:30px 50px;_x000D_
.flash-me {_x000D_
  -webkit-animation: flash linear 1.7s infinite;_x000D_
  animation: flash linear 1.7s infinite;_x000D_
@-webkit-keyframes flash {_x000D_
  0% { opacity: 0; } _x000D_
  80% { opacity: 1; color:#fff; } _x000D_
  83% { opacity: 0; color:#fff; } _x000D_
  86% { opacity: 1; color:#fff;}  _x000D_
  89% { opacity: 0} _x000D_
  92% { opacity: 1; color:#fff;} _x000D_
  95% { opacity: 0; color:#fff;}_x000D_
  100% { opacity: 1; color:#fff;}_x000D_
@keyframes flash {_x000D_
  0% { opacity: 0; } _x000D_
  80% { opacity: 1; color:#fff; } _x000D_
  83% { opacity: 0; color:#fff; } _x000D_
  86% { opacity: 1; color:#fff;}  _x000D_
  89% { opacity: 0} _x000D_
  92% { opacity: 1; color:#fff;} _x000D_
  95% { opacity: 0; color:#fff;}_x000D_
  100% { opacity: 1; color:#fff;}_x000D_
<span class="block">_x000D_
  <span class="flash-me">Flash Me Hard</span>_x000D_

C#: How to add subitems in ListView



to the last line of your code so it will look like this in the end.


Failed to decode downloaded font

I was having the same issue with font awesome v4.4 and I fixed it by removing the woff2 format. I was getting a warning in Chrome only.

@font-face {
  font-family: 'FontAwesome';
  src: url('../fonts/fontawesome-webfont.eot?v=4.4.0');
  src: url('../fonts/fontawesome-webfont.eot?#iefix&v=4.4.0') format('embedded-opentype'), url('../fonts/fontawesome-webfont.woff?v=4.4.0') format('woff'), url('../fonts/fontawesome-webfont.ttf?v=4.4.0') format('truetype'), url('../fonts/fontawesome-webfont.svg?v=4.4.0#fontawesomeregular') format('svg');
  font-weight: normal;
  font-style: normal;

Is it possible to break a long line to multiple lines in Python?

DB related code looks easier on the eyes in multiple lines, enclosed by a pair of triple quotes:

         FROM some_tbl"""

than the following one giant long line:

SQL = "SELECT id, fld_1, fld_2, fld_3, .................................... FROM some_tbl"

Linq order by, group by and order by each group?

try this...

public class Student 
        public int Grade { get; set; }
        public string Name { get; set; }
        public override string ToString()
            return string.Format("Name{0} : Grade{1}", Name, Grade);

class Program
    static void Main(string[] args)

      List<Student> listStudents = new List<Student>();
      listStudents.Add(new Student() { Grade = 10, Name = "Pedro" });
      listStudents.Add(new Student() { Grade = 10, Name = "Luana" });
      listStudents.Add(new Student() { Grade = 10, Name = "Maria" });
      listStudents.Add(new Student() { Grade = 11, Name = "Mario" });
      listStudents.Add(new Student() { Grade = 15, Name = "Mario" });
      listStudents.Add(new Student() { Grade = 10, Name = "Bruno" });
      listStudents.Add(new Student() { Grade = 10, Name = "Luana" });
      listStudents.Add(new Student() { Grade = 11, Name = "Luana" });
      listStudents.Add(new Student() { Grade = 22, Name = "Maria" });
      listStudents.Add(new Student() { Grade = 55, Name = "Bruno" });
      listStudents.Add(new Student() { Grade = 77, Name = "Maria" });
      listStudents.Add(new Student() { Grade = 66, Name = "Maria" });
      listStudents.Add(new Student() { Grade = 88, Name = "Bruno" });
      listStudents.Add(new Student() { Grade = 42, Name = "Pedro" });
      listStudents.Add(new Student() { Grade = 33, Name = "Bruno" });
      listStudents.Add(new Student() { Grade = 33, Name = "Luciana" });
      listStudents.Add(new Student() { Grade = 17, Name = "Maria" });
      listStudents.Add(new Student() { Grade = 25, Name = "Luana" });
      listStudents.Add(new Student() { Grade = 25, Name = "Pedro" });

      listStudents.GroupBy(g => g.Name).OrderBy(g => g.Key).SelectMany(g => g.OrderByDescending(x => x.Grade)).ToList().ForEach(x => Console.WriteLine(x.ToString()));

How to compare 2 files fast using .NET?

Yet another answer, derived from @chsh. MD5 with usings and shortcuts for file same, file not exists and differing lengths:

/// <summary>
/// Performs an md5 on the content of both files and returns true if
/// they match
/// </summary>
/// <param name="file1">first file</param>
/// <param name="file2">second file</param>
/// <returns>true if the contents of the two files is the same, false otherwise</returns>
public static bool IsSameContent(string file1, string file2)
    if (file1 == file2)
        return true;

    FileInfo file1Info = new FileInfo(file1);
    FileInfo file2Info = new FileInfo(file2);

    if (!file1Info.Exists && !file2Info.Exists)
       return true;
    if (!file1Info.Exists && file2Info.Exists)
        return false;
    if (file1Info.Exists && !file2Info.Exists)
        return false;
    if (file1Info.Length != file2Info.Length)
        return false;

    using (FileStream file1Stream = file1Info.OpenRead())
    using (FileStream file2Stream = file2Info.OpenRead())
        byte[] firstHash = MD5.Create().ComputeHash(file1Stream);
        byte[] secondHash = MD5.Create().ComputeHash(file2Stream);
        for (int i = 0; i < firstHash.Length; i++)
            if (i>=secondHash.Length||firstHash[i] != secondHash[i])
                return false;
        return true;

Calling the base constructor in C#

public class MyExceptionClass : Exception
    public MyExceptionClass(string message,
      Exception innerException): base(message, innerException)
        //other stuff here

You can pass inner exception to one of the constructors.

What's the best way to iterate an Android Cursor?

Initially cursor is not on the first row show using moveToNext() you can iterate the cursor when record is not exist then it return false,unless it return true,

while (cursor.moveToNext()) {

Oracle JDBC intermittent Connection Issue

It's hard to say, but if I would check the actual version of the JDBC driver. Make sure it's

Oracle doesn't include the database version in the filename. So the driver for 11.2 is the exact same name as the driver for 11.1 - ojdbc5.jar. I would extract the driver jar file, and find the MANIFEST.MF file, this will contain some version information. Make sure the version of the JDBC driver matches the version of your database. I suspect it may be a version issue, since there isn't a jar file named ojdbc14.jar on Oracle's download page.

If the version matches - I'm out of ideas :)

window.location.href and () methods in JavaScript () will open a new window, whereas window.location.href will open the new URL in your current window.

How to setup Tomcat server in Netbeans?

If TomCat is install. Perhaps it is not installed Java EE. Services-> plug-ins-> additional plug-ins-> in the search dial tomcat. and install the module java ee. then in the services, servers, add the tomcat server.

How to force an entire layout View refresh?

To strictly answer the question: Use invalidate():

public void invalidate () Since: API Level 1

Invalidate the whole view. If the view is visible, onDraw(Canvas) will be called at some point in the future. This must be called from a UI thread. To call from a non-UI thread, call postInvalidate().

ViewGroup vg = findViewById (;

Now, when the Activity resumes, it makes every View to draw itself. No call to invalidate() should be needed. To apply the theme, make sure you do it before any View is drawn, i.e., before setContentView(R.layout.mainscreen);

public void setTheme (int resid) Since: API Level 1

Set the base theme for this context. Note that this should be called before any views are instantiated in the Context (for example before calling setContentView(View) or inflate(int, ViewGroup)).

The API doc reference is here:

Since the onDraw() method works on already instantiated Views, setTheme will not work. I have no experience with themes myself, but two alternative options I can think are:

  1. call setTheme in onCreate() instead, or
  2. redo setContentView (R.layout.mainscreen); to force reinstantiate all the layout.

LogCat message: The Google Play services resources were not found. Check your project configuration to ensure that the resources are included

I had the same issue here. As Magnus said above, for me it was happening due to an SDK update to version 22.0.5.

After performing a full update in my Android SDK (including Google Play Services) and Android plugins in Eclipse, I was able to use play services lib in my application.

Output an Image in PHP

You can use finfo (PHP 5.3+) to get the right MIME type.

$filePath = 'YOUR_FILE.XYZ';
$finfo = finfo_open(FILEINFO_MIME_TYPE);
$contentType = finfo_file($finfo, $filePath);

header('Content-Type: ' . $contentType);

PS: You don't have to specify Content-Length, Apache will do it for you.

Access denied for user 'homestead'@'localhost' (using password: YES)

Check MySQL UNIX Socket

Find unix_socket location using MySQL

mysql -u homestead -p

mysql> show variables like '%sock%';
| Variable_name                           | Value                       |
| performance_schema_max_socket_classes   | 10                          |
| performance_schema_max_socket_instances | 322                         |
| socket                                  | /var/run/mysqld/mysqld.sock |
3 rows in set (0.00 sec)

Then I go to config/database.php

I update this line : 'unix_socket' => '/tmp/mysql.sock',

to : 'unix_socket' => '/var/run/mysqld/mysqld.sock',

That's it. It works for my as my 4th try.I hope these steps help someone. :D

Javascript event handler with parameters

I don't understand exactly what your code is trying to do, but you can make variables available in any event handler using the advantages of function closures:

function addClickHandler(elem, arg1, arg2) {
    elem.addEventListener('click', function(e) {
        // in the event handler function here, you can directly refer
        // to arg1 and arg2 from the parent function arguments
    }, false);

Depending upon your exact coding situation, you can pretty much always make some sort of closure preserve access to the variables for you.

From your comments, if what you're trying to accomplish is this:

element.addEventListener('click', func(event, this.elements[i]))

Then, you could do this with a self executing function (IIFE) that captures the arguments you want in a closure as it executes and returns the actual event handler function:

element.addEventListener('click', (function(passedInElement) {
    return function(e) {func(e, passedInElement); };
}) (this.elements[i]), false);

For more info on how an IIFE works, see these other references:

Javascript wrapping code inside anonymous function

Immediately-Invoked Function Expression (IIFE) In JavaScript - Passing jQuery

What are good use cases for JavaScript self executing anonymous functions?

This last version is perhaps easier to see what it's doing like this:

// return our event handler while capturing an argument in the closure
function handleEvent(passedInElement) {
    return function(e) {
        func(e, passedInElement); 

element.addEventListener('click', handleEvent(this.elements[i]));

It is also possible to use .bind() to add arguments to a callback. Any arguments you pass to .bind() will be prepended to the arguments that the callback itself will have. So, you could do this:

elem.addEventListener('click', function(a1, a2, e) {
    // inside the event handler, you have access to both your arguments
    // and the event object that the event handler passes
}.bind(elem, arg1, arg2));

Unable to start debugging on the web server. Could not start ASP.NET debugging VS 2010, II7, Win 7 x64

I had the same problem. All the answers above did not work for me. The solution was to delete the bin and obj folder manually.

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '''')' at line 2

There is a single quote in $submitsubject or $submit_message

Why is this a problem?

The single quote char terminates the string in MySQL and everything past that is treated as a sql command. You REALLY don't want to write your sql like that. At best, your application will break intermittently (as you're observing) and at worst, you have just introduced a huge security vulnerability.

Imagine if someone submitted '); DROP TABLE private_messages; in submit message.

Your SQL Command would be:

INSERT INTO private_messages (to_id, from_id, time_sent, subject, message) 
        VALUES('sender_id', 'id', now(),'subjet','');

DROP TABLE private_messages;

Instead you need to properly sanitize your values.

AT A MINIMUM you must run each value through mysql_real_escape_string() but you should really be using prepared statements.

If you were using mysql_real_escape_string() your code would look like this:


    $submit_subject="(no subject)";
$sender_id = mysql_real_escape_string($_POST['sender_id']);

Here is a great article on prepared statements and PDO.

How to print object array in JavaScript?

Simply stringify your object and assign it to the innerHTML of an element of your choice.

yourContainer.innerHTML = JSON.stringify(lineChartData);

If you want something prettier, do

yourContainer.innerHTML = JSON.stringify(lineChartData, null, 4);

var lineChartData = [{_x000D_
            date: new Date(2009, 10, 2),_x000D_
            value: 5_x000D_
        }, {_x000D_
            date: new Date(2009, 10, 25),_x000D_
            value: 30_x000D_
        }, {_x000D_
            date: new Date(2009, 10, 26),_x000D_
            value: 72,_x000D_
            customBullet: "images/redstar.png"_x000D_
document.getElementById("whereToPrint").innerHTML = JSON.stringify(lineChartData, null, 4);
<pre id="whereToPrint"></pre>

But if you just do this in order to debug, then you'd better use the console with console.log(lineChartData).

How to close current tab in a browser window?

The following works for me in Chrome 41:

function leave() {
  var myWindow ="", "_self");
  setTimeout (function() {myWindow.close();},1000);

I've tried several ideas for FF including opening an actual web-page, but nothing seems to work. As far as I understand, any browser will close a tab or window with xxx.close() if it was really opened by JS, but FF, at least, cannot be duped into closing a tab by opening new content inside that tab.

That makes sense when you think about it - a user may well not want JS closing a tab or window that has useful history.

Can't import Numpy in Python

Your sys.path is kind of unusual, as each entry is prefixed with /usr/intel. I guess numpy is installed in the usual non-prefixed place, e.g. it. /usr/share/pyshared/numpy on my Ubuntu system.

Try find / -iname '*numpy*'

What does void* mean and how to use it?

Using a void * means that the function can take a pointer that doesn't need to be a specific type. For example, in socket functions, you have

send(void * pData, int nLength)

this means you can call it in many ways, for example

char * data = "blah";
send(data, strlen(data));

p.x = 1;
p.y = 2;
send(&p, sizeof(POINT));

How do I add 24 hours to a unix timestamp in php?

You probably want to add one day rather than 24 hours. Not all days have 24 hours due to (among other circumstances) daylight saving time:

strtotime('+1 day', $timestamp);

Html table tr inside td

Full Example:

<table border="1" style="width:100%;">
    <td>Item 1</td>
    <td>Item 1</td>
      <table border="1" style="width: 100%;">
          <td>Name 1</td>
          <td>Price 1</td>
          <td>Name 2</td>
          <td>Price 2</td>
          <td>Name 3</td>
          <td>Price 3</td>
    <td>Item 1</td>
    <td>Item 2</td>
    <td>Item 2</td>
    <td>Item 2</td>
    <td>Item 2</td>
    <td>Item 3</td>
    <td>Item 3</td>
    <td>Item 3</td>
    <td>Item 3</td>

How to Get a Layout Inflater Given a Context?

You can use the static from() method from the LayoutInflater class:

 LayoutInflater li = LayoutInflater.from(context);

How to write log to file

Declare up top in your global var so all your processes can access if needed.

package main

import (
var (
    outfile, _ = os.Create("path/to/my.log") // update path for your needs
    l      = log.New(outfile, "", 0)

func main() {
    l.Println("hello, log!!!")

How to update Xcode from command line

$ sudo rm -rf /Library/Developer/CommandLineTools
$ xcode-select --install

How do you remove all the options of a select box and then add one option and select it with jQuery?

How about just changing the html to new data.

$('#mySelect').html('<option value="whatever">text</option>');

Another example:

    <option value="1" selected>text1</option>
    <option value="2">text2</option>
    <option value="3" disabled>text3</option>

How to select the row with the maximum value in each group

Another option is slice

group %>%
     group_by(Subject) %>%
#    Subject    pt Event
#    <dbl> <dbl> <dbl>
#1       1     5     2
#2       2    17     2
#3       3     5     2

Auto start print html page using javascript

For me, adding <script>window.print();</script> to the end of the page worked.

I didn't need the type="text/javascript" attribute, or even for the page to be wrapped in a <body> tag. However, all of my previous attempts to intuitively use the answers suggested here, of just writing window.onload=window.print or longer versions such as window.onload=()=>window.print(); did not work, and of course calling print on the newly created window does not wait for the contents to load.

VHDL - How should I create a clock in a testbench?

How to use a clock and do assertions

This example shows how to generate a clock, and give inputs and assert outputs for every cycle. A simple counter is tested here.

The key idea is that the process blocks run in parallel, so the clock is generated in parallel with the inputs and assertions.

library ieee;
use ieee.std_logic_1164.all;

entity counter_tb is
end counter_tb;

architecture behav of counter_tb is
    constant width : natural := 2;
    constant clk_period : time := 1 ns;

    signal clk : std_logic := '0';
    signal data : std_logic_vector(width-1 downto 0);
    signal count : std_logic_vector(width-1 downto 0);

    type io_t is record
        load : std_logic;
        data : std_logic_vector(width-1 downto 0);
        count : std_logic_vector(width-1 downto 0);
    end record;
    type ios_t is array (natural range <>) of io_t;
    constant ios : ios_t := (
        ('1', "00", "00"),
        ('0', "UU", "01"),
        ('0', "UU", "10"),
        ('0', "UU", "11"),

        ('1', "10", "10"),
        ('0', "UU", "11"),
        ('0', "UU", "00"),
        ('0', "UU", "01")
    counter_0: entity work.counter port map (clk, load, data, count);

        for i in ios'range loop
            load <= ios(i).load;
            data <= ios(i).data;
            wait until falling_edge(clk);
            assert count = ios(i).count;
        end loop;
    end process;

        for i in 1 to 2 * ios'length loop
            wait for clk_period / 2;
            clk <= not clk;
        end loop;
    end process;
end behav;

The counter would look like this:

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all; -- unsigned

entity counter is
    generic (
        width : in natural := 2
    port (
        clk, load : in std_logic;
        data : in std_logic_vector(width-1 downto 0);
        count : out std_logic_vector(width-1 downto 0)
end entity counter;

architecture rtl of counter is
    signal cnt : unsigned(width-1 downto 0);
    process(clk) is
        if rising_edge(clk) then
            if load = '1' then
                cnt <= unsigned(data);
                cnt <= cnt + 1;
            end if;
        end if;
    end process;
    count <= std_logic_vector(cnt);
end architecture rtl;


Node.js: printing to console without a trailing newline?

You can use process.stdout.write():

process.stdout.write("hello: ");

See the docs for details.

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

By using T-SQL and cursors like this :

DECLARE @MyField YourFieldDataType;
    SET @MyCursor = CURSOR FOR
    select top 1000 YourField from dbo.table
        where StatusID = 7      

    OPEN @MyCursor 
    FETCH NEXT FROM @MyCursor 
    INTO @MyField

      FETCH NEXT FROM @MyCursor 
      INTO @MyField 

    CLOSE @MyCursor ;
    DEALLOCATE @MyCursor;

Lua String replace


name = "^aH^ai"
name = name:gsub("%^a", "")

See also:

Unable to allocate array with shape and data type

In my case, adding a dtype attribute changed dtype of the array to a smaller type(from float64 to uint8), decreasing array size enough to not throw MemoryError in Windows(64 bit).


mask = np.zeros(edges.shape)


mask = np.zeros(edges.shape,dtype='uint8')

How to create EditText accepts Alphabets only in android?

Put code edittext xml file,


Compare one String with multiple values in one expression

Sorry for reponening this old question, for Java 8+ I think the best solution is the one provided by Elliott Frisch (Stream.of("str1", "str2", "str3").anyMatches(str::equalsIgnoreCase)) but it seems like it's missing one of the simplest solution for eldest version of Java:

if(Arrays.asList("val1", "val2", "val3", ..., "val_n").contains(str.toLowerCase())){

You could apply some error prevenction by checking the non-nullity of variable str, and by caching the list once created, using ArrayList to speed up searches for long lists:

// List of lower-case possibilities
List<String> list = new ArrayList<>(Arrays.asList("val1", "val2", "val3", ..., "val_n"));

if(str != null && list.contains(str.toLowerCase())){


In PHP with PDO, how to check the final SQL parametrized query?

I think easiest way to see final query text when you use pdo is to make special error and look error message. I don't know how to do that, but when i make sql error in yii framework that use pdo i could see query text

Create folder with batch but only if it doesn't already exist

if exist C:\VTS\NUL echo "Folder already exists"

if not exist C:\VTS\NUL echo "Folder does not exist"

See also

(Update March 7, 2018; Microsoft article is down, archive on )

How to convert integer to decimal in SQL Server query?

SELECT CAST(height AS DECIMAL(18,0)) / 10

Edit: How this works under the hood?

The result type is the same as the type of both arguments, or, if they are different, it is determined by the data type precedence table. You can therefore cast either argument to something non-integral.

Now DECIMAL(18,0), or you could equivalently write just DECIMAL, is still a kind of integer type, because that default scale of 0 means "no digits to the right of the decimal point". So a cast to it might in different circumstances work well for rounding to integers - the opposite of what we are trying to accomplish.

However, DECIMALs have their own rules for everything. They are generally non-integers, but always exact numerics. The result type of the DECIMAL division that we forced to occur is determined specially to be, in our case, DECIMAL(29,11). The result of the division will therefore be rounded to 11 places which is no concern for division by 10, but the rounding becomes observable when dividing by 3. You can control the amount of rounding by manipulating the scale of the left hand operand. You can also round more, but not less, by placing another ROUND or CAST operation around the whole expression.

Identical mechanics governs the simpler and nicer solution in the accepted answer:

  SELECT height / 10.0

In this case, the type of the divisor is DECIMAL(3,1) and the type of the result is DECIMAL(17,6). Try dividing by 3 and observe the difference in rounding.

If you just hate all this talk of precisions and scales, and just want SQL server to perform all calculations in good old double precision floating point arithmetics from some point on, you can force that, too:

SELECT height / CAST(10 AS FLOAT(53))

or equivalently just

SELECT height / CAST (10 AS FLOAT)

SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder". error

There is a documentation in SLf4J site to resolve this. I followed that and added slf4j-simple-1.6.1.jar to my aplication along with slf4j-api-1.6.1.jar which i already had.This solved my problem


Iterating over every property of an object in javascript using Prototype?

There's no need for Prototype here: JavaScript has loops. If you're not sure that no one messed with Object.prototype, check hasOwnProperty() as well, ie

for(var prop in obj) {

Print PDF directly from JavaScript

I used this function to download pdf stream from server.

function printPdf(url) {
        var iframe = document.createElement('iframe');
        // = 'pdfIframe'
        document.body.appendChild(iframe); = 'none';
        iframe.onload = function () {
            setTimeout(function () {
                // document.body.removeChild(iframe)
            }, 1);
        iframe.src = url;
        // URL.revokeObjectURL(url)

What's a simple way to get a text input popup dialog box on an iPhone

Just wanted to add an important piece of information that I believe was left out perhaps with the assumption that the ones seeking answers might already know. This problem happens a lot and I too found myself stuck when I tried to implement the viewAlert method for the buttons of the UIAlertView message. To do this you need to 1st add the delegate class which may look something like this:

@interface YourViewController : UIViewController <UIAlertViewDelegate>

Also you can find a very helpful tutorial here!

Hope this helps.

Align items in a stack panel?

If you are having a problem like the one I had where labels were centered in my vertical stack panel, make sure you use full width controls. Delete the Width property, or put your button in a full-width container that allows internal alignment. WPF is all about using containers to control the layout.

<StackPanel Orientation="Vertical">
        <Button HorizontalAlignment="Right">Right</Button>

Vertical StackPanel with Left Label followed by Right Button

I hope this helps.

Role/Purpose of ContextLoaderListener in Spring?

It will give you point of hook to put some code that you wish to be executed on web application deploy time

Add data to JSONObject

In order to have this result:


that holds the same data as:

    "aoColumnDefs": [
     { "aDataSort": [ 0, 1 ], "aTargets": [ 0 ] },
     { "aDataSort": [ 1, 0 ], "aTargets": [ 1 ] },
     { "aDataSort": [ 2, 3, 4 ], "aTargets": [ 2 ] }

you could use this code:

    JSONObject jo = new JSONObject();
    Collection<JSONObject> items = new ArrayList<JSONObject>();

    JSONObject item1 = new JSONObject();
    item1.put("aDataSort", new JSONArray(0, 1));
    item1.put("aTargets", new JSONArray(0));
    JSONObject item2 = new JSONObject();
    item2.put("aDataSort", new JSONArray(1, 0));
    item2.put("aTargets", new JSONArray(1));
    JSONObject item3 = new JSONObject();
    item3.put("aDataSort", new JSONArray(2, 3, 4));
    item3.put("aTargets", new JSONArray(2));

    jo.put("aoColumnDefs", new JSONArray(items));


Changing java platform on which netbeans runs

open etc folder in netbeans folder then edit the netbeans.conf with notepad and you will find a line like this :

Default location of JDK, can be overridden by using --jdkhome :
netbeans_jdkhome="G:\Program Files\Java\jdk1.6.0_13"

here you can set your jdk version.

What is the maximum length of data I can put in a BLOB column in MySQL?

May or may not be accurate, but according to this site:

BLOB A string with a maximum length of 65535 characters.

The MySQL manual says:

The maximum size of a BLOB or TEXT object is determined by its type, but the largest value you actually can transmit between the client and server is determined by the amount of available memory and the size of the communications buffers

I think the first site gets their answers from interpreting the MySQL manual, per

Is it better to use C void arguments "void foo(void)" or not "void foo()"?

C99 quotes

This answer aims to quote and explain the relevant parts of the C99 N1256 standard draft.

Definition of declarator

The term declarator will come up a lot, so let's understand it.

From the language grammar, we find that the following underline characters are declarators:

int f(int x, int y);

int f(int x, int y) { return x + y; }

int f();

int f(x, y) int x; int y; { return x + y; }

Declarators are part of both function declarations and definitions.

There are 2 types of declarators:

  • parameter type list
  • identifier list

Parameter type list

Declarations look like:

int f(int x, int y);

Definitions look like:

int f(int x, int y) { return x + y; }

It is called parameter type list because we must give the type of each parameter.

Identifier list

Definitions look like:

int f(x, y)
    int x;
    int y;
{ return x + y; }

Declarations look like:

int g();

We cannot declare a function with a non-empty identifier list:

int g(x, y);

because "Function declarators (including prototypes)" says:

3 An identifier list in a function declarator that is not part of a definition of that function shall be empty.

It is called identifier list because we only give the identifiers x and y on f(x, y), types come after.

This is an older method, and shouldn't be used anymore. 6.11.6 Function declarators says:

1 The use of function declarators with empty parentheses (not prototype-format parameter type declarators) is an obsolescent feature.

and the Introduction explains what is an obsolescent feature:

Certain features are obsolescent, which means that they may be considered for withdrawal in future revisions of this International Standard. They are retained because of their widespread use, but their use in new implementations (for implementation features) or new programs (for language [6.11] or library features [7.26]) is discouraged

f() vs f(void) for declarations

When you write just:

void f();

it is necessarily an identifier list declaration, because 6.7.5 "Declarators" says defines the grammar as:

    direct-declarator ( parameter-type-list )
    direct-declarator ( identifier-list_opt )

so only the identifier-list version can be empty because it is optional (_opt).

direct-declarator is the only grammar node that defines the parenthesis (...) part of the declarator.

So how do we disambiguate and use the better parameter type list without parameters? Function declarators (including prototypes) says:

10 The special case of an unnamed parameter of type void as the only item in the list specifies that the function has no parameters.


void f(void);

is the way.

This is a magic syntax explicitly allowed, since we cannot use a void type argument in any other way:

void f(void v);
void f(int i, void);
void f(void, int);

What can happen if I use an f() declaration?

Maybe the code will compile just fine: Function declarators (including prototypes):

14 The empty list in a function declarator that is not part of a definition of that function specifies that no information about the number or types of the parameters is supplied.

So you can get away with:

void f();
void f(int x) {}

Other times, UB can creep up (and if you are lucky the compiler will tell you), and you will have a hard time figuring out why:

void f();
void f(float x) {}

See: Why does an empty declaration work for definitions with int arguments but not for float arguments?

f() and f(void) for definitions

f() {}


f(void) {}

are similar, but not identical. Function declarators (including prototypes) says:

14 An empty list in a function declarator that is part of a definition of that function specifies that the function has no parameters.

which looks similar to the description of f(void).

But still... it seems that:

int f() { return 0; }
int main(void) { f(1); }

is conforming undefined behavior, while:

int f(void) { return 0; }
int main(void) { f(1); }

is non conforming as discussed at: Why does gcc allow arguments to be passed to a function defined to be with no arguments?

TODO understand exactly why. Has to do with being a prototype or not. Define prototype.

How do you decompile a swf file

erlswf is an opensource project written in erlang for decompiling .swf files.

Here's the site:

Querying data by joining two tables in two database on different servers

Try this:

SELECT tab2.column_name  
FROM  [DB1.mdf].[dbo].[table_name_1] tab1 INNER JOIN [DB2.mdf].[dbo].[table_name_2]  tab2   
    ON tab1.col_name = tab2.col_name

How to change ViewPager's page?

slide to right


slide to left