Programs & Examples On #Identifier

An identifier is a name that identifies either a unique object or a unique class of objects.

PostgreSQL Error: Relation already exists

Another reason why you might get errors like "relation already exists" is if the DROP command did not execute correctly.

One reason this can happen is if there are other sessions connected to the database which you need to close first.

getting the error: expected identifier or ‘(’ before ‘{’ token

you need to place the opening brace after main , not before it

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main(void)

Using number as "index" (JSON)

JSON is "JavaScript Object Notation". JavaScript specifies its keys must be strings or symbols.

The following quotation from MDN Docs uses the terms "key/property" to refer to what I more often hear termed as "key/value".

In JavaScript, objects can be seen as a collection of properties. With the object literal syntax, a limited set of properties are initialized; then properties can be added and removed. Property values can be values of any type, including other objects, which enables building complex data structures. Properties are identified using key values. A key value is either a String or a Symbol value.

How does jQuery work when there are multiple elements with the same ID value?

There should only be one element with a given id. If you're stuck with that situation, see the 2nd half of my answer for options.

How a browser behaves when you have multiple elements with the same id (illegal HTML) is not defined by specification. You could test all the browsers and find out how they behave, but it's unwise to use this configuration or rely on any particular behavior.

Use classes if you want multiple objects to have the same identifier.

    <span class="a">1</span>
    <span class="a">2</span>

$(function() {
    var w = $("div");
    console.log($(".a").length);            // 2
    console.log($("body .a").length);       // 2
    console.log($(".a", w).length);         // 2

If you want to reliably look at elements with IDs that are the same because you can't fix the document, then you will have to do your own iteration as you cannot rely on any of the built in DOM functions.

You could do so like this:

function findMultiID(id) {
    var results = [];
    var children = $("div").get(0).children;
    for (var i = 0; i < children.length; i++) {
        if (children[i].id == id) {

Or, using jQuery:

$("div *").filter(function() {return( == "a");});

jQuery working example:

As to Why you get different results, that would have to do with the internal implementation of whatever piece of code was carrying out the actual selector operation. In jQuery, you could study the code to find out what any given version was doing, but since this is illegal HTML, there is no guarantee that it will stay the same over time. From what I've seen in jQuery, it first checks to see if the selector is a simple id like #a and if so, just used document.getElementById("a"). If the selector is more complex than that and querySelectorAll() exists, jQuery will often pass the selector off to the built in browser function which will have an implementation specific to that browser. If querySelectorAll() does not exist, then it will use the Sizzle selector engine to manually find the selector which will have it's own implementation. So, you can have at least three different implementations all in the same browser family depending upon the exact selector and how new the browser is. Then, individual browsers will all have their own querySelectorAll() implementations. If you want to reliably deal with this situation, you will probably have to use your own iteration code as I've illustrated above.

Are PostgreSQL column names case-sensitive?

The column names which are mixed case or uppercase have to be double quoted in PostgresQL. So best convention will be to follow all small case with underscore.

Hibernate error: ids for this class must be manually assigned before calling save():

Your @Entity class has a String type for its @Id field, so it can't generate ids for you.

If you change it to an auto increment in the DB and a Long in java, and add the @GeneratedValue annotation:

private Long U_id;

it will handle incrementing id generation for you.

What is the meaning of single and double underscore before an object name?

Accroding to

  • Single Leading Underscore(_var): Naming convention indicating a name is meant for internal use. Generally not enforced by the Python interpreter (except in wildcard imports) and meant as a hint to the programmer only.
  • Single Trailing Underscore(var_): Used by convention to avoid naming conflicts with Python keywords.
  • Double Leading Underscore(__var): Triggers name mangling when used in a class context. Enforced by the Python interpreter.
  • Double Leading and Trailing Underscore(__var__): Indicates special methods defined by the Python language. Avoid this naming scheme for your own attributes.
  • Single Underscore(_): Sometimes used as a name for temporary or insignificant variables (“don’t care”). Also: The result of the last expression in a Python REPL.

How to call on a function found on another file?

Small addition to @user995502's answer on how to run the program.

g++ player.cpp main.cpp -o main.out && ./main.out

Hibernate throws org.hibernate.AnnotationException: No identifier specified for entity: com..domain.idea.MAE_MFEView

I think this issue following model class wrong import.


Normally, it should be:

    import javax.persistence.Id;

PostgreSQL: How to make "case-insensitive" query

The most common approach is to either lowercase or uppercase the search string and the data. But there are two problems with that.

  1. It works in English, but not in all languages. (Maybe not even in most languages.) Not every lowercase letter has a corresponding uppercase letter; not every uppercase letter has a corresponding lowercase letter.
  2. Using functions like lower() and upper() will give you a sequential scan. It can't use indexes. On my test system, using lower() takes about 2000 times longer than a query that can use an index. (Test data has a little over 100k rows.)

There are at least three less frequently used solutions that might be more effective.

  1. Use the citext module, which mostly mimics the behavior of a case-insensitive data type. Having loaded that module, you can create a case-insensitive index by CREATE INDEX ON groups (name::citext);. (But see below.)
  2. Use a case-insensitive collation. This is set when you initialize a database. Using a case-insensitive collation means you can accept just about any format from client code, and you'll still return useful results. (It also means you can't do case-sensitive queries. Duh.)
  3. Create a functional index. Create a lowercase index by using CREATE INDEX ON groups (LOWER(name));. Having done that, you can take advantage of the index with queries like SELECT id FROM groups WHERE LOWER(name) = LOWER('ADMINISTRATOR');, or SELECT id FROM groups WHERE LOWER(name) = 'administrator'; You have to remember to use LOWER(), though.

The citext module doesn't provide a true case-insensitive data type. Instead, it behaves as if each string were lowercased. That is, it behaves as if you had called lower() on each string, as in number 3 above. The advantage is that programmers don't have to remember to lowercase strings. But you need to read the sections "String Comparison Behavior" and "Limitations" in the docs before you decide to use citext.

Updating MySQL primary key

If the primary key happens to be an auto_increment value, you have to remove the auto increment, then drop the primary key then re-add the auto-increment

MODIFY `auto_increment_field` INT, 
ADD PRIMARY KEY (new_primary_key);

then add back the auto increment

ALTER TABLE `xx` ADD INDEX `auto_increment_field` (auto_increment_field),
MODIFY `auto_increment_field` int auto_increment;

then set auto increment back to previous value


Click in OK button inside an Alert (Selenium IDE)

The question isn't clear - is this for an alert on page load? You shouldn't see any alert dialogues when using Selenium, as it replaces alert() with its own version which just captures the message given for verification.

Selenium doesn't support alert() on page load, as it needs to patch the function in the window under test with its own version.

If you can't get rid of onload alerts from the application under test, you should look into using GUI automation to click the popups which are generated, e.g. AutoIT if you're on Windows.

Disable vertical sync for glxgears

For Intel graphics and AMD/ATI opensource graphics drivers

Find the "Device" section of /etc/X11/xorg.conf which contains one of the following directives:

  • Driver "intel"
  • Driver "radeon"
  • Driver "fglrx"

And add the following line to that section:

Option     "SwapbuffersWait"       "false"

And run your application with vblank_mode environment variable set to 0:

$ vblank_mode=0 glxgears

For Nvidia graphics with the proprietary Nvidia driver

$ echo "0/SyncToVBlank=0" >> ~/.nvidia-settings-rc

The same change can be made in the nvidia-settings GUI by unchecking the option at X Screen 0 / OpenGL Settings / Sync to VBlank. Or, if you'd like to just test the setting without modifying your ~/.nvidia-settings-rc file you can do something like:

$ nvidia-settings --load-config-only --assign="SyncToVBlank=0"  # disable vertical sync
$ glxgears  # test it out
$ nvidia-settings --load-config-only  # restore your original vertical sync setting

PHP foreach change original array values

Use foreach($fields as &$field){ - so you will work with the original array.

Here is more about passing by reference.

How do I concatenate strings with variables in PowerShell?

Try the Join-Path cmdlet:

Get-ChildItem c:\code\*\bin\* -Filter *.dll | Foreach-Object {
    Join-Path -Path  $_.DirectoryName -ChildPath "$buildconfig\$($_.Name)" 

Prevent a webpage from navigating away using JavaScript

That suggested error message may duplicate the error message the browser already displays. In chrome, the 2 similar error messages are displayed one after another in the same window.

In chrome, the text displayed after the custom message is: "Are you sure you want to leave this page?". In firefox, it does not display our custom error message at all (but still displays the dialog).

A more appropriate error message might be:

window.onbeforeunload = function() {
    return "If you leave this page, you will lose any unsaved changes.";

Or stackoverflow style: "You have started writing or editing a post."

how to store Image as blob in Sqlite & how to retrieve it?

byte[] byteArray = rs.getBytes("columnname");  

Bitmap bm = BitmapFactory.decodeByteArray(byteArray, 0 ,byteArray.length);

How to choose the right bean scope?

Since JSF 2.3 all the bean scopes defined in package javax.faces.bean package have been deprecated to align the scopes with CDI. Moreover they're only applicable if your bean is using @ManagedBean annotation. If you are using JSF versions below 2.3 refer to the legacy answer at the end.

From JSF 2.3 here are scopes that can be used on JSF Backing Beans:

1. @javax.enterprise.context.ApplicationScoped: The application scope persists for the entire duration of the web application. That scope is shared among all requests and all sessions. This is useful when you have data for whole application.

2. @javax.enterprise.context.SessionScoped: The session scope persists from the time that a session is established until session termination. The session context is shared between all requests that occur in the same HTTP session. This is useful when you wont to save data for a specific client for a particular session.

3. @javax.enterprise.context.ConversationScoped: The conversation scope persists as log as the bean lives. The scope provides 2 methods: Conversation.begin() and Conversation.end(). These methods should called explicitly, either to start or end the life of a bean.

4. @javax.enterprise.context.RequestScoped: The request scope is short-lived. It starts when an HTTP request is submitted and ends after the response is sent back to the client. If you place a managed bean into request scope, a new instance is created with each request. It is worth considering request scope if you are concerned about the cost of session scope storage.

5. @javax.faces.flow.FlowScoped: The Flow scope persists as long as the Flow lives. A flow may be defined as a contained set of pages (or views) that define a unit of work. Flow scoped been is active as long as user navigates with in the Flow.

6. @javax.faces.view.ViewScoped: A bean in view scope persists while the same JSF page is redisplayed. As soon as the user navigates to a different page, the bean goes out of scope.

The following legacy answer applies JSF version before 2.3

As of JSF 2.x there are 4 Bean Scopes:

  • @SessionScoped
  • @RequestScoped
  • @ApplicationScoped
  • @ViewScoped

Session Scope: The session scope persists from the time that a session is established until session termination. A session terminates if the web application invokes the invalidate method on the HttpSession object, or if it times out.

RequestScope: The request scope is short-lived. It starts when an HTTP request is submitted and ends after the response is sent back to the client. If you place a managed bean into request scope, a new instance is created with each request. It is worth considering request scope if you are concerned about the cost of session scope storage.

ApplicationScope: The application scope persists for the entire duration of the web application. That scope is shared among all requests and all sessions. You place managed beans into the application scope if a single bean should be shared among all instances of a web application. The bean is constructed when it is first requested by any user of the application, and it stays alive until the web application is removed from the application server.

ViewScope: View scope was added in JSF 2.0. A bean in view scope persists while the same JSF page is redisplayed. (The JSF specification uses the term view for a JSF page.) As soon as the user navigates to a different page, the bean goes out of scope.

Choose the scope you based on your requirement.

Source: Core Java Server Faces 3rd Edition by David Geary & Cay Horstmann [Page no. 51 - 54] enter image description here

ReferenceError: document is not defined (in plain JavaScript)

try: window.document......

var body = window.document.getElementsByTagName("body")[0];

Django - Static file not found

{'document_root', settings.STATIC_ROOT} needs to be {'document_root': settings.STATIC_ROOT}

or you'll get an error like dictionary update sequence element #0 has length 6; 2 is required

How can I know if a process is running?

This is a way to do it with the name:

Process[] pname = Process.GetProcessesByName("notepad");
if (pname.Length == 0)

You can loop all process to get the ID for later manipulation:

Process[] processlist = Process.GetProcesses();
foreach(Process theprocess in processlist){
   Console.WriteLine("Process: {0} ID: {1}", theprocess.ProcessName, theprocess.Id);

String.equals versus ==

Generally .equals is used for Object comparison, where you want to verify if two Objects have an identical value.

== for reference comparison (are the two Objects the same Object on the heap) & to check if the Object is null. It is also used to compare the values of primitive types.

variable is not declared it may be inaccessible due to its protection level

This error occurred for me when I mistakenly added a comment following a line continuation character in VB.Net. I removed the comment and the problem went away.

Get current directory name (without full path) in a Bash script

The following commands will result in printing your current working directory in a bash script.

pushd .
CURRENT_DIR="`cd $1; pwd`"

How to get file path from OpenFileDialog and FolderBrowserDialog?

For OpenFileDialog:

OpenFileDialog choofdlog = new OpenFileDialog();
choofdlog.Filter = "All Files (*.*)|*.*";
choofdlog.FilterIndex = 1;
choofdlog.Multiselect = true;

if (choofdlog.ShowDialog() == DialogResult.OK)    
    string sFileName = choofdlog.FileName; 
    string[] arrAllFiles = choofdlog.FileNames; //used when Multiselect = true           

For FolderBrowserDialog:

FolderBrowserDialog fbd = new FolderBrowserDialog();
fbd.Description = "Custom Description"; 

if (fbd.ShowDialog() == DialogResult.OK)
    string sSelectedPath = fbd.SelectedPath;

To access selected folder and selected file name you can declare both string at class level.

namespace filereplacer
   public partial class Form1 : Form
      string sSelectedFile;
      string sSelectedFolder;

      public Form1()

      private void direc_Click(object sender, EventArgs e)
         FolderBrowserDialog fbd = new FolderBrowserDialog();
         //fbd.Description = "Custom Description"; //not mandatory

         if (fbd.ShowDialog() == DialogResult.OK)      
               sSelectedFolder = fbd.SelectedPath;
               sSelectedFolder = string.Empty;    

      private void choof_Click(object sender, EventArgs e)
         OpenFileDialog choofdlog = new OpenFileDialog();
         choofdlog.Filter = "All Files (*.*)|*.*";
         choofdlog.FilterIndex = 1;
         choofdlog.Multiselect = true;

         if (choofdlog.ShowDialog() == DialogResult.OK)                 
             sSelectedFile = choofdlog.FileName;            
             sSelectedFile = string.Empty;       

      private void replacebtn_Click(object sender, EventArgs e)
          if(sSelectedFolder != string.Empty && sSelectedFile != string.Empty)
               //use selected folder path and file path


As you have kept choofdlog.Multiselect=true;, that means in the OpenFileDialog() you are able to select multiple files (by pressing ctrl key and left mouse click for selection).

In that case you could get all selected files in string[]:

At Class Level:

string[] arrAllFiles;

Locate this line (when Multiselect=true this line gives first file only):

sSelectedFile = choofdlog.FileName; 

To get all files use this:

arrAllFiles = choofdlog.FileNames; //this line gives array of all selected files

pass post data with window.location.href

Add a form to your HTML, something like this:

<form style="display: none" action="/the/url" method="POST" id="form">
  <input type="hidden" id="var1" name="var1" value=""/>
  <input type="hidden" id="var2" name="var2" value=""/>

and use JQuery to fill these values (of course you can also use javascript to do something similar)


Then finally submit the form


on the server side you should be able to get the data you sent by checking var1 and var2, how to do this depends on what server-side language you are using.

git: fatal: I don't handle protocol '??http'

clonning below :

git clone

gives error:

Cloning into 'ZendSkeletonApplication'...
fatal: I don't handle protocol 'https'

Modified it to:

git clone

works perfectly or you can just git clone the url. I am using os windows 10 and gitbash.

Responsive css background images

         * {
  padding: 0;
  margin: 0;
  box-sizing: border-box;

#res_img {
  background: url("");
  width: 100%;
  height: 500px;
  background-repeat: no-repeat;
  background-size: 100% 100%;
  background-position: center;
  border: 1px solid red;

@media screen and (min-width:300px) and (max-width:500px) {
  #res_img {
    width: 100%;
    height: 200px;


<div id="res_img">

react-router - pass props to handler component

Use the component with or without router based on Rajesh Naroth answer.

class Index extends React.Component {

  constructor(props) {
  render() {
    const foo = (this.props.route) ? :;
    return (
        Index - {foo}

var routes = (
  <Route path="/" foo="bar" component={Index}/>

Or your could do it this way:

export const Index = ({foo, route}) => {
  const content = (foo) ? foo : (route) ? : 'No content found!';
  return <h1>{content}</h1>

Find text string using jQuery?

this function should work. basically does a recursive lookup till we get a distinct list of leaf nodes.

function distinctNodes(search, element) {
    var d, e, ef;
    e = [];
    ef = [];

    if (element) {
        d = $(":contains(\""+ search + "\"):not(script)", element);
    else {
            d = $(":contains(\""+ search + "\"):not(script)");

    if (d.length == 1) {
    else {
        d.each(function () {
            var i, r = distinctNodes(search, this);
            if (r.length === 0) {
            else {
                for (i = 0; i < r.length; ++i) {
    $.each(e, function () {
        for (var i = 0; i < ef.length; ++i) {
            if (this === ef[i]) return;
    return ef;

writing integer values to a file using out.write()

any of these should work

outf.write("%s" % num)


print >> outf, num

Redirect stderr and stdout in Bash

Short answer: Command >filename 2>&1 or Command &>filename


Consider the following code which prints the word "stdout" to stdout and the word "stderror" to stderror.

$ (echo "stdout"; echo "stderror" >&2)

Note that the '&' operator tells bash that 2 is a file descriptor (which points to the stderr) and not a file name. If we left out the '&', this command would print stdout to stdout, and create a file named "2" and write stderror there.

By experimenting with the code above, you can see for yourself exactly how redirection operators work. For instance, by changing which file which of the two descriptors 1,2, is redirected to /dev/null the following two lines of code delete everything from the stdout, and everything from stderror respectively (printing what remains).

$ (echo "stdout"; echo "stderror" >&2) 1>/dev/null
$ (echo "stdout"; echo "stderror" >&2) 2>/dev/null

Now, we can explain why the solution why the following code produces no output:

(echo "stdout"; echo "stderror" >&2) >/dev/null 2>&1

To truly understand this, I highly recommend you read this webpage on file descriptor tables. Assuming you have done that reading, we can proceed. Note that Bash processes left to right; thus Bash sees >/dev/null first (which is the same as 1>/dev/null), and sets the file descriptor 1 to point to /dev/null instead of the stdout. Having done this, Bash then moves rightwards and sees 2>&1. This sets the file descriptor 2 to point to the same file as file descriptor 1 (and not to file descriptor 1 itself!!!! (see this resource on pointers for more info)) . Since file descriptor 1 points to /dev/null, and file descriptor 2 points to the same file as file descriptor 1, file descriptor 2 now also points to /dev/null. Thus both file descriptors point to /dev/null, and this is why no output is rendered.

To test if you really understand the concept, try to guess the output when we switch the redirection order:

(echo "stdout"; echo "stderror" >&2)  2>&1 >/dev/null


The reasoning here is that evaluating from left to right, Bash sees 2>&1, and thus sets the file descriptor 2 to point to the same place as file descriptor 1, ie stdout. It then sets file descriptor 1 (remember that >/dev/null = 1>/dev/null) to point to >/dev/null, thus deleting everything which would usually be send to to the standard out. Thus all we are left with was that which was not send to stdout in the subshell (the code in the parentheses)- i.e. "stderror". The interesting thing to note there is that even though 1 is just a pointer to the stdout, redirecting pointer 2 to 1 via 2>&1 does NOT form a chain of pointers 2 -> 1 -> stdout. If it did, as a result of redirecting 1 to /dev/null, the code 2>&1 >/dev/null would give the pointer chain 2 -> 1 -> /dev/null, and thus the code would generate nothing, in contrast to what we saw above.

Finally, I'd note that there is a simpler way to do this:

From section 3.6.4 here, we see that we can use the operator &> to redirect both stdout and stderr. Thus, to redirect both the stderr and stdout output of any command to \dev\null (which deletes the output), we simply type $ command &> /dev/null or in case of my example:

$ (echo "stdout"; echo "stderror" >&2) &>/dev/null

Key takeaways:

  • File descriptors behave like pointers (although file descriptors are not the same as file pointers)
  • Redirecting a file descriptor "a" to a file descriptor "b" which points to file "f", causes file descriptor "a" to point to the same place as file descriptor b - file "f". It DOES NOT form a chain of pointers a -> b -> f
  • Because of the above, order matters, 2>&1 >/dev/null is != >/dev/null 2>&1. One generates output and the other does not!

Finally have a look at these great resources:

Bash Documentation on Redirection, An Explanation of File Descriptor Tables, Introduction to Pointers

JavaScript load a page on button click

Just window.location = "", or, for local links, window.location = "my_relative_link.html".

You can try it by typing it into your address bar as well, e.g. javascript: window.location = "".

Also note that the protocol part of the URL (http://) is not optional for absolute links; omitting it will make javascript assume a relative link.

space between divs - display table-cell

Use transparent borders if possible.

JSFiddle Demo


<div class="table">
    <div class="row">
        <div class="cell">Cell 1</div>
        <div class="cell">Cell 2</div>
        <div class="cell">Cell 3</div>


.table {
  display: table;
  border: 1px solid black;

.row { display:table-row; }

.cell {
  display: table-cell;
  background-clip: padding-box;
  background-color: gold;
  border-right: 10px solid transparent;

.cell:last-child {
  border-right: 0 none;


You could use the border-spacing property, as the accepted answer suggests, but this not only generates space between the table cells but also between the table cells and the table container. This may be unwanted.

If you don't need visible borders on your table cells you should therefore use transparent borders to generate cell margins. Transparent borders require setting background-clip: padding-box; because otherwise the background color of the table cells is displayed on the border.

Transparent borders and background-clip are supported in IE9 upwards (and all other modern browsers). If you need IE8 compatibility or don't need actual transparent space you can simply set a white border color and leave the background-clip out.

Check if string is in a pandas dataframe

You should check the value of your line of code like adding checking length of it.

    print("Name Present")

Find index of last occurrence of a substring in a string

you can use rindex() function to get the last occurrence of a character in string


Android RecyclerView addition & removal of items

Here are some visual supplemental examples. See my fuller answer for examples of adding and removing a range.

Add single item

Add "Pig" at index 2.

Insert single item

String item = "Pig";
int insertIndex = 2;
data.add(insertIndex, item);

Remove single item

Remove "Pig" from the list.

Remove single item

int removeIndex = 2;

What are all possible pos tags of NLTK?

Just run this verbatim.

import nltk'tagsets')

nltk.tag._POS_TAGGER won't work. It will give AttributeError: module 'nltk.tag' has no attribute '_POS_TAGGER'. It's not available in NLTK 3 anymore.

How to make execution pause, sleep, wait for X seconds in R?

Sys.sleep() will not work if the CPU usage is very high; as in other critical high priority processes are running (in parallel).

This code worked for me. Here I am printing 1 to 1000 at a 2.5 second interval.

for (i in 1:1000)
  while((as.numeric(Sys.time()) - as.numeric(date_time))<2.5){} #dummy while loop

How to import large sql file in phpmyadmin

the answer for those with shared hosting. Best to use this little script which I just used to import a 300mb DB file to my server. The script is called Big Dump.

provides a script to import large DB's on resource-limited servers

How to run eclipse in clean mode? what happens if we do so?

Easier option is to use ./eclipse -clean

HTML5 <video> element on Android

Roman's answer worked fine for me - or at least, it gave me what I was expecting. Opening the video in the phone's native application is exactly the same as what the iPhone does.

It's probably worth adjusting your viewpoint and expect video to be played fullscreen in its own application, and coding for that. It's frustrating that clicking the video isn't sufficient to get it playing in the same way as the iPhone does, but seeing as it only takes an onclick attribute to launch it, it's not the end of the world.

My advice, FWIW, is to use a poster image, and make it obvious that it will play the video. I'm working on a project at the moment that does precisely that, and the clients are happy with it - and also that they're getting the Android version of a web app for free, of course, because the contract was only for an iPhone web app.

Just for illustration, a working Android video tag is below. Nice and simple.

<video src="video/placeholder.m4v" poster="video/placeholder.jpg" onclick=";"/>

How to convert a DataFrame back to normal RDD in pyspark?

Answer given by kennyut/Kistian works very well but to get exact RDD like output when RDD consist of list of attributes e.g. [1,2,3,4] we can use flatmap command as below,

rdd = df.rdd.flatMap(list)
rdd = df.rdd.flatmap(lambda x: list(x))

How to increase editor font size?

Temporarily adjust the font size

Go to Settings (or Preferences in Mac) > Editor > General > Change font size (Zoom) with Ctrl+Mouse Wheel OR Press "Cmd+Shift+A" for mac.

enter image description here

This will allow you to quickly modify the font size whenever you want. However, the font will get reset to the default size the next time you start Android Studio. (The Control+Mouse Wheel functionality will not get reset, though. You only need to do this once.)

Permanently change the default font size

Go to Settings > Editor > Colors & Fonts > Font. Click "Save As..." and choose a new scheme name. Then change the font size and say OK. This will be the default size every time you open Android Studio now.

enter image description here

How do I format a date as ISO 8601 in moment.js?

Answer in 2020 (Includes Timezone Support)

The problem we were having is that, by default, ISOStrings aren't localized to your timezone. So, this is kinda hacky, but here's how we ended up solving this issue:

/** Imports Moment for time utilities. */
const moment = require("moment-timezone")

//** Returns now in ISO format in Central Time */
export function getNowISO() {
  return `${moment().toISOString(true).substring(0, 23)}Z`

This will leave you with an exact ISO-formatted, localized string.

Important note: Moment now suggests using other packages for new projects.

Print empty line?

Python's print function adds a newline character to its input. If you give it no input it will just print a newline character


Will print an empty line. If you want to have an extra line after some text you're printing, you can a newline to your text

my_str = "hello world"
print(my_str + "\n")

If you're doing this a lot, you can also tell print to add 2 newlines instead of just one by changing the end= parameter (by default end="\n")

print("hello world", end="\n\n")

But you probably don't need this last method, the two before are much clearer.

Android failed to load JS bundle

The following made it work for me on Ubuntu 14.04:

cd (App Dir)
react-native start > /dev/null 2>&1 &
adb reverse tcp:8081 tcp:8081

Update: See

Update 2: @scgough We got this error because React Native (RN) was unable to fetch JavaScript from the dev server running on our workstations. You can see why this happens here:

If your RN app detects that you're using Genymotion or the emulator it tries to fetch the JavaScript from GENYMOTION_LOCALHOST ( or EMULATOR_LOCALHOST ( Otherwise it presumes that you're using a device and it tries to fetch the JavaScript from DEVICE_LOCALHOST (localhost). The problem is that the dev server runs on your workstation's localhost, not the device's, so in order to get it to work you need to either:

python variable NameError

In addition to the missing quotes around 100Mb in the last else, you also want to quote the constants in your if-statements if tSizeAns == "1":, because raw_input returns a string, which in comparison with an integer will always return false.

However the missing quotes are not the reason for the particular error message, because it would result in an syntax error before execution. Please check your posted code. I cannot reproduce the error message.

Also if ... elif ... else in the way you use it is basically equivalent to a case or switch in other languages and is neither less readable nor much longer. It is fine to use here. One other way that might be a good idea to use if you just want to assign a value based on another value is a dictionary lookup:

tSize = {"1": "100Mb", "2": "200Mb"}[tSizeAns] 

This however does only work as long as tSizeAns is guaranteed to be in the range of tSize. Otherwise you would have to either catch the KeyError exception or use a defaultdict:

lookup = {"1": "100Mb", "2": "200Mb"} try:     tSize = lookup[tSizeAns] except KeyError:     tSize = "100Mb" 


from collections import defaultdict  [...]  lookup = defaultdict(lambda: "100Mb", {"1": "100Mb", "2": "200Mb"}) tSize = lookup[tSizeAns] 

In your case I think these methods are not justified for two values. However you could use the dictionary to construct the initial output at the same time.

How to resolve TypeError: can only concatenate str (not "int") to str

Problem is you are doing the following

str(chr(char + 7429146))

where char is a string. You cannot add a int with a string. this will cause that error

maybe if you want to get the ascii code and add it with a constant number. if so , you can just do ord(char) and add it to a number. but again, chr can take values between 0 and 1114112

Difference between & and && in Java?

& is bitwise. && is logical.

& evaluates both sides of the operation.
&& evaluates the left side of the operation, if it's true, it continues and evaluates the right side.

Returning JSON object as response in Spring Boot

If you need to return a JSON object using a String, then the following should work:

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.http.ResponseEntity;

public class StudentController {

    public ResponseEntity<JsonNode> get() throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        JsonNode json = mapper.readTree("{\"id\": \"132\", \"name\": \"Alice\"}");
        return ResponseEntity.ok(json);

what are the .map files used for in Bootstrap 3.x?

Map files (source maps) are there to de-reference minified code (css and javascript).

And they are mainly used to help developers debugging a production environment, because developers usually use minified files for production which makes it impossible to debug. Map files help them de-referencing the code to see how the original file looked like.

What's the difference between "app.render" and "res.render" in express.js?

use app.render in scenarios where you need to render a view but not send it to a client via http. html emails springs to mind.

How to use the pass statement?

as the book said, I only ever use it as a temporary placeholder, ie,

# code that does something to to a variable, var
if var == 2000:
    var += 1

and then later fill in the scenario where var == 2000

Solution to "subquery returns more than 1 row" error

= can be used when the subquery returns only 1 value.

When subquery returns more than 1 value, you will have to use IN:

select * 
from table
where id IN (multiple row query);

For example:

FROM Students
WHERE Marks = (SELECT MAX(Marks) FROM Students)   --Subquery returns only 1 value

FROM Students
      (SELECT Marks 
       FROM Students 
       ORDER BY Marks DESC
       LIMIT 10)                       --Subquery returns 10 values

Redirecting Output from within Batch file

echo some output >"your logfile"


 echo some output
 echo more output
)>"Your logfile"

should fill the bill.

If you want to APPEND the output, use >> instead of >. > will start a new logfile.

Efficient way of having a function only execute once in a loop

If I understand the updated question correctly, something like this should work

def function1():
    print "function1 called"

def function2():
    print "function2 called"

def function3():
    print "function3 called"

called_functions = set()
while True:
    n = raw_input("choose a function: 1,2 or 3 ")
    func = {"1": function1,
            "2": function2,
            "3": function3}.get(n)

    if func in called_functions:
        print "That function has already been called"

Why am I getting Unknown error in line 1 of pom.xml?

There is a bug about Eclipse and spring-boot-starter-parent 2.1.5

"if the maven packaging attribute is war then no problem.The problem is in jar type." So you can also fix this problem by changing packaging type.


Problems with entering Git commit message with Vim

I am assuming you are using msys git. If you are, the editor that is popping up to write your commit message is vim. Vim is not friendly at first. You may prefer to switch to a different editor. If you want to use a different editor, look at this answer: How do I use Notepad++ (or other) with msysgit?

If you want to use vim, type i to type in your message. When happy hit ESC. Then type :wq, and git will then be happy.

Or just type git commit -m "your message here" to skip the editor altogether.

ReactJS: Maximum update depth exceeded error

In this case , this code

{<td><span onClick={this.toggle()}>Details</span></td>}

causes toggle function to call immediately and re render it again and again thus making infinite calls.

so passing only the reference to that toggle method will solve the problem.

so ,

{<td><span onClick={this.toggle}>Details</span></td>}

will be the solution code.

If you want to use the () , you should use an arrow function like this

{<td><span onClick={()=> this.toggle()}>Details</span></td>}

In case you want to pass parameters you should choose the last option and you can pass parameters like this

{<td><span onClick={(arg)=>this.toggle(arg)}>Details</span></td>}

In the last case it doesn't call immediately and don't cause the re render of the function, hence avoiding infinite calls.

php resize image on upload

I followed the steps at and to produce this solution:

In my view (I am using the MVC paradigm, but it could be your .html or .php file, or the technology that you use for your front-end):

<form action="../../photos/upload.php" method="post" enctype="multipart/form-data">
<label for="quantity">Width:</label>
  <input type="number" id="picture_width" name="picture_width" min="10" max="800" step="1" value="500">
Select image to upload:
<input type="file" name="fileToUpload" id="fileToUpload">
<input type="submit" value="Upload Image" name="submit">

My upload.php:

/* Get original image x y*/
list($w, $h) = getimagesize($_FILES['fileToUpload']['tmp_name']);
/* calculate new image size with ratio */
$ratio = max($_POST['picture_width']/$w, $new_height/$h);
$h = ceil($new_height / $ratio);
$x = ($w - $_POST['picture_width'] / $ratio) / 2;
$w = ceil($_POST['picture_width'] / $ratio);
/* new file name */
//$path = 'uploads/'.$_POST['picture_width'].'x'.$new_height.'_'.basename($_FILES['fileToUpload']['name']);
$path = 'uploads/'.basename($_FILES['fileToUpload']['name']);
/* read binary data from image file */
$imgString = file_get_contents($_FILES['fileToUpload']['tmp_name']);
/* create image from string */
$image = imagecreatefromstring($imgString);
$tmp = imagecreatetruecolor($_POST['picture_width'], $new_height);
imagecopyresampled($tmp, $image,
    0, 0,
    $x, 0,
    $_POST['picture_width'], $new_height,
    $w, $h);
$uploadOk = 1;
$imageFileType = strtolower(pathinfo($path,PATHINFO_EXTENSION));
// Check if image file is a actual image or fake image
if(isset($_POST["submit"])) {
    $check = getimagesize($_FILES["fileToUpload"]["tmp_name"]);
    if($check !== false) {
        //echo "File is an image - " . $check["mime"] . ".";
        $uploadOk = 1;
    } else {
        //echo "File is not an image.";
        $uploadOk = 0;
// Check if file already exists
if (file_exists($path)) {
    echo "Sorry, file already exists.";
    $uploadOk = 0;
// Check file size
if ($_FILES["fileToUpload"]["size"] > 500000) {
    echo "Sorry, your file is too large.";
    $uploadOk = 0;
// Allow certain file formats
if($imageFileType != "jpg" && $imageFileType != "png" && $imageFileType != "jpeg"
&& $imageFileType != "gif" ) {
    echo "Sorry, only JPG, JPEG, PNG & GIF files are allowed.";
    $uploadOk = 0;
// Check if $uploadOk is set to 0 by an error
if ($uploadOk == 0) {
    echo "Sorry, your file was not uploaded.";
    // if everything is ok, try to upload file
} else {
    /* Save image */
    switch ($_FILES['fileToUpload']['type']) {
        case 'image/jpeg':
            imagejpeg($tmp, $path, 100);
        case 'image/png':
            imagepng($tmp, $path, 0);
        case 'image/gif':
            imagegif($tmp, $path);
    echo "The file ". basename( $_FILES["fileToUpload"]["name"]). " has been uploaded.";
    /* cleanup memory */

The name of the folder where pictures are stored is called 'uploads/'. You need to have that folder previously created and that is where you will see your pictures. It works great for me.

NOTE: This is my form:

enter image description here

The code is uploading and resizing pictures properly. I used this link as a guide: I modified it because in that code they specify both width and height of resized pictures. In my case, I only wanted to specify width. The height I automatically calculated it proportionally, just keeping proper picture proportions. Everything works perfectly. I hope this helps.

How to echo shell commands as they are executed

set -x or set -o xtrace expands variables and prints a little + sign before the line.

set -v or set -o verbose does not expand the variables before printing.

Use set +x and set +v to turn off the above settings.

On the first line of the script, one can put #!/bin/sh -x (or -v) to have the same effect as set -x (or -v) later in the script.

The above also works with /bin/sh.

See the bash-hackers' wiki on set attributes, and on debugging.

$ cat shl

ls $DIR

$ bash -x shl 
+ DIR=/tmp/so
+ ls /tmp/so

decimal vs double! - Which one should I use and when?

My question is when should a use a double and when should I use a decimal type?

decimal for when you work with values in the range of 10^(+/-28) and where you have expectations about the behaviour based on base 10 representations - basically money.

double for when you need relative accuracy (i.e. losing precision in the trailing digits on large values is not a problem) across wildly different magnitudes - double covers more than 10^(+/-300). Scientific calculations are the best example here.

which type is suitable for money computations?

decimal, decimal, decimal

Accept no substitutes.

The most important factor is that double, being implemented as a binary fraction, cannot accurately represent many decimal fractions (like 0.1) at all and its overall number of digits is smaller since it is 64-bit wide vs. 128-bit for decimal. Finally, financial applications often have to follow specific rounding modes (sometimes mandated by law). decimal supports these; double does not.

Proxy setting for R

This post pertains to R proxy issues on *nix. You should know that R has many libraries/methods to fetch data over internet.

For 'curl', 'libcurl', 'wget' etc, just do the following:

  1. Open a terminal. Type the following command:

    sudo gedit /etc/R/
  2. Enter the following lines:

    http_proxy='http://username:[email protected]:port/'
    https_proxy='https://username:[email protected]:port/'

    Replace username, password,, and port with these settings specific to your network.

  3. Quit R and launch again.

This should solve your problem with 'libcurl' and 'curl' method. However, I have not tried it with 'httr'. One way to do that with 'httr' only for that session is as follows:

set_config(use_proxy(url="",port=8080, username="username", password="password"))

You need to substitute settings specific to your n/w in relevant fields.

CodeIgniter Active Record - Get number of returned rows

Just gotta read the docs son!


File name without extension name VBA

Using the Split function seems more elegant than InStr and Left, in my opinion.

Private Sub CommandButton2_Click()

Dim ThisFileName As String
Dim BaseFileName As String

Dim FileNameArray() As String

ThisFileName = ThisWorkbook.Name
FileNameArray = Split(ThisFileName, ".")
BaseFileName = FileNameArray(0)

MsgBox "Base file name is " & BaseFileName

End Sub

How to use apply a custom drawable to RadioButton?

Give your radiobutton a custom style:

<style name="MyRadioButtonStyle" parent="@android:style/Widget.CompoundButton.RadioButton">
    <item name="android:button">@drawable/custom_btn_radio</item>


<selector xmlns:android="">
    <item android:state_checked="true" android:state_window_focused="false"
          android:drawable="@drawable/btn_radio_on" />
    <item android:state_checked="false" android:state_window_focused="false"
          android:drawable="@drawable/btn_radio_off" />

    <item android:state_checked="true" android:state_pressed="true"
          android:drawable="@drawable/btn_radio_on_pressed" />
    <item android:state_checked="false" android:state_pressed="true"
          android:drawable="@drawable/btn_radio_off_pressed" />

    <item android:state_checked="true" android:state_focused="true"
          android:drawable="@drawable/btn_radio_on_selected" />
    <item android:state_checked="false" android:state_focused="true"
          android:drawable="@drawable/btn_radio_off_selected" />

    <item android:state_checked="false" android:drawable="@drawable/btn_radio_off" />
    <item android:state_checked="true" android:drawable="@drawable/btn_radio_on" />

Replace the drawables with your own.

CodeIgniter Active Record not equal

According to the manual this should work:

Custom key/value method:

You can include an operator in the first parameter in order to control the comparison:

$this->db->where('name !=', $name);
$this->db->where('id <', $id);
Produces: WHERE name != 'Joe' AND id < 45

Search for $this->db->where(); and look at item #2.

What is the difference between a 'closure' and a 'lambda'?

When most people think of functions, they think of named functions:

function foo() { return "This string is returned from the 'foo' function"; }

These are called by name, of course:

foo(); //returns the string above

With lambda expressions, you can have anonymous functions:

 @foo = lambda() {return "This is returned from a function without a name";}

With the above example, you can call the lambda through the variable it was assigned to:


More useful than assigning anonymous functions to variables, however, are passing them to or from higher-order functions, i.e., functions that accept/return other functions. In a lot of these cases, naming a function is unecessary:

function filter(list, predicate) 
 { @filteredList = [];
   for-each (@x in list) if (predicate(x)) filteredList.add(x);
   return filteredList;

//filter for even numbers
filter([0,1,2,3,4,5,6], lambda(x) {return (x mod 2 == 0)}); 

A closure may be a named or anonymous function, but is known as such when it "closes over" variables in the scope where the function is defined, i.e., the closure will still refer to the environment with any outer variables that are used in the closure itself. Here's a named closure:

@x = 0;

function incrementX() { x = x + 1;}

incrementX(); // x now equals 1

That doesn't seem like much but what if this was all in another function and you passed incrementX to an external function?

function foo()
 { @x = 0;

   function incrementX() 
    { x = x + 1;
      return x;

   return incrementX;

@y = foo(); // y = closure of incrementX over foo.x
y(); //returns 1 (y.x == 0 + 1)
y(); //returns 2 (y.x == 1 + 1)

This is how you get stateful objects in functional programming. Since naming "incrementX" isn't needed, you can use a lambda in this case:

function foo()
 { @x = 0;

   return lambda() 
           { x = x + 1;
             return x;

Call to undefined function curl_init().?

The CURL extension ext/curl is not installed or enabled in your PHP installation. Check the manual for information on how to install or enable CURL on your system.

Is it possible to run one logrotate check manually?

Yes: logrotate --force $CONFIG_FILE

Best way to list files in Java, sorted by Date Modified?

You might also look at apache commons IO, it has a built in last modified comparator and many other nice utilities for working with files.

Convert string to date then format the date

Tested this code

java.text.DateFormat formatter = new java.text.SimpleDateFormat("MM-dd-yyyy");
java.util.Date newDate = new java.util.Date();
System.out.println(formatter.format(newDate ));,5.0/docs/api/java/text/SimpleDateFormat.html

app-release-unsigned.apk is not signed

For gradle Kotlin dsl

signingConfigs {
    create("releaseConfig") {
        storeFile = file("your keystore file path")
        storePassword = "storePassword"
        keyAlias = "keyAlias"
        keyPassword = "keyPassword"
buildTypes {
    getByName("release") {
        signingConfig = signingConfigs.getByName("releaseConfig")
        isMinifyEnabled = true
        isShrinkResources = true
        proguardFiles(getDefaultProguardFile("proguard-android.txt"), "")

Using COALESCE to handle NULL values in PostgreSQL

You can use COALESCE in conjunction with NULLIF for a short, efficient solution:

COALESCE( NULLIF(yourField,'') , '0' )

The NULLIF function will return null if yourField is equal to the second value ('' in the example), making the COALESCE function fully working on all cases:

                 QUERY                     |                RESULT 
SELECT COALESCE(NULLIF(null  ,''),'0')     |                 '0'
SELECT COALESCE(NULLIF(''    ,''),'0')     |                 '0'
SELECT COALESCE(NULLIF('foo' ,''),'0')     |                 'foo'

A network-related or instance-specific error occurred while establishing a connection to SQL Server

Sql Server fire this error when your application don't have enough rights to access the database. there are several reason about this error . To fix this error you should follow the following instruction.

  1. Try to connect sql server from your server using management studio . if you use windows authentication to connect sql server then set your application pool identity to server administrator .

  2. if you use sql server authentication then check you connection string in web.config of your web application and set user id and password of sql server which allows you to log in .

  3. if your database in other server(access remote database) then first of enable remote access of sql server form sql server property from sql server management studio and enable TCP/IP form sql server configuration manager .

  4. after doing all these stuff and you still can't access the database then check firewall of server form where you are trying to access the database and add one rule in firewall to enable port of sql server(by default sql server use 1433 , to check port of sql server you need to check sql server configuration manager network protocol TCP/IP port).

  5. if your sql server is running on named instance then you need to write port number with sql serer name for example 117.312.21.21/nameofsqlserver,1433.

  6. If you are using cloud hosting like amazon aws or microsoft azure then server or instance will running behind cloud firewall so you need to enable 1433 port in cloud firewall if you have default instance or specific port for sql server for named instance.

  7. If you are using amazon RDS or SQL azure then you need to enable port from security group of that instance.

  8. If you are accessing sql server through sql server authentication mode them make sure you enabled "SQL Server and Windows Authentication Mode" sql server instance property. enter image description here

    1. Restart your sql server instance after making any changes in property as some changes will require restart.

if you further face any difficulty then you need to provide more information about your web site and sql server .

Get Root Directory Path of a PHP project

You could also use realpath.

realpath(".") returns your document root.

You can call realpath with your specific path. Note that it will NOT work if the target folder or file does not exist. In such case it will return false, which could be useful for testing if a file exists.

In my case I needed to specify a path for a new file to be written to disk, and the solution was to append the path relative to document root:

$filepath = realpath(".") . "/path/to/newfile.txt";

Hope this helps anyone.

Capitalize or change case of an NSString in Objective-C

In case anyone needed the above in swift :

SWIFT 3.0 and above :

this will capitalize your string, make the first letter capital :

viewNoteDateMonth.text  = yourString.capitalized

this will uppercase your string, make all the string upper case :

viewNoteDateMonth.text  = yourString.uppercased()

Like Operator in Entity Framework?

I had the same problem.

For now, I've settled with client-side Wildcard/Regex filtering based on - it's simple and works as expected.

I've found another discussion on this topic:
This post looks promising if you use Entity Framework >= 4.0:

Use SqlFunctions.PatIndex:

Like this:

var q = EFContext.Products.Where(x =>
SqlFunctions.PatIndex("%CD%BLUE%", x.ProductName) > 0);

Note: this solution is for SQL-Server only, because it uses non-standard PATINDEX function.

How to decrypt Hash Password in Laravel

For compare hashed password with the plain text password string you can use the PHP password_verify

if(password_verify('1234567', $crypt_password_string)) {
    // in case if "$crypt_password_string" actually hides "1234567"

How do I find out what keystore my JVM is using?

As DimtryB mentioned, by default the keystore is under the user directory. But if you are trying to update the cacerts file, so that the JVM can pick the keys, then you will have to update the cacerts file under jre/lib/security. You can also view the keys by executing the command keytool -list -keystore cacerts to see if your certificate is added.

How to set a tkinter window to a constant size

You turn off pack_propagate by setting pack_propagate(0)

Turning off pack_propagate here basically says don't let the widgets inside the frame control it's size. So you've set it's width and height to be 500. Turning off propagate stills allows it to be this size without the widgets changing the size of the frame to fill their respective width / heights which is what would happen normally

To turn off resizing the root window, you can set root.resizable(0, 0), where resizing is allowed in the x and y directions respectively.

To set a maxsize to window, as noted in the other answer you can set the maxsize attribute or minsize although you could just set the geometry of the root window and then turn off resizing. A bit more flexible imo.

Whenever you set grid or pack on a widget it will return None. So, if you want to be able to keep a reference to the widget object you shouldn't be setting a variabe to a widget where you're calling grid or pack on it. You should instead set the variable to be the widget Widget(master, ....) and then call pack or grid on the widget instead.

import tkinter as tk

def startgame():


mw = tk.Tk()

#If you have a large number of widgets, like it looks like you will for your
#game you can specify the attributes for all widgets simply like this.
mw.option_add("*Button.Background", "black")
mw.option_add("*Button.Foreground", "red")

mw.title('The game')
#You can set the geometry attribute to change the root windows size
mw.geometry("500x500") #You want the size of the app to be 500x500
mw.resizable(0, 0) #Don't allow resizing in the x or y direction

back = tk.Frame(master=mw,bg='black')
back.pack_propagate(0) #Don't allow the widgets inside to determine the frame's width / height
back.pack(fill=tk.BOTH, expand=1) #Expand the frame to fill the root window

#Changed variables so you don't have these set to None from .pack()
go = tk.Button(master=back, text='Start Game', command=startgame)
close = tk.Button(master=back, text='Quit', command=mw.destroy)
info = tk.Label(master=back, text='Made by me!', bg='red', fg='black')


Pause Console in C++ program

I always used a couple lines of code which clear the input stream of any characters and then wait for input to ignore.

Something like:

void pause() {
    cout << endl << "Press any key to continue...";

And then any time I need it in the program I have my own pause(); function, without the overhead of a system pause. This is only really an issue when writing console programs that you want to stay open or stay fixated on a certain point though.

Convert a string to a datetime

Nobody mentioned this, but in some cases the other method fails to recognize the datetime...

You can try this instead, which will convert the specified string representation of a date and time to an equivalent date and time value

string iDate = "05/05/2005";
DateTime oDate = Convert.ToDateTime(iDate);
MessageBox.Show(oDate.Day + " " + oDate.Month + "  " + oDate.Year );

Function to return only alpha-numeric characters from string?

Rather than preg_replace, you could always use PHP's filter functions using the filter_var() function with FILTER_SANITIZE_STRING.

What is the best way to seed a database in Rails?

Add it in database migrations, that way everyone gets it as they update. Handle all of your logic in the ruby/rails code, so you never have to mess with explicit ID settings.

How do I create dynamic properties in C#?

As a replacement for some of orsogufo's code, because I recently went with a dictionary for this same problem myself, here is my [] operator:

public string this[string key]
    get { return properties.ContainsKey(key) ? properties[key] : null; }

        if (properties.ContainsKey(key))
            properties[key] = value;
            properties.Add(key, value);

With this implementation, the setter will add new key-value pairs when you use []= if they do not already exist in the dictionary.

Also, for me properties is an IDictionary and in constructors I initialize it to new SortedDictionary<string, string>().

How can I debug git/git-shell related problems?

For even more verbose output use following:

GIT_CURL_VERBOSE=1 GIT_TRACE=1 git pull origin master

Best practices for circular shift (rotate) operations in C++

Below is a slightly improved version of Dídac Pérez's answer, with both directions implemented, along with a demo of these functions' usages using unsigned char and unsigned long long values. Several notes:

  1. The functions are inlined for compiler optimizations
  2. I used a cout << +value trick for tersely outputting an unsigned char numerically that I found here:
  3. I recommend using the explicit <put the type here> syntax for clarity and safety.
  4. I used unsigned char for the shiftNum parameter because of what I found in the Additional Details section here:

The result of a shift operation is undefined if additive-expression is negative or if additive-expression is greater than or equal to the number of bits in the (promoted) shift-expression.

Here's the code I'm using:

#include <iostream>

using namespace std;

template <typename T>
inline T rotateAndCarryLeft(T rotateMe, unsigned char shiftNum)
    static const unsigned char TBitCount = sizeof(T) * 8U;

    return (rotateMe << shiftNum) | (rotateMe >> (TBitCount - shiftNum));

template <typename T>
inline T rotateAndCarryRight(T rotateMe, unsigned char shiftNum)
    static const unsigned char TBitCount = sizeof(T) * 8U;

    return (rotateMe >> shiftNum) | (rotateMe << (TBitCount - shiftNum));

void main()
    //00010100 == (unsigned char)20U
    //00000101 == (unsigned char)5U == rotateAndCarryLeft(20U, 6U)
    //01010000 == (unsigned char)80U == rotateAndCarryRight(20U, 6U)

    cout << "unsigned char " << 20U << " rotated left by 6 bits == " << +rotateAndCarryLeft<unsigned char>(20U, 6U) << "\n";
    cout << "unsigned char " << 20U << " rotated right by 6 bits == " << +rotateAndCarryRight<unsigned char>(20U, 6U) << "\n";

    cout << "\n";

    for (unsigned char shiftNum = 0U; shiftNum <= sizeof(unsigned char) * 8U; ++shiftNum)
        cout << "unsigned char " << 21U << " rotated left by " << +shiftNum << " bit(s) == " << +rotateAndCarryLeft<unsigned char>(21U, shiftNum) << "\n";

    cout << "\n";

    for (unsigned char shiftNum = 0U; shiftNum <= sizeof(unsigned char) * 8U; ++shiftNum)
        cout << "unsigned char " << 21U << " rotated right by " << +shiftNum << " bit(s) == " << +rotateAndCarryRight<unsigned char>(21U, shiftNum) << "\n";

    cout << "\n";

    for (unsigned char shiftNum = 0U; shiftNum <= sizeof(unsigned long long) * 8U; ++shiftNum)
        cout << "unsigned long long " << 3457347ULL << " rotated left by " << +shiftNum << " bit(s) == " << rotateAndCarryLeft<unsigned long long>(3457347ULL, shiftNum) << "\n";

    cout << "\n";

    for (unsigned char shiftNum = 0U; shiftNum <= sizeof(unsigned long long) * 8U; ++shiftNum)
        cout << "unsigned long long " << 3457347ULL << " rotated right by " << +shiftNum << " bit(s) == " << rotateAndCarryRight<unsigned long long>(3457347ULL, shiftNum) << "\n";

    cout << "\n\n";

Get only the date in timestamp in mysql

$date= new DateTime($row['your_date']) ;  
echo $date->format('Y-m-d');

How to force DNS refresh for a website?

you can't force refresh but you can forward all old ip requests to new one. for a website:

replace [OLD_IP] with old server's ip

replace [NEW_IP] with new server's ip

run & win.

echo "1" > /proc/sys/net/ipv4/ip_forward

iptables -t nat -A PREROUTING -d [OLD_IP] -p tcp --dport 80 -j DNAT --to-destination [NEW_IP]:80

iptables -t nat -A PREROUTING -d [OLD_IP] -p tcp --dport 443 -j DNAT --to-destination [NEW_IP]:443

iptables -t nat -A POSTROUTING -j MASQUERADE

How to resolve git stash conflict without commit?

According to git stash questions, after fixing the conflict, git add <file> is the right course of action.

It was after reading this comment that I understood that the changes are automatically added to the index (by design). That's why git add <file> completes the conflict resolution process.

SqlException from Entity Framework - New transaction is not allowed because there are other threads running in the session

I needed to read a huge ResultSet and update some records in the table. I tried to use chunks as suggested in Drew Noakes's answer.

Unfortunately after 50000 records I've got OutofMemoryException. The answer Entity framework large data set, out of memory exception explains, that

EF creates second copy of data which uses for change detection (so that it can persist changes to the database). EF holds this second set for the lifetime of the context and its this set thats running you out of memory.

The recommendation is to re-create your context for each batch.

So I've retrieved Minimal and Maximum values of the primary key- the tables have primary keys as auto incremental integers.Then I retrieved from the database chunks of records by opening context for each chunk. After processing the chunk context closes and releases the memory. It insures that memory usage is not growing.

Below is a snippet from my code:

  public void ProcessContextByChunks ()
        var tableName = "MyTable";
         var startTime = DateTime.Now;
        int i = 0;
         var minMaxIds = GetMinMaxIds();
        for (int fromKeyID= minMaxIds.From; fromKeyID <= minMaxIds.To; fromKeyID = fromKeyID+_chunkSize)
                using (var context = InitContext())
                    var chunk = GetMyTableQuery(context).Where(r => (r.KeyID >= fromKeyID) && (r.KeyID < fromKeyID+ _chunkSize));
                        foreach (var row in chunk)
                            foundCount = UpdateRowIfNeeded(++i, row);
                    catch (Exception exc)
                        LogChunkException(i, exc);
            catch (Exception exc)
                LogChunkException(i, exc);
        LogSummaryLine(tableName, i, foundCount, startTime);

    private FromToRange<int> GetminMaxIds()
        var minMaxIds = new FromToRange<int>();
        using (var context = InitContext())
            var allRows = GetMyTableQuery(context);
            minMaxIds.From = allRows.Min(n => (int?)n.KeyID ?? 0);  
            minMaxIds.To = allRows.Max(n => (int?)n.KeyID ?? 0);
        return minMaxIds;

    private IQueryable<MyTable> GetMyTableQuery(MyEFContext context)
        return context.MyTable;

    private  MyEFContext InitContext()
        var context = new MyEFContext();
        context.Database.Connection.ConnectionString = _connectionString;
        //context.Database.Log = SqlLog;
        return context;

FromToRange is a simple structure with From and To properties.

How to remove the character at a given index from a string in C?

I know that the question is very old, but I will leave my implementation here:

char    *ft_strdelchr(const char *str,char c)
        int   i;
        int   j;
        char  *s;
        char  *newstr;

        i = 0;
        j = 0;
        // cast to char* to be able to modify, bc the param is const
        // you guys can remove this and change the param too
        s = (char*)str;
        // malloc the new string with the necessary length. 
        // obs: strcountchr returns int number of c(haracters) inside s(tring)
        if (!(newstr = malloc(ft_strlen(s) - ft_strcountchr(s, c) + 1 * sizeof(char))))
                return (NULL);
        while (s[i])
                if (s[i] != c)
                        newstr[j] = s[i];
        return (newstr);

just throw to a new string the characters that are not equal to the character you want to remove.

Why am I seeing net::ERR_CLEARTEXT_NOT_PERMITTED errors after upgrading to Cordova Android 8?

@Der Hochstapler thanks for the solution.
but in IONIC 4 some customization in project config.xml work for me

Add a line in Widget tag

<widget id="" version="1.0.0" 

after this, in the Platform tag for android customize some lines check below
add usesCleartextTraffic=true after networkSecurityConfig and resource-file tags

 <platform name="android">
        <edit-config file="app/src/main/AndroidManifest.xml" mode="merge" target="/manifest/application" xmlns:android="">
            <application android:networkSecurityConfig="@xml/network_security_config" />
        <resource-file src="resources/android/xml/network_security_config.xml" target="app/src/main/res/xml/network_security_config.xml" />
        <edit-config file="AndroidManifest.xml" mode="merge" target="/manifest/application">
            <application android:usesCleartextTraffic="true" />

Undo a particular commit in Git that's been pushed to remote repos

Identify the hash of the commit, using git log, then use git revert <commit> to create a new commit that removes these changes. In a way, git revert is the converse of git cherry-pick -- the latter applies the patch to a branch that's missing it, the former removes it from a branch that has it.

How to include header files in GCC search path?

Using environment variable is sometimes more convenient when you do not control the build scripts / process.

For C includes use C_INCLUDE_PATH.

For C++ includes use CPLUS_INCLUDE_PATH.

See this link for other gcc environment variables.

Example usage in MacOS / Linux

# `pip install` will automatically run `gcc` using parameters
# specified in the `asyncpg` package (that I do not control)

C_INCLUDE_PATH=/home/scott/.pyenv/versions/3.7.9/include/python3.7m pip install asyncpg

Example usage in Windows

set C_INCLUDE_PATH="C:\Users\Scott\.pyenv\versions\3.7.9\include\python3.7m"

pip install asyncpg

# clear the environment variable so it doesn't affect other builds

How to print a double with two decimals in Android?

Before you use DecimalFormat you need to use the following import or your code will not work:

import java.text.DecimalFormat;

The code for formatting is:

DecimalFormat precision = new DecimalFormat("0.00"); 
// dblVariable is a number variable and not a String in this case

Redis connection to failed - connect ECONNREFUSED

Using Windows 10? Go here:

Then run...

    $ wget <- change this to whatever Redis version you want (
    $ tar xzf redis-5.0.5.tar.gz
    $ cd redis-5.0.5
    $ make

invalid_grant trying to get oAuth token from google

There are two major reasons for invalid_grant error which you have to take care prior to the POST request for Refresh Token and Access Token.

  1. Request header must contain "content-type: application/x-www-form-urlencoded"
  2. Your request payload should be url encoded Form Data, don't send as json object.

RFC 6749 OAuth 2.0 defined invalid_grant as: The provided authorization grant (e.g., authorization code, resource owner credentials) or refresh token is invalid, expired, revoked, does not match the redirection URI used in the authorization request, or was issued to another client.

I found another good article, here you will find many other reasons for this error.

How to delete migration files in Rails 3

We can use,

$ rails d migration table_name  

Which will delete the migration.

Remove an element from a Bash array


echo "# define array with six elements"
arr=(zero one two three 'four 4' five)

echo "# unset by index: 0"
unset -v 'arr[0]'
for i in ${!arr[*]}; do echo "arr[$i]=${arr[$i]}"; done

arr_delete_by_content() { # value to delete
        for i in ${!arr[*]}; do
                [ "${arr[$i]}" = "$1" ] && unset -v 'arr[$i]'

echo "# unset in global variable where value: three"
arr_delete_by_content three
for i in ${!arr[*]}; do echo "arr[$i]=${arr[$i]}"; done

echo "# rearrange indices"
arr=( "${arr[@]}" )
for i in ${!arr[*]}; do echo "arr[$i]=${arr[$i]}"; done

delete_value() { # value arrayelements..., returns array decl.
        local e val=$1; new=(); shift
        for e in "${@}"; do [ "$val" != "$e" ] && new+=("$e"); done
        declare -p new|sed 's,^[^=]*=,,'

echo "# new array without value: two"
declare -a arr="$(delete_value two "${arr[@]}")"
for i in ${!arr[*]}; do echo "arr[$i]=${arr[$i]}"; done

delete_values() { # arraydecl values..., returns array decl. (keeps indices)
        declare -a arr="$1"; local i v; shift
        for v in "${@}"; do 
                for i in ${!arr[*]}; do
                        [ "$v" = "${arr[$i]}" ] && unset -v 'arr[$i]'
        declare -p arr|sed 's,^[^=]*=,,'
echo "# new array without values: one five (keep indices)"
declare -a arr="$(delete_values "$(declare -p arr|sed 's,^[^=]*=,,')" one five)"
for i in ${!arr[*]}; do echo "arr[$i]=${arr[$i]}"; done

# new array without multiple values and rearranged indices is left to the reader

How to iterate over columns of pandas dataframe to run regression

You can index dataframe columns by the position using ix.


This returns the first column for example. (0 would be the index)


This returns the first row.


This would be the value at the intersection of row 0 and column 1:


and so on. So you can enumerate() returns.keys(): and use the number to index the dataframe.

HTML / CSS Popup div on text click


In the content area you can provide whatever you want to display in it.

.black_overlay {_x000D_
  display: none;_x000D_
  position: absolute;_x000D_
  top: 0%;_x000D_
  left: 0%;_x000D_
  width: 100%;_x000D_
  height: 100%;_x000D_
  background-color: black;_x000D_
  z-index: 1001;_x000D_
  -moz-opacity: 0.8;_x000D_
  opacity: .80;_x000D_
  filter: alpha(opacity=80);_x000D_
.white_content {_x000D_
  display: none;_x000D_
  position: absolute;_x000D_
  top: 25%;_x000D_
  left: 25%;_x000D_
  width: 50%;_x000D_
  height: 50%;_x000D_
  padding: 16px;_x000D_
  border: 16px solid orange;_x000D_
  background-color: white;_x000D_
  z-index: 1002;_x000D_
  overflow: auto;_x000D_
  <title>LIGHTBOX EXAMPLE</title>_x000D_
  <p>This is the main content. To display a lightbox click <a href="javascript:void(0)" onclick="document.getElementById('light').style.display='block';document.getElementById('fade').style.display='block'">here</a>_x000D_
  <div id="light" class="white_content">This is the lightbox content. <a href="javascript:void(0)" onclick="document.getElementById('light').style.display='none';document.getElementById('fade').style.display='none'">Close</a>_x000D_
  <div id="fade" class="black_overlay"></div>_x000D_

A Java collection of value pairs? (tuples?)

The preferred solution as you've described it is a List of Pairs (i.e. List).

To accomplish this you would create a Pair class for use in your collection. This is a useful utility class to add to your code base.

The closest class in the Sun JDK providing functionality similar to a typical Pair class is AbstractMap.SimpleEntry. You could use this class rather than creating your own Pair class, though you would have to live with some awkward restrictions and I think most people would frown on this as not really the intended role of SimpleEntry. For example SimpleEntry has no "setKey()" method and no default constructor, so you may find it too limiting.

Bear in mind that Collections are designed to contain elements of a single type. Related utility interfaces such as Map are not actually Collections (i.e. Map does not implement the Collection interface). A Pair would not implement the Collection interface either but is obviously a useful class in building larger data structures.

How to Cast Objects in PHP

a better aproach:

class Animal
    private $_name = null;

    public function __construct($name = null)
        $this->_name = $name;

     * casts object
     * @param Animal $to
     * @return Animal
    public function cast($to)
        if ($to instanceof Animal) {
            $to->_name = $this->_name;
        } else {
            throw(new Exception('cant cast ' . get_class($this) . ' to ' . get_class($to)));
        return $to;

    public function getName()
        return $this->_name;

class Cat extends Animal
    private $_preferedKindOfFish = null;

    public function __construct($name = null, $preferedKindOfFish = null)
        $this->_preferedKindOfFish = $preferedKindOfFish;

     * casts object
     * @param Animal $to
     * @return Animal
    public function cast($to)
        if ($to instanceof Cat) {
            $to->_preferedKindOfFish = $this->_preferedKindOfFish;
        return $to;

    public function getPreferedKindOfFish()
        return $this->_preferedKindOfFish;

class Dog extends Animal
    private $_preferedKindOfCat = null;

    public function __construct($name = null, $preferedKindOfCat = null)
        $this->_preferedKindOfCat = $preferedKindOfCat;

     * casts object
     * @param Animal $to
     * @return Animal
    public function cast($to)
        if ($to instanceof Dog) {
            $to->_preferedKindOfCat = $this->_preferedKindOfCat;
        return $to;

    public function getPreferedKindOfCat()
        return $this->_preferedKindOfCat;

$dogs = array(
    new Dog('snoopy', 'vegetarian'),
    new Dog('coyote', 'any'),

foreach ($dogs as $dog) {
    $cat = $dog->cast(new Cat());
    echo get_class($cat) . ' - ' . $cat->getName() . "\n";

Detect key input in Python

Key input is a predefined event. You can catch events by attaching event_sequence(s) to event_handle(s) by using one or multiple of the existing binding methods(bind, bind_class, tag_bind, bind_all). In order to do that:

  1. define an event_handle method
  2. pick an event(event_sequence) that fits your case from an events list

When an event happens, all of those binding methods implicitly calls the event_handle method while passing an Event object, which includes information about specifics of the event that happened, as the argument.

In order to detect the key input, one could first catch all the '<KeyPress>' or '<KeyRelease>' events and then find out the particular key used by making use of event.keysym attribute.

Below is an example using bind to catch both '<KeyPress>' and '<KeyRelease>' events on a particular widget(root):

try:                        # In order to be able to import tkinter for
    import tkinter as tk    # either in python 2 or in python 3
except ImportError:
    import Tkinter as tk

def event_handle(event):
    # Replace the window's title with event.type: input key
    root.title("{}: {}".format(str(event.type), event.keysym))

if __name__ == '__main__':
    root = tk.Tk()
    event_sequence = '<KeyPress>'
    root.bind(event_sequence, event_handle)
    root.bind('<KeyRelease>', event_handle)

AngularJS: ng-show / ng-hide not working with `{{ }}` interpolation

Try wrapping expression with:

$scope.$apply(function() {

Sleep Command in T-SQL?

Look at the WAITFOR command.


-- wait for 1 minute

-- wait for 1 second
WAITFOR DELAY '00:00:01'

This command allows you a high degree of precision but is only accurate within 10ms - 16ms on a typical machine as it relies on GetTickCount. So, for example, the call WAITFOR DELAY '00:00:00:001' is likely to result in no wait at all.

Width of input type=text element

I believe that is just how the browser renders their standard input. If you set a border on the input:

<input type="text" style="width: 10px; padding: 2px; border: 1px solid black"/>
<div style="width: 10px; border: solid 1px black; padding: 2px"> </div>

Then both are the same width, at least in FF.

List all kafka topics

You can try using the below two command and list all Kafka topic

  • bin/ --describe --zookeeper,,
  • bin/ --zookeeper,, --list

How to get summary statistics by group

Besides describeBy, the doBy package is an another option. It provides much of the functionality of SAS PROC SUMMARY. Details:

Decoding UTF-8 strings in Python

You need to properly decode the source text. Most likely the source text is in UTF-8 format, not ASCII.

Because you do not provide any context or code for your question it is not possible to give a direct answer.

I suggest you study how unicode and character encoding is done in Python:

Error in Python IOError: [Errno 2] No such file or directory: 'data.csv'

It's looking for the file in the current directory.

First, go to that directory

cd /users/gcameron/Desktop/map

And then try to run it


Android Fragment onAttach() deprecated

Activity is a context so if you can simply check the context is an Activity and cast it if necessary.

public void onAttach(Context context) {

    Activity a;

    if (context instanceof Activity){
        a=(Activity) context;


Update: Some are claiming that the new Context override is never called. I have done some tests and cannot find a scenario where this is true and according to the source code, it should never be true. In all cases I tested, both pre and post SDK23, both the Activity and the Context versions of onAttach were called. If you can find a scenario where this is not the case, I would suggest you create a sample project illustrating the issue and report it to the Android team.

Update 2: I only ever use the Android Support Library fragments as bugs get fixed faster there. It seems the above issue where the overrides do not get called correctly only comes to light if you use the framework fragments.

PHP array() to javascript array()

            $ConvertDateBack = Zend_Controller_Action_HelperBroker::getStaticHelper('ConvertDate');
            $disabledDaysRange = array();
            foreach($this->reservedDates as $dates) {
                 $date = $ConvertDateBack->ConvertDateBack($dates->reservation_date);
                 $disabledDaysRange[] = $date;
                 array_push($disabledDaysRange, $date);

            $finalArr = json_encode($disabledDaysRange);
var disabledDaysRange = <?=$finalArr?>;


Add a row number to result set of a SQL query

The typical pattern would be as follows, but you need to actually define how the ordering should be applied (since a table is, by definition, an unordered bag of rows):

SELECT t.A, t.B, t.C, number = ROW_NUMBER() OVER (ORDER BY t.A)
  FROM dbo.tableZ AS t

Not sure what the variables in your question are supposed to represent (they don't match).

Use formula in custom calculated field in Pivot Table

I'll post this comment as answer, as I'm confident enough that what I asked is not possible.

I) Couple of similar questions trying to do the same, without success:

II) This article: Excel Pivot Table Calculated Field for example lists many restrictions of Calculated Field:

  • For calculated fields, the individual amounts in the other fields are summed, and then the calculation is performed on the total amount.
  • Calculated field formulas cannot refer to the pivot table totals or subtotals
  • Calculated field formulas cannot refer to worksheet cells by address or by name.
  • Sum is the only function available for a calculated field.
  • Calculated fields are not available in an OLAP-based pivot table.

III) There is tiny limited possibility to use AVERAGE() and similar function for a range of cells, but that applies only if Pivot table doesn't have grouped cells, which allows listing the cells as items in new group (right to "Fileds" listbox in above screenshot) and then user can calculate AVERAGE(), referencing explicitly every item (cell), from Items listbox, as argument. Maybe it's better explained here: Calculate values in a PivotTable report
For my Pivot table it wasn't applicable because my range wasn't small enough, this option to be sane choice.

In Java, what is the best way to determine the size of an object?

When using JetBrains IntelliJ, first enable "Attach memory agent" in File | Settings | Build, Execution, Deployment | Debugger.

When debugging, right-click a variable of interest and choose "Calculate Retained Size": Calculate Retained Size

Wrapping text inside input type="text" element HTML/CSS

That is the textarea's job - for multiline text input. The input won't do it; it wasn't designed to do it.

So use a textarea. Besides their visual differences, they are accessed via JavaScript the same way (use value property).

You can prevent newlines being entered via the input event and simply using a replace(/\n/g, '').

how to convert current date to YYYY-MM-DD format with angular 2

Try this below code it is also works well in angular 2

<span>{{current_date | date: 'yyyy-MM-dd'}}</span>

PHP function use variable from outside

Add second parameter

You need to pass additional parameter to your function:

function parts($site_url, $part) { 
    $structure = 'http://' . $site_url . 'content/'; 
    echo $structure . $part . '.php'; 

In case of closures

If you'd rather use closures then you can import variable to the current scope (the use keyword):

$parts = function($part) use ($site_url) { 
    $structure = 'http://' . $site_url . 'content/'; 
    echo $structure . $part . '.php'; 

global - a bad practice

This post is frequently read, so something needs to be clarified about global. Using it is considered a bad practice (refer to this and this).

For the completeness sake here is the solution using global:

function parts($part) { 
    global $site_url;
    $structure = 'http://' . $site_url . 'content/'; 
    echo($structure . $part . '.php'); 

It works because you have to tell interpreter that you want to use a global variable, now it thinks it's a local variable (within your function).

Suggested reading:

How to return data from promise

One of the fundamental principles behind a promise is that it's handled asynchronously. This means that you cannot create a promise and then immediately use its result synchronously in your code (e.g. it's not possible to return the result of a promise from within the function that initiated the promise).

What you likely want to do instead is to return the entire promise itself. Then whatever function needs its result can call .then() on the promise, and the result will be there when the promise has been resolved.

Here is a resource from HTML5Rocks that goes over the lifecycle of a promise, and how its output is resolved asynchronously:

Android - SMS Broadcast receiver

I tried your code and found it wasn't working.

I had to change

if (intent.getAction() == SMS_RECEIVED) {


if (intent.getAction().equals(SMS_RECEIVED)) {

Now it's working. It's just an issue with java checking equality.

Disable button in WPF?

By code:

btn_edit.IsEnabled = true;


<Button Content="Edit data" Grid.Column="1" Name="btn_edit" Grid.Row="1" IsEnabled="False" />

How to change plot background color?

simpler answer:

ax = plt.axes()

how to save DOMPDF generated content to file?

I have just used dompdf and the code was a little different but it worked.

Here it is:

$files = glob("./pdf/include/*.php");
foreach($files as $file) include_once($file);

$html =
      '<p>Put your html here, or generate it with your favourite '.
      'templating system.</p>'.

    $dompdf = new DOMPDF();
    $output = $dompdf->output();
    file_put_contents('Brochure.pdf', $output);

Only difference here is that all of the files in the include directory are included.

Other than that my only suggestion would be to specify a full directory path for writing the file rather than just the filename.

Using SELECT result in another SELECT

You are missing table NewScores, so it can't be found. Just join this table.

If you really want to avoid joining it directly you can replace NewScores.NetScore with SELECT NetScore FROM NewScores WHERE {conditions on which they should be matched}

How to POST raw whole JSON in the body of a Retrofit request?

Things required to send raw json in Retrofit.

1) Make sure to add the following header and remove any other duplicate header. Since, on Retrofit's official documentation they specifically mention-

Note that headers do not overwrite each other. All headers with the same name will be included in the request.

@Headers({"Content-Type: application/json"})

2) a. If you are using a converter factory you can pass your json as a String, JSONObject, JsonObject and even a POJO. Also have checked, having ScalarConverterFactory is not necessary only GsonConverterFactory does the job.

Call<Response> myApi(@Header("Authorization") String auth, @Header("KEY") String key, 
                     @Body JsonObject/POJO/String requestBody);

2) b. If you are NOT using any converter factory then you MUST use okhttp3's RequestBody as Retrofit's documentation says-

The object will also be converted using a converter specified on the Retrofit instance. If no converter is added, only RequestBody can be used.

RequestBody requestBody=RequestBody.create(MediaType.parse("application/json; charset=utf-8"),jsonString);

Call<Response> myApi(@Header("Authorization") String auth, @Header("KEY") String key, 
                 @Body RequestBody requestBody);

3) Success!!

How to run composer from anywhere?

For running it from other location you can use the composer program that come with the program. It is basically a bash script. If you don't have it you can create one by simply copying the following code into a text file


dir=$(d=$(dirname "$0"); cd "$d" && pwd)

if command -v 'cygpath' >/dev/null 2>&1; then
  dir=$(cygpath -m $dir);

dir=$(echo $dir | sed 's/ /\ /g')
php "${dir}/composer.phar" $*

Then save the file inside your bin folder and name it composer without any file extension. Then add the bin folder to your environment variable f

What is the difference between const int*, const int * const, and int const *?

The C and C++ declaration syntax has repeatedly been described as a failed experiment, by the original designers.

Instead, let's name the type “pointer to Type”; I’ll call it Ptr_:

template< class Type >
using Ptr_ = Type*;

Now Ptr_<char> is a pointer to char.

Ptr_<const char> is a pointer to const char.

And const Ptr_<const char> is a const pointer to const char.


enter image description here

getting JRE system library unbound error in build path

oh boy, this got resolved, I just had to name my Installed JRE appropriately. I had only the jdk installed and eclipse had taken the default jdk name, i renamed it to JavaSE-1.6 and voila it worked, though i had to redo everthing from the scratch.

How do I see which version of Swift I'm using?

I am using Swift from Google Colab. Here's how to check it in Colab.

!/swift/toolchain/usr/bin/swift --version

The result is 5.0-dev

How to find all combinations of coins when given some dollar value

I looked into this once a long time ago, and you can read my little write-up on it. Here’s the Mathematica source.

By using generating functions, you can get a closed-form constant-time solution to the problem. Graham, Knuth, and Patashnik’s Concrete Mathematics is the book for this, and contains a fairly extensive discussion of the problem. Essentially you define a polynomial where the nth coefficient is the number of ways of making change for n dollars.

Pages 4-5 of the writeup show how you can use Mathematica (or any other convenient computer algebra system) to compute the answer for 10^10^6 dollars in a couple seconds in three lines of code.

(And this was long enough ago that that’s a couple of seconds on a 75Mhz Pentium...)

Full Page <iframe>

This is what I have used in the past.

html, body {
  height: 100%;
  overflow: auto;

Also in the iframe add the following style

border: 0; position:fixed; top:0; left:0; right:0; bottom:0; width:100%; height:100%

Cannot open solution file in Visual Studio Code

Use vscode-solution-explorer extension:

This extension adds a Visual Studio Solution File explorer panel in Visual Studio Code. Now you can navigate into your solution following the original Visual Studio structure.

enter image description here

Thanks @fernandoescolar

How to find a number in a string using JavaScript?

var str = "you can enter maximum 500 choices";
str.replace(/[^0-9]/g, "");
console.log(str); // "500"

Can I style an image's ALT text with CSS?

You can use img[alt] {styles} to style only the alternative text.

Python: Removing spaces from list objects

for element in range(0,len(hello)):
      d[element] = hello[element].strip()

jQuery.parseJSON throws “Invalid JSON” error due to escaped single quote in JSON

If you need a single quote inside of a string, since \' is undefined by the spec, use \u0027 see for all of them

edit: please excuse my misuse of the word backticks in the comments. I meant backslash. My point here is that in the event you have nested strings inside other strings, I think it can be more useful and readable to use unicode instead of lots of backslashes to escape a single quote. If you are not nested however it truly is easier to just put a plain old quote in there.

How to resolve Unneccessary Stubbing exception

Replace @RunWith(MockitoJUnitRunner.class) with @RunWith(MockitoJUnitRunner.Silent.class).

How to sum a variable by group

ddply(tbl, .(Category), summarise, sum = sum(Frequency))

How do I make a branch point at a specific commit?

git branch -f <branchname> <commit>

I go with Mark Longair's solution and comments and recommend anyone reads those before acting, but I'd suggest the emphasis should be on

git branch -f <branchname> <commit>

Here is a scenario where I have needed to do this.


Develop on the wrong branch and hence need to reset it.

Start Okay

Cleanly develop and release some software.

So far so good

Develop on wrong branch

Mistake: Accidentally stay on the release branch while developing further.

After a mistake

Realize the mistake

"OH NO! I accidentally developed on the release branch." The workspace is maybe cluttered with half changed files that represent work-in-progress and we really don't want to touch and mess with. We'd just like git to flip a few pointers to keep track of the current state and put that release branch back how it should be.

Create a branch for the development that is up to date holding the work committed so far and switch to it.

git branch development
git checkout development 

Changed to another branch

Correct the branch

Now we are in the problem situation and need its solution! Rectify the mistake (of taking the release branch forward with the development) and put the release branch back how it should be.

Correct the release branch to point back to the last real release.

git branch -f release release2

The release branch is now correct again, like this ...


What if I pushed the mistake to a remote?

git push -f <remote> <branch> is well described in another thread, though the word "overwrite" in the title is misleading. Force "git push" to overwrite remote files

error: command 'gcc' failed with exit status 1 while installing eventlet

On MacOS I had trouble installing fbprophet which requires pystan which requires gcc to compile. I would consistently get the same error: command 'gcc' failed with exit status 1

I think I fixed the problem for myself thus:

I used brew install gcc to install the newest version, which ended up being gcc-8

Then I made sure that when gcc ran it would use gcc-8 instead.

It either worked because I added alias gcc='gcc-8 in my .zshrc (same as .bashrc but for zsh), or because I ran export PATH=/usr/local/bin:$PATH (see comment)

Also: all my attempts were inside a virtual environment and I only succeeded by installing fbprophet globally (with pip), but still no success inside a venv

Create a list with initial capacity in Python

Short version: use

pre_allocated_list = [None] * size

to preallocate a list (that is, to be able to address 'size' elements of the list instead of gradually forming the list by appending). This operation is very fast, even on big lists. Allocating new objects that will be later assigned to list elements will take much longer and will be the bottleneck in your program, performance-wise.

Long version:

I think that initialization time should be taken into account.

Since in Python everything is a reference, it doesn't matter whether you set each element into None or some string - either way it's only a reference. Though it will take longer if you want to create a new object for each element to reference.

For Python 3.2:

import time
import copy

def print_timing (func):
  def wrapper (*arg):
    t1 = time.time()
    res = func (*arg)
    t2 = time.time ()
    print ("{} took {} ms".format (func.__name__, (t2 - t1) * 1000.0))
    return res

  return wrapper

def prealloc_array (size, init = None, cp = True, cpmethod = copy.deepcopy, cpargs = (), use_num = False):
  result = [None] * size
  if init is not None:
    if cp:
      for i in range (size):
          result[i] = init
      if use_num:
        for i in range (size):
            result[i] = cpmethod (i)
        for i in range (size):
            result[i] = cpmethod (cpargs)
  return result

def prealloc_array_by_appending (size):
  result = []
  for i in range (size):
    result.append (None)
  return result

def prealloc_array_by_extending (size):
  result = []
  none_list = [None]
  for i in range (size):
    result.extend (none_list)
  return result

def main ():
  n = 1000000
  x = prealloc_array_by_appending(n)
  y = prealloc_array_by_extending(n)
  a = prealloc_array(n, None)
  b = prealloc_array(n, "content", True)
  c = prealloc_array(n, "content", False, "some object {}".format, ("blah"), False)
  d = prealloc_array(n, "content", False, "some object {}".format, None, True)
  e = prealloc_array(n, "content", False, copy.deepcopy, "a", False)
  f = prealloc_array(n, "content", False, copy.deepcopy, (), False)
  g = prealloc_array(n, "content", False, copy.deepcopy, [], False)

  print ("x[5] = {}".format (x[5]))
  print ("y[5] = {}".format (y[5]))
  print ("a[5] = {}".format (a[5]))
  print ("b[5] = {}".format (b[5]))
  print ("c[5] = {}".format (c[5]))
  print ("d[5] = {}".format (d[5]))
  print ("e[5] = {}".format (e[5]))
  print ("f[5] = {}".format (f[5]))
  print ("g[5] = {}".format (g[5]))

if __name__ == '__main__':


prealloc_array_by_appending took 118.00003051757812 ms
prealloc_array_by_extending took 102.99992561340332 ms
prealloc_array took 3.000020980834961 ms
prealloc_array took 49.00002479553223 ms
prealloc_array took 316.9999122619629 ms
prealloc_array took 473.00004959106445 ms
prealloc_array took 1677.9999732971191 ms
prealloc_array took 2729.999780654907 ms
prealloc_array took 3001.999855041504 ms
x[5] = None
y[5] = None
a[5] = None
b[5] = content
c[5] = some object blah
d[5] = some object 5
e[5] = a
f[5] = []
g[5] = ()

As you can see, just making a big list of references to the same None object takes very little time.

Prepending or extending takes longer (I didn't average anything, but after running this a few times I can tell you that extending and appending take roughly the same time).

Allocating new object for each element - that is what takes the most time. And S.Lott's answer does that - formats a new string every time. Which is not strictly required - if you want to preallocate some space, just make a list of None, then assign data to list elements at will. Either way it takes more time to generate data than to append/extend a list, whether you generate it while creating the list, or after that. But if you want a sparsely-populated list, then starting with a list of None is definitely faster.

Is there a "do ... while" loop in Ruby?

ppl = []
while (input=gets.chomp)
 if !input.empty?
  ppl << input
 p ppl; puts "Goodbye"; break

powershell mouse move does not prevent idle mode

I had a similar situation where a download needed to stay active overnight and required a key press that refreshed my connection. I also found that the mouse move does not work. However, using notepad and a send key function appears to have done the trick. I send a space instead of a "." because if there is a [yes/no] popup, it will automatically click the default response using the spacebar. Here is the code used.

param($minutes = 120)

$myShell = New-Object -com "Wscript.Shell"

for ($i = 0; $i -lt $minutes; $i++) {
  Start-Sleep -Seconds 30
  $myShell.sendkeys(" ")

This function will work for the designated 120 minutes (2 Hours), but can be modified for the timing desired by increasing or decreasing the seconds of the input, or increasing or decreasing the assigned value of the minutes parameter.

Just run the script in powershell ISE, or powershell, and open notepad. A space will be input at the specified interval for the desired length of time ($minutes).

Good Luck!

How is Pythons glob.glob ordered?

'''my file name is 
"0_male_0.wav", "0_male_2.wav"... "0_male_30.wav"... 
"1_male_0.wav", "1_male_2.wav"... "1_male_30.wav"... 
"8_male_0.wav", "8_male_2.wav"... "8_male_30.wav"

when I I want to read them in a sorted torder, i.e., "0_male_0.wav"
"0_male_2.wav" ...
"1_male_2.wav" ...
so this is how I did it.

Just take all files start with "0_*" as an example. Others you can just put it in a loop

import as wav
import glob 
from os.path import isfile, join

#get all the file names in file_names. THe order is totally messed up
file_names = [f for f in listdir(audio_folder_dir) if isfile(join(audio_folder_dir, f)) and '.wav' in f] 
#find files that belongs to "0_*" group
filegroup0 = glob.glob(audio_folder_dir+'/0_*')
#now you get sorted files in group '0_*' by the last number in the filename
filegroup0 = sorted(filegroup0, key=getKey)

def getKey(filename):
    file_text_name = os.path.splitext(os.path.basename(filename))  #you get the file's text name without extension
    file_last_num = os.path.basename(file_text_name[0]).split('_')  #you get three elements, the last one is the number. You want to sort it by this number
    return int(file_last_num[2])

That's how I did my particular case. Hope it's helpful.

jQuery check if <input> exists and has a value

Just for the heck of it, I tracked this down in the jQuery code. The .val() function currently starts at line 165 of attributes.js. Here's the relevant section, with my annotations:

val: function( value ) {
    var hooks, ret, isFunction,
        elem = this[0];

    if ( !arguments.length ) {

        if ( elem ) {
            hooks = jQuery.valHooks[ elem.type ] || jQuery.valHooks[ elem.nodeName.toLowerCase() ];

            if ( hooks && "get" in hooks && (ret = hooks.get( elem, "value" )) !== undefined ) {
                return ret;

            ret = elem.value;

            return typeof ret === "string" ?
                // handle most common string cases
                ret.replace(rreturn, "") :
                // handle cases where value is null/undef or number
                ret == null ? "" : ret;


So, you'll either get undefined or "" or null -- all of which evaluate as false in if statements.

Why an abstract class implementing an interface can miss the declaration/implementation of one of the interface's methods?

Abstract classes are not required to implement the methods. So even though it implements an interface, the abstract methods of the interface can remain abstract. If you try to implement an interface in a concrete class (i.e. not abstract) and you do not implement the abstract methods the compiler will tell you: Either implement the abstract methods or declare the class as abstract.

How to call on a function found on another file?

Small addition to @user995502's answer on how to run the program.

g++ player.cpp main.cpp -o main.out && ./main.out

ASP.NET Core Web API exception handling

Firstly, thanks to Andrei as I've based my solution on his example.

I'm including mine as it's a more complete sample and might save readers some time.

The limitation of Andrei's approach is that doesn't handle logging, capturing potentially useful request variables and content negotiation (it will always return JSON no matter what the client has requested - XML / plain text etc).

My approach is to use an ObjectResult which allows us to use the functionality baked into MVC.

This code also prevents caching of the response.

The error response has been decorated in such a way that it can be serialized by the XML serializer.

public class ExceptionHandlerMiddleware
    private readonly RequestDelegate next;
    private readonly IActionResultExecutor<ObjectResult> executor;
    private readonly ILogger logger;
    private static readonly ActionDescriptor EmptyActionDescriptor = new ActionDescriptor();

    public ExceptionHandlerMiddleware(RequestDelegate next, IActionResultExecutor<ObjectResult> executor, ILoggerFactory loggerFactory)
    { = next;
        this.executor = executor;
        logger = loggerFactory.CreateLogger<ExceptionHandlerMiddleware>();

    public async Task Invoke(HttpContext context)
            await next(context);
        catch (Exception ex)
            logger.LogError(ex, $"An unhandled exception has occurred while executing the request. Url: {context.Request.GetDisplayUrl()}. Request Data: " + GetRequestData(context));

            if (context.Response.HasStarted)

            var routeData = context.GetRouteData() ?? new RouteData();


            var actionContext = new ActionContext(context, routeData, EmptyActionDescriptor);

            var result = new ObjectResult(new ErrorResponse("Error processing request. Server error."))
                StatusCode = (int) HttpStatusCode.InternalServerError,

            await executor.ExecuteAsync(actionContext, result);

    private static string GetRequestData(HttpContext context)
        var sb = new StringBuilder();

        if (context.Request.HasFormContentType && context.Request.Form.Any())
            sb.Append("Form variables:");
            foreach (var x in context.Request.Form)
                sb.AppendFormat("Key={0}, Value={1}<br/>", x.Key, x.Value);

        sb.AppendLine("Method: " + context.Request.Method);

        return sb.ToString();

    private static void ClearCacheHeaders(HttpResponse response)
        response.Headers[HeaderNames.CacheControl] = "no-cache";
        response.Headers[HeaderNames.Pragma] = "no-cache";
        response.Headers[HeaderNames.Expires] = "-1";

    [DataContract(Name= "ErrorResponse")]
    public class ErrorResponse
        [DataMember(Name = "Message")]
        public string Message { get; set; }

        public ErrorResponse(string message)
            Message = message;

How do I check if a Socket is currently connected in Java?

Assuming you have some level of control over the protocol, I'm a big fan of sending heartbeats to verify that a connection is active. It's proven to be the most fail proof method and will often give you the quickest notification when a connection has been broken.

TCP keepalives will work, but what if the remote host is suddenly powered off? TCP can take a long time to timeout. On the other hand, if you have logic in your app that expects a heartbeat reply every x seconds, the first time you don't get them you know the connection no longer works, either by a network or a server issue on the remote side.

See Do I need to heartbeat to keep a TCP connection open? for more discussion.

Angularjs dynamic ng-pattern validation

Used pattern :


Used reference file:

 '<script src=""></script>'

Example for Input:

 <input type="number" require ng-pattern="/^\d{0,9}(\.\d{1,9})?$/"><input type="submit">

How to overwrite existing files in batch?

You can refer Windows command prompt help using following command : xcopy /?

How to solve SyntaxError on autogenerated

just you describe your python version

=> python3.5 runserver

(my python version=3.5)

Get scroll position using jquery

I believe the best method with jQuery is using .scrollTop():

var pos = $('body').scrollTop();

JQuery html() vs. innerHTML

"This method uses the browser's innerHTML property." - jQuery API

How can I read a text file from the SD card in Android?

In your layout you'll need something to display the text. A TextView is the obvious choice. So you'll have something like this:


And your code will look like this:

//Find the directory for the SD Card using the API
//*Don't* hardcode "/sdcard"
File sdcard = Environment.getExternalStorageDirectory();

//Get the text file
File file = new File(sdcard,"file.txt");

//Read text from file
StringBuilder text = new StringBuilder();

try {
    BufferedReader br = new BufferedReader(new FileReader(file));
    String line;

    while ((line = br.readLine()) != null) {
catch (IOException e) {
    //You'll need to add proper error handling here

//Find the view by its id
TextView tv = (TextView)findViewById(;

//Set the text

This could go in the onCreate() method of your Activity, or somewhere else depending on just what it is you want to do.

How to auto-generate a C# class file from a JSON string

If you install Web Essentials into Visual studio you can go to Edit => Past special => paste JSON as class.

That is probably the easiest there is.

Web Essentials:

Get the cell value of a GridView row

I suggest you use a HiddenField inside template field use FindControl to find this field.



                        <asp:HiddenField ID="hfFname" runat="server" Value='<%# Eval("FileName") %>' />

Code behind

protected void gvAttachments_RowDeleting(object sender, GridViewDeleteEventArgs e)
        GridView gv1 = (GridView)sender;
        GridViewRow gvr1 = (GridViewRow)gv1.Rows[e.RowIndex];

        //get hidden field value and not directly from the GridviewRow, as that will be null or empty!
        HiddenField hf1 = (HiddenField)gvr1.FindControl("hfFname");
        if (hf1 != null)

List all environment variables from the command line

If you want to see the environment variable you just set, you need to open a new command window.

Variables set with setx variables are available in future command windows only, not in the current command window. (Setx, Examples)

Arduino Sketch upload issue - avrdude: stk500_recv(): programmer is not responding

Try to load a program without -b (the baud rate option). In ~/.arduino15/preferences.txt set build.verbose=true, when is not running. In the verbose output you will find the hex file which you should load from a console:

avrdude -v -v -v -v -C/usr/share/arduino/hardware/tools/avr/etc/avrdude.conf -patmega328p -carduino -P/dev/ttyUSB2  -D -Uflash:w:/tmp/build2314497724350388190.tmp/sketch_nov13b.cpp.hex:i

I just replace the chip 128 with the 328 version and from Decimile my board name was changed to Uno or Ethernet due to the new baud rate 115200.

Android ADT error, dx.jar was not loaded from the SDK folder

This is caused by incomplete/messy upgrade to latest version which results in dx.jar missing from {Android SDK dir}\platform-tools\lib\.


Find your latest dx.jar in {Android SDK dir}\platforms\*

and copy it to:

{Android SDK dir}\platform-tools\lib\

Restart eclipse, clean your project and everything should work as expected.

(If platform-tools\lib directory is missing entirely you will have to reinstall "Android SDK platform-tools" using SDK manager. After reinstall dx.jar should be in there so no copying will be needed)

If you can't find dx.jar in any of {Android SDK dir}\platforms\* subdirs you will have to start SDK manager and install Android 1.6 SDK.

For example on my machine latest was in {Android SDK dir}\platforms\android-4\tools\lib\. (I did not find any newer version as of 2012-01-22 Android SDK R15).

I really hope that this is useful for someone because I've wasted half a day investigating and looking for solution of such a trivial bug... :-(

How to get hostname from IP (Linux)?

In order to use nslookup, host or gethostbyname() then the target's name will need to be registered with DNS or statically defined in the hosts file on the machine running your program. Yes, you could connect to the target with SSH or some other application and query it directly, but for a generic solution you'll need some sort of DNS entry for it.

NotificationCompat.Builder deprecated in Android O

Simple Sample

    public void showNotification (String from, String notification, Intent intent) {
        PendingIntent pendingIntent = PendingIntent.getActivity(

        String NOTIFICATION_CHANNEL_ID = "my_channel_id_01";
        NotificationManager notificationManager = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);

        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            NotificationChannel notificationChannel = new NotificationChannel(NOTIFICATION_CHANNEL_ID, "My Notifications", NotificationManager.IMPORTANCE_DEFAULT);

            // Configure the notification channel.
            notificationChannel.setDescription("Channel description");
            notificationChannel.setVibrationPattern(new long[]{0, 1000, 500, 1000});

        NotificationCompat.Builder builder = new NotificationCompat.Builder(context, NOTIFICATION_CHANNEL_ID);
        Notification mNotification = builder

//                .setTicker("Hearty365")
//                .setContentInfo("Info")
                //     .setPriority(Notification.PRIORITY_MAX)


//                .setDefaults(Notification.DEFAULT_ALL)
//                .setWhen(System.currentTimeMillis())
                .setLargeIcon(BitmapFactory.decodeResource(context.getResources(), R.mipmap.ic_launcher))

        notificationManager.notify(/*notification id*/Notification_ID, mNotification);


why numpy.ndarray is object is not callable in my simple for python loop

The error TypeError: 'numpy.ndarray' object is not callable means that you tried to call a numpy array as a function.



Instead of


"psql: could not connect to server: Connection refused" Error when connecting to remote database

In my case I had removed a locale and generated another locale. Database failed to open because of fatal errors in the postgresql.conf file, on 'lc_messages', 'lc_monetary', 'lc_numberic', and 'lc_time'.

Restoring the locale sorted it out for me.

Read a file line by line with VB.NET

Like this... I used it to read Chinese characters...

Dim reader as StreamReader = My.Computer.FileSystem.OpenTextFileReader(filetoimport.Text)
Dim a as String

   a = reader.ReadLine
   ' Code here
Loop Until a Is Nothing


Clean out Eclipse workspace metadata

There is no easy way to remove the "outdated" stuff from an existing workspace. Using the "clean" parameter will not really help, as many of the files you refer to are "free form data", only known to the plugins that are no longer available.

Your best bet is to optimize the re-import, where I would like to point out the following:

  • When creating a new workspace, you can already choose to have some settings being copied from the current to the new workspace.
  • You can export the preferences of the current workspace (using the Export menu) and re-import them in the new workspace.
  • There are lots of recommendations on the Internet to just copy the ${old_workspace}/.metadata/.plugins/org.eclipse.core.runtime/.settings folder from the old to the new workspace. This is surely the fastest way, but it may lead to weird behaviour, because some of your plugins may depend on these settings and on some of the mentioned "free form data" stored elsewhere. (There are even people symlinking these folders over multiple workspaces, but this really requires to use the same plugins on all workspaces.)
  • You may want to consider using more project specific settings than workspace preferences in the future. So for instance all the Java compiler settings can either be set on the workspace level or on the project level. If set on the project level, you can put them under version control and are independent of the workspace.

Sending XML data using HTTP POST with PHP

you can use cURL library for posting data:

$ch = curl_init();
curl_setopt($ch, CURLOPT_HEADER, 0);
curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
curl_setopt($ch, CURLOPT_URL, "http://websiteURL");
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, "XML=".$xmlcontent."&password=".$password."&etc=etc");

where postfield contains XML you need to send - you will need to name the postfield the API service (Clickatell I guess) expects

Pass multiple parameters to rest API - Spring

Yes its possible to pass JSON object in URL

queryString = "{\"left\":\"" + params.get("left") + "}";
                    Endpoint + "/A/B?query={queryString}",
                    HttpMethod.GET, entity, z.class, queryString);

How to get cookie expiration date / creation date from javascript?

The information is not available through document.cookie, but if you're really desperate for it, you could try performing a request through the XmlHttpRequest object to the current page and access the cookie header using getResponseHeader().

ERROR Error: Uncaught (in promise), Cannot match any routes. URL Segment

As the error says your router link should match the existing routes configured

It should be just routerLink="/about" mvc3 return raw html to view

That looks fine, unless you want to pass it as Model string

public class HomeController : Controller
    public ActionResult Index()
        string model = "<HTML></HTML>";
        return View(model);

@model string
    ViewBag.Title = "Index";


mySQL :: insert into table, data from another table?

INSERT INTO action_2_members (campaign_id, mobile, vote, vote_date)  
SELECT campaign_id, from_number, received_msg, date_received
  FROM `received_txts`
 WHERE `campaign_id` = '8'

Exploring Docker container's file system

Before Container Creation :

If you to explore the structure of the image that is mounted inside the container you can do

sudo docker image save image_name > image.tar
tar -xvf image.tar

This would give you the visibility of all the layers of an image and its configuration which is present in json files.

After container creation :

For this there are already lot of answers above. my preferred way to do this would be -

docker exec -t -i container /bin/bash

Save multiple sheets to .pdf

In Excel 2013 simply select multiple sheets and do a "Save As" and select PDF as the file type. The multiple pages will open in PDF when you click save.

Automatically open Chrome developer tools when new tab/new window is opened

Use --auto-open-devtools-for-tabs flag while running chrome from command line

/Applications/Google\\ Chrome --auto-open-devtools-for-tabs

How to disable margin-collapsing?

I know that this is a very old post but just wanted to say that using flexbox on a parent element would disable margin collapsing for its child elements.

X-Frame-Options on apache

See X-Frame-Options header on error response

You can simply add following line to .htaccess

Header always unset X-Frame-Options

How can I sort a std::map first by value, then by key?

You can use std::set instead of std::map.

You can store both key and value in std::pair and the type of container will look like this:

std::set< std::pair<int, std::string> > items;

std::set will sort it's values both by original keys and values that were stored in std::map.

How do I install a module globally using npm?

In Ubuntu, set path of node_modules in .bashrc file

export PATH="/home/username/node_modules/.bin:$PATH"

Inner join with count() on three tables

It makes more sense to join the item with the orders than with the people !

    COUNT(distinct orders.ord_id) AS num_orders,
    COUNT(items.item_id) AS num_items
    INNER JOIN orders ON orders.pe_id = people.pe_id
         INNER JOIN items ON items.ord_id = orders.ord_id

Joining the items with the people provokes a lot of doublons. For example, the cake items in order 3 will be linked with the order 2 via the join between the people, and you don't want this to happen !!

So :

1- You need a good understanding of your schema. Items are link to orders, and not to people.

2- You need to count distinct orders for one person, else you will count as many items as orders.

Regex empty string or email

this will solve, it will accept empty string or exact an email id


How do I clear the std::queue efficiently?

You could create a class that inherits from queue and clear the underlying container directly. This is very efficient.

template<class T>
class queue_clearable : public std::queue<T>
    void clear()

Maybe your a implementation also allows your Queue object (here JobQueue) to inherit std::queue<Job> instead of having the queue as a member variable. This way you would have direct access to c.clear() in your member functions.

Android Facebook integration with invalid key hash

The following code will give you your hash for Facebook, but you have to follow these steps in order to get the release candidate hash.

  1. Copy and paste this code in your main activity

    try {
        PackageInfo info = getPackageManager().getPackageInfo(
        for (Signature signature : info.signatures) {
            MessageDigest md = MessageDigest.getInstance("SHA");
            Log.d("KeyHash:", Base64.encodeToString(md.digest(), Base64.DEFAULT));
    catch (NameNotFoundException e) {
    catch (NoSuchAlgorithmException e) {
  2. Generate a signed APK file.

  3. Connect your phone to a laptop and make sure it stays connected.
  4. Install and run the APK file in your phone by manually moving the release APK to your phone.
  5. Now look at Android LogCat (use filter KeyHash:). You should see your release hash key for Facebook. Simply copy and paste it in your It's under settings.
  6. Now you can test the app it should work perfectly well.

Script @php artisan package:discover handling the post-autoload-dump event returned with error code 1

I simply ran composer update and it resolved my issue - Laravel 6.*

int to hex string

Try C# string interpolation introduced in C# 6:

var id = 100;
var hexid = $"0x{id:X}";

hexid value:


Best Python IDE on Linux

I haven't played around with it much but eclipse/pydev feels nice.

Functional programming vs Object Oriented programming

  1. If you're in a heavily concurrent environment, then pure functional programming is useful. The lack of mutable state makes concurrency almost trivial. See Erlang.

  2. In a multiparadigm language, you may want to model some things functionally if the existence of mutable state is must an implementation detail, and thus FP is a good model for the problem domain. For example, see list comprehensions in Python or std.range in the D programming language. These are inspired by functional programming.

Factory Pattern. When to use factory methods?

It's really a matter of taste. Factory classes can be abstracted/interfaced away as necessary, whereas factory methods are lighter weight (and also tend to be testable, since they don't have a defined type, but they will require a well-known registration point, akin to a service locator but for locating factory methods).

How to switch between python 2.7 to python 3 from command line?

You can try to rename the python executable in the python3 folder to python3, that is if it was named python formally... it worked for me

How to restrict user to type 10 digit numbers in input element?

The snippet below does the job as expected!

<input type="text" name="AUS" pattern="[0-9]{10}" title="You can enter only 10 digits..." />

//type="text" <!-- always -->
//name="AUS" <!-- for Australia -->
//pattern="[0-9]{10}" <!-- 10 digits from 0 to 9 -->
//title="You can enter only 10 digits..." <!-- Pops a warning when input mismatches -->

Using Thymeleaf when the value is null

you can use this solution it is working for me

<span th:text="${#objects.nullSafe(doctor?.cabinet?.name,'')}"></span>

How to convert a column number (e.g. 127) into an Excel column (e.g. AA)

Another VBA way

Public Function GetColumnName(TargetCell As Range) As String
    GetColumnName = Split(CStr(TargetCell.Cells(1, 1).Address), "$")(1)
End Function

Good Free Alternative To MS Access

for sqlite, check out the firefox extension. It offers a serviceable GUI.

HTML Text with tags to formatted text in an Excel cell

Nice! Very slick.

I was disappointed that Excel doesn't let us paste to a merged cell and also pastes results containing a break into successive rows below the "target" cell though, as that meant it simply doesn't work for me. I tried a few tweaks (unmerge/remerge, etc.) but then Excel dropped anything below a break, so that was a dead end.

Ultimately, I came up with a routine that'll handle simple tags and not use the "native" Unicode converter that is causing the issue with merged fields. Hope others find this useful:

Public Sub AddHTMLFormattedText(rngA As Range, strHTML As String, Optional blnShowBadHTMLWarning As Boolean = False)
    ' Adds converts text formatted with basic HTML tags to formatted text in an Excel cell
    ' NOTE: Font Sizes not handled perfectly per HTML standard, but I find this method more useful!

    Dim strActualText As String, intSrcPos As Integer, intDestPos As Integer, intDestSrcEquiv() As Integer
    Dim varyTags As Variant, varTag As Variant, varEndTag As Variant, blnTagMatch As Boolean
    Dim intCtr As Integer
    Dim intStartPos As Integer, intEndPos As Integer, intActualStartPos As Integer, intActualEndPos As Integer
    Dim intFontSizeStartPos As Integer, intFontSizeEndPos As Integer, intFontSize As Integer

    varyTags = Array("<b>", "</b>", "<i>", "</i>", "<u>", "</u>", "<sub>", "</sub>", "<sup>", "</sup>")

    ' Remove unhandled/unneeded tags, convert <br> and <p> tags to line feeds
    strHTML = Trim(strHTML)
    strHTML = Replace(strHTML, "<html>", "")
    strHTML = Replace(strHTML, "</html>", "")
    strHTML = Replace(strHTML, "<p>", "")
    While LCase(Right$(strHTML, 4)) = "</p>" Or LCase(Right$(strHTML, 4)) = "<br>"
        strHTML = Left$(strHTML, Len(strHTML) - 4)
        strHTML = Trim(strHTML)
    strHTML = Replace(strHTML, "<br>", vbLf)
    strHTML = Replace(strHTML, "</p>", vbLf)

    strHTML = Trim(strHTML)

    ReDim intDestSrcEquiv(1 To Len(strHTML))
    strActualText = ""
    intSrcPos = 1
    intDestPos = 1
    Do While intSrcPos <= Len(strHTML)
        blnTagMatch = False
        For Each varTag In varyTags
            If LCase(Mid$(strHTML, intSrcPos, Len(varTag))) = varTag Then
                blnTagMatch = True
                intSrcPos = intSrcPos + Len(varTag)
                If intSrcPos > Len(strHTML) Then Exit Do
                Exit For
            End If
        If blnTagMatch = False Then
            varTag = "<font size"
            If LCase(Mid$(strHTML, intSrcPos, Len(varTag))) = varTag Then
                blnTagMatch = True
                intEndPos = InStr(intSrcPos, strHTML, ">")
                intSrcPos = intEndPos + 1
                If intSrcPos > Len(strHTML) Then Exit Do
                varTag = "</font>"
                If LCase(Mid$(strHTML, intSrcPos, Len(varTag))) = varTag Then
                    blnTagMatch = True
                    intSrcPos = intSrcPos + Len(varTag)
                    If intSrcPos > Len(strHTML) Then Exit Do
                End If
            End If
        End If
        If blnTagMatch = False Then
            strActualText = strActualText & Mid$(strHTML, intSrcPos, 1)
            intDestSrcEquiv(intSrcPos) = intDestPos
            intDestPos = intDestPos + 1
            intSrcPos = intSrcPos + 1
        End If

    ' Clear any bold/underline/italic/superscript/subscript formatting from cell
    rngA.Font.Bold = False
    rngA.Font.Underline = False
    rngA.Font.Italic = False
    rngA.Font.Subscript = False
    rngA.Font.Superscript = False

    rngA.Value = strActualText

    ' Now start applying Formats!"
    ' Start with Font Size first
    intSrcPos = 1
    intDestPos = 1
    Do While intSrcPos <= Len(strHTML)
        varTag = "<font size"
        If LCase(Mid$(strHTML, intSrcPos, Len(varTag))) = varTag Then
            intFontSizeStartPos = InStr(intSrcPos, strHTML, """") + 1
            intFontSizeEndPos = InStr(intFontSizeStartPos, strHTML, """") - 1
            If intFontSizeEndPos - intFontSizeStartPos <= 3 And intFontSizeEndPos - intFontSizeStartPos > 0 Then
                Debug.Print Mid$(strHTML, intFontSizeStartPos, intFontSizeEndPos - intFontSizeStartPos + 1)
                If Mid$(strHTML, intFontSizeStartPos, 1) = "+" Then
                    intFontSizeStartPos = intFontSizeStartPos + 1
                    intFontSize = 11 + 2 * Mid$(strHTML, intFontSizeStartPos, intFontSizeEndPos - intFontSizeStartPos + 1)
                ElseIf Mid$(strHTML, intFontSizeStartPos, 1) = "-" Then
                    intFontSizeStartPos = intFontSizeStartPos + 1
                    intFontSize = 11 - 2 * Mid$(strHTML, intFontSizeStartPos, intFontSizeEndPos - intFontSizeStartPos + 1)
                    intFontSize = Mid$(strHTML, intFontSizeStartPos, intFontSizeEndPos - intFontSizeStartPos + 1)
                End If
                ' Error!
                GoTo HTML_Err
            End If
            intEndPos = InStr(intSrcPos, strHTML, ">")
            intSrcPos = intEndPos + 1
            intStartPos = intSrcPos
            If intSrcPos > Len(strHTML) Then Exit Do
            While intDestSrcEquiv(intStartPos) = 0 And intStartPos < Len(strHTML)
                intStartPos = intStartPos + 1
            If intStartPos >= Len(strHTML) Then GoTo HTML_Err ' HTML is bad!
            varEndTag = "</font>"
            intEndPos = InStr(intSrcPos, LCase(strHTML), varEndTag)
            If intEndPos = 0 Then GoTo HTML_Err ' HTML is bad!
            While intDestSrcEquiv(intEndPos) = 0 And intEndPos > intSrcPos
                intEndPos = intEndPos - 1
            If intEndPos > intSrcPos Then
                intActualStartPos = intDestSrcEquiv(intStartPos)
                intActualEndPos = intDestSrcEquiv(intEndPos)
                rngA.Characters(intActualStartPos, intActualEndPos - intActualStartPos + 1) _
                    .Font.Size = intFontSize
            End If
        End If
        intSrcPos = intSrcPos + 1

    'Now do remaining tags
    intSrcPos = 1
    intDestPos = 1
    Do While intSrcPos <= Len(strHTML)
        If intDestSrcEquiv(intSrcPos) = 0 Then
            ' This must be a Tag!
            For intCtr = 0 To UBound(varyTags) Step 2
                varTag = varyTags(intCtr)
                intStartPos = intSrcPos + Len(varTag)
                While intDestSrcEquiv(intStartPos) = 0 And intStartPos < Len(strHTML)
                    intStartPos = intStartPos + 1
                If intStartPos >= Len(strHTML) Then GoTo HTML_Err ' HTML is bad!
                If LCase(Mid$(strHTML, intSrcPos, Len(varTag))) = varTag Then
                    varEndTag = varyTags(intCtr + 1)
                    intEndPos = InStr(intSrcPos, LCase(strHTML), varEndTag)
                    If intEndPos = 0 Then GoTo HTML_Err ' HTML is bad!
                    While intDestSrcEquiv(intEndPos) = 0 And intEndPos > intSrcPos
                        intEndPos = intEndPos - 1
                    If intEndPos > intSrcPos Then
                        intActualStartPos = intDestSrcEquiv(intStartPos)
                        intActualEndPos = intDestSrcEquiv(intEndPos)
                        With rngA.Characters(intActualStartPos, intActualEndPos - intActualStartPos + 1).Font
                            If varTag = "<b>" Then
                                .Bold = True
                            ElseIf varTag = "<i>" Then
                                .Italic = True
                            ElseIf varTag = "<u>" Then
                                .Underline = True
                            ElseIf varTag = "<sup>" Then
                                .Superscript = True
                            ElseIf varTag = "<sub>" Then
                                .Subscript = True
                            End If
                        End With
                    End If
                    intSrcPos = intSrcPos + Len(varTag) - 1
                    Exit For
                End If
        End If
        intSrcPos = intSrcPos + 1
        intDestPos = intDestPos + 1
    Exit Sub
    ' There was an error with the Tags. Show warning if requested.
    If blnShowBadHTMLWarning Then
        MsgBox "There was an error with the Tags in the HTML file. Could not apply formatting."
    End If
End Sub

Note this doesn't care about tag nesting, instead only requiring a close tag for every open tag, and assuming the close tag nearest the opening tag applies to the opening tag. Properly nested tags will work fine, while improperly nested tags will not be rejected and may or may not work.

How should I resolve java.lang.IllegalArgumentException: protocol = https host = null Exception?

URLs use forward slashes (/), not backward ones (as windows). Try:

serverURLS = "";

The reason why you get the error is that the URL class can't parse the host part of the string and therefore, host is null.

formatFloat : convert float number to string

Try this

package main

import "fmt"
import "strconv"

func FloatToString(input_num float64) string {
    // to convert a float number to a string
    return strconv.FormatFloat(input_num, 'f', 6, 64)

func main() {

If you just want as many digits precision as possible, then the special precision -1 uses the smallest number of digits necessary such that ParseFloat will return f exactly. Eg

strconv.FormatFloat(input_num, 'f', -1, 64)

Personally I find fmt easier to use. (Playground link)

fmt.Printf("x = %.6f\n", 21312421.213123)

Or if you just want to convert the string

fmt.Sprintf("%.6f", 21312421.213123)

Create a file if it doesn't exist

I think this should work:

#open file for reading
fn = input("Enter file to open: ")
    fh = open(fn,'r')
# if file does not exist, create it
    fh = open(fn,'w')

Also, you incorrectly wrote fh = open ( fh, "w") when the file you wanted open was fn

How to approach a "Got minus one from a read call" error when connecting to an Amazon RDS Oracle instance

in my case, I got the same exception because the user that I configured in the app did not existed in the DB, creating the user and granting needed permissions solved the problem.