Programs & Examples On #Drop table

The SQL command for deleting an entire table.

Drop multiple tables in one shot in MySQL

SET foreign_key_checks = 0;
SET foreign_key_checks = 1;

Then you do not have to worry about dropping them in the correct order, nor whether they actually exist.

N.B. this is for MySQL only (as in the question). Other databases likely have different methods for doing this.


You forgot the table in your syntax:

drop table [table_name]

which drops a table.


drop table if exists [table_name]

checks if the table exists before dropping it.
If it exists, it gets dropped.
If not, no error will be thrown and no action be taken.

How to solve : SQL Error: ORA-00604: error occurred at recursive SQL level 1

I was able to solve "ORA-00604: error" by Droping with purge.


Can't drop table: A foreign key constraint fails

But fortunately, with the MySQL FOREIGN_KEY_CHECKS variable, you don't have to worry about the order of your DROP TABLE statements at all, and you can write them in any order you like -- even the exact opposite -- like this:

drop table if exists customers;
drop table if exists orders;
drop table if exists order_details;

For more clarification, check out the link below:

SQL DROP TABLE foreign key constraint

If you are on a mysql server and if you don't mind loosing your tables, you can use a simple query to delete multiple tables at once:

SET foreign_key_checks = 0;
DROP TABLE IF EXISTS table_a,table_b,table_c,table_etc;
SET foreign_key_checks = 1;

In this way it doesn't matter in what order you use the table in you query.

If anybody is going to say something about the fact that this is not a good solution if you have a database with many tables: I agree!

How to read one single line of csv data in Python?

To print a range of line, in this case from line 4 to 7

import csv

with open('california_housing_test.csv') as csv_file:
    data = csv.reader(csv_file)
    for row in list(data)[4:7]:

How do I truncate a .NET string?

Still no Truncate method in 2016 for C# strings. But - Using C# 6.0 Syntax:

public static class StringExtension
  public static string Truncate(this string s, int max) 
    return s?.Length > max ? s.Substring(0, max) : s ?? throw new ArgumentNullException(s); 

It works like a charm:

"Truncate me".Truncate(8);
Result: "Truncate"

How to write a test which expects an Error to be thrown in Jasmine?

In my case the function throwing error was async so I followed here:

await expectAsync(asyncFunction()).toBeRejected();
await expectAsync(asyncFunction()).toBeRejectedWithError(...);

How do I save a stream to a file in C#?

Here's an example that uses proper usings and implementation of idisposable:

static void WriteToFile(string sourceFile, string destinationfile, bool append = true, int bufferSize = 4096)
    using (var sourceFileStream = new FileStream(sourceFile, FileMode.OpenOrCreate))
        using (var destinationFileStream = new FileStream(destinationfile, FileMode.OpenOrCreate))
            while (sourceFileStream.Position < sourceFileStream.Length)

...and there's also this

    public static void WriteToFile(Stream stream, string destinationFile, int bufferSize = 4096, FileMode mode = FileMode.OpenOrCreate, FileAccess access = FileAccess.ReadWrite, FileShare share = FileShare.ReadWrite)
        using (var destinationFileStream = new FileStream(destinationFile, mode, access, share))
            while (stream.Position < stream.Length) 

The key is understanding the proper use of using (which should be implemented on the instantiation of the object that implements idisposable as shown above), and having a good idea as to how the properties work for streams. Position is literally the index within the stream (which starts at 0) that is followed as each byte is read using the readbyte method. In this case I am essentially using it in place of a for loop variable and simply letting it follow through all the way up to the length which is LITERALLY the end of the entire stream (in bytes). Ignore in bytes because it is practically the same and you will have something simple and elegant like this that resolves everything cleanly.

Keep in mind, too, that the ReadByte method simply casts the byte to an int in the process and can simply be converted back.

I'm gonna add another implementation I recently wrote to create a dynamic buffer of sorts to ensure sequential data writes to prevent massive overload

private void StreamBuffer(Stream stream, int buffer)
    using (var memoryStream = new MemoryStream())
        var memoryBuffer = memoryStream.GetBuffer();

        for (int i = 0; i < memoryBuffer.Length;)
            var networkBuffer = new byte[buffer];
            for (int j = 0; j < networkBuffer.Length && i < memoryBuffer.Length; j++)
                networkBuffer[j] = memoryBuffer[i];
            //Assuming destination file
            destinationFileStream.Write(networkBuffer, 0, networkBuffer.Length);

The explanation is fairly simple: we know that we need to keep in mind the entire set of data we wish to write and also that we only want to write certain amounts, so we want the first loop with the last parameter empty (same as while). Next, we initialize a byte array buffer that is set to the size of what's passed, and with the second loop we compare j to the size of the buffer and the size of the original one, and if it's greater than the size of the original byte array, end the run.

virtualenvwrapper and Python 3

The latest version of virtualenvwrapper is tested under Python3.2. Chances are good it will work with Python3.3 too.

Pentaho Data Integration SQL connection

In addition to the other answers here, here's how you can do it on Ubuntu (14.04):

sudo apt-get install libmysql-java

this will download mysql-connector-java-5.x.x.jar to /usr/share/java/, which i believe also automatically creates a symlink named mysql-connector-java.jar.

Then, create a symlink in /your/path/to/data-integration/lib/:

ln -s /usr/share/java/mysql-connector-java.jar /your/path/to/data-integration/lib/mysql-connector-java.jar

How does Java handle integer underflows and overflows and how would you check for it?

If it overflows, it goes back to the minimum value and continues from there. If it underflows, it goes back to the maximum value and continues from there.

You can check that beforehand as follows:

public static boolean willAdditionOverflow(int left, int right) {
    if (right < 0 && right != Integer.MIN_VALUE) {
        return willSubtractionOverflow(left, -right);
    } else {
        return (~(left ^ right) & (left ^ (left + right))) < 0;

public static boolean willSubtractionOverflow(int left, int right) {
    if (right < 0) {
        return willAdditionOverflow(left, -right);
    } else {
        return ((left ^ right) & (left ^ (left - right))) < 0;

(you can substitute int by long to perform the same checks for long)

If you think that this may occur more than often, then consider using a datatype or object which can store larger values, e.g. long or maybe java.math.BigInteger. The last one doesn't overflow, practically, the available JVM memory is the limit.

If you happen to be on Java8 already, then you can make use of the new Math#addExact() and Math#subtractExact() methods which will throw an ArithmeticException on overflow.

public static boolean willAdditionOverflow(int left, int right) {
    try {
        Math.addExact(left, right);
        return false;
    } catch (ArithmeticException e) {
        return true;

public static boolean willSubtractionOverflow(int left, int right) {
    try {
        Math.subtractExact(left, right);
        return false;
    } catch (ArithmeticException e) {
        return true;

The source code can be found here and here respectively.

Of course, you could also just use them right away instead of hiding them in a boolean utility method.

How to set environment variables in Jenkins?

You can try something like this

stages {
        stage('Build') {
            environment { 
                    AOEU= sh (returnStdout: true, script: 'echo aoeu').trim()
            steps {
                sh 'env'
                sh 'echo $AOEU'

How is Docker different from a virtual machine?

Docker, basically containers, supports OS virtualization i.e. your application feels that it has a complete instance of an OS whereas VM supports hardware virtualization. You feel like it is a physical machine in which you can boot any OS.

In Docker, the containers running share the host OS kernel, whereas in VMs they have their own OS files. The environment (the OS) in which you develop an application would be same when you deploy it to various serving environments, such as "testing" or "production".

For example, if you develop a web server that runs on port 4000, when you deploy it to your "testing" environment, that port is already used by some other program, so it stops working. In containers there are layers; all the changes you have made to the OS would be saved in one or more layers and those layers would be part of image, so wherever the image goes the dependencies would be present as well.

In the example shown below, the host machine has three VMs. In order to provide the applications in the VMs complete isolation, they each have their own copies of OS files, libraries and application code, along with a full in-memory instance of an OS. Without Containers Whereas the figure below shows the same scenario with containers. Here, containers simply share the host operating system, including the kernel and libraries, so they don’t need to boot an OS, load libraries or pay a private memory cost for those files. The only incremental space they take is any memory and disk space necessary for the application to run in the container. While the application’s environment feels like a dedicated OS, the application deploys just like it would onto a dedicated host. The containerized application starts in seconds and many more instances of the application can fit onto the machine than in the VM case. enter image description here


Running a cron job on Linux every six hours

0 */6 * * *

crontab every 6 hours is a commonly used cron schedule.

What are the best practices for using a GUID as a primary key, specifically regarding performance?

GUIDs may seem to be a natural choice for your primary key - and if you really must, you could probably argue to use it for the PRIMARY KEY of the table. What I'd strongly recommend not to do is use the GUID column as the clustering key, which SQL Server does by default, unless you specifically tell it not to.

You really need to keep two issues apart:

  1. the primary key is a logical construct - one of the candidate keys that uniquely and reliably identifies every row in your table. This can be anything, really - an INT, a GUID, a string - pick what makes most sense for your scenario.

  2. the clustering key (the column or columns that define the "clustered index" on the table) - this is a physical storage-related thing, and here, a small, stable, ever-increasing data type is your best pick - INT or BIGINT as your default option.

By default, the primary key on a SQL Server table is also used as the clustering key - but that doesn't need to be that way! I've personally seen massive performance gains when breaking up the previous GUID-based Primary / Clustered Key into two separate key - the primary (logical) key on the GUID, and the clustering (ordering) key on a separate INT IDENTITY(1,1) column.

As Kimberly Tripp - the Queen of Indexing - and others have stated a great many times - a GUID as the clustering key isn't optimal, since due to its randomness, it will lead to massive page and index fragmentation and to generally bad performance.

Yes, I know - there's newsequentialid() in SQL Server 2005 and up - but even that is not truly and fully sequential and thus also suffers from the same problems as the GUID - just a bit less prominently so.

Then there's another issue to consider: the clustering key on a table will be added to each and every entry on each and every non-clustered index on your table as well - thus you really want to make sure it's as small as possible. Typically, an INT with 2+ billion rows should be sufficient for the vast majority of tables - and compared to a GUID as the clustering key, you can save yourself hundreds of megabytes of storage on disk and in server memory.

Quick calculation - using INT vs. GUID as Primary and Clustering Key:

  • Base Table with 1'000'000 rows (3.8 MB vs. 15.26 MB)
  • 6 nonclustered indexes (22.89 MB vs. 91.55 MB)

TOTAL: 25 MB vs. 106 MB - and that's just on a single table!

Some more food for thought - excellent stuff by Kimberly Tripp - read it, read it again, digest it! It's the SQL Server indexing gospel, really.

PS: of course, if you're dealing with just a few hundred or a few thousand rows - most of these arguments won't really have much of an impact on you. However: if you get into the tens or hundreds of thousands of rows, or you start counting in millions - then those points become very crucial and very important to understand.

Update: if you want to have your PKGUID column as your primary key (but not your clustering key), and another column MYINT (INT IDENTITY) as your clustering key - use this:

 .... add more columns as needed ...... )



Basically: you just have to explicitly tell the PRIMARY KEY constraint that it's NONCLUSTERED (otherwise it's created as your clustered index, by default) - and then you create a second index that's defined as CLUSTERED

This will work - and it's a valid option if you have an existing system that needs to be "re-engineered" for performance. For a new system, if you start from scratch, and you're not in a replication scenario, then I'd always pick ID INT IDENTITY(1,1) as my clustered primary key - much more efficient than anything else!

How to get the class of the clicked element?

I saw this question so I thought I might expand on it a little more. This is an expansion of the idea that @SteveFenton had. Instead of binding a click event to each li element, it would be more efficient to delegate the events from the ul down.

For jQuery 1.7 and higher

$("ul.tabs").on('click', 'li', function(e) {

Documentation: .on()

For jQuery 1.4.2 - 1.7

$("ul.tabs").delegate('li', 'click', function(e) {

Documentation: .delegate()

As a last resort for jQuery 1.3 - 1.4

$("ul.tabs").children('li').live('click', function(e) {


$("ul.tabs > li").live('click', function(e) {

Documentation: .live()

Is there an equivalent to CTRL+C in IPython Notebook in Firefox to break cells that are running?

Here are shortcuts for the IPython Notebook.

Ctrl-m i interrupts the kernel. (that is, the sole letter i after Ctrl-m)

According to this answer, I twice works as well.

Passing a Bundle on startActivity()?

You have a few options:

1) Use the Bundle from the Intent:

Intent mIntent = new Intent(this, Example.class);
Bundle extras = mIntent.getExtras();
extras.putString(key, value);  

2) Create a new Bundle

Intent mIntent = new Intent(this, Example.class);
Bundle mBundle = new Bundle();
mBundle.putString(key, value);

3) Use the putExtra() shortcut method of the Intent

Intent mIntent = new Intent(this, Example.class);
mIntent.putExtra(key, value);

Then, in the launched Activity, you would read them via:

String value = getIntent().getExtras().getString(key)

NOTE: Bundles have "get" and "put" methods for all the primitive types, Parcelables, and Serializables. I just used Strings for demonstrational purposes.

Span inside anchor or anchor inside span or doesn't matter?

It can matter if for instance you are using some sort icon font. I had this just now with:

<span class="fa fa-print fa-3x"><a href="some_link"></a></span>

Normally I would put the span inside the A but the styling wasn't taking effect until swapped it round.

How do I find out what is hammering my SQL Server?

You can run the SQL Profiler, and filter by CPU or Duration so that you're excluding all the "small stuff". Then it should be a lot easier to determine if you have a problem like a specific stored proc that is running much longer than it should (could be a missing index or something).

Two caveats:

  • If the problem is massive amounts of tiny transactions, then the filter I describe above would exclude them, and you'd miss this.
  • Also, if the problem is a single, massive job (like an 8-hour analysis job or a poorly designed select that has to cross-join a billion rows) then you might not see this in the profiler until it is completely done, depending on what events you're profiling (sp:completed vs sp:statementcompleted).

But normally I start with the Activity Monitor or sp_who2.

How to replace space with comma using sed?

If you want the output on terminal then,

$sed 's/ /,/g' filename.txt

But if you want to edit the file itself i.e. if you want to replace space with the comma in the file then,

$sed -i 's/ /,/g' filename.txt

CSS hover vs. JavaScript mouseover

In reguards to using jQuery to do hover, I always use the plugin HoverIntent as it doesn't fire the event until you pause over an element for brief period of time... this stops firing off lots of mouse over events if you accidentally run the mouse over them or simply whilst choosing an option.

Detect click outside React component

I made a solution for all occasions.

You should use a High Order Component to wrap the component that you would like to listen for clicks outside it.

This component example has only one prop: "onClickedOutside" that receives a function.

import React, { Component } from "react";

export default class ClickedOutside extends Component {
  componentDidMount() {
    document.addEventListener("mousedown", this.handleClickOutside);

  componentWillUnmount() {
    document.removeEventListener("mousedown", this.handleClickOutside);

  handleClickOutside = event => {
    // IF exists the Ref of the wrapped component AND his dom children doesnt have the clicked component 
    if (this.wrapperRef && !this.wrapperRef.contains( {
      // A props callback for the ClikedClickedOutside

  render() {
    // In this piece of code I'm trying to get to the first not functional component
    // Because it wouldn't work if use a functional component (like <Fade/> from react-reveal)
    let firstNotFunctionalComponent = this.props.children;
    while (typeof firstNotFunctionalComponent.type === "function") {
      firstNotFunctionalComponent = firstNotFunctionalComponent.props.children;

    // Here I'm cloning the element because I have to pass a new prop, the "reference" 
    const children = React.cloneElement(firstNotFunctionalComponent, {
      ref: node => {
        this.wrapperRef = node;
      // Keeping all the old props with the new element

    return <React.Fragment>{children}</React.Fragment>;

Environment variables in Mac OS X

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

Find an element by class name, from a known parent element

var element = $("#parentDiv .myClassNameOfInterest")

How to set the From email address for mailx command?

Just ran into this syntax problem on a CentOS 7 machine.

On a very old Ubuntu machine running mail, the syntax for a nicely composed email is

echo -e "$body" | mail -s "$subject" -a "From: Sender Name <$sender>" "$recipient"

However on a CentOS 7 box which came with mailx installed, it's quite different:

echo -e "$body" | mail -s "$subject" -S "from=Sender Name <$sender>" "$recipient"

Consulting man mail indicates that -r is deprecated and the 'From' sender address should now be set directly using -S "variable=value".

In these and subsequent examples, I'm defining $sender as "Sender Name <[email protected]>" and $recipients as "[email protected]" as I do in my bash script.

You may then find, as I did, that when you try to generate the email's body content in your script at the point of sending the email, you encounter a strange behaviour where the email body is instead attached as a binary file ("ATT00001.bin", "application/octet-stream" or "noname", depending on client).

This behaviour is how Heirloom mailx handles unrecognised / control characters in text input. (More info:, which itself references the mailx man page for the solution.)

To get around this, I used a method which pipes the generated output through tr before passing to mail, and also specifies the charset of the email:

echo -e "$body" | tr -d \\r | mail -s "$subject" -S "from=$sender" -S "sendcharsets=utf-8,iso-8859-1" "$recipients"

In my script, I'm also explicitly delaring the locale beforehand as it's run as a cronjob (and cron doesn't inherit environmental variables):

LANG="en_GB.UTF8" ; export LANG ;

(An alternate method of setting locales for cronjobs is discussed here)

More info on these workarounds via and

Receiving login prompt using integrated windows authentication

I tried the above IIS configuration tricks and loopback registry hack, and I reviewed and recreated app pool permissions and a dozen other things and still wasn't able to get rid of the authentication loop running on my development workstation with IIS Express or IIS 7.5, from a local or remote browsing session. I received four 401.2 status responses and a blank page. The exact same site deployed to my IIS 8.5 staging server works flawlessly.

Finally I noticed markup in the Response Body that was rendered blank by the browser contained the default page for a successful log in. I determined that Custom Error handling for ASP.NET and HTTP for the 401 error was preventing/interfering with Windows Authentication my workstation but not the staging server. I spent several hours fiddling with this, but as soon as I removed custom handling for just the 401 error, the workstation was back to normal. I present this as yet one another way to shoot your own foot.

How to specify names of columns for x and y when joining in dplyr?

This is more a workaround than a real solution. You can create a new object test_data with another column name:

left_join("names<-"(test_data, "name"), kantrowitz, by = "name")

     name gender
1    john      M
2    bill either
3 madison      M
4    abby either
5     zzz   <NA>

How to send objects through bundle

One More way to send objects through bundle is by using bundle.putByteArray
Sample code

public class DataBean implements Serializable {
private Date currentTime;

public setDate() {
    currentTime = Calendar.getInstance().getTime();

public Date getCurrentTime() {
    return currentTime;

put Object of DataBean in to Bundle:

class FirstClass{
public void onCreate(Bundle savedInstanceState) {
//Your code...

//When you want to start new Activity...
Intent dataIntent =new Intent(FirstClass.this, SecondClass.class);
            Bundle dataBundle=new Bundle();
            DataBean dataObj=new DataBean();
            try {
                dataBundle.putByteArray("Obj_byte_array", object2Bytes(dataObj));

            } catch (IOException e) {
                // TODO Auto-generated catch block




Converting objects to byte arrays

 * Converting objects to byte arrays
static public byte[] object2Bytes( Object o ) throws IOException {
      ByteArrayOutputStream baos = new ByteArrayOutputStream();
      ObjectOutputStream oos = new ObjectOutputStream( baos );
      oos.writeObject( o );
      return baos.toByteArray();

Get Object back from Bundle:

class SecondClass{
DataBean dataBean;
public void onCreate(Bundle savedInstanceState) {
//Your code...

//Get Info from Bundle...
    Bundle infoBundle=getIntent().getExtras();
    try {
        dataBean = (DataBean)bytes2Object(infoBundle.getByteArray("Obj_byte_array"));
    } catch (IOException e) {
        // TODO Auto-generated catch block
    } catch (ClassNotFoundException e) {
        // TODO Auto-generated catch block

Method to get objects from byte arrays:

 * Converting byte arrays to objects
static public Object bytes2Object( byte raw[] )
        throws IOException, ClassNotFoundException {
      ByteArrayInputStream bais = new ByteArrayInputStream( raw );
      ObjectInputStream ois = new ObjectInputStream( bais );
      Object o = ois.readObject();
      return o;

Hope this will help to other buddies.

Best JavaScript compressor

Revisiting this question a few years later, UglifyJS, seems to be the best option as of now.

As stated below, it runs on the NodeJS platform, but can be easily modified to run on any JavaScript engine.

--- Old answer below---

Google released Closure Compiler which seems to be generating the smallest files so far as seen here and here

Previous to that the various options were as follow

Basically Packer does a better job at initial compression , but if you are going to gzip the files before sending on the wire (which you should be doing) YUI Compressor gets the smallest final size.

The tests were done on jQuery code btw.

  • Original jQuery library 62,885 bytes , 19,758 bytes after gzip
  • jQuery minified with JSMin 36,391 bytes , 11,541 bytes after gzip
  • jQuery minified with Packer 21,557 bytes , 11,119 bytes after gzip
  • jQuery minified with the YUI Compressor 31,822 bytes , 10,818 bytes after gzip

@daniel james mentions in the comment compressorrater which shows Packer leading the chart in best compression, so I guess ymmv

PHP session handling errors

I'm using php-5.4.45 and I got the same problem.

If you are a php-fpm user, try edit php-fpm.conf and change listen.owner and to the right one. My nginx user is apache, so here I change these to params to apache, then it works well for me.

For apache user, I guess you should edit your fast-cgi params refer the two params I mention above.

Selecting a row of pandas series/dataframe by integer index

you can loop through the data frame like this .

for ad in range(1,dataframe_c.size):

Rails formatting date




%F - The ISO 8601 date format (%Y-%m-%d)
%T - 24-hour time (%H:%M:%S)

Following are some of the frequently used useful list of Date and Time formats that you could specify in strftime method:

Date (Year, Month, Day):
  %Y - Year with century (can be negative, 4 digits at least)
          -0001, 0000, 1995, 2009, 14292, etc.
  %C - year / 100 (round down.  20 in 2009)
  %y - year % 100 (00..99)

  %m - Month of the year, zero-padded (01..12)
          %_m  blank-padded ( 1..12)
          %-m  no-padded (1..12)
  %B - The full month name (``January'')
          %^B  uppercased (``JANUARY'')
  %b - The abbreviated month name (``Jan'')
          %^b  uppercased (``JAN'')
  %h - Equivalent to %b

  %d - Day of the month, zero-padded (01..31)
          %-d  no-padded (1..31)
  %e - Day of the month, blank-padded ( 1..31)

  %j - Day of the year (001..366)

Time (Hour, Minute, Second, Subsecond):
  %H - Hour of the day, 24-hour clock, zero-padded (00..23)
  %k - Hour of the day, 24-hour clock, blank-padded ( 0..23)
  %I - Hour of the day, 12-hour clock, zero-padded (01..12)
  %l - Hour of the day, 12-hour clock, blank-padded ( 1..12)
  %P - Meridian indicator, lowercase (``am'' or ``pm'')
  %p - Meridian indicator, uppercase (``AM'' or ``PM'')

  %M - Minute of the hour (00..59)

  %S - Second of the minute (00..59)

  %L - Millisecond of the second (000..999)
  %N - Fractional seconds digits, default is 9 digits (nanosecond)
          %3N  millisecond (3 digits)
          %6N  microsecond (6 digits)
          %9N  nanosecond (9 digits)
          %12N picosecond (12 digits)

For the complete list of formats for strftime method please visit APIDock

Getting list of parameter names inside python function

If you also want the values you can use the inspect module

import inspect

def func(a, b, c):
    frame = inspect.currentframe()
    args, _, _, values = inspect.getargvalues(frame)
    print 'function name "%s"' % inspect.getframeinfo(frame)[2]
    for i in args:
        print "    %s = %s" % (i, values[i])
    return [(i, values[i]) for i in args]

>>> func(1, 2, 3)
function name "func"
    a = 1
    b = 2
    c = 3
[('a', 1), ('b', 2), ('c', 3)]

What can cause a “Resource temporarily unavailable” on sock send() command

That's because you're using a non-blocking socket and the output buffer is full.

From the send() man page

   When the message does not fit into  the  send  buffer  of  the  socket,
   send() normally blocks, unless the socket has been placed in non-block-
   ing I/O mode.  In non-blocking mode it  would  return  EAGAIN  in  this

EAGAIN is the error code tied to "Resource temporarily unavailable"

Consider using select() to get a better control of this behaviours

What is the inclusive range of float and double in Java?

Java's Primitive Data Types

boolean: 1-bit. May take on the values true and false only.

byte: 1 signed byte (two's complement). Covers values from -128 to 127.

short: 2 bytes, signed (two's complement), -32,768 to 32,767

int: 4 bytes, signed (two's complement). -2,147,483,648 to 2,147,483,647.

long: 8 bytes signed (two's complement). Ranges from -9,223,372,036,854,775,808 to +9,223,372,036,854,775,807.

float: 4 bytes, IEEE 754. Covers a range from 1.40129846432481707e-45 to 3.40282346638528860e+38 (positive or negative).

double: 8 bytes IEEE 754. Covers a range from 4.94065645841246544e-324d to 1.79769313486231570e+308d (positive or negative).

char: 2 bytes, unsigned, Unicode, 0 to 65,535

redirect while passing arguments

You could pass the messages as explicit URL parameter (appropriately encoded), or store the messages into session (cookie) variable before redirecting and then get the variable before rendering the template. For example:

from flask import session, url_for

def do_baz():
    messages = json.dumps({"main":"Condition failed on page baz"})
    session['messages'] = messages
    return redirect(url_for('.do_foo', messages=messages))

def do_foo():
    messages = request.args['messages']  # counterpart for url_for()
    messages = session['messages']       # counterpart for session
    return render_template("foo.html", messages=json.loads(messages))

(encoding the session variable might not be necessary, flask may be handling it for you, but can't recall the details)

Or you could probably just use Flask Message Flashing if you just need to show simple messages.

Entity Framework Migrations renaming tables and columns

Nevermind. I was making this way more complicated than it really needed to be.

This was all that I needed. The rename methods just generate a call to the sp_rename system stored procedure and I guess that took care of everything, including the foreign keys with the new column name.

public override void Up()
    RenameTable("ReportSections", "ReportPages");
    RenameTable("ReportSectionGroups", "ReportSections");
    RenameColumn("ReportPages", "Group_Id", "Section_Id");

public override void Down()
    RenameColumn("ReportPages", "Section_Id", "Group_Id");
    RenameTable("ReportSections", "ReportSectionGroups");
    RenameTable("ReportPages", "ReportSections");

Can I apply a CSS style to an element name?

This is the perfect job for the query selector...

var Set1=document.querySelectorAll('input[type=button]');  // by type

var Set2=document.querySelectorAll('input[name=goButton]'); // by name

var Set3=document.querySelectorAll('input[value=Go]'); // by value

You can then loop through these collections to operate on elements found.

Upgrading PHP in XAMPP for Windows?

To update with latest PHP version in xampp without losing your htdocs data you need to download the zip file of your desired version of PHP from, then copy the PHP folder from the extracted file and paste it into your xampp folder.

NOTE: Don't forget to rename the old PHP file folder which already exists.

Then simply edit your php.ini file with the current path to reach the right PHP folder

After that, you need to re-run your xampp.

I found a video on youtube which can help you. how to update php version in xampp

Maximum number of threads in a .NET app?

You should be using the thread pool (or async delgates, which in turn use the thread pool) so that the system can decide how many threads should run.

Python match a string with regex

r stands for a raw string, so things like \ will be automatically escaped by Python.

Normally, if you wanted your pattern to include something like a backslash you'd need to escape it with another backslash. raw strings eliminate this problem.

short explanation

In your case, it does not matter much but it's a good habit to get into early otherwise something like \b will bite you in the behind if you are not careful (will be interpreted as backspace character instead of word boundary)

As per re.match vs here's an example that will clarify it for you:

>>> import re
>>> testString = 'hello world'
>>> re.match('hello', testString)
<_sre.SRE_Match object at 0x015920C8>
>>>'hello', testString)
<_sre.SRE_Match object at 0x02405560>
>>> re.match('world', testString)
>>>'world', testString)
<_sre.SRE_Match object at 0x015920C8>

So search will find a match anywhere, match will only start at the beginning

Is there a Python caching library?

keyring is the best python caching library. You can use


json_res= keyring.get_password("service","jsonkey")

json_res= keyring.core.delete_password("service","jsonkey")

Word count from a txt file program

Below code from Python | How to Count the frequency of a word in the text file? worked for me.

 import re
    frequency = {}
    #Open the sample text file in read mode.
    document_text = open('sample.txt', 'r')
    #convert the string of the document in lowercase and assign it to text_string variable.
    text =
    pattern = re.findall(r'\b[a-z]{2,15}\b', text)
    for word in pattern:
         count = frequency.get(word,0)
         frequency[word] = count + 1
     frequency_list = frequency.keys()
     for words in frequency_list:
         print(words, frequency[words])

OUTPUT: enter image description here

Height of an HTML select box (dropdown)

This is not a perfect solution but it sort of does work.

In the select tag, include the following attributes where 'n' is the number of dropdown rows that would be visible.

<select size="1" position="absolute" onclick="size=(size!=1)?n:1;" ...>

There are three problems with this solution. 1) There is a quick flash of all the elements shown during the first mouse click. 2) The position is set to 'absolute' 3) Even if there are less than 'n' items the dropdown box will still be for the size of 'n' items.

python object() takes no parameters error

I struggled for a while about this. Stupid rule for __init__. It is two "_" together to be "__"

Does Android keep the .apk files? if so where?

If you are rooted, download the app Root Explorer. Best File manager for rooted users. Anyways, System/app has all the default apks that came with the phone, and data/apk has all the apks of the apps you have installed. Just long press on the apk you want (while in Root Explorer), get to your /sdcard folder and just paste.

How to set up ES cluster?

Elastic Search 7 changed the configurations for cluster initialisation. What is important to note is the ES instances communicate internally using the Transport layer(TCP) and not the HTTP protocol which is normally used to perform ops on the indices. Below is sample config for 2 machines cluster. cluster-new node-1
node.master: true true
bootstrap.memory_lock: true
http.port: 9200 102.123.322.211
transport.tcp.port: 9300
discovery.seed_hosts: [“102.123.322.211:9300”,"102.123.322.212:9300”]
        - "node-1"
        - "node-2”

Machine 2 config:- cluster-new node-2
node.master: true true
bootstrap.memory_lock: true
http.port: 9200 102.123.322.212
transport.tcp.port: 9300
discovery.seed_hosts: [“102.123.322.211:9300”,"102.123.322.212:9300”]
        - "node-1"
        - "node-2” This has be same across all the machines that are going to be part of a cluster. : Identifier for the ES instance. Defaults to machine name if not given.

node.master: specifies whether this ES instance is going to be master or not specifies whether this ES instance is going to be data node or not(hold data)

bootsrap.memory_lock: disable swapping.You can start the cluster without setting this flag. But its recommended to set the lock.More info: if you want to expose the ES instance over network. is different from aka localhost or loopback address). It means all IPv4 addresses on the machine. If machine has multiple ip addresses with a server listening on, the client can reach the machine from any of the IPv4 addresses.

http.port: port on which this ES instance will listen to for HTTP requests The IPv4 address of the host(this will be used to communicate with other ES instances running on different machines). More info:

transport.tcp.port: 9300 (the port where the machine will accept the tcp connections)

discovery.seed_hosts: This was changed in recent versions. Initialise all the IPv4 addresses with TCP port(important) of ES instances that are going to be part of this cluster. This is going to be same across all ES instances that are part of this cluster.

cluster.initial_master_nodes: node names( of the ES machines that are going to participate in master election.(Quorum based decision making :-

UTF-8 in Windows 7 CMD

This question has been already answered in Unicode characters in Windows command line - how?

You missed one step -> you need to use Lucida console fonts in addition to executing chcp 65001 from cmd console.

How to get everything after last slash in a URL?

Split the url and pop the last element url.split('/').pop()

Closing Application with Exit button

try this for close app


CSS3 Transition not working

If you have a <script> tag anywhere on your page (even in the HTML, even if it is an empty tag with a src), then a transition must be activated by some event (it won't fire automatically when the page loads).

Inner join vs Where

They're logically identical, but in the earlier versions of Oracle that adopted ANSI syntax there were often bugs with it in more complex cases, so you'll sometimes encounter resistance from Oracle developers when using it.

How to fix Broken pipe?

I have implemented data downloading functionality through FTP server and found the same exception there too while resuming that download. To resolve this exception, you will always have to disconnect from the previous session and create new instance of the Client and new connection with the server. This same approach could be helpful for HTTPClient too.

How to open a folder in Windows Explorer from VBA?

I may not use shell command because of security in the company so the best way I found on internet.

Sub OpenFileOrFolderOrWebsite() 
'Shows how to open files and / or folders and / or websites / or create    emails using the FollowHyperlink method
Dim strXLSFile As String, strPDFFile As String, strFolder As String, strWebsite As String 
Dim strEmail As String, strSubject As String, strEmailHyperlink As     String 

strFolder = "C:\Test Files\" 
strXLSFile = strFolder & "Test1.xls" 
strPDFFile = strFolder & "Test.pdf" 
strWebsite = "" 

strEmail = "mailto:[email protected]" 
strSubject = "?subject=Test" 
strEmailHyperlink = strEmail & strSubject 

 'Open Folder
ActiveWorkbook.FollowHyperlink Address:=strFolder, NewWindow:=True 
 'Open excel workbook
ActiveWorkbook.FollowHyperlink Address:=strXLSFile, NewWindow:=True 
 'Open PDF file
ActiveWorkbook.FollowHyperlink Address:=strPDFFile, NewWindow:=True 
 'Open VBAX
ActiveWorkbook.FollowHyperlink Address:=strWebsite, NewWindow:=True 
 'Create New Email
ActiveWorkbook.FollowHyperlink Address:=strEmailHyperlink, NewWindow:=True 
End Sub 

so actually its

strFolder = "C:\Test Files\"


ActiveWorkbook.FollowHyperlink Address:=strFolder, NewWindow:=True 

This declaration has no storage class or type specifier in C++

This is a mistake:


That code has to go inside a function. Your class definition can only contain declarations and functions.

Classes don't "run", they provide a blueprint for how to make an object.

The line Message m; means that an Orderbook will contain Message called m, if you later create an Orderbook.

What is the difference between and localhost

The main difference is that the connection can be made via Unix Domain Socket, as stated here: localhost vs.

Stopping a JavaScript function when a certain condition is met

Return is how you exit out of a function body. You are using the correct approach.

I suppose, depending on how your application is structured, you could also use throw. That would typically require that your calls to your function are wrapped in a try / catch block.

How do I restart a service on a remote machine in Windows?

Well, if you have Visual Studio (I know it's in 2005, not sure about earlier versions though), you can add the remote machine to your "Server Explorer" tag. At that point, you'll have access to the SERVICES that are running, or can be ran, from that machine (as well as event logs, and queues, and a couple other interesting things).

Copy directory to another directory using ADD command

You can use COPY. You need to specify the directory explicitly. It won't be created by itself

COPY go /usr/local/go

Reference: Docker CP reference

rails 3.1.0 ActionView::Template::Error (application.css isn't precompiled)

You probably have a syntax error in the css you are using.

Run this command

$ bundle exec rake assets:precompile RAILS_ENV=development --trace

It will give the exception, fixed that and you are all done.


"git rebase origin" vs."git rebase origin/master"

git rebase origin means "rebase from the tracking branch of origin", while git rebase origin/master means "rebase from the branch master of origin"

You must have a tracking branch in ~/Desktop/test, which means that git rebase origin knows which branch of origin to rebase with. If no tracking branch exists (in the case of ~/Desktop/fallstudie), git doesn't know which branch of origin it must take, and fails.

To fix this, you can make the branch track origin/master with:

git branch --set-upstream-to=origin/master 

Or, if master isn't the currently checked-out branch:

git branch --set-upstream-to=origin/master master

How to find rows in one table that have no corresponding row in another table

select from tableA left outer join tableB on ( =
where is null
order by desc 

If your db knows how to do index intersections, this will only touch the primary key index

<SELECT multiple> - how to allow only one item selected?

Late to answer but might help someone else, here is how to do it without removing the 'multiple' attribute.

    //Here you can change the value of the maximum allowed options
    max_selected_options: 1

Android button background color

No need to be that hardcore.
Try this :


Dealing with multiple Python versions and PIP?

I ran into this issue myself recently and found that I wasn't getting the right pip for Python 3, on my Linux system that also has Python 2.

First you must ensure that you have installed pip for your python version:

For Python 2:

sudo apt-get install python-pip

For Python 3:

sudo apt-get install python3-pip

Then to install packages for one version of Python or the other, simply use the following for Python 2:

pip install <package>

or for Python 3:

pip3 install <package>

CodeIgniter Select Query

$query= $this->m_general->get('users' , array('id'=> $id ));
echo $query[''];

is ok ;)

How do I debug Windows services in Visual Studio?

Use the following code in service OnStart method:


Choose the Visual Studio option from the pop up message.

Note: To use it in only Debug mode, a #if DEBUG compiler directive can be used, as follows. This will prevent accidental or debugging in release mode on a production server.


Nginx: stat() failed (13: permission denied)

I had the same issue, I am using Plesk Onyx 17 with Centos7. I could see this error in proxy_error_log under the affected domain's logs. All the dirs/files in /var/www/vhosts/ are owned by respective users (domain owners) and you can see that all of them are in psacln group. So solution was to add nginx also to this group, so he can see what he needs:

usermod -aG psacln nginx

And indeed, restart nginx and reload page with Ctrl+F5.

How can I force input to uppercase in an ASP.NET textbox?

Why not use a combination of the CSS and backend? Use:


on the TextBox, and in your codebehind use:


You can also easily change your regex on the validator to use lowercase and uppercase letters. That's probably the easier solution than forcing uppercase on them.

Ping with timestamp on Windows CLI


option 1

ping.exe -t COMPUTERNAME|Foreach{"{0} - {1}" -f (Get-Date),$_}

option 2

Test-Connection -Count 9999 -ComputerName COMPUTERNAME | Format-Table @{Name='TimeStamp';Expression={Get-Date}},Address,ProtocolAddress,ResponseTime

How can I list the contents of a directory in Python?

In Python 3.4+, you can use the new pathlib package:

from pathlib import Path
for path in Path('.').iterdir():

Path.iterdir() returns an iterator, which can be easily turned into a list:

contents = list(Path('.').iterdir())

psql: FATAL: role "postgres" does not exist

For me, this code worked:

/Applications/ -s postgres

it came from here:

How do I tell if an object is a Promise?

Not an answer to the full question but I think it's worth to mention that in Node.js 10 a new util function called isPromise was added which checks if an object is a native Promise or not:

const utilTypes = require('util').types
const b_Promise = require('bluebird')

utilTypes.isPromise(Promise.resolve(5)) // true
utilTypes.isPromise(b_Promise.resolve(5)) // false

Getting MAC Address

For Linux you can retrieve the MAC address using a SIOCGIFHWADDR ioctl.

struct ifreq    ifr;
uint8_t         macaddr[6];

if ((s = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP)) < 0)
    return -1;

strcpy(ifr.ifr_name, "eth0");

if (ioctl(s, SIOCGIFHWADDR, (void *)&ifr) == 0) {
    if (ifr.ifr_hwaddr.sa_family == ARPHRD_ETHER) {
        memcpy(macaddr, ifr.ifr_hwaddr.sa_data, 6);
        return 0;
... etc ...

You've tagged the question "python". I don't know of an existing Python module to get this information. You could use ctypes to call the ioctl directly.

Reset textbox value in javascript

this is might be a possible solution

void 0 != document.getElementById("ad") &&       (document.getElementById("ad").onclick =function(){
 var a = $("#client_id").val();
 var b = $("#contact").val();
 var c = $("#message").val();
 var Qdata = { client_id: a, contact:b, message:c }
 var respo='';

return $.ajax({

    url: applicationPath ,
    type: "POST",
    data: Qdata,
    success: function(e) {
         $("#mcg").html("msg send successfully");




How to resolve "Server Error in '/' Application" error?

I also got this error when I moved an entity framework edmx file into a "Models" sub-folder. This automatically changed the metadata in my connection string setting in my app.config.

So before the connection string changed... it looked something like this:

    <add name="MyDbEntities" connectionString="metadata=res://*/MyDb.csdl|res://*/MyDb.ssdl|res://*/MyDb.msl; ...

And after... it added the "Models" subfolder name (btw... it also added "Models" to the namespace for the EF classes generated) and the connection string now looks something like this:

    <add name="MyDbEntities" connectionString="metadata=res://*/Models.MyDb.csdl|res://*/Models.MyDb.ssdl|res://*/Models.MyDb.msl; ...

I have a website project that references this Entity Framework DB project. But its web.config did not have the updates to the connection string... and that's when I started getting the compilation error being discussed here.

To fix this error, I updated the connection string in the web.config in the website project to match the app.config in my EntityFramework project.

Detecting attribute change of value of an attribute I made

You would have to watch the DOM node changes. There is an API called MutationObserver, but it looks like the support for it is very limited. This SO answer has a link to the status of the API, but it seems like there is no support for it in IE or Opera so far.

One way you could get around this problem is to have the part of the code that modifies the data-select-content-val attribute dispatch an event that you can listen to.

For example, see: on how to tie it together.

The code here is

$(function() {  
  // Here you register for the event and do whatever you need to do.
  $(document).on('data-attribute-changed', function() {
    var data = $('#contains-data').data('mydata');
    alert('Data changed to: ' + data);

  $('#button').click(function() {
    $('#contains-data').data('mydata', 'foo');
    // Whenever you change the attribute you will user the .trigger
    // method. The name of the event is arbitrary

   $('#getbutton').click(function() {
    var data = $('#contains-data').data('mydata');
    alert('Data is: ' + data);

Storing a Key Value Array into a compact JSON string

So why don't you simply use a key-value literal?

var params = {
    'slide0001.html': 'Looking Ahead',
    'slide0002.html': 'Forecase',

return params['slide0001.html']; // returns: Looking Ahead

Converting string format to datetime in mm/dd/yyyy

You can change the format too by doing this

string fecha = DateTime.Now.ToString(format:"dd-MM-yyyy");

// this change the "/" for the "-"

Java SSL: how to disable hostname verification

The answer from @Nani doesn't work anymore with Java 1.8u181. You still need to use your own TrustManager, but it needs to be a X509ExtendedTrustManager instead of a X509TrustManager:



public class Test {

   public static void main (String [] args) throws IOException {
      // This URL has a certificate with a wrong name
      URL url = new URL ("");

      try {
         // opening a connection will fail
         url.openConnection ().connect ();
      } catch (SSLHandshakeException e) {
         System.out.println ("Couldn't open connection: " + e.getMessage ());

      // Bypassing the SSL verification to execute our code successfully
      disableSSLVerification ();

      // now we can open the connection
      url.openConnection ().connect ();

      System.out.println ("successfully opened connection to " + url + ": " + ((HttpURLConnection) url.openConnection ()).getResponseCode ());

   // Method used for bypassing SSL verification
   public static void disableSSLVerification () {

      TrustManager [] trustAllCerts = new TrustManager [] {new X509ExtendedTrustManager () {
         public void checkClientTrusted (X509Certificate [] chain, String authType, Socket socket) {


         public void checkServerTrusted (X509Certificate [] chain, String authType, Socket socket) {


         public void checkClientTrusted (X509Certificate [] chain, String authType, SSLEngine engine) {


         public void checkServerTrusted (X509Certificate [] chain, String authType, SSLEngine engine) {


         public [] getAcceptedIssuers () {
            return null;

         public void checkClientTrusted (X509Certificate [] certs, String authType) {

         public void checkServerTrusted (X509Certificate [] certs, String authType) {


      SSLContext sc = null;
      try {
         sc = SSLContext.getInstance ("SSL");
         sc.init (null, trustAllCerts, new ());
      } catch (KeyManagementException | NoSuchAlgorithmException e) {
         e.printStackTrace ();
      HttpsURLConnection.setDefaultSSLSocketFactory (sc.getSocketFactory ());

Can you split a stream into two streams?

I stumbled across this question to my self and I feel that a forked stream has some use cases that could prove valid. I wrote the code below as a consumer so that it does not do anything but you could apply it to functions and anything else you might come across.

class PredicateSplitterConsumer<T> implements Consumer<T>
  private Predicate<T> predicate;
  private Consumer<T>  positiveConsumer;
  private Consumer<T>  negativeConsumer;

  public PredicateSplitterConsumer(Predicate<T> predicate, Consumer<T> positive, Consumer<T> negative)
    this.predicate = predicate;
    this.positiveConsumer = positive;
    this.negativeConsumer = negative;

  public void accept(T t)
    if (predicate.test(t))

Now your code implementation could be something like this:

        new PredicateSplitterConsumer<>(
            person -> person.getDateOfBirth().isPresent(),
            person -> System.out.println(person.getName()),
            person -> System.out.println(person.getName() + " does not have Date of birth")));

LaTeX: remove blank page after a \part or \chapter

I believe that in the book class all \part and \chapter are set to start on a recto page.

from book.cls:


you should be able to renew that command, and something similar for the \chapter.

Fixing Segmentation faults in C++

I don't know of any methodology to use to fix things like this. I don't think it would be possible to come up with one either for the very issue at hand is that your program's behavior is undefined (I don't know of any case when SEGFAULT hasn't been caused by some sort of UB).

There are all kinds of "methodologies" to avoid the issue before it arises. One important one is RAII.

Besides that, you just have to throw your best psychic energies at it.

In Swift how to call method with parameters on GCD main thread?

Don't forget to weakify self if you are using self inside of the closure.

dispatch_async(dispatch_get_main_queue(),{ [weak self] () -> () in
    if let strongSelf = self {

Replacing last character in a String with java

Modify the code as fieldName = fieldName.replace("," , " ");

How to use BeginInvoke C#

Action is a Type of Delegate provided by the .NET framework. The Action points to a method with no parameters and does not return a value.

() => is lambda expression syntax. Lambda expressions are not of Type Delegate. Invoke requires Delegate so Action can be used to wrap the lambda expression and provide the expected Type to Invoke()

Invoke causes said Action to execute on the thread that created the Control's window handle. Changing threads is often necessary to avoid Exceptions. For example, if one tries to set the Rtf property on a RichTextBox when an Invoke is necessary, without first calling Invoke, then a Cross-thread operation not valid exception will be thrown. Check Control.InvokeRequired before calling Invoke.

BeginInvoke is the Asynchronous version of Invoke. Asynchronous means the thread will not block the caller as opposed to a synchronous call which is blocking.

Getting the count of unique values in a column in bash


#!/usr/bin/env ruby
Dir["*"].each do |file|
    open(file).each do |row|
        row.chomp.split("\t").each do |w|
            h[ w ] += 1
    h.sort{|a,b| b[1]<=>a[1] }.each{|x,y| print "#{x}:#{y}\n" }

Bulk Insert to Oracle using .NET

I'm loading 50,000 records in 15 or so seconds using Array Binding in ODP.NET

It works by repeatedly invoking a stored procedure you specify (and in which you can do updates/inserts/deletes), but it passes the multiple parameter values from .NET to the database in bulk.

Instead of specifying a single value for each parameter to the stored procedure you specify an array of values for each parameter.

Oracle passes the parameter arrays from .NET to the database in one go, and then repeatedly invokes the stored procedure you specify using the parameter values you specified.


SQL Server 2008 - Case / If statements in SELECT Clause

Try something like

    CASE var
        WHEN xyz THEN col1
        WHEN zyx THEN col2
        ELSE col7
    END AS col1,

In other words, use a conditional expression to select the value, then rename the column.

Alternately, you could build up some sort of dynamic SQL hack to share the query tail; I've done this with iBatis before.

catch forEach last iteration

const arr= [1, 2, 3]
 if(arr[arr.length-1] === element){
  console.log("Last Element")

Difference between Git and GitHub

In the SVN analogy, Git replaces SVN, while GitHub replaces SourceForge :P

If this project of yours is new, then you can still commit to your local Git, then you can push to GitHub later on. You will need to add your GitHub repo as a 'remote repository' in your Git setup.

They seem to have something for Eclipse users :

Otherwise, if you are new to Git :

Can't push to the heroku

If you are using django app to deploy on heroku

make sure to put request library in the requirements.txt file.

Google Spreadsheet, Count IF contains a string

Try just =COUNTIF(A2:A51,"iPad")

What is Bootstrap?

Disclaimer: I have used bootstrap in the past, but I never really appreciated what it actually is before, this description comes from me coming to my own definition, today. And I know that bootstrap v4 is out, but I found the bootstrap v3 documentation to be much clearer, so I used that. The library is not going to fundamentally change what it provides.


Bootstrap is a collection of CSS and javascript files that provides some nice-looking default styling for standard html elements, and a few common web content objects that are not standard html elements.

To make an analogy, it's kind of like applying a theme in powerpoint, but for your website: it makes things look pretty nice without too much initial effort.

What does it consist of?

The official v3 documentation breaks it up into three sections:

These roughly correspond to the three main things that Bootstrap provides:

  • Plain CSS files that style standard html elements. So, Bootstrap makes your standard elements pretty-looking. e.g. html: <input class="btn btn-default" type="button" value="Input">Click me</button>
  • CSS files that use styling on standard html elements to make them into something that is not a standard html element but is a standard Bootstrap element (e.g. In this way Bootstrap extends the list of "standard" web elements in a visually consistent way. e.g. html: <span class="glyphicon glyphicon-align-left"></span>
  • The CSS classes are designed with jQuery in mind. Internally, Bootstrap uses jQuery selectors to modify the styles on the fly and interact with the DOM, and thus provides the user the same capability. I believe this requires more explanation, so...

Using Javascript/jQuery

Bootstrap extends jQuery quite a bit. If we look at the source code, we can see that it uses jQuery to do things like: set up listeners for keydown event to interact with dropdowns. It does all of this jQuery setup when you import it in your <script> tag, so you need to make sure jQuery is loaded before Bootstrap is.

Additionally, it ties the javascript to the DOM more tightly than plain jQuery, providing a javascript class interface. e.g. toggle a button programmatically. Remember that CSS just defines how a thing looks, so the major job of these operations will tend to be to modify which CSS classes apply to the element at that moment in time. This kind of change, based on user input, can't be done with plain CSS.

There are other standard interactions with a user that we denizens of the internet are used to that are not covered by CSS. Like, clicking a link that scrolls you down a page instead of changing pages. One of the things that Bootstrap gives you is an easy way to implement this behaviour on your own website.


I have mentioned the word "standard" a lot here, and for good reason. I think the best thing that Bootstrap provides is a set of good-looking standards. You're free to modify the default theme as much as you want, but it's a better baseline than raw html, css and js. And this is why it's called "framework".

Different web browsers have different default styles and can act differently, and need different CSS prefixes and things like that. A major benefit of Bootstrap is that it is much more reliable than writing all that cross-browser stuff yourself (you will still have problems, I'm sure, but it's easier).

I think that Bootstrap was preferred more when gulp and babel weren't as popular. Looking at Bootstrap it seems to come from a time before everyone compiled their javascript. It's still relevant, but you can get some of the benefits from other sources now.

More recent versions of CSS have allowed you to define transitions between these static lists as they change. The original version of Bootstrap actually predates wide-spread adoption of this capability in browsers, so they still have their own animation classes. There are a few bits of Bootstrap that are like this: that other stuff has come up around it and makes it look a bit redundant.

How to subtract X days from a date using Java calendar?

I believe a clean and nice way to perform subtraction or addition of any time unit (months, days, hours, minutes, seconds, ...) can be achieved using the java.time.Instant class.

Example for subtracting 5 days from the current time and getting the result as Date:

new Date(, ChronoUnit.DAYS).toEpochMilli());

Another example for subtracting 1 hour and adding 15 minutes:


If you need more accuracy, Instance measures up to nanoseconds. Methods manipulating nanosecond part:


Also, keep in mind, that Date is not as accurate as Instant.

Application.WorksheetFunction.Match method

You are getting this error because the value cannot be found in the range. String or integer doesn't matter. Best thing to do in my experience is to do a check first to see if the value exists.

I used CountIf below, but there is lots of different ways to check existence of a value in a range.

Public Sub test()

Dim rng As Range
Dim aNumber As Long

aNumber = 666

Set rng = Sheet5.Range("B16:B615")

    If Application.WorksheetFunction.CountIf(rng, aNumber) > 0 Then

        rowNum = Application.WorksheetFunction.Match(aNumber, rng, 0)

        MsgBox aNumber & " does not exist in range " & rng.Address
    End If

End Sub


Public Sub test()
    Dim rng As Range
    Dim aNumber As Variant
    Dim rowNum As Long

    aNumber = "2gg"

    Set rng = Sheet5.Range("B1:B20")

    If Not IsError(Application.Match(aNumber, rng, 0)) Then
        rowNum = Application.Match(aNumber, rng, 0)
        MsgBox rowNum
        MsgBox "error"
    End If
End Sub


Public Sub test()
    Dim rng As Range
    Dim aNumber As Variant
    Dim rowNum As Variant

    aNumber = "2gg"

    Set rng = Sheet5.Range("B1:B20")

    rowNum = Application.Match(aNumber, rng, 0)

    If Not IsError(rowNum) Then
        MsgBox rowNum
        MsgBox "error"
    End If
End Sub

Android studio takes too much memory

To run Android envirorment on low configuration machine.

  1. Close the uncessesory web tabs in browser
  2. For Antivirus users, exclude the build folder which is auto generated
  3. Android studio have 1.2 Gb default heap can decrease to 512 MB

Help > Edit custom VM options


Layouts performace will be speed up

  1. For Gradle one of the core component in Android studio Mkae sure like right now 3.0beta is latest one

Below tips can affect the code quality so please use with cautions:

  1. Studio contain Power safe Mode when turned on it will close background operations that lint , code complelitions and so on.

  2. You can run manually lint check when needed ./gradlew lint

  3. Most of are using Android emulators on average it consume 2 GB RAM so if possible use actual Android device these will reduce your resource load on your computer. Alternatively you can reduce the RAM of the emulator and it will automatically reduce the virtual memory consumption on your computer. you can find this in virtual device configuration and advance setting.

  4. Gradle offline mode is a feature for bandwidth limited users to disable the downloading of build dependencies. It will reduce the background operation that will help to increase the performance of Android studio.

  5. Android studio offers an optimization to compile multiple modules in parallel. On low RAM machines this feature will likely have a negative impact on the performance. You can disable it in the compiler settings dialog.

More elegant "ps aux | grep -v grep"

You could use preg_split instead of explode and split on [ ]+ (one or more spaces). But I think in this case you could go with preg_match_all and capturing:

preg_match_all('/[ ]php[ ]+\S+[ ]+(\S+)/', $input, $matches);
$result = $matches[1];

The pattern matches a space, php, more spaces, a string of non-spaces (the path), more spaces, and then captures the next string of non-spaces. The first space is mostly to ensure that you don't match php as part of a user name but really only as a command.

An alternative to capturing is the "keep" feature of PCRE. If you use \K in the pattern, everything before it is discarded in the match:

preg_match_all('/[ ]php[ ]+\S+[ ]+\K\S+/', $input, $matches);
$result = $matches[0];

I would use preg_match(). I do something similar for many of my system management scripts. Here is an example:

$test = "user     12052  0.2  0.1 137184 13056 ?        Ss   10:00   0:00 php /home/user/public_html/utilities/runProcFile.php cust1 cron
user     12054  0.2  0.1 137184 13064 ?        Ss   10:00   0:00 php /home/user/public_html/utilities/runProcFile.php cust3 cron
user     12055  0.6  0.1 137844 14220 ?        Ss   10:00   0:00 php /home/user/public_html/utilities/runProcFile.php cust4 cron
user     12057  0.2  0.1 137184 13052 ?        Ss   10:00   0:00 php /home/user/public_html/utilities/runProcFile.php cust89 cron
user     12058  0.2  0.1 137184 13052 ?        Ss   10:00   0:00 php /home/user/public_html/utilities/runProcFile.php cust435 cron
user     12059  0.3  0.1 135112 13000 ?        Ss   10:00   0:00 php /home/user/public_html/utilities/runProcFile.php cust16 cron
root     12068  0.0  0.0 106088  1164 pts/1    S+   10:00   0:00 sh -c ps aux | grep utilities > /home/user/public_html/logs/dashboard/currentlyPosting.txt
root     12070  0.0  0.0 103240   828 pts/1    R+   10:00   0:00 grep utilities";

$lines = explode("\n", $test);

foreach($lines as $line){
        if(preg_match("/.php[\s+](cust[\d]+)[\s+]cron/i", $line, $matches)){


The above prints:

    [0] => .php cust1 cron
    [1] => cust1
    [0] => .php cust3 cron
    [1] => cust3
    [0] => .php cust4 cron
    [1] => cust4
    [0] => .php cust89 cron
    [1] => cust89
    [0] => .php cust435 cron
    [1] => cust435
    [0] => .php cust16 cron
    [1] => cust16

You can set $test to equal the output from exec. the values you are looking for would be in the if statement under the foreach. $matches[1] will have the custx value.

What is the most appropriate way to store user settings in Android application

First of all I think User's data shouldn't be stored on phone, and if it is must to store data somewhere on the phone it should be encrypted with in the apps private data. Security of users credentials should be the priority of the application.

The sensitive data should be stored securely or not at all. In the event of a lost device or malware infection, data stored insecurely can be compromised.

Download and save PDF file with Python requests module

In Python 3, I find pathlib is the easiest way to do this. Request's response.content marries up nicely with pathlib's write_bytes.

from pathlib import Path
import requests
filename = Path('metadata.pdf')
url = ''
response = requests.get(url)

How to sort a file, based on its numerical values for a field?

You must do the following command:

sort -n -k1 filename

That should do it :)

In CSS how do you change font size of h1 and h2

h1 {
  font-weight: bold;
  color: #fff;
  font-size: 32px;

h2 {
  font-weight: bold;
  color: #fff;
  font-size: 24px;

Note that after color you can use a word (e.g. white), a hex code (e.g. #fff) or RGB (e.g. rgb(255,255,255)) or RGBA (e.g. rgba(255,255,255,0.3)).


i got similar issue once, what i observed was, package name in my Androidmanifest.xml was started with one empty space character. like " com.example.test" instead of "com.example.test"

I removed all such invalid spaces from my manifest file, it solved my problem

Edit 1: '-' in package name also cause same issue on some android versions

How to draw a line with matplotlib?

This will draw a line that passes through the points (-1, 1) and (12, 4), and another one that passes through the points (1, 3) et (10, 2)

x1 are the x coordinates of the points for the first line, y1 are the y coordinates for the same -- the elements in x1 and y1 must be in sequence.

x2 and y2 are the same for the other line.

import matplotlib.pyplot as plt
x1, y1 = [-1, 12], [1, 4]
x2, y2 = [1, 10], [3, 2]
plt.plot(x1, y1, x2, y2, marker = 'o')

enter image description here

I suggest you spend some time reading / studying the basic tutorials found on the very rich matplotlib website to familiarize yourself with the library.

What if I don't want line segments?

There are no direct ways to have lines extend to infinity... matplotlib will either resize/rescale the plot so that the furthest point will be on the boundary and the other inside, drawing line segments in effect; or you must choose points outside of the boundary of the surface you want to set visible, and set limits for the x and y axis.

As follows:

import matplotlib.pyplot as plt
x1, y1 = [-1, 12], [1, 10]
x2, y2 = [-1, 10], [3, -1]
plt.xlim(0, 8), plt.ylim(-2, 8)
plt.plot(x1, y1, x2, y2, marker = 'o')

enter image description here

How do you handle a form change in jQuery?

$('form :input').change(function() {
    // Something has changed

Random shuffling of an array

This is knuth shuffle algorithm.

public class Knuth { 

    // this class should not be instantiated
    private Knuth() { }

     * Rearranges an array of objects in uniformly random order
     * (under the assumption that <tt>Math.random()</tt> generates independent
     * and uniformly distributed numbers between 0 and 1).
     * @param a the array to be shuffled
    public static void shuffle(Object[] a) {
        int n = a.length;
        for (int i = 0; i < n; i++) {
            // choose index uniformly in [i, n-1]
            int r = i + (int) (Math.random() * (n - i));
            Object swap = a[r];
            a[r] = a[i];
            a[i] = swap;

     * Reads in a sequence of strings from standard input, shuffles
     * them, and prints out the results.
    public static void main(String[] args) {

        // read in the data
        String[] a = StdIn.readAllStrings();

        // shuffle the array

        // print results.
        for (int i = 0; i < a.length; i++)

How to list all installed packages and their versions in Python?

If you have pip install and you want to see what packages have been installed with your installer tools you can simply call this:

pip freeze

It will also include version numbers for the installed packages.


pip has been updated to also produce the same output as pip freeze by calling:

pip list


The output from pip list is formatted differently, so if you have some shell script that parses the output (maybe to grab the version number) of freeze and want to change your script to call list, you'll need to change your parsing code.

Correct way to initialize empty slice

They are equivalent. See this code:

mySlice1 := make([]int, 0)
mySlice2 := []int{}
fmt.Println("mySlice1", cap(mySlice1))
fmt.Println("mySlice2", cap(mySlice2))


mySlice1 0
mySlice2 0

Both slices have 0 capacity which implies both slices have 0 length (cannot be greater than the capacity) which implies both slices have no elements. This means the 2 slices are identical in every aspect.

See similar questions:

What is the point of having nil slice and empty slice in golang?

nil slices vs non-nil slices vs empty slices in Go language

java.lang.IllegalAccessError: tried to access method

Just an addition to the solved answer:

This COULD be a problem with Android Studio's Instant Run feature, for example, if you realized you forgot to add the line of code: finish() to your activity after opening another one, and you already re-opened the activity you shouldn't have reopened (which the finish() solved), then you add finish() and Instant Run occurs, then the app will crash since the logic has been broken.


This is not necessarily a code problem, just an Instant Run problem

How to handle command-line arguments in PowerShell

You are reinventing the wheel. Normal PowerShell scripts have parameters starting with -, like script.ps1 -server http://devserver

Then you handle them in param section in the beginning of the file.

You can also assign default values to your params, read them from console if not available or stop script execution:

 param (
    [string]$server = "http://defaultserver",
    [string]$password = $( Read-Host "Input password, please" )

Inside the script you can simply

write-output $server

since all parameters become variables available in script scope.

In this example, the $server gets a default value if the script is called without it, script stops if you omit the -username parameter and asks for terminal input if -password is omitted.

Update: You might also want to pass a "flag" (a boolean true/false parameter) to a PowerShell script. For instance, your script may accept a "force" where the script runs in a more careful mode when force is not used.

The keyword for that is [switch] parameter type:

 param (
    [string]$server = "http://defaultserver",
    [string]$password = $( Read-Host "Input password, please" ),
    [switch]$force = $false

Inside the script then you would work with it like this:

if ($force) {
  //deletes a file or does something "bad"

Now, when calling the script you'd set the switch/flag parameter like this:

.\yourscript.ps1 -server "http://otherserver" -force

If you explicitly want to state that the flag is not set, there is a special syntax for that

.\yourscript.ps1 -server "http://otherserver" -force:$false

Links to relevant Microsoft documentation (for PowerShell 5.0; tho versions 3.0 and 4.0 are also available at the links):

C# find biggest number

Use Math.Max:

int x = 3, y = 4, z = 5;
Console.WriteLine(Math.Max(Math.Max(x, y), z));

How to remove all event handlers from an event

This is not an answer to the OP, but I thought I'd post this here in case it can help others.

  /// <summary>
  /// Method to remove a (single) SocketAsyncEventArgs.Completed event handler. This is 
  /// partially based on information found here:
  /// But note that this may not be a good idea, being very .Net implementation-dependent. Note 
  /// in particular use of "m_Completed" instead of "Completed".
  /// </summary>
  private static void RemoveCompletedEventHandler(SocketAsyncEventArgs eventArgs)
     FieldInfo fieldInfo = typeof(SocketAsyncEventArgs).GetField("m_Completed", 
                                                BindingFlags.Instance | BindingFlags.NonPublic);
     eventArgs.Completed -= (EventHandler<SocketAsyncEventArgs>)fieldInfo.GetValue(eventArgs);

What is the Python equivalent of Matlab's tic and toc functions?

Updating Eli's answer to Python 3:

class Timer(object):
    def __init__(self, name=None, filename=None): = name
        self.filename = filename

    def __enter__(self):
        self.tstart = time.time()

    def __exit__(self, type, value, traceback):
        message = 'Elapsed: %.2f seconds' % (time.time() - self.tstart)
            message = '[%s] ' % + message
        if self.filename:
            with open(self.filename,'a') as file:
                print(str(": ",message,file=file)

Just like Eli's, it can be used as a context manager:

import time 
with Timer('Count'):
    for i in range(0,10_000_000):


[Count] Elapsed: 0.27 seconds

I have also updated it to print the units of time reported (seconds) and trim the number of digits as suggested by Can, and with the option of also appending to a log file. You must import datetime to use the logging feature:

import time
import datetime 
with Timer('Count', 'log.txt'):    
    for i in range(0,10_000_000):

C# Threading - How to start and stop a thread

Use a static AutoResetEvent in your spawned threads to call back to the main thread using the Set() method. This guy has a fairly good demo in SO on how to use it.

AutoResetEvent clarification

Invariant Violation: _registerComponent(...): Target container is not a DOM element

I ran into the same error. It turned out to be caused by a simple typo after changing my code from:




Notice the missing '#' It should have been


Just posting in case it helps anyone else solve this error.

How do I manage MongoDB connections in a Node.js web application?

The primary committer to node-mongodb-native says:

You open do MongoClient.connect once when your app boots up and reuse the db object. It's not a singleton connection pool each .connect creates a new connection pool.

So, to answer your question directly, reuse the db object that results from MongoClient.connect(). This gives you pooling, and will provide a noticeable speed increase as compared with opening/closing connections on each db action.

JavaScript: Passing parameters to a callback function

Let me give you a very plain Node.js style example of using a callback:

 * Function expects these arguments: 
 * 2 numbers and a callback function(err, result)
var myTest = function(arg1, arg2, callback) {
  if (typeof arg1 !== "number") {
    return callback('Arg 1 is not a number!', null); // Args: 1)Error, 2)No result
  if (typeof arg2 !== "number") {
    return callback('Arg 2 is not a number!', null); // Args: 1)Error, 2)No result
  if (arg1 === arg2) {
    // Do somethign complex here..
    callback(null, 'Actions ended, arg1 was equal to arg2'); // Args: 1)No error, 2)Result
  } else if (arg1 > arg2) {
    // Do somethign complex here..
    callback(null, 'Actions ended, arg1 was > from arg2'); // Args: 1)No error, 2)Result
  } else {
    // Do somethign else complex here..
    callback(null, 'Actions ended, arg1 was < from arg2'); // Args: 1)No error, 2)Result

 * Call it this way: 
 * Third argument is an anonymous function with 2 args for error and result
myTest(3, 6, function(err, result) {
  var resultElement = document.getElementById("my_result");
  if (err) {
    resultElement.innerHTML = 'Error! ' + err; = "red";
    //throw err; // if you want
  } else {
    resultElement.innerHTML = 'Result: ' + result; = "green";

and the HTML that will render the result:

<div id="my_result">
  Result will come here!

You can play with it here: - for example try to pass string instead of number: myTest('some string', 6, function(err, result).. and see the result.

I hope this example helps because it represents the very basic idea of callback functions.

Refresh a page using JavaScript or HTML

If it has something to do control updates on cached pages here I have a nice method how to do this.

  • add some javascript to the page that always get the versionnumber of the page as a string (ajax) at loading. for example:[date]
  • Compare it to the stored versionnumber (stored in cookie or localStorage) if user has visited the page once, otherwise store it directly.
  • If version is not the same as local version, refresh the page using window.location.reload(true)
  • You will see any changes made on the page.

This method requires at least one request even when no request is needed because it already exists in the local browser cache. But the overhead is less comparing to using no cache at all (to be sure the page will show the right updated content). This requires just a few bytes for each page request instead of all content for each page.

IMPORTANT: The version info request must be implemented on your server otherwise it will return the whole page.

Example of version string returned by[date]: skg2pl-v8kqb

To give you an example in code, here is a part of my library (I don't think you can use it but maybe it gives you some idea how to do it):

o.gCheckDocVersion = function() // Because of the hard caching method, check document for changes with ajax 
  var sUrl = o.getQuerylessUrl(window.location.href),
      sDocVer = o.gGetData( sUrl, false );

  o.ajaxRequest({ url:sUrl+'?getVer=1&'+o.uniqueId(), cache:0, dataType:'text' }, 
                   if( typeof sVer == 'string' && sVer.length )
                     var bReload = (( typeof sDocVer == 'string' ) && sDocVer != sVer );
                     if( bReload || !sDocVer )
                        o.gSetData( sUrl, sVer ); 
                        sDocVer = o.gGetData( sUrl, false );
                        if( bReload && ( typeof sDocVer != 'string' || sDocVer != sVer ))
                         { bReload = false; }
                     if( bReload )
                      {  // Hard refresh page contents
                        window.location.reload(true); }
                }, false, false );

If you are using version independent resources like javascript or css files, add versionnumbers (implemented with a url rewrite and not with a query because they mostly won't be cached). For example:

For me, this method is working great, maybe it can help you too.

Get year, month or day from numpy datetime64

I find the following tricks give between 2x and 4x speed increase versus the pandas method described above (i.e. pd.DatetimeIndex(dates).year etc.). The speed of [dt.year for dt in dates.astype(object)] I find to be similar to the pandas method. Also these tricks can be applied directly to ndarrays of any shape (2D, 3D etc.)

dates = np.arange(np.datetime64('2000-01-01'), np.datetime64('2010-01-01'))
years = dates.astype('datetime64[Y]').astype(int) + 1970
months = dates.astype('datetime64[M]').astype(int) % 12 + 1
days = dates - dates.astype('datetime64[M]') + 1

Get the selected option id with jQuery

$('#my_select option:selected').attr('id');

Convert Bitmap to File

Hope this helps u

class MainActivity : AppCompatActivity() {

override fun onCreate(savedInstanceState: Bundle?) {

    // Get the bitmap from assets and display into image view
    val bitmap = assetsToBitmap("tulip.jpg")
    // If bitmap is not null
    bitmap?.let {

    // Click listener for button widget
            // Save the bitmap to a file and display it into image view
            val uri = bitmapToFile(bitmap)

            // Display the saved bitmap's uri in text view
            text_view.text = uri.toString()

            // Show a toast message
            toast("Bitmap saved in a file.")
            toast("bitmap not found.")

// Method to get a bitmap from assets
private fun assetsToBitmap(fileName:String):Bitmap?{
    return try{
        val stream =
    }catch (e:IOException){

// Method to save an bitmap to a file
private fun bitmapToFile(bitmap:Bitmap): Uri {
    // Get the context wrapper
    val wrapper = ContextWrapper(applicationContext)

    // Initialize a new file instance to save bitmap object
    var file = wrapper.getDir("Images",Context.MODE_PRIVATE)
    file = File(file,"${UUID.randomUUID()}.jpg")

        // Compress the bitmap and save in jpg format
        val stream:OutputStream = FileOutputStream(file)
    }catch (e:IOException){

    // Return the saved bitmap uri
    return Uri.parse(file.absolutePath)


Fastest way to check if a file exist using standard C++/C++11/C?

Same as suggested by PherricOxide but in C

#include <sys/stat.h>
int exist(const char *name)
  struct stat   buffer;
  return (stat (name, &buffer) == 0);

Foreach Control in form, how can I do something to all the TextBoxes in my Form?

Even better, you can encapsule this to clear any type of controls you want in one method, like this:

public static void EstadoControles<T>(object control, bool estado, bool limpiar = false) where T : Control
            foreach (var textEdits in ((T)control).Controls.OfType<TextEdit>()) textEdits.Enabled = estado;
            foreach (var textLookUpEdits in ((T)control).Controls.OfType<LookUpEdit>()) textLookUpEdits.Enabled = estado;

            if (!limpiar) return;
                foreach (var textEdits in ((T)control).Controls.OfType<TextEdit>()) textEdits.Text = string.Empty;
                foreach (var textLookUpEdits in ((T)control).Controls.OfType<LookUpEdit>()) textLookUpEdits.EditValue = @"-1";

Return value from exec(@sql)

that's my procedure

CREATE PROC sp_count
    @CompanyId sysname,
    @codition sysname
    ( NumRows int )

    DECLARE @intCount int
         , @vcSQL varchar(255)

    SELECT    @vcSQL = ' INSERT #ctr FROM dbo.Comm_Services 
                       WHERE CompanyId = '+@CompanyId+' and '+@condition+')'
    EXEC      (@vcSQL)

    IF @@ERROR = 0
         SELECT    @intCount = NumRows
         FROM #ctr

         DROP TABLE #ctr
         RETURN @intCount
         DROP TABLE #ctr
         RETURN -1

moment.js 24h format

//Format 24H use HH:mm_x000D_
let currentDate = moment().format('YYYY-MM-DD HH:mm')_x000D_
//example of current time with defined Time zone +1_x000D_
let currentDateTm = moment().utcOffset('+0100').format('YYYY-MM-DD HH:mm')_x000D_
<script src=""></script>

Manually Triggering Form Validation using jQuery

I'm not sure it's worth it for me to type this all up from scratch since this article published in A List Apart does a pretty good job explaining it. MDN also has a handy guide for HTML5 forms and validation (covering the API and also the related CSS).

Read and write a String from text file

Xcode 8, Swift 3 way to read file from the app bundle:

if let path = Bundle.main.path(forResource: filename, ofType: nil) {
    do {
        let text = try String(contentsOfFile: path, encoding: String.Encoding.utf8)
    } catch {
        printError("Failed to read text from \(filename)")
} else {
    printError("Failed to load file from app bundle \(filename)")

Here's a convenient copy and paste Extension

public extension String {
    func contentsOrBlank()->String {
        if let path = Bundle.main.path(forResource:self , ofType: nil) {
            do {
                let text = try String(contentsOfFile:path, encoding: String.Encoding.utf8)
                return text
                } catch { print("Failed to read text from bundle file \(self)") }
        } else { print("Failed to load file from bundle \(self)") }
        return ""

For example

let t = "yourFile.txt".contentsOrBlank()

You almost always want an array of lines:

let r:[String] = "yourFile.txt"
     .split(separator: "\n", omittingEmptySubsequences:ignore)

What is the difference between gravity and layout_gravity in Android?

If a we want to set the gravity of content inside a view then we will use "android:gravity", and if we want to set the gravity of this view (as a whole) within its parent view then we will use "android:layout_gravity".

How to print the current Stack Trace in .NET without any exception?

An alternative to System.Diagnostics.StackTrace is to use System.Environment.StackTrace which returns a string-representation of the stacktrace.

Another useful option is to use the $CALLER and $CALLSTACK debugging variables in Visual Studio since this can be enabled run-time without rebuilding the application.

How to alter a column and change the default value?

If you want to add a default value for the already created column, this works for me:


Attach (open) mdf file database with SQL Server Management Studio

I don't know about the older versions but for SSMS 2016 you can go to the Object Explorer and right click on the Databases entry. Then select Attach... in the context menu. Here you can browse to the .mdf file and open it. screenshot

fatal error: iostream.h no such file or directory

Using standard C++ calling (note that you should use namespace std for cout or add using namespace std;)

#include <iostream>

int main()
    std::cout<<"Hello World!\n";
    return 0;

Add all files to a commit except a single file?

Now git supports exclude certain paths and files by pathspec magic :(exclude) and its short form :!. So you can easily achieve it as the following command.

git add --all -- :!main/dontcheckmein.txt
git add -- . :!main/dontcheckmein.txt

Actually you can specify more:

git add --all -- :!path/to/file1 :!path/to/file2 :!path/to/folder1/*
git add -- . :!path/to/file1 :!path/to/file2 :!path/to/folder1/*

For Mac and Linux, surround each file/folder path with quotes

git add --all -- ':!path/to/file1' ':!path/to/file2' ':!path/to/folder1/*'

How does the communication between a browser and a web server take place?

There is a commercial product with an interesting logo which lets you see all kind of traffic between server and client named charles.

Another open source tools include: Live HttpHeaders, Wireshark or Firebug.

How to configure static content cache per folder and extension in IIS7?

You can do it on a per file basis. Use the path attribute to include the filename

<?xml version="1.0" encoding="UTF-8"?>
    <location path="YourFileNameHere.xml">
                <clientCache cacheControlMode="DisableCache" />

How to get the date from jQuery UI datepicker


var jsDate = $('#your_datepicker_id').datepicker('getDate');
if (jsDate !== null) { // if any date selected in datepicker
    jsDate instanceof Date; // -> true

Why is there no Char.Empty like String.Empty?

If you want to remove characters that satisfy a specific condition, you may use this:

string s = "SoMEthInG";
s = new string(s.Where(c => char.IsUpper(c)).ToArray());

(This will leave only the uppercase characters in the string.)

In other words, you may "use" the string as an IEnumerable<char>, make changes on it and then convert it back to a string as shown above.

Again, this enables to not only remove a specific char because of the lambda expression, although you can do so if you change the lambda expression like this: c => c != 't'.

How can I undo git reset --hard HEAD~1?

If you're really lucky, like I was, you can go back into your text editor and hit 'undo'.

I know that's not really a proper answer, but it saved me half a day's work so hopefully it'll do the same for someone else!

Run a JAR file from the command line and specify classpath

Alternatively, use the manifest to specify the class-path and main-class if you like, so then you don't need to use -cp or specify the main class. In your case it would contain lines like this:

Main-Class: com.test.App
Class-Path: lib/one.jar lib/two.jar

Unfortunately you need to spell out each jar in the manifest (not a biggie as you only do once, and you can use a script to build the file or use a build tool like ANT or Maven or Gradle). And the reference has to be a relative or absolute directory to where you run the java -jar MyJar.jar.

Then execute it with

java -jar MyJar.jar

List all devices, partitions and volumes in Powershell

Run command:

Get-PsDrive -PsProvider FileSystem

For more info see:

How can I use an ES6 import in Node.js?

If you are using the modules system on the server side, you do not need to use Babel at all. To use modules in Node.js ensure that:

  1. Use a version of node that supports the --experimental-modules flag
  2. Your *.js files must then be renamed to *.mjs

That's it.

However and this is a big however, while your shinny pure ES6 code will run in an environment like Node.js (e.g., 9.5.0) you will still have the craziness of transpilling just to test. Also bear in mind that Ecma has stated that release cycles for JavaScript are going to be faster, with newer features delivered on a more regular basis. Whilst this will be no problems for single environments like Node.js, it's a slightly different proposition for browser environments. What is clear is that testing frameworks have a lot to do in catching up. You will still need to probably transpile for testing frameworks. I'd suggest using Jest.

Also be aware of bundling frameworks. You will be running into problems there.

Create a map with clickable provinces/states using SVG, HTML/CSS, ImageMap

jQuery plugin for decorating image maps (highlights, select areas, tooltips):

Disclosure: I wrote it.

SQL Server copy all rows from one table into another i.e duplicate table

select * into x_history from your_table_here;
truncate table your_table_here;

Installing R on Mac - Warning messages: Setting LC_CTYPE failed, using "C"

  1. Open Terminal
  2. Write or paste in: defaults write org.R-project.R force.LANG en_US.UTF-8
  3. Close Terminal (including any RStudio window)
  4. Start R

For someone runs R in a docker environment (under root), try to run R with below command,

# instead of just `R`

How to implement a FSM - Finite State Machine in Java

EasyFSM is a dynamic Java Library which can be used to implement an FSM.

You can find documentation for the same at : Finite State Machine in Java

Also, you can download the library at : Java FSM Library : DynamicEasyFSM

Serialize Property as Xml Attribute in Element

Kind of, use the XmlAttribute instead of XmlElement, but it won't look like what you want. It will look like the following:

<SomeModel SomeStringElementName="testData"> 

The only way I can think of to achieve what you want (natively) would be to have properties pointing to objects named SomeStringElementName and SomeInfoElementName where the class contained a single getter named "value". You could take this one step further and use DataContractSerializer so that the wrapper classes can be private. XmlSerializer won't read private properties.

// TODO: make the class generic so that an int or string can be used.
public class SerializationClass
    public SerializationClass(string value)
        this.Value = value;

    public string Value { get; }

public class SomeModel                     
    public string SomeString { get; set; }                     

    public int SomeInfo { get; set; }  

    public SerializationClass SomeStringElementName
        get { return new SerializationClass(this.SomeString); }

Failing to run jar file from command line: “no main manifest attribute”

First run your application from eclipse to create launch configuration. Then just follow the steps:

  1. From the menu bar's File menu, select Export.
  2. Expand the Java node and select Runnable JAR file. Click Next.
  3. In the Runnable JAR File Specification page, select a 'Java Application' launch configuration to use to create a runnable JAR.
  4. In the Export destination field, either type or click Browse to select a location for the JAR file.
  5. Select an appropriate library handling strategy.
  6. Optionally, you can also create an ANT script to quickly regenerate a previously created runnable JAR file.

Source: Creating a New Runnable JAR File at

How to consume a webApi from Web API to store result in database?

For some unexplained reason this solution doesn't work for me (maybe some incompatibility of types), so I came up with a solution for myself:

HttpResponseMessage response = await client.GetAsync("api/yourcustomobjects");
if (response.IsSuccessStatusCode)
    var data = await response.Content.ReadAsStringAsync();
    var product = JsonConvert.DeserializeObject<Product>(data);

This way my content is parsed into a JSON string and then I convert it to my object.

Trim Whitespaces (New Line and Tab space) in a String in Oracle

Try the code below. It will work if you enter multiple lines in a single column.

create table  products (prod_id number , prod_desc varchar2(50));

insert into products values(1,'test first

test second

test third');

select replace(replace(prod_desc,chr(10),' '),chr(13),' ') from products  where prod_id=2; 

Output :test first test second test third

Generate unique random numbers between 1 and 100

How about using object properties as a hash table? This way your best scenario is to only randomize 8 times. It would only be effective if you want a small part of the range of numbers. It's also much less memory intensive than Fisher-Yates because you don't have to allocate space for an array.

var ht={}, i=rands=8;
while ( i>0 || keys(ht).length<rands) ht[Math.ceil(Math.random()*100)]=i--;

I then found out that Object.keys(obj) is an ECMAScript 5 feature so the above is pretty much useless on the internets right now. Fear not, because I made it ECMAScript 3 compatible by adding a keys function like this.

if (typeof keys == "undefined") 
  var keys = function(obj) 
    for (k in ht) if (ht.hasOwnProperty(k)) props.push(k);
    return props;

What is std::move(), and when should it be used?

std::move itself doesn't really do much. I thought that it called the moved constructor for an object, but it really just performs a type cast (casting an lvalue variable to an rvalue so that the said variable can be passed as an argument to a move constructor or assignment operator).

So std::move is just used as a precursor to using move semantics. Move semantics is essentially an efficient way for dealing with temporary objects.

Consider Object A = B + C + D + E + F;

This is nice looking code, but E + F produces a temporary object. Then D + temp produces another temporary object and so on. In each normal "+" operator of a class, deep copies occur.

For example

Object Object::operator+ (const Object& rhs) {
    Object temp (*this);
    // logic for adding
    return temp;

The creation of the temporary object in this function is useless - these temporary objects will be deleted at the end of the line anyway as they go out of scope.

We can rather use move semantics to "plunder" the temporary objects and do something like

 Object& Object::operator+ (Object&& rhs) {
     // logic to modify rhs directly
     return rhs;

This avoids needless deep copies being made. With reference to the example, the only part where deep copying occurs is now E + F. The rest uses move semantics. The move constructor or assignment operator also needs to be implemented to assign the result to A.

Run a single test method with maven

This command works !! mvn "-DTest=JoinTeamTestCases#validateJoinTeam" test Note that "-DTest" starts with UPPER CASE 'T'.

How to deal with persistent storage (e.g. databases) in Docker

I recently wrote about a potential solution and an application demonstrating the technique. I find it to be pretty efficient during development and in production. Hope it helps or sparks some ideas.


denied: requested access to the resource is denied : docker

My issue was very simply using invalid characters (an extra /) in my image name:


is an invalid image name. Try myusername/something-image. Hope this helps someone.

Can I position an element fixed relative to parent?

I know this is an older post, but I think a good example of what Jiew Meng was trying to do can already be found on this site. Check out the side menu located here: Looking at it without getting into it too deep, I can tell javascript attaches a fixed position once the scrolling hits below the anchor tag and removes the fixed positioning if the scrolling goes above that same anchor tag. Hopefully, that will get someone started in the right direction.

Check if an array contains duplicate values

let arr = [11,22,11,22];

let hasDuplicate = arr.some((val, i) => arr.indexOf(val) !== i);
// hasDuplicate = true

True -> array has duplicates

False -> uniqe array

Vertically align text within input field of fixed-height without display: table or padding?

   height: 15px; 
   line-height: 15px;

this is correct way to set vertical-middle position.

How to get multiple selected values of select box in php?

You can use this code to retrieve values from multiple select combo box


<form action="c3.php" method="post">
  <select name="ary[]" multiple="multiple">
    <option value="Option 1" >Option 1</option>
    <option value="Option 2">Option 2</option>
    <option value="Option 3">Option 3</option>
    <option value="Option 4">Option 4</option>
    <option value="Option 5">Option 5</option>
  <input type="submit">


$values = $_POST['ary'];

foreach ($values as $a){
    echo $a;

Field 'browser' doesn't contain a valid alias configuration

I'm building a React server-side renderer and found this can also occur when building a separate server config from scratch. If you're seeing this error, try the following:

  1. Make sure your "entry" value is properly pathed relative to your "context" value. Mine was missing the preceeding "./" before the entry file name.
  2. Make sure you have your "resolve" value included. Your imports on anything in node_modules will default to looking in your "context" folder, otherwise.


const serverConfig = {
name: 'server',
context: path.join(__dirname, 'src'),
entry: {serverEntry: ['./server-entry.js']},
output: {
    path: path.join(__dirname, 'public'),
    filename: 'server.js',
    publicPath: 'public/',
    libraryTarget: 'commonjs2'
module: {
    rules: [/*...*/]
resolveLoader: {
    modules: [
        path.join(__dirname, 'node_modules')
resolve: {
    modules: [
        path.join(__dirname, 'node_modules')

Bootstrap 3 Horizontal and Vertical Divider

I made the following little scss mixin to build for all the bootstrap breakpoints...

With it I get .col-xs-divider-left or col-lg-divider-right etc.

Note: this uses v4-alpha bootstrap syntax...

@import 'variables';

$divider-height: 100%;

@mixin make-column-dividers($breakpoints: $grid-breakpoints) {
    // Common properties for all breakpoints
    %col-divider {
        position: absolute;
        content: " ";
        top: (100% - $divider-height)/2;
        height: $divider-height;
        width: $hr-border-width;
        background-color: $hr-border-color;
    @each $breakpoint in map-keys($breakpoints) {
        .col-#{$breakpoint}-divider-right:before {
            @include media-breakpoint-up($breakpoint) {
                @extend %col-divider;
                right: 0;
        .col-#{$breakpoint}-divider-left:before {
            @include media-breakpoint-up($breakpoint) {
                @extend %col-divider;
                left: 0;

Quantile-Quantile Plot using SciPy

Using qqplot of statsmodels.api is another option:

Very basic example:

import numpy as np
import statsmodels.api as sm
import pylab

test = np.random.normal(0,1, 1000)

sm.qqplot(test, line='45')


enter image description here

Documentation and more example are here

Benefits of using the conditional ?: (ternary) operator

I'd recommend limiting the use of the ternary(?:) operator to simple single line assignment if/else logic. Something resembling this pattern:

if(<boolCondition>) {
    <variable> = <value>;
else {
    <variable> = <anotherValue>;

Could be easily converted to:

<variable> = <boolCondition> ? <value> : <anotherValue>;

I would avoid using the ternary operator in situations that require if/else if/else, nested if/else, or if/else branch logic that results in the evaluation of multiple lines. Applying the ternary operator in these situations would likely result in unreadable, confusing, and unmanageable code. Hope this helps.

Using "If cell contains #N/A" as a formula condition.

A possible alternative approach in Excel 2010 or later versions:


In AGGREGATE function the first 6 indicates PRODUCT operation and the second 6 denotes "ignore errors"


If "0" then leave the cell blank

Use =IF(H15+G16-F16=0,"",H15+G16-F16)

Failed to configure a DataSource: 'url' attribute is not specified and no embedded datasource could be configured

It can be that your resources directory is not added to classpath when creating a project via Spring Initializr. So your application is never loading the file that you have configured.

To make a quick test if this is the case, add the following to your file:


Now when running your application you should see in the spring boot console output something like this:

INFO  o.s.b.w.e.tomcat.TomcatWebServer - Tomcat started on port(s): **8081** (http) with context path ''

If your port is still default 8080 and not changed to 8081, your files is obviously not loading.

You can also check if your application runs with gradle bootRun from command line. Which most likely will be work.


  1. Close IntelliJ, then inside your project folder delete the ".idea" folder
  2. Reimport your project to IntelliJ like following: "Import Project" -> "select ONLY your build.gradle file to import". (IntelliJ will automatically grab the rest)
  3. build and run your application again

See official answer by IntelliJ Support: IDEA-221673

Reporting Services Remove Time from DateTime in Expression

I'm coming late in the game but I tried all of the solutions above! couldn't get it to drop the zero's in the parameter and give me a default (it ignored the formatting or appeared blank). I was using SSRS 2005 so was struggling with its clunky / buggy issues.

My workaround was to add a column to the custom [DimDate] table in my database that I was pulling dates from. I added a column that was a string representation in the desired format of the [date] column. I then created 2 new Datasets in SSRS that pulled in the following queries for 2 defaults for my 'To' & 'From' date defaults -


    SELECT  Datestring
    FROM    dbo.dimDate
    WHERE   [date] = ( SELECT   MAX(date)
                       FROM     dbo.dimdate
                       WHERE    date < DATEADD(month, -3, GETDATE()


    SELECT  Datestring
    FROM    dbo.dimDate
    WHERE   [date] = ( SELECT   MAX(date)
                       FROM     dbo.dimdate
                       WHERE    date <= GETDATE()

Full Screen Theme for AppCompat

Issues arise among before and after versions of Android 4.0 (API level 14).

from here I created my own solution.

protected void onResume()

    if (Build.VERSION.SDK_INT < 16)
        // Hide the status bar
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
        // Hide the action bar
        // Hide the status bar
        / Hide the action bar

I write this code in onResume() method because if you exit from your app and then you reopen it, the action bar remains active! (and so this fix the problem)

I hope it was helpful ;)

change <audio> src with javascript

If you are storing metadata in a tag use data attributes eg.

<li id="song1" data-value="song1.ogg"><button onclick="updateSource()">Item1</button></li>

Now use the attribute to get the name of the song

var audio = document.getElementById('audio');
audio.src='audio/ogg/' + document.getElementById('song1').getAttribute('data-value');

How to get anchor text/href on click using jQuery?

Updated code

  var currentAnchor = $(this);

How to launch an EXE from Web page (

In windows, specified protocol for application can be registered in Registry. In this msdn doc shows Registering an Application to a URI Scheme.

For example, an executable files 'alert.exe' is to be started. The following item can be registered.

      (Default) = "URL:Alert Protocol"
      URL Protocol = ""
         (Default) = "alert.exe,1"
               (Default) = "C:\Program Files\Alert\alert.exe"

Then you can write a html to test


    <a href="alert:" >alert</a>

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

Unix timestamp is in seconds, so simply add the corresponding number of seconds to the timestamp:

$timeInFuture = time() + (60 * 60 * 24);

Best way to format multiple 'or' conditions in an if statement (Java)

If the set of possibilities is "compact" (i.e. largest-value - smallest-value is, say, less than 200) you might consider a lookup table. This would be especially useful if you had a structure like

if (x == 12 || x == 16 || x == 19 || ...)
else if (x==34 || x == 55 || ...)
else if (...)

Set up an array with values identifying the branch to be taken (1, 2, 3 in the example above) and then your tests become

    case 1:
    case 2:
    case 3:

Whether or not this is appropriate depends on the semantics of the problem.

If an array isn't appropriate, you could use a Map<Integer,Integer>, or if you just want to test membership for a single statement, a Set<Integer> would do. That's a lot of firepower for a simple if statement, however, so without more context it's kind of hard to guide you in the right direction.

how to open a page in new tab on button click in

Try This

<a href="#" target="_blank">Link</a>

install beautiful soup using pip

The easy method that will work even in corrupted setup environment is :

To download and run it using command line



Extracting in c:\uu\uu\appdata\local\temp\tmpjxvil3 Now working in c:\u\u\appdata\local\temp\tmpjxvil3\setuptools-5.6 Installing Setuptools


pip install beautifulsoup4


Downloading/unpacking beautifulsoup4 Running ... egg_info for package Installing collected packages: beautifulsoup4 Running install for beautifulsoup4 Successfully installed beautifulsoup4 Cleaning up...

Bam ! |Done¬

How to bring back "Browser mode" in IE11?

Easiest way, especially if in MSDN,,wasted hours of my time, stupid MS

  1. Open the Developer Tools pane. To do this, press F12.
  2. Open the Emulation screen. To do this, press Ctrl+8.
  3. On the Document mode list under Mode, click 9.
  4. On the User agent string list under Mode, click Internet Explorer 9.

Package signatures do not match the previously installed version

You need to uninstall it because you are using a different signature than the original. If it is not working it might be because it is still installed for another user on the device. To completely uninstall, go to Settings -> Apps -> (specific app)-> Options (the three dots on top right) -> Uninstall for all users.

I am also got this issue that time already installed ionic app(same package name) remove from my phone after that working perfectly.

Creating random numbers with no duplicates

Here is an efficient solution for fast creation of a randomized array. After randomization you can simply pick the n-th element e of the array, increment n and return e. This solution has O(1) for getting a random number and O(n) for initialization, but as a tradeoff requires a good amount of memory if n gets large enough.

How to remove the last character from a string?

We can use substring. Here's the example,

public class RemoveStringChar 
    public static void main(String[] args) 
        String strGiven = "Java";
        System.out.println("Before removing string character - " + strGiven);
        System.out.println("After removing string character - " + removeCharacter(strGiven, 3));

    public static String removeCharacter(String strRemove, int position)
        return strRemove.substring(0, position) + strRemove.substring(position + 1);    

resource error in android studio after update: No Resource Found

you should change your compiledsdkversion and targetversion to 23 in the build gradle file specific to the app.Make sure you installed sdk 23, version 6.0 before this.You can watch this vid for more help.

What causes a TCP/IP reset (RST) flag to be sent?

Some firewalls do that if a connection is idle for x number of minutes. Some ISPs set their routers to do that for various reasons as well.

In this day and age, you'll need to gracefully handle (re-establish as needed) that condition.

How to wrap text around an image using HTML/CSS

Addition to BeNdErR's answer:
The "other TEXT" element should have float:none, like:

    <div style="width:100%;">_x000D_
        <div style="float:left;width:30%; background:red;">...something something something  random text</div>_x000D_
        <div style="float:none; background:yellow;"> text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text  </div>_x000D_

Gunicorn worker timeout error

I had very similar problem, I also tried using "runserver" to see if I could find anything but all I had was a message Killed

So I thought it could be resource problem, and I went ahead to give more RAM to the instance, and it worked.

The "backspace" escape character '\b': unexpected behavior?

Your result will vary depending on what kind of terminal or console program you're on, but yes, on most \b is a nondestructive backspace. It moves the cursor backward, but doesn't erase what's there.

So for the hello worl part, the code outputs

hello worl

...(where ^ shows where the cursor is) Then it outputs two \b characters which moves the cursor backward two places without erasing (on your terminal):

hello worl

Note the cursor is now on the r. Then it outputs d, which overwrites the r and gives us:

hello wodl

Finally, it outputs \n, which is a non-destructive newline (again, on most terminals, including apparently yours), so the l is left unchanged and the cursor is moved to the beginning of the next line.

How to convert a table to a data frame

While the results vary in this case because the column names are numbers, another way I've used is data.frame(rbind(mytable)). Using the example from @X.X:

> freq_t = table(cyl = mtcars$cyl, gear = mtcars$gear)

> freq_t
cyl  3  4  5
  4  1  8  2
  6  2  4  1
  8 12  0  2

> data.frame(rbind(freq_t))
  X3 X4 X5
4  1  8  2
6  2  4  1
8 12  0  2

If the column names do not start with numbers, the X won't get added to the front of them.

use std::fill to populate vector with increasing numbers

You should use std::iota algorithm (defined in <numeric>):

  std::vector<int> ivec(100);
  std::iota(ivec.begin(), ivec.end(), 0); // ivec will become: [0..99]

Because std::fill just assigns the given fixed value to the elements in the given range [n1,n2). And std::iota fills the given range [n1, n2) with sequentially increasing values, starting with the initial value and then using ++value.You can also use std::generate as an alternative.

Don't forget that std::iota is C++11 STL algorithm. But a lot of modern compilers support it e.g. GCC, Clang and VS2012 :

P.S. This function is named after the integer function ? from the programming language APL, and signifies a Greek letter iota. I speculate that originally in APL this odd name was chosen because it resembles an “integer” (even though in mathematics iota is widely used to denote the imaginary part of a complex number).

Moving all files from one directory to another using Python

suprised this doesn't have an answer using pathilib which was introduced in python 3.4+

additionally, shutil updated in python 3.6 to accept a pathlib object more details in this PEP-0519


from pathlib import Path

src_path = '\tmp\files_to_move'

for each_file in Path(src_path).glob('*.*'): # grabs all files
    trg_path = each_file.parent.parent # gets the parent of the folder 
    each_file.rename(trg_path.joinpath( # moves to parent folder.

Pathlib & shutil to copy files.

from pathlib import Path
import shutil

src_path = '\tmp\files_to_move'
trg_path = '\tmp'

for src_file in Path(src_path).glob('*.*'):
    shutil.copy(src_file, trg_path)

How to validate date with format "mm/dd/yyyy" in JavaScript?

Use the following regular expression to validate:

var date_regex = /^(0[1-9]|1[0-2])\/(0[1-9]|1\d|2\d|3[01])\/(19|20)\d{2}$/;
if (!(date_regex.test(testDate))) {
    return false;

This is working for me for MM/dd/yyyy.

Create a tar.xz in one command

If you like the pipe mode, this is the most clean solution:

tar c some-dir | xz > some-dir.tar.xz

It's not necessary to put the f option in order to deal with files and then to use - to specify that the file is the standard input. It's also not necessary to specify the -z option for xz, because it's default.

It works with gzip and bzip2 too:

tar c some-dir | gzip > some-dir.tar.gz


tar c some-dir | bzip2 > some-dir.tar.bz2

Decompressing is also quite straightforward:

xzcat tarball.tar.xz | tar x
bzcat tarball.tar.bz2 | tar x
zcat tarball.tar.gz | tar x

If you have only tar archive, you can use cat:

cat archive.tar | tar x

If you need to list the files only, use tar t.

How do I replace multiple spaces with a single space in C#?

Here is a slight modification on Nolonar original answer.

Checking if the character is not just a space, but any whitespace, use this:

It will replace any multiple whitespace character with a single space.

public static string FilterWhiteSpaces(string input)
    if (input == null)
        return string.Empty;

    var stringBuilder = new StringBuilder(input.Length);
    for (int i = 0; i < input.Length; i++)
        char c = input[i];
        if (i == 0 || !char.IsWhiteSpace(c) || (char.IsWhiteSpace(c) && 
            !char.IsWhiteSpace(strValue[i - 1])))
    return stringBuilder.ToString();

How can I monitor the thread count of a process on linux?

VisualVM can show clear states of threads of a given JVM process

enter image description here

For vs. while in C programming?

They are pretty much same except for do-while loop. The for loop is good when you have a counter kind of variable. It makes it obvious. while loop makes sense in cases where a flag is being checked as show below :

while (!done) {
   if (some condtion) 
      done = true;

Is there an advantage to use a Synchronized Method instead of a Synchronized Block?

Synchronizing with threads. 1) NEVER use synchronized(this) in a thread it doesn't work. Synchronizing with (this) uses the current thread as the locking thread object. Since each thread is independent of other threads, there is NO coordination of synchronization. 2) Tests of code show that in Java 1.6 on a Mac the method synchronization does not work. 3) synchronized(lockObj) where lockObj is a common shared object of all threads synchronizing on it will work. 4) ReenterantLock.lock() and .unlock() work. See Java tutorials for this.

The following code shows these points. It also contains the thread-safe Vector which would be substituted for the ArrayList, to show that many threads adding to a Vector do not lose any information, while the same with an ArrayList can lose information. 0) Current code shows loss of information due to race conditions A) Comment the current labeled A line, and uncomment the A line above it, then run, method loses data but it shouldn't. B) Reverse step A, uncomment B and // end block }. Then run to see results no loss of data C) Comment out B, uncomment C. Run, see synchronizing on (this) loses data, as expected. Don't have time to complete all the variations, hope this helps. If synchronizing on (this), or the method synchronization works, please state what version of Java and OS you tested. Thank you.

import java.util.*;

/** RaceCondition - Shows that when multiple threads compete for resources 
     thread one may grab the resource expecting to update a particular 
     area but is removed from the CPU before finishing.  Thread one still 
     points to that resource.  Then thread two grabs that resource and 
     completes the update.  Then thread one gets to complete the update, 
     which over writes thread two's work.
     DEMO:  1) Run as is - see missing counts from race condition, Run severa times, values change  
            2) Uncomment "synchronized(countLock){ }" - see counts work
            Synchronized creates a lock on that block of code, no other threads can 
            execute code within a block that another thread has a lock.
        3) Comment ArrayList, unComment Vector - See no loss in collection
            Vectors work like ArrayList, but Vectors are "Thread Safe"
         May use this code as long as attribution to the author remains intact.

public class RaceCondition {
    private ArrayList<Integer> raceList = new ArrayList<Integer>(); // simple add(#)
//  private Vector<Integer> raceList = new Vector<Integer>(); // simple add(#)

    private String countLock="lock";    // Object use for locking the raceCount
    private int raceCount = 0;        // simple add 1 to this counter
    private int MAX = 10000;        // Do this 10,000 times
    private int NUM_THREADS = 100;    // Create 100 threads

    public static void main(String [] args) {
    new RaceCondition();

    public RaceCondition() {
    ArrayList<Thread> arT = new ArrayList<Thread>();

    // Create thread objects, add them to an array list
    for( int i=0; i<NUM_THREADS; i++){
        Thread rt = new RaceThread( ); // i );
        arT.add( rt );

    // Start all object at once.
    for( Thread rt : arT ){

    // Wait for all threads to finish before we can print totals created by threads
    for( int i=0; i<NUM_THREADS; i++){
        try { arT.get(i).join(); }
        catch( InterruptedException ie ) { System.out.println("Interrupted thread "+i); }

    // All threads finished, print the summary information.
    // (Try to print this informaiton without the join loop above)
    System.out.printf("\nRace condition, should have %,d. Really have %,d in array, and count of %,d.\n",
                MAX*NUM_THREADS, raceList.size(), raceCount );
    System.out.printf("Array lost %,d. Count lost %,d\n",
             MAX*NUM_THREADS-raceList.size(), MAX*NUM_THREADS-raceCount );
    }   // end RaceCondition constructor

    class RaceThread extends Thread {
    public void run() {
        for ( int i=0; i<MAX; i++){
        try {
            update( i );        
        }    // These  catches show when one thread steps on another's values
        catch( ArrayIndexOutOfBoundsException ai ){ System.out.print("A"); }
        catch( OutOfMemoryError oome ) { System.out.print("O"); }

    // so we don't lose counts, need to synchronize on some object, not primitive
    // Created "countLock" to show how this can work.
    // Comment out the synchronized and ending {, see that we lose counts.

//    public synchronized void update(int i){   // use A
    public void update(int i){                  // remove this when adding A
//      synchronized(countLock){            // or B
//      synchronized(this){             // or C
        raceCount = raceCount + 1;
        raceList.add( i );      // use Vector  
//          }           // end block for B or C
    }   // end update

    }   // end RaceThread inner class

} // end RaceCondition outter class

jquery drop down menu closing by clicking outside

You would need to attach your click event to some element. If there are lots of other elements on the page you would not want to attach a click event to all of them.

One potential way would be to create a transparent div below your dropdown menu but above all other elements on the page. You would show it when the drop down was shown. Have the element have a click hander that hides the drop down and the transparent div.

$('#clickCatcher').click(function () { _x000D_
#dropContainer { z-index: 101; ... }_x000D_
#clickCatcher { position: absolute; top: 0; left: 0; width: 100%; height: 100%; z-index: 100; }
<script src=""></script>_x000D_
<div id="dropDown"></div>_x000D_
<div id="clickCatcher"></div>

What is the best comment in source code you have ever encountered?

This was the only comment we found in a smartcard product that a previous employer bought in. A load of embedded C and assembler written by a bunch of Dutch cryptography PhDs

// echt halmaal gek - no way!

(It means something like "really completely stupid"...which didn't help us either)

Android Get Current timestamp?

You can get Current timestamp in Android by trying below code


and timeStamp to time format

SimpleDateFormat formatter = new SimpleDateFormat("dd/MM/yyyy");
String dateString = formatter.format(new Date(Long.parseLong(time.getText().toString())));

How do I post form data with fetch api?

With fetch api it turned out that you do NOT have to include headers "Content-type": "multipart/form-data".

So the following works:

let formData = new FormData()
formData.append("nameField", fileToSend)

fetch(yourUrlToPost, {
   method: "POST",
   body: formData

Note that with axios I had to use the content-type.