Programs & Examples On #Pfx

pfx is a file format containing public key together with the private key for encryption and chain of trust certificates attached to the public key if such a chain exists. Pfx files are protected by a password to access.

Converting pfx to pem using openssl

You can use the OpenSSL Command line tool. The following commands should do the trick

openssl pkcs12 -in client_ssl.pfx -out client_ssl.pem -clcerts

openssl pkcs12 -in client_ssl.pfx -out root.pem -cacerts

If you want your file to be password protected etc, then there are additional options.

You can read the entire documentation here.

Convert .pfx to .cer

I wanted to add a method which I think was simplest of all.

  1. Simply right click the pfx file, click "Install" follow the wizard, and add it to a store (I added to the Personal store).

  2. In start menu type certmgr.msc and go to CertManager program.

  3. Find your pfx certificate (tabs at top are the various stores), click the export button and follow the wizard (there is an option to export as .CER)

Essentially it does the same thing as Andrew's answer, but it avoids using Windows Management Console (goes straight to the import/export).

Cannot import the keyfile 'blah.pfx' - error 'The keyfile may be password protected'

I solved this issue for myself by changing the following line in the Visual Studio project's .csproj file:

This threw the 'cannot import' error:


Changing the value to false made the error go away.

How to Programmatically Add Views to Views

LinearLayout is a subclass of ViewGroup, which has a method called addView. The addView method should be what you are after.

How to create the pom.xml for a Java project with Eclipse

If you have plugin for Maven in Eclipse, you can do following:

  • right click on your project -> Maven -> Enable Dependency Management

This will convert your project to Maven and creates a pom.xml. Fast and simple...

How to render pdfs using C#

The easiest lib I have used is Paolo Gios's library. It's basically

Create GiosPDFDocument object
Create TextArea object
Add text, images, etc to TextArea object
Add TextArea object to PDFDocument object
Write to stream

This is a great tutorial to get you started.

How to convert a string to ASCII

You can do it by using LINQ-expression.

  public static List<int> StringToAscii(string value)
        if (string.IsNullOrEmpty(value))
            throw new ArgumentException("Value cannot be null or empty.", nameof(value));

        return value.Select(System.Convert.ToInt32).ToList();

How to add dll in c# project

The DLL must be present at all times - as the name indicates, a reference only tells VS that you're trying to use stuff from the DLL. In the project file, VS stores the actual path and file name of the referenced DLL. If you move or delete it, VS is not able to find it anymore.

I usually create a libs folder within my project's folder where I copy DLLs that are not installed to the GAC. Then, I actually add this folder to my project in VS (show hidden files in VS, then right-click and "Include in project"). I then reference the DLLs from the folder, so when checking into source control, the library is also checked in. This makes it much easier when more than one developer will have to change the project.

(Please make sure to set the build type to "none" and "don't copy to output folder" for the DLL in your project.)

PS: I use a German Visual Studio, so the captions I quoted may not exactly match the English version...

How can I put strings in an array, split by new line?


As other answers have specified, be sure to use explode rather than split because as of PHP 5.3.0 split is deprecated. i.e. the following is NOT the way you want to do it:

$your_array = split(chr(10), $your_string);

LF = "\n" = chr(10), CR = "\r" = chr(13)


What are .a and .so files?

Archive libraries (.a) are statically linked i.e when you compile your program with -c option in gcc. So, if there's any change in library, you need to compile and build your code again.

The advantage of .so (shared object) over .a library is that they are linked during the runtime i.e. after creation of your .o file -o option in gcc. So, if there's any change in .so file, you don't need to recompile your main program. But make sure that your main program is linked to the new .so file with ln command.

This will help you to build the .so files.

Hope this helps.

Set background image on grid in WPF using C#

I have my images in a separate class library ("MyClassLibrary") and they are placed in the folder "Images". In the example I used "myImage.jpg" as the background image.

  ImageBrush myBrush = new ImageBrush();
  Image image = new Image();
  image.Source = new BitmapImage(
      new Uri(
  myBrush.ImageSource = image.Source;
  Grid grid = new Grid();
  grid.Background = myBrush;          

What's a clean way to stop mongod on Mac OS X?

It's probably because launchctl is managing your mongod instance. If you want to start and shutdown mongod instance, unload that first:

launchctl unload -w ~/Library/LaunchAgents/org.mongodb.mongod.plist

Then start mongod manually:

mongod -f path/to/mongod.conf --fork

You can find your mongod.conf location from ~/Library/LaunchAgents/org.mongodb.mongod.plist.

After that, db.shutdownServer() would work just fine.

Added Feb 22 2014:

If you have mongodb installed via homebrew, homebrew actually has a handy brew services command. To show current running services:

brew services list

To start mongodb:

brew services start mongodb-community

To stop mongodb if it's already running:

brew services stop mongodb-community


As edufinn pointed out in the comment, brew services is now available as user-defined command and can be installed with following command: brew tap gapple/services.

What is the fastest way to compare two sets in Java?

There is a method in Guava Sets which can help here:

public static <E>  boolean equals(Set<? extends E> set1, Set<? extends E> set2){
return Sets.symmetricDifference(set1,set2).isEmpty();

Redirecting to another page in ASP.NET MVC using JavaScript/jQuery

<script type="text/javascript">
    function lnkLogout_Confirm()
        var bResponse = confirm('Are you sure you want to exit?');

        if (bResponse === true) {
            ////console.log("lnkLogout_Confirm clciked.");
            var url = '@Url.Action("Login", "Login")';
            window.location.href = url;
        return bResponse;


How can I count occurrences with groupBy?

Here is example for list of Objects

Map<String, Long> requirementCountMap =, Collectors.counting()));

PHP mySQL - Insert new record into table with auto-increment on primary key

You can also use blank single quotes for the auto_increment column. something like this. It worked for me.

$query = "INSERT INTO myTable VALUES ('','Fname', 'Lname', 'Website')";

How to get char from string by index?

Another recommended exersice for understanding lists and indexes:

L = ['a', 'b', 'c']
for index, item in enumerate(L):
    print index + '\n' + item


Disable-web-security in Chrome 48+

On OS X, to open a new Chrome window - without having to close the already open windows first - pass in the additional -n flag. Make sure to specify empty string for data-dir (necessary for newer versions of Chrome, like v50 something+).

open -na /Applications/Google\ --args --disable-web-security --user-data-dir=""

I found that using Chrome 60+ on Mac OS X Sierra, the above command no longer worked, but a slight modification does:

open -n -a /Applications/Google\\ Chrome --args --user-data-dir="/tmp/chrome_dev_sess_1" --disable-web-security

The data directory path is important. Even if you're standing in your home directory when issuing the command, you can't simply refer to a local directory. It needs to be an absolute path.

Update style of a component onScroll in React.js

You can pass a function to the onScroll event on the React element:


Another answer that is similar:

how to set start value as "0" in chartjs?

If you need use it as a default configuration, just place min: 0 inside the node defaults.scale.ticks, as follows:

defaults: {
  global: {...},
  scale: {
    ticks: { min: 0 },


How to convert HTML to PDF using iText

This links might be helpful to convert.

If it is a college Project, you can even go for these,

Example is given to convert HTML to PDF

Ajax success event not working

I had same problem. it happen because javascript expect json data type in returning data. but if you use echo or print in your php this situation occur. if you use echo function in php to return data, Simply remove dataType : "json" working pretty well.

Check if table exists in SQL Server

Please see the below approaches,


We can write a query like below to check if a Customers Table exists in the current database.

    PRINT 'Table Exists'

Approach 2: Using OBJECT_ID() function

We can use OBJECT_ID() function like below to check if a Customers Table exists in the current database.

IF OBJECT_ID(N'dbo.Customers', N'U') IS NOT NULL
    PRINT 'Table Exists'

Approach 3: Using sys.Objects Catalog View

We can use the Sys.Objects catalog view to check the existence of the Table as shown below:

IF EXISTS(SELECT 1 FROM sys.Objects WHERE  Object_id = OBJECT_ID(N'dbo.Customers') AND Type = N'U')
   PRINT 'Table Exists'

Approach 4: Using sys.Tables Catalog View

We can use the Sys.Tables catalog view to check the existence of the Table as shown below:

 IF EXISTS(SELECT 1 FROM sys.Tables WHERE  Name = N'Customers' AND Type = N'U')
      PRINT 'Table Exists'

Approach 5: Avoid Using sys.sysobjects System table

We should avoid using sys.sysobjects System Table directly, direct access to it will be deprecated in some future versions of the Sql Server. As per Microsoft BOL link, Microsoft is suggesting to use the catalog views sys.objects/sys.tables instead of sys.sysobjects system table directly.

  IF EXISTS(SELECT name FROM sys.sysobjects WHERE Name = N'Customers' AND xtype = N'U')
     PRINT 'Table Exists'

referred from:

What's the difference between __PRETTY_FUNCTION__, __FUNCTION__, __func__?

__func__ is an implicitly declared identifier that expands to a character array variable containing the function name when it is used inside of a function. It was added to C in C99. From C99 §

The identifier __func__ is implicitly declared by the translator as if, immediately following the opening brace of each function definition, the declaration

static const char __func__[] = "function-name";

appeared, where function-name is the name of the lexically-enclosing function. This name is the unadorned name of the function.

Note that it is not a macro and it has no special meaning during preprocessing.

__func__ was added to C++ in C++11, where it is specified as containing "an implementation-de?ned string" (C++11 §8.4.1[dcl.fct.def.general]/8), which is not quite as useful as the specification in C. (The original proposal to add __func__ to C++ was N1642).

__FUNCTION__ is a pre-standard extension that some C compilers support (including gcc and Visual C++); in general, you should use __func__ where it is supported and only use __FUNCTION__ if you are using a compiler that does not support it (for example, Visual C++, which does not support C99 and does not yet support all of C++0x, does not provide __func__).

__PRETTY_FUNCTION__ is a gcc extension that is mostly the same as __FUNCTION__, except that for C++ functions it contains the "pretty" name of the function including the signature of the function. Visual C++ has a similar (but not quite identical) extension, __FUNCSIG__.

For the nonstandard macros, you will want to consult your compiler's documentation. The Visual C++ extensions are included in the MSDN documentation of the C++ compiler's "Predefined Macros". The gcc documentation extensions are described in the gcc documentation page "Function Names as Strings."

git remove merge commit from history

Starting with the repo in the original state

Original repo history

To remove the merge commit and squash the branch into a single commit in the mainline

Squashed commits, no merge commit

Use these commands (replacing 5 and 1 with the SHAs of the corresponding commits):

git checkout 5
git reset --soft 1
git commit --amend -m '1 2 3 4 5'
git rebase HEAD master

To retain a merge commit but squash the branch commits into one:

Squashed commits, retained merge commit

Use these commands (replacing 5, 1 and C with the SHAs of the corresponding commits):

git checkout -b tempbranch 5
git reset --soft 1
git commit --amend -m '1 2 3 4 5'
git checkout C
git merge --no-ff tempbranch
git rebase HEAD master

To remove the merge commit and replace it with individual commits from the branch

Branch moved into mainline, no merge commit

Just do (replacing 5 with the SHA of the corresponding commit):

git rebase 5 master

And finally, to remove the branch entirely

Branch removed entirely

Use this command (replacing C and D with the SHAs of the corresponding commits):

git rebase --onto C D~ master

Googlemaps API Key for Localhost

If you are working on localhost, create a separate APIkey for your development and then remove restrictions on that key so that your localhost can use it. Remember to not use this key on production, so you don't expose your key to hunters online.

I had the same issue and all attempts to get the restrictions working on my localhost environment was not successful until I created a separate apikey specifically for development and then removed its restrictions. However I don't use that key on production environment, and once am done with developments, I will delete the API key immediately.

I Know this post is late, but for people that will likely face this issue in the future, this is the best route to go.

How can I disable ARC for a single file in a project?

It is possible to disable ARC (Automatic Reference Counting) for particular file in Xcode.

Select Target -> Build Phases -> Compile Sources -> Select File (double click) -> Add "-fno-objc-arc" to pop-up window.

I had encountered this situation in using "Reachibility" files.

This is shown in below figure :

enter image description here

Rails 4: assets not loading in production

I may be wrong but those who recommend changing

config.assets.compile = true

The comment on this line reads: #Do not fallback to assets pipeline if a precompiled asset is missed.

This suggests that by setting this to true you are not fixing the problem but rather bypassing it and running the pipeline every time. This must surely kill your performance and defeat the purpose of the pipeline?

I had this same error and it was due to the application running in a sub folder that rails didn't know about.

So my css file where in home/subfolder/app/public/.... but rails was looking in home/app/public/...

try either moving your app out of the subfolder or telling rails that it is in a subfolder.

Visual studio equivalent of java System.out

In System.Diagnostics,


etc. will print to the Output window in VS.

Checking if a variable exists in javascript

if ( typeof variableName !== 'undefined' && variableName )
//// could throw an error if var doesnt exist at all

if ( window.variableName )
//// could be true if var == 0

////further on it depends on what is stored into that var
// if you expect an object to be stored in that var maybe
if ( !!window.variableName )
//could be the right way

best way => see what works for your case

Make a Bash alias that takes a parameter?

If you're looking for a generic way to apply all params to a function, not just one or two or some other hardcoded amount, you can do that this way:

#!/usr/bin/env bash

# you would want to `source` this file, maybe in your .bash_profile?
function runjar_fn(){
    java -jar myjar.jar "$@";

alias runjar=runjar_fn;

So in the example above, i pass all parameters from when i run runjar to the alias.

For example, if i did runjar hi there it would end up actually running java -jar myjar.jar hi there. If i did runjar one two three it would run java -jar myjar.jar one two three.

I like this $@ - based solution because it works with any number of params.

Understanding dict.copy() - shallow or deep?

In your second part, you should use new = original.copy()

.copy and = are different things.

What is the difference between user and kernel modes in operating systems?

CPU rings are the most clear distinction

In x86 protected mode, the CPU is always in one of 4 rings. The Linux kernel only uses 0 and 3:

  • 0 for kernel
  • 3 for users

This is the most hard and fast definition of kernel vs userland.

Why Linux does not use rings 1 and 2: CPU Privilege Rings: Why rings 1 and 2 aren't used?

How is the current ring determined?

The current ring is selected by a combination of:

  • global descriptor table: a in-memory table of GDT entries, and each entry has a field Privl which encodes the ring.

    The LGDT instruction sets the address to the current descriptor table.

    See also:

  • the segment registers CS, DS, etc., which point to the index of an entry in the GDT.

    For example, CS = 0 means the first entry of the GDT is currently active for the executing code.

What can each ring do?

The CPU chip is physically built so that:

  • ring 0 can do anything

  • ring 3 cannot run several instructions and write to several registers, most notably:

    • cannot change its own ring! Otherwise, it could set itself to ring 0 and rings would be useless.

      In other words, cannot modify the current segment descriptor, which determines the current ring.

    • cannot modify the page tables: How does x86 paging work?

      In other words, cannot modify the CR3 register, and paging itself prevents modification of the page tables.

      This prevents one process from seeing the memory of other processes for security / ease of programming reasons.

    • cannot register interrupt handlers. Those are configured by writing to memory locations, which is also prevented by paging.

      Handlers run in ring 0, and would break the security model.

      In other words, cannot use the LGDT and LIDT instructions.

    • cannot do IO instructions like in and out, and thus have arbitrary hardware accesses.

      Otherwise, for example, file permissions would be useless if any program could directly read from disk.

      More precisely thanks to Michael Petch: it is actually possible for the OS to allow IO instructions on ring 3, this is actually controlled by the Task state segment.

      What is not possible is for ring 3 to give itself permission to do so if it didn't have it in the first place.

      Linux always disallows it. See also: Why doesn't Linux use the hardware context switch via the TSS?

How do programs and operating systems transition between rings?

  • when the CPU is turned on, it starts running the initial program in ring 0 (well kind of, but it is a good approximation). You can think this initial program as being the kernel (but it is normally a bootloader that then calls the kernel still in ring 0).

  • when a userland process wants the kernel to do something for it like write to a file, it uses an instruction that generates an interrupt such as int 0x80 or syscall to signal the kernel. x86-64 Linux syscall hello world example:

        .ascii "hello world\n"
        hello_world_len = . - hello_world
    .global _start
        /* write */
        mov $1, %rax
        mov $1, %rdi
        mov $hello_world, %rsi
        mov $hello_world_len, %rdx
        /* exit */
        mov $60, %rax
        mov $0, %rdi

    compile and run:

    as -o hello_world.o hello_world.S
    ld -o hello_world.out hello_world.o

    GitHub upstream.

    When this happens, the CPU calls an interrupt callback handler which the kernel registered at boot time. Here is a concrete baremetal example that registers a handler and uses it.

    This handler runs in ring 0, which decides if the kernel will allow this action, do the action, and restart the userland program in ring 3. x86_64

  • when the exec system call is used (or when the kernel will start /init), the kernel prepares the registers and memory of the new userland process, then it jumps to the entry point and switches the CPU to ring 3

  • If the program tries to do something naughty like write to a forbidden register or memory address (because of paging), the CPU also calls some kernel callback handler in ring 0.

    But since the userland was naughty, the kernel might kill the process this time, or give it a warning with a signal.

  • When the kernel boots, it setups a hardware clock with some fixed frequency, which generates interrupts periodically.

    This hardware clock generates interrupts that run ring 0, and allow it to schedule which userland processes to wake up.

    This way, scheduling can happen even if the processes are not making any system calls.

What is the point of having multiple rings?

There are two major advantages of separating kernel and userland:

  • it is easier to make programs as you are more certain one won't interfere with the other. E.g., one userland process does not have to worry about overwriting the memory of another program because of paging, nor about putting hardware in an invalid state for another process.
  • it is more secure. E.g. file permissions and memory separation could prevent a hacking app from reading your bank data. This supposes, of course, that you trust the kernel.

How to play around with it?

I've created a bare metal setup that should be a good way to manipulate rings directly:

I didn't have the patience to make a userland example unfortunately, but I did go as far as paging setup, so userland should be feasible. I'd love to see a pull request.

Alternatively, Linux kernel modules run in ring 0, so you can use them to try out privileged operations, e.g. read the control registers: How to access the control registers cr0,cr2,cr3 from a program? Getting segmentation fault

Here is a convenient QEMU + Buildroot setup to try it out without killing your host.

The downside of kernel modules is that other kthreads are running and could interfere with your experiments. But in theory you can take over all interrupt handlers with your kernel module and own the system, that would be an interesting project actually.

Negative rings

While negative rings are not actually referenced in the Intel manual, there are actually CPU modes which have further capabilities than ring 0 itself, and so are a good fit for the "negative ring" name.

One example is the hypervisor mode used in virtualization.

For further details see:


In ARM, the rings are called Exception Levels instead, but the main ideas remain the same.

There exist 4 exception levels in ARMv8, commonly used as:

  • EL0: userland

  • EL1: kernel ("supervisor" in ARM terminology).

    Entered with the svc instruction (SuperVisor Call), previously known as swi before unified assembly, which is the instruction used to make Linux system calls. Hello world ARMv8 example:


    .global _start
        /* write */
        mov x0, 1
        ldr x1, =msg
        ldr x2, =len
        mov x8, 64
        svc 0
        /* exit */
        mov x0, 0
        mov x8, 93
        svc 0
        .ascii "hello syscall v8\n"
    len = . - msg

    GitHub upstream.

    Test it out with QEMU on Ubuntu 16.04:

    sudo apt-get install qemu-user gcc-arm-linux-gnueabihf
    arm-linux-gnueabihf-as -o hello.o hello.S
    arm-linux-gnueabihf-ld -o hello hello.o
    qemu-arm hello

    Here is a concrete baremetal example that registers an SVC handler and does an SVC call.

  • EL2: hypervisors, for example Xen.

    Entered with the hvc instruction (HyperVisor Call).

    A hypervisor is to an OS, what an OS is to userland.

    For example, Xen allows you to run multiple OSes such as Linux or Windows on the same system at the same time, and it isolates the OSes from one another for security and ease of debug, just like Linux does for userland programs.

    Hypervisors are a key part of today's cloud infrastructure: they allow multiple servers to run on a single hardware, keeping hardware usage always close to 100% and saving a lot of money.

    AWS for example used Xen until 2017 when its move to KVM made the news.

  • EL3: yet another level. TODO example.

    Entered with the smc instruction (Secure Mode Call)

The ARMv8 Architecture Reference Model DDI 0487C.a - Chapter D1 - The AArch64 System Level Programmer's Model - Figure D1-1 illustrates this beautifully:

enter image description here

The ARM situation changed a bit with the advent of ARMv8.1 Virtualization Host Extensions (VHE). This extension allows the kernel to run in EL2 efficiently:

enter image description here

VHE was created because in-Linux-kernel virtualization solutions such as KVM have gained ground over Xen (see e.g. AWS' move to KVM mentioned above), because most clients only need Linux VMs, and as you can imagine, being all in a single project, KVM is simpler and potentially more efficient than Xen. So now the host Linux kernel acts as the hypervisor in those cases.

Note how ARM, maybe due to the benefit of hindsight, has a better naming convention for the privilege levels than x86, without the need for negative levels: 0 being the lower and 3 highest. Higher levels tend to be created more often than lower ones.

The current EL can be queried with the MRS instruction: what is the current execution mode/exception level, etc?

ARM does not require all exception levels to be present to allow for implementations that don't need the feature to save chip area. ARMv8 "Exception levels" says:

An implementation might not include all of the Exception levels. All implementations must include EL0 and EL1. EL2 and EL3 are optional.

QEMU for example defaults to EL1, but EL2 and EL3 can be enabled with command line options: qemu-system-aarch64 entering el1 when emulating a53 power up

Code snippets tested on Ubuntu 18.10.

CSS-Only Scrollable Table with fixed headers

Ive achieved this easily using this code :

So you have a structure like this :


just style the thead with :

    position: -webkit-sticky;
    position: -moz-sticky;
    position: -ms-sticky;
    position: -o-sticky;
    position: sticky;
    top: 0px;

Three things to consider :

First, this property is new. It’s not supported at all, apart from the beta builds of Webkit-based browsers. So caveat formator. Again, if you really want for your users to benefit from sticky headers, go with a javascript implementation.

Second, if you do use it, you’ll need to incorporate vendor prefixes. Perhaps position: sticky will work one day. For now, though, you need to use position:-webkit-sticky (and the others; check the block of css further up in this post).

Third, there aren’t any positioning defaults at the moment, so you need to at least include top: 0; in the same css declaration as the position:-webkit-sticky. Otherwise, it’ll just scroll off-screen.

generate random string for div id

Here is the reusable function to generate the random IDs :

function revisedRandId() {
     return Math.random().toString(36).replace(/[^a-z]+/g, '').substr(2, 10);

// It will not start with the any number digit so it will be supported by CSS3

Difference between Grunt, NPM and Bower ( package.json vs bower.json )

Npm and Bower are both dependency management tools. But the main difference between both is npm is used for installing Node js modules but bower js is used for managing front end components like html, css, js etc.

A fact that makes this more confusing is that npm provides some packages which can be used in front-end development as well, like grunt and jshint.

These lines add more meaning

Bower, unlike npm, can have multiple files (e.g. .js, .css, .html, .png, .ttf) which are considered the main file(s). Bower semantically considers these main files, when packaged together, a component.

Edit: Grunt is quite different from Npm and Bower. Grunt is a javascript task runner tool. You can do a lot of things using grunt which you had to do manually otherwise. Highlighting some of the uses of Grunt:

  1. Zipping some files (e.g. zipup plugin)
  2. Linting on js files (jshint)
  3. Compiling less files (grunt-contrib-less)

There are grunt plugins for sass compilation, uglifying your javascript, copy files/folders, minifying javascript etc.

Please Note that grunt plugin is also an npm package.


When I want to add a package (and check in the dependency into git), where does it belong - into package.json or into bower.json

It really depends where does this package belong to. If it is a node module(like grunt,request) then it will go in package.json otherwise into bower json.


When should I ever install packages explicitly like that without adding them to the file that manages dependencies

It does not matter whether you are installing packages explicitly or mentioning the dependency in .json file. Suppose you are in the middle of working on a node project and you need another project, say request, then you have two options:

  • Edit the package.json file and add a dependency on 'request'
  • npm install


  • Use commandline: npm install --save request

--save options adds the dependency to package.json file as well. If you don't specify --save option, it will only download the package but the json file will be unaffected.

You can do this either way, there will not be a substantial difference.

Difference between Key, Primary Key, Unique Key and Index in MySQL

PRIMARY KEY AND UNIQUE KEY are similar except it has different functions. Primary key makes the table row unique (i.e, there cannot be 2 row with the exact same key). You can only have 1 primary key in a database table.

Unique key makes the table column in a table row unique (i.e., no 2 table row may have the same exact value). You can have more than 1 unique key table column (unlike primary key which means only 1 table column in the table is unique).

INDEX also creates uniqueness. MySQL (example) will create a indexing table for the column that is indexed. This way, it's easier to retrieve the table row value when the query is queried on that indexed table column. The disadvantage is that if you do many updating/deleting/create, MySQL has to manage the indexing tables (and that can be a performance bottleneck).

Hope this helps.

What svn command would list all the files modified on a branch?

This will list only modified files:

svn status -u | grep M

How to concatenate multiple column values into a single column in Panda dataframe

df = DataFrame({'foo':['a','b','c'], 'bar':[1, 2, 3], 'new':['apple', 'banana', 'pear']})

df['combined'] = df['foo'].astype(str)+'_'+df['bar'].astype(str)

If you concatenate with string('_') please you convert the column to string which you want and after you can concatenate the dataframe.

Uncaught SyntaxError: Unexpected end of JSON input at JSON.parse (<anonymous>)

You are calling:


But when you defined scatterSeries, you said:

var scatterSeries = []; 

When you try to parse it as JSON it is converted to a string (""), which is empty, so you reach the end of the string before having any of the possible content of a JSON text.

scatterSeries is not JSON. Do not try to parse it as JSON.

data is not JSON either (getJSON will parse it as JSON automatically).

ch is JSON … but shouldn't be. You should just create a plain object in the first place:

var ch = {
    "name": "graphe1",
    "items": data.results[1]


In short, for what you are doing, you shouldn't have JSON.parse anywhere in your code. The only place it should be is in the jQuery library itself.

How do I get an OAuth 2.0 authentication token in C#

I used ADAL.NET/ Microsoft Identity Platform to achieve this. The advantage of using it was that we get a nice wrapper around the code to acquire AccessToken and we get additional features like Token Cache out-of-the-box. From the documentation:

Why use ADAL.NET ?

ADAL.NET V3 (Active Directory Authentication Library for .NET) enables developers of .NET applications to acquire tokens in order to call secured Web APIs. These Web APIs can be the Microsoft Graph, or 3rd party Web APIs.

Here is the code snippet:

    // Import Nuget package: Microsoft.Identity.Client
    public class AuthenticationService
         private readonly List<string> _scopes;
         private readonly IConfidentialClientApplication _app;

        public AuthenticationService(AuthenticationConfiguration authentication)

             _app = ConfidentialClientApplicationBuilder

           _scopes = new List<string> {$"{authentication.Audience}/.default"};

       public async Task<string> GetAccessToken()
           var authenticationResult = await _app.AcquireTokenForClient(_scopes) 
           return authenticationResult.AccessToken;

Changing directory in Google colab (breaking out of the python interpreter)


%cd SwitchFrequencyAnalysis

to change the current working directory for the notebook environment (and not just the subshell that runs your ! command).

you can confirm it worked with the pwd command like this:


further information about jupyter / ipython magics:

disable textbox using jquery?

I know it is not a good habit to answer an old question but I'm putting this answer for people who would see the question afterwards.

The best way to change the state in JQuery now is through

$("#input").prop('disabled', true); 
$("#input").prop('disabled', false);

Please check this link for full illustration. Disable/enable an input with jQuery?

Creating a static class with no instances

Seems that you need classmethod:

class World(object):

    allAirports = []

    def initialize(cls):

        if not cls.allAirports:
            f = open(os.path.expanduser("~/Desktop/1000airports.csv"))
            file_reader = csv.reader(f)

            for col in file_reader:

        return cls.allAirports

What is the !! (not not) operator in JavaScript?

here is a piece of code from angular js

var requestAnimationFrame = $window.requestAnimationFrame ||
                                $window.webkitRequestAnimationFrame ||

 var rafSupported = !!requestAnimationFrame;

their intention is to set rafSupported to true or false based on the availability of function in requestAnimationFrame

it can be achieved by checking in following way in general:

if(typeof  requestAnimationFrame === 'function')
rafSupported =true;
rafSupported =false;

the short way could be using !!

rafSupported = !!requestAnimationFrame ;

so if requestAnimationFrame was assigned a function then !requestAnimationFrame would be false and one more ! of it would be true

if requestAnimationFrame was assinged undefined then !requestAnimationFrame would be true and one more ! of it would be false

nginx: how to create an alias url route?

server {
  root /path/to/root;
  location / {
    # bla bla
  location /demo {
    alias /path/to/root/production/folder/here;

If you need to use try_files inside /demo you'll need to replace alias with a root and do a rewrite because of the bug explained here

Using GroupBy, Count and Sum in LINQ Lambda Expressions

        var q = from b in listOfBoxes
                group b by b.Owner into g
                select new
                               Owner = g.Key,
                               Boxes = g.Count(),
                               TotalWeight = g.Sum(item => item.Weight),
                               TotalVolume = g.Sum(item => item.Volume)

Align an element to bottom with flexbox

When setting your display to flex, you could simply use the flex property to mark which content can grow and which content cannot.

Flex property

div.content {_x000D_
 height: 300px;_x000D_
 display: flex;_x000D_
 flex-direction: column;_x000D_
div.up {_x000D_
  flex: 1;_x000D_
div.down {_x000D_
  flex: none;_x000D_
<div class="content">_x000D_
  <div class="up">_x000D_
    <h1>heading 1</h1>_x000D_
    <h2>heading 2</h2>_x000D_
    <p>Some more or less text</p>_x000D_
  <div class="down">_x000D_
    <a href="/" class="button">Click me</a>_x000D_

My httpd.conf is empty

OK - what you're missing is that its designed to be more industrial and serve many sites, so the config you want is probably:


which on my system is linked to from /etc/apache2/sites-enabled/

if you want to have different sites with different options, copy the file and then change those... error in opening zip file

On Windows7 I had this problem over a Samba network connection for a Java8 Jar File >80 MBytes big. Copying the file to a local drive fixed the issue.

Replace last occurrence of a string in a string

$string = "picture_0007_value";
$findChar =strrpos($string,"_");
if($findChar !== FALSE) {

echo $string;

Apart from the mistakes in the code, Faruk Unal has the best anwser. One function does the trick.

round value to 2 decimals javascript

If you want it visually formatted to two decimals as a string (for output) use toFixed():

var priceString = someValue.toFixed(2);

The answer by @David has two problems:

  1. It leaves the result as a floating point number, and consequently holds the possibility of displaying a particular result with many decimal places, e.g. 134.1999999999 instead of "134.20".

  2. If your value is an integer or rounds to one tenth, you will not see the additional decimal value:

    var n = 1.099;
    (Math.round( n * 100 )/100 ).toString() //-> "1.1"
    n.toFixed(2)                            //-> "1.10"
    var n = 3;
    (Math.round( n * 100 )/100 ).toString() //-> "3"
    n.toFixed(2)                            //-> "3.00"

And, as you can see above, using toFixed() is also far easier to type. ;)

/** and /* in Java Comments

Java supports two types of comments:

  • /* multiline comment */ : The compiler ignores everything from /* to */. The comment can span over multiple lines.

  • // single line : The compiler ignores everything from // to the end of the line.

Some tool such as javadoc use a special multiline comment for their purpose. For example /** doc comment */ is a documentation comment used by javadoc when preparing the automatically generated documentation, but for Java it's a simple multiline comment.

How to close TCP and UDP ports via windows command line

You can't close sockets on your server without owning those sockets hence you can't actually close the socket down without having code running in the process that owns the server socket.

However, there is another option which is telling the client to close its socket. Sending a RST TCP packet to the port the client is connecting on will cause the client to drop their connection. You can do that with RST scanning using nmap.

HTTPS connection Python

import requests
r = requests.get("") 
data = r.content  # Content of response

print r.status_code  # Status code of response
print data

What's a good IDE for Python on Mac OS X?

Python support on netbeans is surprisingly good, and comes with most of the features you're looking for.

Can gcc output C code after preprocessing?

Yes. Pass gcc the -E option. This will output preprocessed source code.

What causes: "Notice: Uninitialized string offset" to appear?

The error may occur when the number of times you iterate the array is greater than the actual size of the array. for example:

    echo ' '.$one[$i];

will show the error. first case u can take the mod of i.. for example

function mod($i,$length){
  $m = $i % $size;
  if ($m > $size)
  return $m;

  echo ' '.$one[$k];

or might be it not an array (maybe it was a value and you tried to access it like an array) for example:

$k = 2;

How to convert float to varchar in SQL Server

this is the solution I ended up using in sqlserver 2012 (since all the other suggestions had the drawback of truncating fractional part or some other drawback).

declare @float float = 1000000000.1234;
select format(@float, N'#.##############################');



this has the further advantage (in my case) to make thousands separator and localization easy:

select format(@float, N'#,##0.##########', 'de-DE');


HTML 5 Video "autoplay" not automatically starting in CHROME

Extremeandy has mentioned as of Chrome 66 autoplay video has been disabled.

After looking into this I found that muted videos are still able to be autoplayed. In my case the video didn't have any audio, but adding muted to the video tag has fixed it:

Hopefully this will help others also.

TypeError: only length-1 arrays can be converted to Python scalars while plot showing

The error "only length-1 arrays can be converted to Python scalars" is raised when the function expects a single value but you pass an array instead.

If you look at the call signature of, you'll see that it accepts a single value, not an array. In general, if you want to apply a function that accepts a single element to every element in an array, you can use np.vectorize:

import numpy as np
import matplotlib.pyplot as plt

def f(x):
f2 = np.vectorize(f)
x = np.arange(1, 15.1, 0.1)
plt.plot(x, f2(x))

You can skip the definition of f(x) and just pass to the vectorize function: f2 = np.vectorize(

Note that np.vectorize is just a convenience function and basically a for loop. That will be inefficient over large arrays. Whenever you have the possibility, use truly vectorized functions or methods (like astype(int) as @FFT suggests).

How to view DB2 Table structure

The easiest way as many have mentioned already is to do a DESCRIBE TABLE

However you can also get some the same + additional information from



I usually use SYSCAT.COLUMNS to find the related tables in the database where I already know the column name :)

Another good way if you want to get the DDL of a particular table or the whole database is to use the db2look

# db2look -d *dbname* -t *tablename* > tablestructure.out

This will generate the ".out" file for you which will contain the particular table's DDL script.

# db2look -d *dbname* -e > dbstructure.out

This will generate the entire database's DDL as a single script file, this is usually used to replicate the database, "-e" is to indicate that one wants to export DDL suitable recreate exact same setup in a new database.

Hope this can help someone looking for such answers :)

jQuery disable/enable submit button

To remove disabled attribute use,


and to add disabled attribute use,

$("#elementID").prop("disabled", true);

Enjoy :)

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

If you are using C# 3.0 or higher you can do the following

foreach ( TextBox tb in this.Controls.OfType<TextBox>()) {

Without C# 3.0 you can do the following

foreach ( Control c in this.Controls ) {
  TextBox tb = c as TextBox;
  if ( null != tb ) {

Or even better, write OfType in C# 2.0.

public static IEnumerable<T> OfType<T>(IEnumerable e) where T : class { 
  foreach ( object cur in e ) {
    T val = cur as T;
    if ( val != null ) {
      yield return val;

foreach ( TextBox tb in OfType<TextBox>(this.Controls)) {

Connecting to via command line

Using Linux or OSx, do what Sorin recommended but use port 465 instead. 25 is the generic SMTP port, but not what GMail uses. Also, I don't believe you want to use -starttls smtp

openssl s_client -connect

You should get lots of information on the SSL session and the response:

220 ...

Type in


and you'll receive:

250 at your service

From there it is not quite as straightforward as just sending SMTP messages because Gmail has protections in place to ensure you only send emails appearing to be from accounts that actually belong to you. Instead of typing in "Helo", use "Ehlo". I don't know much about SMTP so I cannot explain the difference, and don't have time to research much. Perhaps someone with more knowledge can explain.

Then, type "auth login" and you will receive the following:

334 VXNlcm5hbWU6

This is essentially the word "Username" encoded in Base 64. Using a Base 64 encoder such as this one, encode your user name and enter it. Do the same for your password, which is requested next. You should see:

235 2.7.0 Accepted

And that's it, you're logged in.

There is one more oddity to overcome if you're using OSx or Linux terminals. Just pressing the "ENTER" key does not apparently result in a CRLF which SMTP needs to end a message. You have to use "CTRL+V+ENTER". So, this should look like the following:

250 2.0.0 OK

Confirm Password with jQuery Validate

Remove the required: true rule.

Demo: Fiddle

            rules : {
                password : {
                    minlength : 5
                password_confirm : {
                    minlength : 5,
                    equalTo : "#password"

How to read a CSV file from a URL with Python?

import pandas as pd
data = pd.read_csv(url,sep=";") # use sep="," for coma separation. 

enter image description here

How to get nth jQuery element

.eq() -An integer indicating the 0-based position of the element.


Consider a page with a simple list on it:

<li>list item 1</li>
<li>list item 2</li>
<li>list item 3</li>
<li>list item 4</li>

We can apply this method to the set of list items:

$( "li" ).eq( 2 ).css( "background-color", "red" );

For more information : .eq()

DateTime's representation in milliseconds?

In C#, you can write

(long)(date - new DateTime(1970, 1, 1)).TotalMilliseconds

'' is not recognized as an internal or external command, operable program or batch file

When you want to run an executable file from the Command prompt, (cmd.exe), or a batch file, it will:

  • Search the current working directory for the executable file.
  • Search all locations specified in the %PATH% environment variable for the executable file.

If the file isn't found in either of those options you will need to either:

  1. Specify the location of your executable.
  2. Change the working directory to that which holds the executable.
  3. Add the location to %PATH% by apending it, (recommended only with extreme caution).

You can see which locations are specified in %PATH% from the Command prompt, Echo %Path%.

Because of your reported error we can assume that Mobile.exe is not in the current directory or in a location specified within the %Path% variable, so you need to use 1., 2. or 3..

Examples for 1.



"C:\directory path with spaces\My-App\Mobile.exe"

Alternatively you may try:

Start C:\directory_path_without_spaces\My-App\Mobile.exe


Start "" "C:\directory path with spaces\My-App\Mobile.exe"

Where "" is an empty title, (you can optionally add a string between those doublequotes).

Examples for 2.

CD /D C:\directory_path_without_spaces\My-App


CD /D "C:\directory path with spaces\My-App"

You could also use the /D option with Start to change the working directory for the executable to be run by the start command

Start /D C:\directory_path_without_spaces\My-App Mobile.exe


Start "" /D "C:\directory path with spaces\My-App" Mobile.exe

JavaScript: Class.method vs. Class.prototype.method

Yes, the first one is a static method also called class method, while the second one is an instance method.

Consider the following examples, to understand it in more detail.

In ES5

function Person(firstName, lastName) {
   this.firstName = firstName;
   this.lastName = lastName;

Person.isPerson = function(obj) {
   return obj.constructor === Person;

Person.prototype.sayHi = function() {
   return "Hi " + this.firstName;

In the above code, isPerson is a static method, while sayHi is an instance method of Person.

Below, is how to create an object from Person constructor.

var aminu = new Person("Aminu", "Abubakar");

Using the static method isPerson.

Person.isPerson(aminu); // will return true

Using the instance method sayHi.

aminu.sayHi(); // will return "Hi Aminu"

In ES6

class Person {
   constructor(firstName, lastName) {
      this.firstName = firstName;
      this.lastName = lastName;

   static isPerson(obj) {
      return obj.constructor === Person;

   sayHi() {
      return `Hi ${this.firstName}`;

Look at how static keyword was used to declare the static method isPerson.

To create an object of Person class.

const aminu = new Person("Aminu", "Abubakar");

Using the static method isPerson.

Person.isPerson(aminu); // will return true

Using the instance method sayHi.

aminu.sayHi(); // will return "Hi Aminu"

NOTE: Both examples are essentially the same, JavaScript remains a classless language. The class introduced in ES6 is primarily a syntactical sugar over the existing prototype-based inheritance model.

How to get UTC time in Python?

import datetime
import pytz

# datetime object with timezone awareness:

# seconds from epoch: 

# ms from epoch:
int( * 1000) 

Should I write script in the body or the head of the html?

I always put my scripts in the header. My reasons:

  1. I like to separate code and (static) text
  2. I usually load my script from external sources
  3. The same script is used from several pages, so it feels like an include file (which also goes in the header)

Objective-C declared @property attributes (nonatomic, copy, strong, weak)

This link has the break down

assign implies __unsafe_unretained ownership.

copy implies __strong ownership, as well as the usual behavior of copy semantics on the setter.

retain implies __strong ownership.

strong implies __strong ownership.

unsafe_unretained implies __unsafe_unretained ownership.

weak implies __weak ownership.

How to have an automatic timestamp in SQLite?

Just declare a default value for a field:

    Name TEXT,
    Other STUFF,

However, if your INSERT command explicitly sets this field to NULL, it will be set to NULL.

Detecting request type in PHP (GET, POST, PUT or DELETE)

You can get any query string data i.e

You must get data using $_GET['id'] or $_REQUEST['id'].

Post data means like form <form action='' method='POST'> you must use $_POST or $_REQUEST.

What is an "index out of range" exception, and how do I fix it?

Why does this error occur?

Because you tried to access an element in a collection, using a numeric index that exceeds the collection's boundaries.

The first element in a collection is generally located at index 0. The last element is at index n-1, where n is the Size of the collection (the number of elements it contains). If you attempt to use a negative number as an index, or a number that is larger than Size-1, you're going to get an error.

How indexing arrays works

When you declare an array like this:

var array = new int[6]

The first and last elements in the array are

var firstElement = array[0];
var lastElement = array[5];

So when you write:

var element = array[5];

you are retrieving the sixth element in the array, not the fifth one.

Typically, you would loop over an array like this:

for (int index = 0; index < array.Length; index++)

This works, because the loop starts at zero, and ends at Length-1 because index is no longer less than Length.

This, however, will throw an exception:

for (int index = 0; index <= array.Length; index++)

Notice the <= there? index will now be out of range in the last loop iteration, because the loop thinks that Length is a valid index, but it is not.

How other collections work

Lists work the same way, except that you generally use Count instead of Length. They still start at zero, and end at Count - 1.

for (int index = 0; i < list.Count; index++)

However, you can also iterate through a list using foreach, avoiding the whole problem of indexing entirely:

foreach (var element in list)

You cannot index an element that hasn't been added to a collection yet.

var list = new List<string>();
Console.WriteLine(list[3]);  // Throws exception.

What is the proper way to URL encode Unicode characters?

The general rule seems to be that browsers encode form responses according to the content-type of the page the form was served from. This is a guess that if the server sends us "text/xml; charset=iso-8859-1", then they expect responses back in the same format.

If you're just entering a URL in the URL bar, then the browser doesn't have a base page to work on and therefore just has to guess. So in this case it seems to be doing utf-8 all the time (since both your inputs produced three-octet form values).

The sad truth is that AFAIK there's no standard for what character set the values in a query string, or indeed any characters in the URL, should be interpreted as. At least in the case of values in the query string, there's no reason to suppose that they necessarily do correspond to characters.

It's a known problem that you have to tell your server framework which character set you expect the query string to be encoded as--- for instance, in Tomcat, you have to call request.setEncoding() (or some similar method) before you call any of the request.getParameter() methods. The dearth of documentation on this subject probably reflects the lack of awareness of the problem amongst many developers. (I regularly ask Java interviewees what the difference between a Reader and an InputStream is, and regularly get blank looks)

Invoking Java main method with parameters from Eclipse

AFAIK there isn't a built-in mechanism in Eclipse for this.

The closest you can get is to create a wrapper that prompts you for these values and invokes the (hardcoded) main. You then get you execution history as long as you don't clear terminated processes. Two variations on this are either to use JUNit, or to use injection or parameter so that your wrapper always connects to the correct class for its main.

bootstrap responsive table content wrapping

use it in css external file.

word-wrap: break-word;
word-break: break-all;  
white-space: normal !important;
text-align: justify;

Mythical man month 10 lines per developer day - how close on large projects?

How are other people doing?

I am the only full-time dev at our company and have written 500,000 lines of OCaml and F# code over the past 7 years, which equates to about 200 lines of code per day. However, the vast majority of that code is tutorial examples consisting of hundreds of separate projects each a few hundred lines long. Also, there is a lot of duplication between the OCaml and the F#. We are not maintaining any in-house code bases larger than 50kLOC.

In addition to developing and maintaining our own software, I have also consulted for many clients in industry over the past 7 years. For the first client, I wrote 2,000 lines of OCaml over 3 months which is 20 lines of code per day. For the next client, four of us wrote a compiler that generated millions of lines of C/C++/Python/Java/OCaml code as well as documentation in 6 months which is 2,000 lines of code per day per developer. For another client, I replaced 50kLOC of C++ with 6kLOC of F# in 6 months which is -352 lines of code per day. For yet another client, I am rewriting 15kLOC of OCaml in F# which will be the same size so 0 lines of code per day.

For our current client, I will replace 1,600,000 lines of C++ and Mathematica code with ~160kLOC of F# in 1 year (by writing a bespoke compiler) which will be -6,000 lines of code per day. This will be my most successful project to date and will save our client millions of dollars a year in on-going costs. I think everyone should aim to write -6,000 lines of code per day.

Linux command-line call not returning what it should from os.system?

I can not add a comment to IonicBurger because I do not have "50 reputation" so I will add a new entry. My apologies. os.popen() is the best for multiple/complicated commands (my opinion) and also for getting the return value in addition to getting stdout like the following more complicated multiple commands:

import os
out = [ i.strip() for i in os.popen(r"ls *.py | grep -i '.*file' 2>/dev/null; echo $? ").readlines()]
print "     stdout: ", out[:-1]
print "returnValue: ", out[-1]

This will list all python files that have the word 'file' anywhere in their name. The [...] is a list comprehension to remove (strip) the newline character from each entry. The echo $? is a shell command to show the return status of the last command executed which will be the grep command and the last item of the list in this example. the 2>/dev/null says to print the stderr of the grep command to /dev/null so it does not show up in the output. The 'r' before the 'ls' command is to use the raw string so the shell will not interpret metacharacters like '*' incorrectly. This works in python 2.7. Here is the sample output:

      stdout:  ['', '', '', '']
 returnValue:  0

MySQL 1062 - Duplicate entry '0' for key 'PRIMARY'

Run the following query in the mysql console:

SHOW CREATE TABLE momento_distribution

Check for the line that looks something like

CONSTRAINT `momento_distribution_FK_1` FOREIGN KEY (`momento_id`) REFERENCES `momento` (`id`)

It may be different, I just put a guess as to what it could be. If you have a foreign key on both 'momento_id' & 'momento_idmember', you will get two foreign key names. The next step is to delete the foreign keys. Run the following queries:

ALTER TABLE momento_distribution DROP FOREIGN KEY momento_distribution_FK_1
ALTER TABLE momento_distribution DROP FOREIGN KEY momento_distribution_FK_2

Be sure to change the foreign key name to what you got from the CREATE TABLE query. Now you don't have any foreign keys so you can easily remove the primary key. Try the following:

ALTER TABLE  `momento_distribution` DROP PRIMARY KEY

Add the required column as follows:


This query also adds numbers so you won't need to depend on @rowid. Now you need to add the foreign key back to the earlier columns. For that, first make these indexes:

ALTER TABLE  `momento_distribution` ADD INDEX (  `momento_id` )
ALTER TABLE  `momento_distribution` ADD INDEX (  `momento_idmember` )

Now add the foreign keys. Change the Reference Table/column as you need:

ALTER TABLE  `momento_distribution` ADD FOREIGN KEY ( `momento_id`) REFERENCES  `momento` (`id`) ON DELETE RESTRICT ON UPDATE RESTRICT 
ALTER TABLE  `momento_distribution` ADD FOREIGN KEY ( `momento_idmember`) REFERENCES  `member` (`id`) ON DELETE RESTRICT ON UPDATE RESTRICT 

Hope that helps. If you get any errors, please edit the question with the structure of the reference tables & the error code(s) that you are getting.

Proper indentation for Python multiline strings

You probably want to line up with the """

def foo():
    string = """line one
             line two
             line three"""

Since the newlines and spaces are included in the string itself, you will have to postprocess it. If you don't want to do that and you have a whole lot of text, you might want to store it separately in a text file. If a text file does not work well for your application and you don't want to postprocess, I'd probably go with

def foo():
    string = ("this is an "
              "implicitly joined "

If you want to postprocess a multiline string to trim out the parts you don't need, you should consider the textwrap module or the technique for postprocessing docstrings presented in PEP 257:

def trim(docstring):
    if not docstring:
        return ''
    # Convert tabs to spaces (following the normal Python rules)
    # and split into a list of lines:
    lines = docstring.expandtabs().splitlines()
    # Determine minimum indentation (first line doesn't count):
    indent = sys.maxint
    for line in lines[1:]:
        stripped = line.lstrip()
        if stripped:
            indent = min(indent, len(line) - len(stripped))
    # Remove indentation (first line is special):
    trimmed = [lines[0].strip()]
    if indent < sys.maxint:
        for line in lines[1:]:
    # Strip off trailing and leading blank lines:
    while trimmed and not trimmed[-1]:
    while trimmed and not trimmed[0]:
    # Return a single string:
    return '\n'.join(trimmed)

How to open .SQLite files

I would suggest using R and the package RSQLite

#install.packages("RSQLite") #perhaps needed

# connect to the sqlite file
sqlite    <- dbDriver("SQLite")
exampledb <- dbConnect(sqlite,"database.sqlite")


Cannot open backup device. Operating System error 5

I had a similar issue. I added write permissions to the .bak file itself, and my folder that I was writing the backup to for the NETWORK SERVICE user. To add permissions just right-click what file/directory you want to alter, select the security tab, and add the appropriate users/permissions there.

Removing duplicate characters from a string

As string is a list of characters, converting it to dictionary will remove all duplicates and will retain the order.


Reload a DIV without reloading the whole page

<script type="text/javascript" src="" />

<div class="View"><?php include 'Small.php'; ?></div>

<script type="text/javascript">
$(document).ready(function() {
var auto_refresh = setInterval(
    function ()
    }, 15000); // refresh every 15000 milliseconds
        $.ajaxSetup({ cache: true });

Bash syntax error: unexpected end of file

I know I am too late to the party. Hope this may help someone.

Check your .bashrc file. Perhaps rename or move it.

Discussion here: Unable to source a simple bash script

IntelliJ IDEA 13 uses Java 1.5 despite setting to 1.7

In IntelliJ Community Edition 2019.02, Changing the following settings worked for me

  1. Update File->Project structure->Project Settings->Project->Project Language level to Java 11 (update to the java version that you wish to use in your project) using drop down.

  2. Update File->Project structure->Project Settings->Modules->Language level

  3. Update File->Settings->Build,Execution,Deployment -> Compiler -> Java Compiler-> Project ByteCode Version to java 11.

  4. Update Target version for all the entries under File->Settings->Build,Execution,Deployment -> Compiler -> Java Compiler-> Per module Byte Code Version.

Check a radio button with javascript

By using document.getElementById() function you don't have to pass # before element's id.


document.getElementById('_1234').checked = true;

Demo: JSFiddle

Checking session if empty or not

You need to check that Session["emp_num"] is not null before trying to convert it to a string otherwise you will get a null reference exception.

I'd go with your first example - but you could make it slightly more "elegant".

There are a couple of ways, but the ones that springs to mind are:

if (Session["emp_num"] is string)


if (!string.IsNullOrEmpty(Session["emp_num"] as string))

This will return null if the variable doesn't exist or isn't a string.

How to fix error ::Format of the initialization string does not conform to specification starting at index 0::

For anyone who may stumble across this thread while trying to fix this same error that results by running Enable-Migrations, chances are none of the solutions above will help you (I tried them all).

I encountered this same issue in Web API 2 after running this in PM console:

Enable-Migrations -EnableAutomaticMigrations -ConnectionString IdentityConnection -ConnectionProviderName System.Data.SqlClient -Force

I fixed it by changing it to actually use the ApplicationDbContext created in IdentityModels.

Enable-Migrations -ContextTypeName ApplicationDbContext -EnableAutomaticMigrations -Force

The interesting thing is not only does this reference the same exact connection string, but the constructor includes code that 4castle said was a potential fix (i.e., the throwIfV1Schema: false suggestion.

Note that the -Force parameter is only being used because the Configuration.cs file already exists.

Main differences between SOAP and RESTful web services in Java

SOAP Web services:

  1. If your application needs a guaranteed level of reliability and security then SOAP offers additional standards to ensure this type of operation.
  2. If both sides (service provider and service consumer) have to agree on the exchange format then SOAP gives the rigid specifications for this type of interaction.

RestWeb services:

  1. Totally stateless operations: for stateless CRUD (Create, Read, Update, and Delete) operations.
  2. Caching situations: If the information needs to be cached.

Connecting to Oracle Database through C#?

Using Nuget

  1. Right click Project, select Manage NuGet packages...
  2. Select the Browse tab, search for Oracle and install Oracle.ManagedDataAccess

Oracle NuGet package

  1. In code use the following command (Ctrl+. to automatically add the using directive).

  2. Note the different DataSource string which in comparison to Java is different.

    // create connection
    OracleConnection con = new OracleConnection();
    // create connection string using builder
    OracleConnectionStringBuilder ocsb = new OracleConnectionStringBuilder();
    ocsb.Password = "autumn117";
    ocsb.UserID = "john";
    ocsb.DataSource = "database.url:port/databasename";
    // connect
    con.ConnectionString = ocsb.ConnectionString;
    Console.WriteLine("Connection established (" + con.ServerVersion + ")");

How to delete session cookie in Postman?

I tried clearing the chrome cookies to get rid of postman cookies, as one of the answers given here. But it didn't work for me. I checked my postman version, found that it's an old version 5.5.4. So I just tried a Postman update to its latest version 7.3.4. Cool, the issue fixed !!

How can I force WebKit to redraw/repaint to propagate style changes?

Not that this question needs another answer, but I found simply changing the color by a single bit forced a repaint in my particular situation.

//Assuming black is the starting color, we tweak it by a single bit = '#000001';

//Change back to black
setTimeout(function() { = '#000000';
}, 0);

The setTimeout proved critical to move the second style change outside the current event loop.

Best way to convert string to bytes in Python 3?

The absolutely best way is neither of the 2, but the 3rd. The first parameter to encode defaults to 'utf-8' ever since Python 3.0. Thus the best way is

b = mystring.encode()

This will also be faster, because the default argument results not in the string "utf-8" in the C code, but NULL, which is much faster to check!

Here be some timings:

In [1]: %timeit -r 10 'abc'.encode('utf-8')
The slowest run took 38.07 times longer than the fastest. 
This could mean that an intermediate result is being cached.
10000000 loops, best of 10: 183 ns per loop

In [2]: %timeit -r 10 'abc'.encode()
The slowest run took 27.34 times longer than the fastest. 
This could mean that an intermediate result is being cached.
10000000 loops, best of 10: 137 ns per loop

Despite the warning the times were very stable after repeated runs - the deviation was just ~2 per cent.

Using encode() without an argument is not Python 2 compatible, as in Python 2 the default character encoding is ASCII.

>>> 'äöä'.encode()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 in position 0: ordinal not in range(128)

How to select a schema in postgres when using psql?

if you in psql just type

set schema 'temp';

and after that \d shows all relations in "temp

How can I convert a stack trace to a string?

if you are using Java 8, try this

you can find the code for getStackTrace() function provided by as :

public StackTraceElement[] getStackTrace() {
    return getOurStackTrace().clone();

and for StackTraceElement, it provides toString() as follows:

public String toString() {
    return getClassName() + "." + methodName +
        (isNativeMethod() ? "(Native Method)" :
         (fileName != null && lineNumber >= 0 ?
          "(" + fileName + ":" + lineNumber + ")" :
          (fileName != null ?  "("+fileName+")" : "(Unknown Source)")));

So just join the StackTraceElement with "\n".

PHP DateTime __construct() Failed to parse time string (xxxxxxxx) at position x

You should use setTimestamp instead, if you hardcode it:

$start_date = new DateTime();

in your case

$start_date = new DateTime();

How can I find script's directory?

import os
script_dir = os.path.dirname(os.path.realpath(__file__)) + os.sep

substring of an entire column in pandas dataframe

I needed to convert a single column of strings of form nn.n% to float. I needed to remove the % from the element in each row. The attend data frame has two columns.

attend.iloc[:,1:2]=attend.iloc[:,1:2].applymap(lambda x: float(x[:-1]))

Its an extenstion to the original answer. In my case it takes a dataframe and applies a function to each value in a specific column. The function removes the last character and converts the remaining string to float.

How to get the real path of Java application at runtime?

Since the application path of a JAR and an application running from inside an IDE differs, I wrote the following code to consistently return the correct current directory:


public class ProgramDirectoryUtilities
    private static String getJarName()
        return new File(ProgramDirectoryUtilities.class.getProtectionDomain()

    private static boolean runningFromJAR()
        String jarName = getJarName();
        return jarName.contains(".jar");

    public static String getProgramDirectory()
        if (runningFromJAR())
            return getCurrentJARDirectory();
        } else
            return getCurrentProjectDirectory();

    private static String getCurrentProjectDirectory()
        return new File("").getAbsolutePath();

    private static String getCurrentJARDirectory()
            return new File(ProgramDirectoryUtilities.class.getProtectionDomain().getCodeSource().getLocation().toURI().getPath()).getParent();
        } catch (URISyntaxException exception)

        return null;

Simply call getProgramDirectory() and you should be good either way.

batch file to check 64bit or 32bit OS

None of the answers here were working in my case (64 bit processor but 32 bit OS), so here's the solution which worked for me:

(set | find "ProgramFiles(x86)" > NUL) && (echo "%ProgramFiles(x86)%" | find "x86") > NUL && set bits=64 || set bits=32

Move all files except one

The following is not a 100% guaranteed method, and should not at all be attempted for scripting. But some times it is good enough for quick interactive shell usage. A file file glob like


(which will match all files with names starting with a, b or c) can be negated by inserting a "^" character first, i.e.


I sometimes use this for not matching the "lost+found" directory, like for instance:

mv /mnt/usbdisk/[^l]* /home/user/stuff/.

Of course if there are other files starting with l I have to process those afterwards.

Access props inside quotes in React JSX

Instead of adding variables and strings, you can use the ES6 template strings! Here is an example:

<img className="image" src={`images/${this.props.image}`} />

As for all other JavaScript components inside JSX, use template strings inside of curly braces. To "inject" a variable use a dollar sign followed by curly braces containing the variable you would like to inject. For example:

{`string ${variable} another string`}

Set Colorbar Range in matplotlib

Using vmin and vmax forces the range for the colors. Here's an example:

enter image description here

import matplotlib as m
import matplotlib.pyplot as plt
import numpy as np

cdict = {
  'red'  :  ( (0.0, 0.25, .25), (0.02, .59, .59), (1., 1., 1.)),
  'green':  ( (0.0, 0.0, 0.0), (0.02, .45, .45), (1., .97, .97)),
  'blue' :  ( (0.0, 1.0, 1.0), (0.02, .75, .75), (1., 0.45, 0.45))

cm = m.colors.LinearSegmentedColormap('my_colormap', cdict, 1024)

x = np.arange(0, 10, .1)
y = np.arange(0, 10, .1)
X, Y = np.meshgrid(x,y)

data = 2*( np.sin(X) + np.sin(3*Y) )

def do_plot(n, f, title):
    plt.subplot(1, 3, n)
    plt.pcolor(X, Y, f(data), cmap=cm, vmin=-4, vmax=4)

do_plot(1, lambda x:x, "all")
do_plot(2, lambda x:np.clip(x, -4, 0), "<0")
do_plot(3, lambda x:np.clip(x, 0, 4), ">0")

Use tab to indent in textarea

Modern way that both is straight-forward and does not lose the ability to undo (Ctrl+Z) the last changes.

$('#your-textarea').keydown(function (e) {
    var keyCode = e.keyCode || e.which;

    if (keyCode === $.ui.keyCode.TAB) {

        const TAB_SIZE = 4;

        // The one-liner that does the magic
        document.execCommand('insertText', false, ' '.repeat(TAB_SIZE));

More about execCommand:


As pointed out in the comment (and while this was once a "modern" solution), the feature has gone obsolete. Quoting the docs:

This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.

bad operand types for binary operator "&" java

Because & has a lesser priority than ==.

Your code is equivalent to a[0] & (1 == 0), and unless a[0] is a boolean this won't compile...

You need to:

(a[0] & 1) == 0

etc etc.

(yes, Java does hava a boolean & operator -- a non shortcut logical and)

How do I put all required JAR files in a library folder inside the final JAR file with Maven?

I found this answer to the question:

Not only do you get the dependent lib files in a lib folder, you also get a bin director with both a unix and a dos executable.

The executable ultimately calls java with a -cp argument that lists all of your dependent libs too.

The whole lot sits in an appasembly folder inside the target folder. Epic.

============= Yes I know this is an old thread, but it's still coming high on search results so I thought it might help someone like me.

How to run or debug php on Visual Studio Code (VSCode)

There is a much easier way to run PHP, no configuration needed:

  1. Install the Code Runner Extension
  2. Open the PHP code file in Text Editor
    • use shortcut Ctrl+Alt+N
    • or press F1 and then select/type Run Code,
    • or right click the Text Editor and then click Run Code in editor context menu
    • or click Run Code button in editor title menu
    • or click Run Code button in context menu of file explorer

Besides, you could select part of the PHP code and run the code snippet. Very convenient!

curl error 18 - transfer closed with outstanding read data remaining

I got this error when i was accidentally downloading a file onto itself.
(I had created a symlink in an sshfs mount of the remote directory to make it available for download, forgot to switch the working directory, and used -OJ).

I guess it won’t really »help« you when you read this, since it means your file got trashed.

Equivalent of shell 'cd' command to change the working directory?

Changing the current directory of the script process is trivial. I think the question is actually how to change the current directory of the command window from which a python script is invoked, which is very difficult. A Bat script in Windows or a Bash script in a Bash shell can do this with an ordinary cd command because the shell itself is the interpreter. In both Windows and Linux Python is a program and no program can directly change its parent's environment. However the combination of a simple shell script with a Python script doing most of the hard stuff can achieve the desired result. For example, to make an extended cd command with traversal history for backward/forward/select revisit, I wrote a relatively complex Python script invoked by a simple bat script. The traversal list is stored in a file, with the target directory on the first line. When the python script returns, the bat script reads the first line of the file and makes it the argument to cd. The complete bat script (minus comments for brevity) is:

if _%1 == _. goto cdDone
if _%1 == _? goto help
if /i _%1 NEQ _-H goto doCd
echo d.bat and 2016.03.05. Extended chdir.
echo -C = clear traversal list.
echo -B or nothing = backward (to previous dir).
echo -F or - = forward (to next dir).
echo -R = remove current from list and return to previous.
echo -S = select from list.
echo -H, -h, ? = help.
echo . = make window title current directory.
echo Anything else = target directory.
goto done

:doCd %1
for /F %%d in ( %~dp0dSupList ) do (
    cd %%d
    if errorlevel 1 ( -R )
    goto cdDone
title %CD%

The python script, is:

import sys, os, msvcrt

def indexNoCase ( slist, s ) :
    for idx in range( len( slist )) :
        if slist[idx].upper() == s.upper() :
            return idx
    raise ValueError

# .........main process ...................
if len( sys.argv ) < 2 :
    cmd = 1 # No argument defaults to -B, the most common operation
elif sys.argv[1][0] == '-':
    if len(sys.argv[1]) == 1 :
        cmd = 2 # '-' alone defaults to -F, second most common operation.
    else :
        cmd = 'CBFRS'.find( sys.argv[1][1:2].upper())
else :
    cmd = -1
    dir = os.path.abspath( sys.argv[1] ) + '\n'

# cmd is -1 = path, 0 = C, 1 = B, 2 = F, 3 = R, 4 = S

fo = open( os.path.dirname( sys.argv[0] ) + '\\dSupList', mode = 'a+t' ) 0 )
dlist = fo.readlines( -1 )
if len( dlist ) == 0 :
    dlist.append( os.getcwd() + '\n' ) # Prime new directory list with current.

if cmd == 1 : # B: move backward, i.e. to previous
    target = dlist.pop(0)
    dlist.append( target )
elif cmd == 2 : # F: move forward, i.e. to next
    target = dlist.pop( len( dlist ) - 1 )
    dlist.insert( 0, target )
elif cmd == 3 : # R: remove current from list. This forces cd to previous, a
                # desireable side-effect
    dlist.pop( 0 )
elif cmd == 4 : # S: select from list
# The current directory (dlist[0]) is included essentially as ESC.
    for idx in range( len( dlist )) :
        print( '(' + str( idx ) + ')', dlist[ idx ][:-1])
    while True :
        inp = msvcrt.getche()
        if inp.isdigit() :
            inp = int( inp )
            if inp < len( dlist ) :
                print( '' ) # Print the newline we didn't get from getche.
        print( ' is out of range' )
# Select 0 means the current directory and the list is not changed. Otherwise
# the selected directory is moved to the top of the list. This can be done by
# either rotating the whole list until the selection is at the head or pop it
# and insert it to 0. It isn't obvious which would be better for the user but
# since pop-insert is simpler, it is used.
    if inp > 0 :
        dlist.insert( 0, dlist.pop( inp ))

elif cmd == -1 : # -1: dir is the requested new directory.
# If it is already in the list then remove it before inserting it at the head.
# This takes care of both the common case of it having been recently visited
# and the less common case of user mistakenly requesting current, in which
# case it is already at the head. Deleting and putting it back is a trivial
# inefficiency.
        dlist.pop( indexNoCase( dlist, dir ))
    except ValueError :
    dlist = dlist[:9] # Control list length by removing older dirs (should be
                      # no more than one).
    dlist.insert( 0, dir ) 

fo.truncate( 0 )
if cmd != 0 : # C: clear the list
    fo.writelines( dlist )


Axios handling errors

Actually, it's not possible with axios as of now. The status codes which falls in the range of 2xx only, can be caught in .then().

A conventional approach is to catch errors in the catch() block like below:

  .catch(function (error) {
    if (error.response) {
      // Request made and server responded
    } else if (error.request) {
      // The request was made but no response was received
    } else {
      // Something happened in setting up the request that triggered an Error
      console.log('Error', error.message);


Another approach can be intercepting requests or responses before they are handled by then or catch.

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

// Add a response interceptor
axios.interceptors.response.use(function (response) {
    // Do something with response data
    return response;
  }, function (error) {
    // Do something with response error
    return Promise.reject(error);

How can I use an http proxy with node.js http.Client?

Node should support using the http_proxy environmental variable - so it is cross platform and works on system settings rather than requiring a per-application configuration.

Using the provided solutions, I would recommend the following:


get_url = (url, response) ->
  if process.env.http_proxy?
    match = process.env.http_proxy.match /^(http:\/\/)?([^:\/]+)(:([0-9]+))?/i
    if match
      http.get { host: match[2], port: (if match[4]? then match[4] else 80), path: url }, response
  http.get url, response


get_url = function(url, response) {
  var match;
  if (process.env.http_proxy != null) {
    match = process.env.http_proxy.match(/^(http:\/\/)?([^:\/]+)(:([0-9]+))?/i);
    if (match) {
        host: match[2],
        port: (match[4] != null ? match[4] : 80),
        path: url
      }, response);
  return http.get(url, response);

Usage To use the method, effectively just replace http.get, for instance the following writes the index page of google to a file called test.htm:

file = fs.createWriteStream path.resolve(__dirname, "test.htm")
get_url "", (response) ->
  response.pipe file
  response.on "end", ->
    console.log "complete"

How to semantically add heading to a list

According to (note that this link is in the long-expired draft HTML 3.0 spec):

An unordered list typically is a bulleted list of items. HTML 3.0 gives you the ability to customise the bullets, to do without bullets and to wrap list items horizontally or vertically for multicolumn lists.

The opening list tag must be <UL>. It is followed by an optional list header (<LH>caption</LH>) and then by the first list item (<LI>). For example:

  <LH>Table Fruit</LH>

which could be rendered as:

Table Fruit

  • apples
  • oranges
  • bananas

Note: Some legacy documents may include headers or plain text before the first LI element. Implementors of HTML 3.0 user agents are advised to cater for this possibility in order to handle badly formed legacy documents.

How to register multiple implementations of the same interface in Asp.Net Core?

My solution for what it's worth... considered switching to Castle Windsor as can't say I liked any of the solutions above. Sorry!!

public interface IStage<out T> : IStage { }

public interface IStage {
      void DoSomething();

Create your various implementations

public class YourClassA : IStage<YouClassA> { 
    public void DoSomething() 

public class YourClassB : IStage<YourClassB> { .....etc. }


services.AddTransient<IStage<YourClassA>, YourClassA>()
services.AddTransient<IStage<YourClassB>, YourClassB>()

Constructor and instance usage...

public class Whatever
   private IStage ClassA { get; }

   public Whatever(IStage<YourClassA> yourClassA)
         ClassA = yourClassA;

   public void SomeWhateverMethod()

Testing whether a value is odd or even

To complete Robert Brisita's bit test .

if ( ~i & 1 ) {
    // Even

Using AES encryption in C#

here is a neat and clean code to understand AES 256 algorithm implemented in C# call Encrypt function as encryptedstring = cryptObj.Encrypt(username, "AGARAMUDHALA", "EZHUTHELLAM", "SHA1", 3, "@1B2c3D4e5F6g7H8", 256);

public class Crypt
    public string Encrypt(string passtext, string passPhrase, string saltV, string hashstring, int Iterations, string initVect, int keysize)
        string functionReturnValue = null;
        // Convert strings into byte arrays.
        // Let us assume that strings only contain ASCII codes.
        // If strings include Unicode characters, use Unicode, UTF7, or UTF8
        // encoding.
        byte[] initVectorBytes = null;
        initVectorBytes = Encoding.ASCII.GetBytes(initVect);
        byte[] saltValueBytes = null;
        saltValueBytes = Encoding.ASCII.GetBytes(saltV);

        // Convert our plaintext into a byte array.
        // Let us assume that plaintext contains UTF8-encoded characters.
        byte[] plainTextBytes = null;
        plainTextBytes = Encoding.UTF8.GetBytes(passtext);
        // First, we must create a password, from which the key will be derived.
        // This password will be generated from the specified passphrase and
        // salt value. The password will be created using the specified hash
        // algorithm. Password creation can be done in several iterations.
        PasswordDeriveBytes password = default(PasswordDeriveBytes);
        password = new PasswordDeriveBytes(passPhrase, saltValueBytes, hashstring, Iterations);
        // Use the password to generate pseudo-random bytes for the encryption
        // key. Specify the size of the key in bytes (instead of bits).
        byte[] keyBytes = null;
        keyBytes = password.GetBytes(keysize/8);
        // Create uninitialized Rijndael encryption object.
        RijndaelManaged symmetricKey = default(RijndaelManaged);
        symmetricKey = new RijndaelManaged();

        // It is reasonable to set encryption mode to Cipher Block Chaining
        // (CBC). Use default options for other symmetric key parameters.
        symmetricKey.Mode = CipherMode.CBC;
        // Generate encryptor from the existing key bytes and initialization
        // vector. Key size will be defined based on the number of the key
        // bytes.
        ICryptoTransform encryptor = default(ICryptoTransform);
        encryptor = symmetricKey.CreateEncryptor(keyBytes, initVectorBytes);

        // Define memory stream which will be used to hold encrypted data.
        MemoryStream memoryStream = default(MemoryStream);
        memoryStream = new MemoryStream();

        // Define cryptographic stream (always use Write mode for encryption).
        CryptoStream cryptoStream = default(CryptoStream);
        cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write);
        // Start encrypting.
        cryptoStream.Write(plainTextBytes, 0, plainTextBytes.Length);

        // Finish encrypting.
        // Convert our encrypted data from a memory stream into a byte array.
        byte[] cipherTextBytes = null;
        cipherTextBytes = memoryStream.ToArray();

        // Close both streams.

        // Convert encrypted data into a base64-encoded string.
        string cipherText = null;
        cipherText = Convert.ToBase64String(cipherTextBytes);

        functionReturnValue = cipherText;
        return functionReturnValue;
    public string Decrypt(string cipherText, string passPhrase, string saltValue, string hashAlgorithm, int passwordIterations, string initVector, int keySize)
        string functionReturnValue = null;

        // Convert strings defining encryption key characteristics into byte
        // arrays. Let us assume that strings only contain ASCII codes.
        // If strings include Unicode characters, use Unicode, UTF7, or UTF8
        // encoding.

            byte[] initVectorBytes = null;
            initVectorBytes = Encoding.ASCII.GetBytes(initVector);

            byte[] saltValueBytes = null;
            saltValueBytes = Encoding.ASCII.GetBytes(saltValue);

            // Convert our ciphertext into a byte array.
            byte[] cipherTextBytes = null;
            cipherTextBytes = Convert.FromBase64String(cipherText);

            // First, we must create a password, from which the key will be
            // derived. This password will be generated from the specified
            // passphrase and salt value. The password will be created using
            // the specified hash algorithm. Password creation can be done in
            // several iterations.
            PasswordDeriveBytes password = default(PasswordDeriveBytes);
            password = new PasswordDeriveBytes(passPhrase, saltValueBytes, hashAlgorithm, passwordIterations);

            // Use the password to generate pseudo-random bytes for the encryption
            // key. Specify the size of the key in bytes (instead of bits).
            byte[] keyBytes = null;
            keyBytes = password.GetBytes(keySize / 8);

            // Create uninitialized Rijndael encryption object.
            RijndaelManaged symmetricKey = default(RijndaelManaged);
            symmetricKey = new RijndaelManaged();

            // It is reasonable to set encryption mode to Cipher Block Chaining
            // (CBC). Use default options for other symmetric key parameters.
            symmetricKey.Mode = CipherMode.CBC;

            // Generate decryptor from the existing key bytes and initialization
            // vector. Key size will be defined based on the number of the key
            // bytes.
            ICryptoTransform decryptor = default(ICryptoTransform);
            decryptor = symmetricKey.CreateDecryptor(keyBytes, initVectorBytes);

            // Define memory stream which will be used to hold encrypted data.
            MemoryStream memoryStream = default(MemoryStream);
            memoryStream = new MemoryStream(cipherTextBytes);

            // Define memory stream which will be used to hold encrypted data.
            CryptoStream cryptoStream = default(CryptoStream);
            cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Read);

            // Since at this point we don't know what the size of decrypted data
            // will be, allocate the buffer long enough to hold ciphertext;
            // plaintext is never longer than ciphertext.
            byte[] plainTextBytes = null;
            plainTextBytes = new byte[cipherTextBytes.Length + 1];

            // Start decrypting.
            int decryptedByteCount = 0;
            decryptedByteCount = cryptoStream.Read(plainTextBytes, 0, plainTextBytes.Length);

            // Close both streams.

            // Convert decrypted data into a string.
            // Let us assume that the original plaintext string was UTF8-encoded.
            string plainText = null;
            plainText = Encoding.UTF8.GetString(plainTextBytes, 0, decryptedByteCount);

            // Return decrypted string.
            functionReturnValue = plainText;

        return functionReturnValue;

Difference between JOIN and INNER JOIN

They are functionally equivalent, but INNER JOIN can be a bit clearer to read, especially if the query has other join types (i.e. LEFT or RIGHT or CROSS) included in it.

How to view changes made to files on a certain revision in Subversion

The equivalent command in svn is:

svn log --diff -r revision

What does $(function() {} ); do?

It's just shorthand for $(document).ready(), as in: $(document).ready(function() { YOUR_CODE_HERE });. Sometimes you have to use it because your function is running before the DOM finishes loading.

Everything is explained here:$(document).ready()

Objective-C: Reading a file line by line

As others have answered both NSInputStream and NSFileHandle are fine options, but it can also be done in a fairly compact way with NSData and memory mapping:


#import <Foundation/Foundation.h>

@interface BRLineReader : NSObject

@property (readonly, nonatomic) NSData *data;
@property (readonly, nonatomic) NSUInteger linesRead;
@property (strong, nonatomic) NSCharacterSet *lineTrimCharacters;
@property (readonly, nonatomic) NSStringEncoding stringEncoding;

- (instancetype)initWithFile:(NSString *)filePath encoding:(NSStringEncoding)encoding;
- (instancetype)initWithData:(NSData *)data encoding:(NSStringEncoding)encoding;
- (NSString *)readLine;
- (NSString *)readTrimmedLine;
- (void)setLineSearchPosition:(NSUInteger)position;



#import "BRLineReader.h"

static unsigned char const BRLineReaderDelimiter = '\n';

@implementation BRLineReader
    NSRange _lastRange;

- (instancetype)initWithFile:(NSString *)filePath encoding:(NSStringEncoding)encoding
    self = [super init];
    if (self) {
        NSError *error = nil;
        _data = [NSData dataWithContentsOfFile:filePath options:NSDataReadingMappedAlways error:&error];
        if (!_data) {
            NSLog(@"%@", [error localizedDescription]);
        _stringEncoding = encoding;
        _lineTrimCharacters = [NSCharacterSet whitespaceAndNewlineCharacterSet];

    return self;

- (instancetype)initWithData:(NSData *)data encoding:(NSStringEncoding)encoding
    self = [super init];
    if (self) {
        _data = data;
        _stringEncoding = encoding;
        _lineTrimCharacters = [NSCharacterSet whitespaceAndNewlineCharacterSet];

    return self;

- (NSString *)readLine
    NSUInteger dataLength = [_data length];
    NSUInteger beginPos = _lastRange.location + _lastRange.length;
    NSUInteger endPos = 0;
    if (beginPos == dataLength) {
        // End of file
        return nil;

    unsigned char *buffer = (unsigned char *)[_data bytes];
    for (NSUInteger i = beginPos; i < dataLength; i++) {
        endPos = i;
        if (buffer[i] == BRLineReaderDelimiter) break;

    // End of line found
    _lastRange = NSMakeRange(beginPos, endPos - beginPos + 1);
    NSData *lineData = [_data subdataWithRange:_lastRange];
    NSString *line = [[NSString alloc] initWithData:lineData encoding:_stringEncoding];

    return line;

- (NSString *)readTrimmedLine
    return [[self readLine] stringByTrimmingCharactersInSet:_lineTrimCharacters];

- (void)setLineSearchPosition:(NSUInteger)position
    _lastRange = NSMakeRange(position, 0);
    _linesRead = 0;


Refreshing data in RecyclerView and keeping its scroll position

Here is an option for people who use DataBinding for RecyclerView. I have var recyclerViewState: Parcelable? in my adapter. And I use a BindingAdapter with a variation of @DawnYu's answer to set and update data in the RecyclerView:

fun setRecyclerViewItems(
    recyclerView: RecyclerView,
    items: List<RecyclerViewItem>?
) {
    var adapter = (recyclerView.adapter as? RecyclerViewAdapter)
    if (adapter == null) {
        adapter = RecyclerViewAdapter()
        recyclerView.adapter = adapter

    adapter.recyclerViewState = recyclerView.layoutManager?.onSaveInstanceState()
    // the main idea is in this call with a lambda. It allows to avoid blinking on data update
    adapter.submitList(items.orEmpty()) {
        adapter.recyclerViewState?.let {

Finally, the XML part looks like:


How to make PDF file downloadable in HTML link?

Instead of linking to the .PDF file, instead do something like

<a href="pdf_server.php?file=pdffilename">Download my eBook</a>

which outputs a custom header, opens the PDF (binary safe) and prints the data to the user's browser, then they can choose to save the PDF despite their browser settings. The pdf_server.php should look like this:

header("Content-Type: application/octet-stream");

$file = $_GET["file"] .".pdf";
header("Content-Disposition: attachment; filename=" . urlencode($file));   
header("Content-Type: application/octet-stream");
header("Content-Type: application/download");
header("Content-Description: File Transfer");            
header("Content-Length: " . filesize($file));
flush(); // this doesn't really matter.
$fp = fopen($file, "r");
while (!feof($fp))
    echo fread($fp, 65536);
    flush(); // this is essential for large downloads

PS: and obviously run some sanity checks on the "file" variable to prevent people from stealing your files such as don't accept file extensions, deny slashes, add .pdf to the value

Is quitting an application frowned upon?

First of all, never never never use System.exit(0). It is like making a person sleep punching him on the head!

Second: I'm facing this problem. Before sharing my solution a I want to share my thoughts.

I think that an "Exit Button" is stupid. Really really really stupid. And I think that users (consumer) that ask for an exit button for your application is stupid too. They don't understand how the OS is working and how is managing resources (and it does a great job).

I think that if you write a good piece of code that do the right things (updates, saves, and pushes) at the right moment and conditions and using the correct things (Service and Receiver) it will work pretty well and no one will complain.

But to do that you have to study and learn how things works on Android. Anyway, this is my solution to provide to users an "Exit Button".

I created an Options Menu always visible in each activity (I've a super activity that do that).

When the user clicks on that button this is what happens:

Intent intent = new Intent(this, DashBoardActivity.class);

SharedPreferences settings = getSharedPreferences(getString(PREF_ID), Context.MODE_PRIVATE);
SharedPreferences.Editor editor = settings.edit();
editor.putBoolean(FORCE_EXIT_APPLICATION, true);

  // Commit the edits!

So I'm saving in SharedPreferences that I want to kill my app, and I start an Intent. Please look at those flags; those will clear all my backstack calling my DashBoard Activity that is my "home" activity.

So in my Dashboard Activity I run this method in the onResume:

private void checkIfForceKill() {


    // Restore preferences
    SharedPreferences settings = getSharedPreferences(
            getString(MXMSettingHolder.PREF_ID), Context.MODE_PRIVATE);
    boolean forceKill = settings.getBoolean(
            MusicSinglePaneActivity.FORCE_EXIT_APPLICATION, false);

    if (forceKill) {

        SharedPreferences.Editor editor = settings.edit();
        editor.putBoolean(FORCE_EXIT_APPLICATION, false);

        // Commit the edits!


And it will work pretty well.

The only thing that I don't understand why it's happening is that when I do the last finish (and I've checked: it's following all the correct flow of onPause ? onStop ? onDestroy) the application is still on the recent activity (but it's blank).

It seems like the latest intent (that has started the DashboardActivity) is still in the system.

I've to dig more in order to also remove it.

ssh: Could not resolve hostname [hostname]: nodename nor servname provided, or not known

If your command is:

$ ssh -p 1122  path/to/pemfile user@[hostip/hostname]

You will also face the same error

ssh: Could not resolve hostname [hostname]: nodename nor servname provided, or not known

when you miss the option -i /path/to/pemfile of ssh

So Command should be:

$ ssh -p 1122 -i path/to/pemfile user@[hostip/hostname]

How do you merge two Git repositories?

The submodule approach is good if you want to maintain the project separately. However, if you really want to merge both projects into the same repository, then you have a bit more work to do.

The first thing would be to use git filter-branch to rewrite the names of everything in the second repository to be in the subdirectory where you would like them to end up. So instead of foo.c, bar.html, you would have projb/foo.c and projb/bar.html.

Then, you should be able to do something like the following:

git remote add projb [wherever]
git pull projb

The git pull will do a git fetch followed by a git merge. There should be no conflicts, if the repository you're pulling to does not yet have a projb/ directory.

Further searching indicates that something similar was done to merge gitk into git. Junio C Hamano writes about it here:[email protected]/msg03395.html

capture div into image using html2canvas

If you just want to have screenshot of a div, you can do it like this

html2canvas($('#div'), {
  onrendered: function(canvas) {
    var img = canvas.toDataURL();

Jenkins Host key verification failed


ssh-keygen -R hostname

-R hostname Removes all keys belonging to hostname from a known_hosts file. This option is useful to delete hashed hosts

How to change TextBox's Background color?

In WinForms and WebForms you can do:

txtName.BackColor = Color.Aqua;

How can I find out which server hosts LDAP on my windows domain?

If the machine you are on is part of the AD domain, it should have its name servers set to the AD name servers (or hopefully use a DNS server path that will eventually resolve your AD domains). Using your example of dc=domain,dc=com, if you look up in the AD name servers it will return a list of the IPs of each AD Controller. Example from my company (w/ the domain name changed, but otherwise it's a real example):

    mokey 0 /home/jj33 > nslookup

    Non-authoritative answer:

Note I'm actually making the query from a non-AD machine, but our unix name servers know to send queries for our AD domain ( over to the AD DNS servers.

I'm sure there's a super-slick windowsy way to do this, but I like using the DNS method when I need to find the LDAP servers from a non-windows server.

How to select all and copy in vim?

There are a few important informations missing from your question:

  • output of $ vim --version?
  • OS?
  • CLI or GUI?
  • local or remote?
  • do you use tmux? screen?

If your Vim was built with clipboard support, you are supposed to use the clipboard register like this, in normal mode:


If your Vim doesn't have clipboard support, you can manage to copy text from Vim to your OS clipboard via other programs. This pretty much depends on your OS but you didn't say what it is so we can't really help.

However, if your Vim is crippled, the best thing to do is to install a proper build with clipboard support but I can't tell you how either because I don't know what OS you use.


On debian based systems, the following command will install a proper Vim with clipboard, ruby, python… support.

$ sudo apt-get install vim-gnome

When to Redis? When to MongoDB?

Redis is an in memory data store, that can persist it's state to disk (to enable recovery after restart). However, being an in-memory data store means the size of the data store (on a single node) cannot exceed the total memory space on the system (physical RAM + swap space). In reality, it will be much less that this, as Redis is sharing that space with many other processes on the system, and if it exhausts the system memory space it will likely be killed off by the operating system.

Mongo is a disk based data store, that is most efficient when it's working set fits within physical RAM (like all software). Being a disk based data means there are no intrinsic limits on the size of a Mongo database, however configuration options, available disk space, and other concerns may mean that databases sizes over a certain limit may become impractical or inefficient.

Both Redis and Mongo can be clustered for high availability, backup and to increase the overall size of the datastore.

What does "while True" mean in Python?

while loops continue to loop until the condition is false. For instance (pseudocode):

i = 0
while i < 10

With each iteration of the loop, i will be incremented by 1, until it is 10. At that point, the condition i < 10 is no longer true, and the loop will complete.

Since the condition in while True is explicitly and always true, the loop will never end (until it is broken out of some other way, usually by a construct like break within the loop body).

How to send a simple email from a Windows batch file?

It works for me, by using double quotes around variables.

I am using batch script to call powershell Send-MailMessage

Batch Script:send_email.bat

C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe  -command 'E:\path\send_email.ps1

Pwershell Script send_email.ps1

Send-MailMessage -From "noreply@$env:computername" -To '<[email protected]>' -Subject 'Blah Blah' -SmtpServer  ''  -Attachments 'E:\path\file.log' -BODY "Blah Blah on Host: $env:computername "

How to change DataTable columns order

Try to use the DataColumn.SetOrdinal method. For example:


UPDATE: This answer received much more attention than I expected. To avoid confusion and make it easier to use I decided to create an extension method for column ordering in DataTable:

Extension method:

public static class DataTableExtensions
    public static void SetColumnsOrder(this DataTable table, params String[] columnNames)
        int columnIndex = 0;
        foreach(var columnName in columnNames)


table.SetColumnsOrder("Qty", "Unit", "Id");


table.SetColumnsOrder(new string[]{"Qty", "Unit", "Id"});

C# Checking if button was clicked

i am very new to this website. I am an undergraduate student, doing my Bachelor Of Computer Application. I am doing a simple program in Visual Studio using C# and I came across the same problem, how to check whether a button is clicked? I wanted to do this,

if(-button1 is clicked-) then
this should happen;
if(-button2 is clicked-) then
this should happen;

I didn't know what to do, so I tried searching for the solution in the internet. I got many solutions which didn't help me. So, I tried something on my own and did this,

int i;
private void button1_Click(object sender, EventArgs e)
            i = 1;
            label3.Text = "Principle";
            label4.Text = "Rate";
            label5.Text = "Time";
            label6.Text = "Simple Interest";

private void button2_Click(object sender, EventArgs e)
            i = 2;
            label3.Text = "SI";
            label4.Text = "Rate";
            label5.Text = "Time";
            label6.Text = "Principle";
private void button5_Click(object sender, EventArgs e)

                if (i == 1)
                    si = (Convert.ToInt32(textBox1.Text) * Convert.ToInt32(textBox2.Text) * Convert.ToInt32(textBox3.Text)) / 100;
                    textBox4.Text = Convert.ToString(si);
                if (i == 2)
                    p = (Convert.ToInt32(textBox1.Text) * 100) / (Convert.ToInt32(textBox2.Text) * Convert.ToInt32(textBox3.Text));
                    textBox4.Text = Convert.ToString(p);

I declared a variable "i" and assigned it with different values in different buttons and checked the value of i in the if function. It worked. Give your suggestions if any. Thank you.

How to save an HTML5 Canvas as an image on a server?

I played with this two weeks ago, it's very simple. The only problem is that all the tutorials just talk about saving the image locally. This is how I did it:

1) I set up a form so I can use a POST method.

2) When the user is done drawing, he can click the "Save" button.

3) When the button is clicked I take the image data and put it into a hidden field. After that I submit the form.

document.getElementById('my_hidden').value = canvas.toDataURL('image/png');

4) When the form is submited I have this small php script:

$upload_dir = somehow_get_upload_dir();  //implement this function yourself
$img = $_POST['my_hidden'];
$img = str_replace('data:image/png;base64,', '', $img);
$img = str_replace(' ', '+', $img);
$data = base64_decode($img);
$file = $upload_dir."image_name.png";
$success = file_put_contents($file, $data);
header('Location: '.$_POST['return_url']);

jQuery select2 get value of select tag?

This solution allows you to forget select element. Helpful when you do not have an id on select elements.

.on("select2:select", function (e) {
    var selected_element = $(e.currentTarget);
    var select_val = selected_element.val();

/lib/ bad ELF interpreter: No such file or directory

looks to me yum install glibc.i686 should have worked. Unless Peter was not root. He has the 64 bit glib installed, he is installing a 32 bit package that requires the 32 bit glib which is glib.i686 for intel processors.

Remove IE10's "clear field" X button on certain inputs?

I think it's worth noting that all the style and CSS based solutions don't work when a page is running in compatibility mode. The compatibility mode renderer ignores the ::-ms-clear element, even though the browser shows the x.

If your page needs to run in compatibility mode, you may be stuck with the X showing.

In my case, I am working with some third party data bound controls, and our solution was to handle the "onchange" event and clear the backing store if the field is cleared with the x button.

Set div height equal to screen size

You need to give height for the parent element too! Check out this fiddle.


html, body {height: 100%;}

#content, .container-fluid, .span9
    border: 1px solid #000;

JavaScript (using jQuery) Way:


Violation of PRIMARY KEY constraint. Cannot insert duplicate key in object

Pretty sure pk_OrderID is the PK of AC_Shipping_Addresses

And you are trying to insert a duplicate via the _Order.OrderNumber

Do a

select * from AC_Shipping_Addresses where pk_OrderID = 165863;

or select count(*) ....

Pretty sure you will get a row returned.

What it is telling you is you are already using pk_OrderID = 165863 and cannot have another row with that value.

if you want to not insert if there is a row

insert into table (pk, value) 
select 11 as pk, 'val' as value 
where not exists (select 1 from table where pk = 11) 

WARNING: sanitizing unsafe style value url

I got the same issue while adding dynamic url in Image tag in Angular 7. I searched a lot and found this solution.

First, write below code in the component file.

constructor(private sanitizer: DomSanitizer) {}
public getSantizeUrl(url : string) {
    return this.sanitizer.bypassSecurityTrustUrl(url);

Now in your html image tag, you can write like this.

<img class="image-holder" [src]=getSantizeUrl(item.imageUrl) />

You can write as per your requirement instead of item.imageUrl

I got a reference from this site.dynamic urls. Hope this solution will help you :)

Change Bootstrap tooltip color

This is true solution


.tooltip { 
    font-family: inherit; 
.tooltip-inner { 
    background-color: #5264e9; 
.bs-tooltip-auto[x-placement^=bottom] .arrow::before,
.bs-tooltip-bottom .arrow::before { 
    border-bottom-color: #5264e9;

Collapsing Sidebar with Bootstrap

EDIT: I've added one more option for bootstrap sidebars.

There are actually three manners in which you can make a bootstrap 3 sidebar. I tried to keep the code as simple as possible.

Fixed sidebar

Here you can see a demo of a simple fixed sidebar I've developed with the same height as the page

Sidebar in a column

I've also developed a rather simple column sidebar that works in a two or three column page inside a container. It takes the length of the longest column. Here you can see a demo


If you google bootstrap dashboard, you can find multiple suitable dashboard, such as this one. However, most of them require a lot of coding. I've developed a dashboard that works without additional javascript (next to the bootstrap javascript). Here is a demo

For all three examples you off course have to include the jquery, bootstrap css, js and theme.css files.


If you want the sidebar to hide on pressing a button this is also possible with only a little javascript.Here is a demo

Python module os.chmod(file, 664) does not change the permission to rw-rw-r-- but -w--wx----

Found this on a different forum

If you're wondering why that leading zero is important, it's because permissions are set as an octal integer, and Python automagically treats any integer with a leading zero as octal. So os.chmod("file", 484) (in decimal) would give the same result.

What you are doing is passing 664 which in octal is 1230

In your case you would need

os.chmod("/tmp/test_file", 436)

[Update] Note, for Python 3 you have prefix with 0o (zero oh). E.G, 0o666

Kotlin Ternary Conditional Operator

You can do it many way in Kotlin

  1. Using if

    if(a) b else c
  2. Using when

    when (a) { 
        true -> print("value b") 
        false -> print("value c") 
        else -> {  
            print("default return in any other case") 
  3. Null Safety

    val a = b ?: c

Adding a css class to select using @Html.DropDownList()

As the signature from the error message implies, the second argument must be an IEnumerable, more specifically, an IEnumerable of SelectListItem. It is the list of choices. You can use the SelectList type, which is a IEnumerable of SelectListItem. For a list with no choices:

@Html.DropDownList("PriorityID", new List<SelectListItem>(), new {@class="textbox"} )

For a list with a few choices:

    new List<SelectListItem> 
        new SelectListItem { Text = "High", Value = 1 }, 
        new SelectListItem { Text = "Low",  Value = 0 },
    new {@class="textbox"})

Maybe this tutorial can be of help: How to create a DropDownList with ASP.NET MVC

Pretty printing XML in Python

BeautifulSoup has a easy to use prettify() method.

It indents one space per indentation level. It works much better than lxml's pretty_print and is short and sweet.

from bs4 import BeautifulSoup

bs = BeautifulSoup(open(xml_file), 'xml')
print bs.prettify()

How to downgrade Node version

For windows 10,

  • Uninstalling the node from the "Add or remove programs"
  • Installing the required version from

worked for me.

Sorting an Array of int using BubbleSort

I use this method for bubble sorting

public static int[] bubbleSort (int[] a) {
    int n = a.length;
    int j = 0;
    boolean swap = true;
    while (swap) {
        swap = false;
        for (int j = 1; j < n; j++) {
            if (a[j-1] > a[j]) {
                j = a[j-1];
                a[j-1] = a[j];
                a[j] = j;
                swap = true;
        n = n - 1;
    return a;
}//end bubbleSort

How do I set a ViewModel on a window in XAML using DataContext property?

Try this instead.

<Window x:Class="BuildAssistantUI.BuildAssistantWindow"
        <VM:MainViewModel />

Learning to write a compiler

One book not yet suggested but very important is "Linkers and Loaders" by John Levine. If you're not using an external assembler, you'll need a way to output a object file that can be linked into your final program. Even if you're using an external assembler, you'll probably need to understand relocations and how the whole program loading process works to make a working tool. This book collects a lot of the random lore around this process for various systems, including Win32 and Linux.

How to handle the new window in Selenium WebDriver using Java?

I have an utility method to switch to the required window as shown below

public class Utility 
    public static WebDriver getHandleToWindow(String title){

        //parentWindowHandle = WebDriverInitialize.getDriver().getWindowHandle(); // save the current window handle.
        WebDriver popup = null;
        Set<String> windowIterator = WebDriverInitialize.getDriver().getWindowHandles();
        System.err.println("No of windows :  " + windowIterator.size());
        for (String s : windowIterator) {
          String windowHandle = s; 
          popup = WebDriverInitialize.getDriver().switchTo().window(windowHandle);
          System.out.println("Window Title : " + popup.getTitle());
          System.out.println("Window Url : " + popup.getCurrentUrl());
          if (popup.getTitle().equals(title) ){
              System.out.println("Selected Window Title : " + popup.getTitle());
              return popup;

                System.out.println("Window Title :" + popup.getTitle());
            return popup;

It will take you to desired window once title of the window is passed as parameter. In your case you can do.

Webdriver childDriver = Utility.getHandleToWindow("titleOfChildWindow");

and then again switch to parent window using the same method

Webdriver parentDriver = Utility.getHandleToWindow("titleOfParentWindow");

This method works effectively when dealing with multiple windows.

JavaScript to get rows count of a HTML table


Chrome Uncaught Syntax Error: Unexpected Token ILLEGAL

There's some sort of bogus character at the end of that source. Try deleting the last line and adding it back.

I can't figure out exactly what's there, yet ...

edit — I think it's a zero-width space, Unicode 200B. Seems pretty weird and I can't be sure of course that it's not a Stackoverflow artifact, but when I copy/paste that last function including the complete last line into the Chrome console, I get your error.

A notorious source of such characters are websites like jsfiddle. I'm not saying that there's anything wrong with them — it's just a side-effect of something, maybe the use of content-editable input widgets.

If you suspect you've got a case of this ailment, and you're on MacOS or Linux/Unix, the od command line tool can show you (albeit in a fairly ugly way) the numeric values in the characters of the source code file. Some IDEs and editors can show "funny" characters as well. Note that such characters aren't always a problem. It's perfectly OK (in most reasonable programming languages, anyway) for there to be embedded Unicode characters in string constants, for example. The problems start happening when the language parser encounters the characters when it doesn't expect them.

How to return data from PHP to a jQuery ajax call

It's an argument passed to your success function:

  type: "POST",
  url: "somescript.php",
  datatype: "html",
  data: dataString,
  success: function(data) {

The full signature is success(data, textStatus, XMLHttpRequest), but you can use just he first argument if it's a simple string coming back. As always, see the docs for a full explanation :)

How to display svg icons(.svg files) in UI using React Component?

If you want to use SVG files as React components to perform customizations and do not use create-react-app, do the following:

  1. Install the Webpack loader called svgr
yarn add --dev @svgr/webpack
  1. Update your webpack.config.js
  module: {
    rules: [
      // SVG loader
        test: /\.svg$/,
        use: ['@svgr/webpack'],
  1. Import SVG files as React component
import SomeImage from 'path/to/image.svg'


<SomeImage width={100} height={50} fill="pink" stroke="#0066ff" />

JSHint and jQuery: '$' is not defined

To fix this error when using the online JSHint implementation:

  • Click "CONFIGURE" (top of the middle column on the page)
  • Enable "jQuery" (under the "ASSUME" section at the bottom)

css padding is not working in outlook

All styling including padding have to be added to a td not a span.

Another solution put the text into <p>text</p> and define margins, and that should give the required padding.

For example:

<p style="margin-top: 10px; margin-bottom: 10; margin-right: 12; margin-left: 12;">text</p>

Convert an integer to a float number


// ToFloat32 converts a int num to a float32 num
func ToFloat32(in int) float32 {
    return float32(in)

// ToFloat64 converts a int num to a float64 num
func ToFloat64(in int) float64 {
    return float64(in)

open program minimized via command prompt


start  "" "C:\Program Files (x86)\Microsoft Office\Office12\WINWORD.EXE" --new-window/min

I had the same problem, but I was trying to open chrome.exe maximized. If I put the /min anywhere else in the command line, like before or after the empty title, it was ignored.

Download history stock prices automatically from yahoo finance in python

There is already a library in Python called yahoo_finance so you'll need to download the library first using the following command line:

sudo pip install yahoo_finance

Then once you've installed the yahoo_finance library, here's a sample code that will download the data you need from Yahoo Finance:

import yahoo_finance
import pandas as pd

symbol = yahoo_finance.Share("GOOG")
google_data = symbol.get_historical("1999-01-01", "2016-06-30")
google_df = pd.DataFrame(google_data)

# Output data into CSV

This should do it. Let me know if it works.

UPDATE: The yahoo_finance library is no longer supported.

What does 'low in coupling and high in cohesion' mean

In software design high cohesion means that class should do one thing and one thing very well. High cohesion is closely related to Single responsibility principle.

Low coupling suggest that class should have least possible dependencies. Also, dependencies that must exist should be weak dependencies - prefer dependency on interface rather than dependency on concrete class, or prefer composition over inheritance .

High Cohesion and low coupling give us better designed code that is easier to maintain.

Finish all activities at a time

If you're looking for a solution that seems to be more "by the book" and methodologically designed (using a BroadcastReceiver), you better have a look at the following link:

A slight change is required in the proposed implementation that appears in that link - you should use the sendStickyBroadcast(Intent) method (don't forget to add the BROADCAST_STICKY permission to your manifest) rather than sendBroadcast(Intent), in order to enable your paused activities to be able to receive the broadcast and process it, and this means that you should also remove that sticky broadcast while restarting your application by calling the removeStickyBroadcast(Intent) method in your opening Activity's onCreate() method.

Although the above mentioned startActivity(...) based solutions, at first glance - seem to be very nice, elegant, short, fast and easy to implement - they feel a bit "wrong" (to start an activity - with all the possible overhead and resources that may be required and involved in it, just in order to kill it?...)

Get first element from a dictionary

convert to Array

var array = like.ToArray();
var first = array[0];

Convert all strings in a list to int

You can do it simply in one line when taking input.

[int(i) for i in input().split("")]

Split it where you want.

If you want to convert a list not list simply put your list name in the place of input().split("").

How to check if a symlink exists

  1. first you can do with this style:

    if [ ! -L "${mda}" ]; then
      echo "=> File doesn't exist"
  2. if you want to do it in more advanced style you can write it like below:

    if [ -e "$1" ]; then
        if [ ! -L "$1" ]
            echo "you entry is not symlink"
            echo "your entry is symlink"
      echo "=> File doesn't exist"

the result of above is like:

root@linux:~# ./ /etc/passwd
you entry is not symlink
root@linux:~# ./ /usr/mda 
your entry is symlink
root@linux:~# ./ 
=> File doesn't exist

Group by month and year in MySQL

You are grouping by month only, you have to add YEAR() to the group by

Add Auto-Increment ID to existing table?


Java word count program

public class wordCount
public static void main(String ar[]) throws Exception
System.out.println("Simple Java Word Count Program");

    int wordCount = 1,count=1;
 BufferedReader br = new BufferedReader(new FileReader("C:/file.txt"));
            String str2 = "", str1 = "";

            while ((str1 = br.readLine()) != null) {

                    str2 += str1;


    for (int i = 0; i < str2.length(); i++) 
        if (str2.charAt(i) == ' ' && str2.charAt(i+1)!=' ') 


    System.out.println("Word count is = " +(wordCount));


Is it possible to get the index you're sorting over in Underscore.js?

I think it's worth mentioning how the Underscore's _.each() works internally. The _.each(list, iteratee) checks if the passed list is an array object, or an object.

In the case that the list is an array, iteratee arguments will be a list element and index as in the following example:

var a = ['I', 'like', 'pancakes', 'a', 'lot', '.'];
_.each( a, function(v, k) { console.log( k + " " + v); });

0 I
1 like
2 pancakes
3 a
4 lot
5 .

On the other hand, if the list argument is an object the iteratee will take a list element and a key:

var o = {name: 'mike', lastname: 'doe', age: 21};
_.each( o, function(v, k) { console.log( k + " " + v); });

name mike
lastname doe
age 21

For reference this is the _.each() code from Underscore.js 1.8.3

_.each = _.forEach = function(obj, iteratee, context) {
   iteratee = optimizeCb(iteratee, context);
   var i, length;
   if (isArrayLike(obj)) {
      for (i = 0, length = obj.length; i < length; i++) {
         iteratee(obj[i], i, obj);
   } else {
      var keys = _.keys(obj);
      for (i = 0, length = keys.length; i < length; i++) {
         iteratee(obj[keys[i]], keys[i], obj);
   return obj;

How to change the author and committer name and e-mail of multiple commits in Git?

I use the following to rewrite the author for an entire repository, including tags and all branches:

git filter-branch --tag-name-filter cat --env-filter "
  export GIT_AUTHOR_NAME='New name';
  export GIT_AUTHOR_EMAIL='New email'
" -- --all

Then, as described in the MAN page of filter-branch, remove all original refs backed up by filter-branch (this is destructive, backup first):

git for-each-ref --format="%(refname)" refs/original/ | \
xargs -n 1 git update-ref -d

changing visibility using javascript

Use display instead of visibility. display: none for invisible and no setting for visible.

getting the screen density programmatically in android?

Actualy if you want to have the real display dpi the answer is somewhere in between if you query for display metrics:

DisplayMetrics dm = new DisplayMetrics();
int dpiClassification = dm.densityDpi;
float xDpi = dm.xdpi;
float yDpi = dm.ydpi;

densityDpi * 160 will give you the values/suggestion which density you should use

0.75 - ldpi - 120 dpi
1.0 - mdpi - 160 dpi
1.5 - hdpi - 240 dpi
2.0 - xhdpi - 320 dpi
3.0 - xxhdpi - 480 dpi
4.0 - xxxhdpi - 640 dpi

as specified in previous posts

but dm.xdpi won't give you always the REAL dpi of given display: Example:

Device: Sony ericsson xperia mini pro (SK17i)
Density: 1.0 (e.g. suggests you use 160dpi resources)
xdpi: 193.5238
Real device ppi is arround 193ppi

Device: samsung GT-I8160 (Samsung ace 2)
Density 1.5 (e.g. suggests you use 240dpi resources)
xdpi 160.42105
Real device ppi is arround 246ppi

so maybe real dpi of the display should be Density*xdpi .. but i'm not sure if this is the correct way to do!

MVC4 input field placeholder

An alternative to using a plugin is using an editor template. What you need to do is to create a template file in Shared\EditorTemplates folder and call it String.cshtml. Then put this in that file:

    new { placeholder = ViewData.ModelMetadata.Watermark })

Then use it in your view like this:


The downside, this works for properties of type string, and you will have to create a template for each type that you want support for a watermark.

How do I properly force a Git push?

This was our solution for replacing master on a corporate gitHub repository while maintaining history.

push -f to master on corporate repositories is often disabled to maintain branch history. This solution worked for us.

git fetch desiredOrigin
git checkout -b master desiredOrigin/master // get origin master

git checkout currentBranch  // move to target branch
git merge -s ours master  // merge using ours over master
// vim will open for the commit message
git checkout master  // move to master
git merge currentBranch  // merge resolved changes into master

push your branch to desiredOrigin and create a PR

Initializing a list to a known number of elements in Python

Not quite sure why everyone is giving you a hard time for wanting to do this - there are several scenarios where you'd want a fixed size initialised list. And you've correctly deduced that arrays are sensible in these cases.

import array

For the non-pythonistas, the (0,)*1000 term is creating a tuple containing 1000 zeros. The comma forces python to recognise (0) as a tuple, otherwise it would be evaluated as 0.

I've used a tuple instead of a list because they are generally have lower overhead.

Source file 'Properties\AssemblyInfo.cs' could not be found

This can also happen if you have a solution containing the project open in Visual Studio, then use your source control software to change to an older commit that does not contain that project. Normally, this would be obvious as all the project files would disappear as well. But, if it's a new project with very few or no files at all, it could be puzzling to see that just this one file, AssemblyInfo.cs, is missing. And, it's more likely you'd be messing about with an AssemblyInfo.cs when a project is new, so might miss that another file or two is also missing.

The cure is to do any of the following:

  • Fetch the missing AssemblyInfo.cs and any other missing files from another commit, taking care to manage and save your .csproj file so the referenced files don't vanish from the project—perhaps by adding and removing a random .cs file to cause changes to need to be saved (since visual studio thinks the .csproj file has been saved when it hasn't).
  • Close and reopen Visual Studio without saving (if the project file isn't really saved) or remove the project. Removing makes sense if you didn't actually want the project created yet, since it will be created in the later commit.
  • Recreate the AssemblyInfo.cs file manually. Just copy another project, and change the details, especially the GUID so it matches the one from the .sln file.

Why do I get "a label can only be part of a statement and a declaration is not a statement" if I have a variable that is initialized after a label?

The language standard simply doesn't allow for it. Labels can only be followed by statements, and declarations do not count as statements in C. The easiest way to get around this is by inserting an empty statement after your label, which relieves you from keeping track of the scope the way you would need to inside a block.

#include <stdio.h>
int main () 
    printf("Hello ");
    goto Cleanup;
Cleanup: ; //This is an empty statement.
    char *str = "World\n";
    printf("%s\n", str);

Can I add extension methods to an existing static class?

It's not possible.

And yes, I think MS made a mistake here.

Their decision does not make sense and forces programmers to write (as described above) a pointless wrapper class.

Here is a good example: Trying to extend static MS Unit testing class Assert: I want 1 more Assert method AreEqual(x1,x2).

The only way to do this is to point to different classes or write a wrapper around 100s of different Assert methods. Why!?

If the decision was being made to allow extensions of instances, I see no logical reason to not allow static extensions. The arguments about sectioning libraries does not stand up once instances can be extended.

Why is IoC / DI not common in Python?

Actually, it is quite easy to write sufficiently clean and compact code with DI (I wonder, will it be/stay pythonic then, but anyway :) ), for example I actually perefer this way of coding:

def polite(name_str):
    return "dear " + name_str

def rude(name_str):
    return name_str + ", you, moron"

def greet(name_str, call=polite):
    print "Hello, " + call(name_str) + "!"


Hello, dear Peter!
>>greet("Jack", rude)
Hello, Jack, you, moron!

Yes, this can be viewed as just a simple form of parameterizing functions/classes, but it does its work. So, maybe Python's default-included batteries are enough here too.

P.S. I have also posted a larger example of this naive approach at Dynamically evaluating simple boolean logic in Python.

Ranges of floating point datatype in C?

These numbers come from the IEEE-754 standard, which defines the standard representation of floating point numbers. Wikipedia article at the link explains how to arrive at these ranges knowing the number of bits used for the signs, mantissa, and the exponent.

load iframe in bootstrap modal

I came across this implementation in Codepen. I hope you find it helpful.

this.on('', function(){
      $(this).find('iframe').html("").attr("src", "");

Disable submit button ONLY after submit

Test with a setTimeout, that worked for me and I could submit my form, refers to this answer

$(document).ready(function () {
    $("#btnSubmit").click(function () {
        setTimeout(function () { disableButton(); }, 0);

    function disableButton() {
        $("#btnSubmit").prop('disabled', true);

Custom UITableViewCell from nib in Swift

For fix the "Overriding method... has incompatible type..." error I've changed the function declaration to

override func tableView(tableView: (UITableView!), 
                        cellForRowAtIndexPath indexPath: (NSIndexPath!)) 
    -> UITableViewCell {...}

(was -> UITableViewCell! -- with exclamation mark at the end)

Negate if condition in bash script

If you're feeling lazy, here's a terse method of handling conditions using || (or) and && (and) after the operation:

wget -q --tries=10 --timeout=20 --spider || \
{ echo "Sorry you are Offline" && exit 1; }

Extension exists but uuid_generate_v4 fails

The extension is available but not installed in this database.


Html attributes for EditorFor() in ASP.NET MVC

MVC 5.1 and higher solution (will merge local HtmlAttributes and defined in the EditorTemplates):


@Html.TextBoxFor(model => model, new { @class = "form-control", placeholder = ViewData.ModelMetadata.Watermark }.ToExpando().MergeHtmlAttributes(ViewData["htmlAttributes"].ToExpando()))


public static IDictionary<string, object> MergeHtmlAttributes(this ExpandoObject source1, dynamic source2)
    Condition.Requires(source1, "source1").IsNotNull().IsLongerThan(0);

    IDictionary<string, object> result = source2 == null
        ? new Dictionary<string, object>()
        : (IDictionary<string, object>) source2;

    var dictionary1 = (IDictionary<string, object>) source1;

    string[] commonKeys = result.Keys.Where(dictionary1.ContainsKey).ToArray();
    foreach (var key in commonKeys)
        result[key] = string.Format("{0} {1}", dictionary1[key], result[key]);

    foreach (var item in dictionary1.Where(pair => !result.ContainsKey(pair.Key)))

    return result;

public static ExpandoObject ToExpando(this object anonymousObject)
    IDictionary<string, object> anonymousDictionary = new RouteValueDictionary(anonymousObject);
    IDictionary<string, object> expando = new ExpandoObject();
    foreach (var item in anonymousDictionary)
    return (ExpandoObject)expando;

public static bool HasProperty(this ExpandoObject expando, string key)
    return ((IDictionary<string, object>)expando).ContainsKey(key);


@Html.EditorFor(m => m.PromotionalCode, new { htmlAttributes = new { ng_model = "roomCtrl.searchRoomModel().promoCode" }})

How can I compare strings in C using a `switch` statement?

This is how you do it. No, not really.

#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <stdint.h>

 #define p_ntohl(u) ({const uint32_t Q=0xFF000000;       \
                     uint32_t S=(uint32_t)(u);           \
                   (*(uint8_t*)&Q)?S:                    \
                   ( (S<<24)|                            \
                     ((S<<8)&0x00FF0000)|                \
                     ((S>>8)&0x0000FF00)|                \
                     ((S>>24)&0xFF) );  })

main (void)
    uint32_t s[0x40]; 
    assert((unsigned char)1 == (unsigned char)(257));
    memset(s, 0, sizeof(s));
    fgets((char*)s, sizeof(s), stdin);

    switch (p_ntohl(s[0])) {
        case 'open':
        case 'read':
        case 'seek':
        case 'rm\n\0':
            puts("not authorized");
            puts("unrecognized command");  
    return 0;

How to inject JPA EntityManager using spring

The latest Spring + JPA versions solve this problem fundamentally. You can learn more how to use Spring and JPA togather in a separate thread

how to fix java.lang.IndexOutOfBoundsException

lstpp is empty. You cant access the first element of an empty list.

In general, you can check if size > index.

In your case, you need to check if lstpp is empty. (you can use !lstpp.isEmpty())

Add left/right horizontal padding to UILabel

Sometimes it's convenient to use UNICODE partial spaces to achieve alignment while prototyping. This can be handy in prototyping, proof-of-concept, or just to defer implementation of graphics algorithms.

If you use UNICODE spaces for convenience, be aware that at least one of the UNICODE spaces has a size based on the font it is displayed from, specifically the actual space character itself (U+0020, ASCII 32)

If you're using the default iOS system font in a UILabel, the default System font characteristics could change in a subsequent iOS release and suddenly introduce an unwanted misalignment by changing your app's precise spacing. This can and does happen, for example the "San Francisco" font replaced a previous iOS system font in an iOS release.

UNICODE easy to specify in Swift, for example:

let six_per_em_space = "\u{2006}"

Alternatively, cut/paste the space from an HTML page directly into the UILabel's text field in Interface Builder.

Note: Attached pic is a screenshot, not HTML, so visit the linked page if you want to cut/paste the space.

UNICODE spaces

Setting the default Java character encoding

We set there two system properties together and it makes the system take everything into utf8


@Media min-width & max-width

If website on small devices behavior like desktop screen then you have to put this meta tag into header before

<meta name="viewport" content="width=device-width, initial-scale=1">

For media queries you can set this as

this will cover your all mobile/cellphone widths

 @media only screen and (min-width: 200px) and (max-width: 767px)  {
    //Put your CSS here for 200px to 767px width devices (cover all width between 200px to 767px //

For iPad and iPad pro you have to use

  @media only screen and (min-width: 768px) and (max-width: 1024px)  {
        //Put your CSS here for 768px to 1024px width devices(covers all width between 768px to 1024px //   

If you want to add css for Landscape mode you can add this

and (orientation : landscape)

  @media only screen and (min-width: 200px) and (max-width: 767px) and (orientation : portrait) {
        //Put your CSS here for 200px to 767px width devices (cover all mobile portrait width //        

Inserting line breaks into PDF

I have simply replaced the "\n" with "<br>" tag. Worked fine. It seems TCPDF render the text as HTML

$strText = str_replace("\n","<br>",$strText);
$pdf->MultiCell($width, $height,$strText, 0, 'J', 0, 1, '', '', true, null, true);

Mongoose: findOneAndUpdate doesn't return updated document

For whoever stumbled across this using ES6 / ES7 style with native promises, here is a pattern you can adopt...

const user = { id: 1, name: "Fart Face 3rd"};
const userUpdate = { name: "Pizza Face" };

try {
    user = await new Promise( ( resolve, reject ) => {
        User.update( { _id: }, userUpdate, { upsert: true, new: true }, ( error, obj ) => {
            if( error ) {
                console.error( JSON.stringify( error ) );
                return reject( error );

            resolve( obj );
} catch( error ) { /* set the world on fire */ }