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Sprintf equivalent in Java

Strings are immutable types. You cannot modify them, only return new string instances.

Because of that, formatting with an instance method makes little sense, as it would have to be called like:

String formatted = "%s: %s".format(key, value);

The original Java authors (and .NET authors) decided that a static method made more sense in this situation, as you are not modifying the target, but instead calling a format method and passing in an input string.

Here is an example of why format() would be dumb as an instance method. In .NET (and probably in Java), Replace() is an instance method.

You can do this:

 "I Like Wine".Replace("Wine","Beer");

However, nothing happens, because strings are immutable. Replace() tries to return a new string, but it is assigned to nothing.

This causes lots of common rookie mistakes like:

inputText.Replace(" ", "%20");

Again, nothing happens, instead you have to do:

inputText = inputText.Replace(" ","%20");

Now, if you understand that strings are immutable, that makes perfect sense. If you don't, then you are just confused. The proper place for Replace() would be where format() is, as a static method of String:

 inputText = String.Replace(inputText, " ", "%20");

Now there is no question as to what's going on.

The real question is, why did the authors of these frameworks decide that one should be an instance method, and the other static? In my opinion, both are more elegantly expressed as static methods.

Regardless of your opinion, the truth is that you are less prone to make a mistake using the static version, and the code is easier to understand (No Hidden Gotchas).

Of course there are some methods that are perfect as instance methods, take String.Length()

int length = "123".Length();

In this situation, it's obvious we are not trying to modify "123", we are just inspecting it, and returning its length. This is a perfect candidate for an instance method.

My simple rules for Instance Methods on Immutable Objects:

  • If you need to return a new instance of the same type, use a static method.
  • Otherwise, use an instance method.

How do I efficiently iterate over each entry in a Java Map?

Most compact with Java 8:


How do you create a foreign key relationship in a SQL Server CE (Compact Edition) Database?

Alan is correct when he says there's designer support. Rhywun is incorrect when he implies you cannot choose the foreign key table. What he means is that in the UI the foreign key table drop down is greyed out - all that means is he has not right clicked on the correct table to add the foreign key to.

In summary, right click on the foriegn key table and then via the 'Table Properties' > 'Add Relations' option you select the related primary key table.

I've done it numerous times and it works.

How can I send an email by Java application using GMail, Yahoo, or Hotmail?

First download the JavaMail API and make sure the relevant jar files are in your classpath.

Here's a full working example using GMail.

import java.util.*;
import javax.mail.*;
import javax.mail.internet.*;

public class Main {

    private static String USER_NAME = "*****";  // GMail user name (just the part before "")
    private static String PASSWORD = "********"; // GMail password
    private static String RECIPIENT = "[email protected]";

    public static void main(String[] args) {
        String from = USER_NAME;
        String pass = PASSWORD;
        String[] to = { RECIPIENT }; // list of recipient email addresses
        String subject = "Java send mail example";
        String body = "Welcome to JavaMail!";

        sendFromGMail(from, pass, to, subject, body);

    private static void sendFromGMail(String from, String pass, String[] to, String subject, String body) {
        Properties props = System.getProperties();
        String host = "";
        props.put("mail.smtp.starttls.enable", "true");
        props.put("", host);
        props.put("mail.smtp.user", from);
        props.put("mail.smtp.password", pass);
        props.put("mail.smtp.port", "587");
        props.put("mail.smtp.auth", "true");

        Session session = Session.getDefaultInstance(props);
        MimeMessage message = new MimeMessage(session);

        try {
            message.setFrom(new InternetAddress(from));
            InternetAddress[] toAddress = new InternetAddress[to.length];

            // To get the array of addresses
            for( int i = 0; i < to.length; i++ ) {
                toAddress[i] = new InternetAddress(to[i]);

            for( int i = 0; i < toAddress.length; i++) {
                message.addRecipient(Message.RecipientType.TO, toAddress[i]);

            Transport transport = session.getTransport("smtp");
            transport.connect(host, from, pass);
            transport.sendMessage(message, message.getAllRecipients());
        catch (AddressException ae) {
        catch (MessagingException me) {

Naturally, you'll want to do more in the catch blocks than print the stack trace as I did in the example code above. (Remove the catch blocks to see which method calls from the JavaMail API throw exceptions so you can better see how to properly handle them.)

Thanks to @jodonnel and everyone else who answered. I'm giving him a bounty because his answer led me about 95% of the way to a complete answer.

When do you use POST and when do you use GET?

Short Version

GET: Usually used for submitted search requests, or any request where you want the user to be able to pull up the exact page again.

Advantages of GET:

  • URLs can be bookmarked safely.
  • Pages can be reloaded safely.

Disadvantages of GET:

POST: Used for higher security requests where data may be used to alter a database, or a page that you don't want someone to bookmark.

Advantages of POST:

  • Name-value pairs are not displayed in url. (Security += 1)
  • Unlimited number of name-value pairs can be passed via POST. Reference.

Disadvantages of POST:

  • Page that used POST data cannot be bookmark. (If you so desired.)

Longer Version

Directly from the Hypertext Transfer Protocol -- HTTP/1.1:

9.3 GET

The GET method means retrieve whatever information (in the form of an entity) is identified by the Request-URI. If the Request-URI refers to a data-producing process, it is the produced data which shall be returned as the entity in the response and not the source text of the process, unless that text happens to be the output of the process.

The semantics of the GET method change to a "conditional GET" if the request message includes an If-Modified-Since, If-Unmodified-Since, If-Match, If-None-Match, or If-Range header field. A conditional GET method requests that the entity be transferred only under the circumstances described by the conditional header field(s). The conditional GET method is intended to reduce unnecessary network usage by allowing cached entities to be refreshed without requiring multiple requests or transferring data already held by the client.

The semantics of the GET method change to a "partial GET" if the request message includes a Range header field. A partial GET requests that only part of the entity be transferred, as described in section 14.35. The partial GET method is intended to reduce unnecessary network usage by allowing partially-retrieved entities to be completed without transferring data already held by the client.

The response to a GET request is cacheable if and only if it meets the requirements for HTTP caching described in section 13.

See section 15.1.3 for security considerations when used for forms.

9.5 POST

The POST method is used to request that the origin server accept the entity enclosed in the request as a new subordinate of the resource identified by the Request-URI in the Request-Line. POST is designed to allow a uniform method to cover the following functions:

  • Annotation of existing resources;

  • Posting a message to a bulletin board, newsgroup, mailing list, or similar group of articles;

  • Providing a block of data, such as the result of submitting a form, to a data-handling process;

  • Extending a database through an append operation.

The actual function performed by the POST method is determined by the server and is usually dependent on the Request-URI. The posted entity is subordinate to that URI in the same way that a file is subordinate to a directory containing it, a news article is subordinate to a newsgroup to which it is posted, or a record is subordinate to a database.

The action performed by the POST method might not result in a resource that can be identified by a URI. In this case, either 200 (OK) or 204 (No Content) is the appropriate response status, depending on whether or not the response includes an entity that describes the result.

Response.Redirect with POST instead of Get?

Typically, all you'll ever need is to carry some state between these two requests. There's actually a really funky way to do this which doesn't rely on JavaScript (think <noscript/>).

Set-Cookie: name=value; Max-Age=120; Path=/redirect.html

With that cookie there, you can in the following request to /redirect.html retrieve the name=value info, you can store any kind of information in this name/value pair string, up to say 4K of data (typical cookie limit). Of course you should avoid this and store status codes and flag bits instead.

Upon receiving this request you in return respond with a delete request for that status code.

Set-Cookie: name=value; Max-Age=0; Path=/redirect.html

My HTTP is a bit rusty I've been going trough RFC2109 and RFC2965 to figure how reliable this really is, preferably I would want the cookie to round trip exactly once but that doesn't seem to be possible, also, third-party cookies might be a problem for you if you are relocating to another domain. This is still possible but not as painless as when you're doing stuff within your own domain.

The problem here is concurrency, if a power user is using multiple tabs and manages to interleave a couple of requests belonging to the same session (this is very unlikely, but not impossible) this may lead to inconsistencies in your application.

It's the <noscript/> way of doing HTTP round trips without meaningless URLs and JavaScript

I provide this code as a prof of concept: If this code is run in a context that you are not familiar with I think you can work out what part is what.

The idea is that you call Relocate with some state when you redirect, and the URL which you relocated calls GetState to get the data (if any).

const string StateCookieName = "state";

static int StateCookieID;

protected void Relocate(string url, object state)
    var key = "__" + StateCookieName + Interlocked
        .Add(ref StateCookieID, 1).ToInvariantString();

    var absoluteExpiration = DateTime.Now
        .Add(new TimeSpan(120 * TimeSpan.TicksPerSecond));

    Context.Cache.Insert(key, state, null, absoluteExpiration,

    var path = Context.Response.ApplyAppPathModifier(url);

        .Add(new HttpCookie(StateCookieName, key)
            Path = path,
            Expires = absoluteExpiration

    Context.Response.Redirect(path, false);

protected TData GetState<TData>()
    where TData : class
    var cookie = Context.Request.Cookies[StateCookieName];
    if (cookie != null)
        var key = cookie.Value;
        if (key.IsNonEmpty())
            var obj = Context.Cache.Remove(key);

                .Add(new HttpCookie(StateCookieName)
                    Path = cookie.Path, 
                    Expires = new DateTime(1970, 1, 1) 

            return obj as TData;
    return null;

htmlentities() vs. htmlspecialchars()

One small example, I needed to have 2 client names indexed in a function:

[1] => Altisoxxce Soluxxons S.à r.l.
[5] => Joxxson & Joxxson

I originally $term = get_term_by('name', htmlentities($name), 'client'); which resulted in term names that only included the ampersand array item (&) but not the accented item. But when I changed the variable setting to htmlspecialchars both were able to run through the function. Hope this helps!

Possible to perform cross-database queries with PostgreSQL?

see [published 2017]

These days you also have the option to use

You can run SQL on that PrestoDB node and it will distribute the SQL query as required. It can connect to the same node twice for different databases, or it might be connecting to different nodes on different hosts.

It does not support:


So you should only use it for SELECT and JOIN needs. Connect directly to each database for the above needs. (It looks like you can also INSERT or UPDATE which is nice)

Client applications connect to PrestoDB primarily using JDBC, but other types of connection are possible including a Tableu compatible web API

This is an open source tool governed by the Linux Foundation and Presto Foundation.

The founding members of the Presto Foundation are: Facebook, Uber, Twitter, and Alibaba.

The current members are: Facebook, Uber, Twitter, Alibaba, Alluxio, Ahana, Upsolver, and Intel.

How to validate an email address in JavaScript

If you are using AngularJS, just add type="email" to the input element:

In case there is no input element, it can be created dynamically:

var isEmail = $compile('<input ng-model="m" type="email">')($rootScope.$new()).

if (isEmail('[email protected]')) {

How do you move a file?

If you are moving folders via Repository Browser, then there is no Move option on right-click; the only way is to drag and drop.

php execute a background process

Assuming this is running on a Linux machine, I've always handled it like this:

exec(sprintf("%s > %s 2>&1 & echo $! >> %s", $cmd, $outputfile, $pidfile));

This launches the command $cmd, redirects the command output to $outputfile, and writes the process id to $pidfile.

That lets you easily monitor what the process is doing and if it's still running.

function isRunning($pid){
        $result = shell_exec(sprintf("ps %d", $pid));
        if( count(preg_split("/\n/", $result)) > 2){
            return true;
    }catch(Exception $e){}

    return false;

How do you add an image?

In order to add attributes, XSL wants

<xsl:element name="img">

instead of just


Although, yes, if you're just copying the element as-is, you don't need any of that.

How do you automatically set the focus to a textbox when a web page loads?

As a general advice, I would recommend not stealing the focus from the address bar. (Jeff already talked about that.)

Web page can take some time to load, which means that your focus change can occur some long time after the user typed the pae URL. Then he could have changed his mind and be back to url typing while you will be loading your page and stealing the focus to put it in your textbox.

That's the one and only reason that made me remove Google as my start page.

Of course, if you control the network (local network) or if the focus change is to solve an important usability issue, forget all I just said :)

SQL: How to get the id of values I just INSERTed?

There's no standard way to do it (just as there is no standard way to create auto-incrementing IDs). Here are two ways to do it in PostgreSQL. Assume this is your table:

CREATE TABLE mytable (
  lastname VARCHAR NOT NULL,
  firstname VARCHAR

You can do it in two statements as long as they're consecutive statements in the same connection (this will be safe in PHP with connection pooling because PHP doesn't give the connection back to the pool until your script is done):

INSERT INTO mytable (lastname, firstname) VALUES ('Washington', 'George');
SELECT lastval();

lastval() gives you the last auto-generated sequence value used in the current connection.

The other way is to use PostgreSQL's RETURNING clause on the INSERT statement:

INSERT INTO mytable (lastname) VALUES ('Cher') RETURNING id;

This form returns a result set just like a SELECT statement, and is also handy for returning any kind of calculated default value.

How do you detect/avoid Memory leaks in your (Unmanaged) code?

Are you counting the allocs and frees by interpolating your own syscall functions which record the calls and then pass the call to the real function?

This is the only way you can keep track of calls originating from code that you haven't written.

Have a look at the man page for Or on some systems.

Also do Google LD_PRELOAD and you'll find some interesting articles explaining the technique over on

Get month and year from a datetime in SQL Server 2005

the best way to do that is with :


it will keep your datetime type

MySQL Error 1093 - Can't specify target table for update in FROM clause

As far as concerns, you want to delete rows in story_category that do not exist in category.

Here is your original query to identify the rows to delete:

FROM  story_category 
WHERE category_id NOT IN (
    FROM category INNER JOIN 
       story_category ON

Combining NOT IN with a subquery that JOINs the original table seems unecessarily convoluted. This can be expressed in a more straight-forward manner with not exists and a correlated subquery:

select sc.*
from story_category sc
where not exists (select 1 from category c where = sc.category_id);

Now it is easy to turn this to a delete statement:

delete from story_category
where not exists (select 1 from category c where = story_category.category_id);    

This quer would run on any MySQL version, as well as in most other databases that I know.

Demo on DB Fiddle:

-- set-up
create table story_category(category_id int);
create table category (id int);
insert into story_category values (1), (2), (3), (4), (5);
insert into category values (4), (5), (6), (7);

-- your original query to identify offending rows
FROM  story_category 
WHERE category_id NOT IN (
    FROM category INNER JOIN 
       story_category ON;
| category_id |
| ----------: |
|           1 |
|           2 |
|           3 |
-- a functionally-equivalent, simpler query for this
select sc.*
from story_category sc
where not exists (select 1 from category c where = sc.category_id)
| category_id |
| ----------: |
|           1 |
|           2 |
|           3 |
-- the delete query
delete from story_category
where not exists (select 1 from category c where = story_category.category_id);

-- outcome
select * from story_category;
| category_id |
| ----------: |
|           4 |
|           5 |

How do you force Visual Studio to regenerate the .designer files for aspx/ascx files?

I know I'm late to the party, but I thought if after trying the accepted answer by @Glenn Slaven and the current highest rated answer by @Espo you are still out of luck, the following might save some people out there some trouble.

User Controls (.ascx) are what constantly stop auto-generating for me. I've found that in the instances where I use other User Control(s) in my User Control, it breaks the auto-generation.

The solution I came up with was to use the trick we all know of for getting IntelliSense to work in User Controls or Skin files when using CSS classes from external sources. Instead of just referencing the CSS file, now I Register the other User Control(s) that I need. It looks something like this:

<% If False Then %>
<%@ Register TagPrefix="uc" TagName="Title" Src="~/controls/title.ascx" %>
<link rel="stylesheet" type="text/css" href="../css/common.css"  />
<% End If %>

After that, I Save the file, which prompts the auto-generation to regenerate, and I'm back up and running.

Why does the order in which libraries are linked sometimes cause errors in GCC?

Another alternative would be to specify the list of libraries twice:

gcc prog.o libA.a libB.a libA.a libB.a -o prog.x

Doing this, you don't have to bother with the right sequence since the reference will be resolved in the second block.

How to parse a string into a nullable int

I found and adapted some code for a Generic NullableParser class. The full code is on my blog Nullable TryParse

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Globalization;
namespace SomeNamespace
    /// <summary>
    /// A parser for nullable types. Will return null when parsing fails.
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public static class NullableParser<T> where T : struct
        public delegate bool TryParseDelegate(string s, out T result);
        /// <summary>
        /// A generic Nullable Parser. Supports parsing of all types that implements the tryParse method;
        /// </summary>
        /// <param name="text">Text to be parsed</param>
        /// <param name="result">Value is true for parse succeeded</param>
        /// <returns>bool</returns>
        public static bool TryParse(string s, out Nullable<T> result)
            bool success = false;
                if (string.IsNullOrEmpty(s))
                    result = null;
                    success = true;
                    IConvertible convertableString = s as IConvertible;
                    if (convertableString != null)
                        result = new Nullable<T>((T)convertableString.ToType(typeof(T),
                        success = true;
                        success = false;
                        result = null;
                success = false;
                result = null;
            return success;

Safely turning a JSON string into an object


There are already good answer for this question, but I was curious about performance and today 2020.09.21 I conduct tests on MacOs HighSierra 10.13.6 on Chrome v85, Safari v13.1.2 and Firefox v80 for chosen solutions.


  • eval/Function (A,B,C) approach is fast on Chrome (but for big-deep object N=1000 they crash: "maximum stack call exceed)
  • eval (A) is fast/medium fast on all browsers
  • JSON.parse (D,E) are fastest on Safari and Firefox

enter image description here


I perform 4 tests cases:

  • for small shallow object HERE
  • for small deep object HERE
  • for big shallow object HERE
  • for big deep object HERE

Object used in above tests came from HERE

let obj_ShallowSmall = {
  field0: false,
  field1: true,
  field2: 1,
  field3: 0,
  field4: null,
  field5: [],
  field6: {},
  field7: "text7",
  field8: "text8",

let obj_DeepSmall = {
  level0: {
   level1: {
    level2: {
     level3: {
      level4: {
       level5: {
        level6: {
         level7: {
          level8: {
           level9: [[[[[[[[[['abc']]]]]]]]]],

let obj_ShallowBig = Array(1000).fill(0).reduce((a,c,i) => (a['field'+i]=getField(i),a) ,{});

let obj_DeepBig = genDeepObject(1000);

// ------------------
// Show objects
// ------------------


// ------------------
// ------------------

function getField(k) {
  let i=k%10;
  if(i==0) return false;
  if(i==1) return true;
  if(i==2) return k;
  if(i==3) return 0;
  if(i==4) return null;
  if(i==5) return [];
  if(i==6) return {};  
  if(i>=7) return "text"+k;

function genDeepObject(N) {
  // generate: {level0:{level1:{...levelN: {end:[[[...N-times...['abc']...]]] }}}...}}}
  let obj={};
  let o=obj;
  let arr = [];
  let a=arr;

  for(let i=0; i<N; i++) {
    let aa=[];

  return obj;

Below snippet presents chosen solutions

// src:
function A(json) {
  return eval("(" + json + ')');

function B(json) {
  return (new Function('return ('+json+')'))()

// improved
function C(json) {
  return Function('return ('+json+')')()

// src:
function D(json) {
  return JSON.parse(json);

// src:
function E(json) {
  return $.parseJSON(json)

// --------------------
// --------------------

let json = '{"a":"abc","b":"123","d":[1,2,3],"e":{"a":1,"b":2,"c":3}}';

[A,B,C,D,E].map(f=> {  
  console.log( + ' ' + JSON.stringify(f(json))
<script src=""></script>
This shippet only presents functions used in performance tests - it not perform tests itself!

And here are example results for chrome

enter image description here

Complex CSS selector for parent of active child

I actually ran into the same issue as the original poster. There is a simple solution of just using .parent() jQuery selector. My problem was, I was using .parent instead of .parent(). Stupid mistake I know.

Bind the events (in this case since my tabs are in Modal I needed to bind them with .live instead of a basic .click.

$('#testTab1 .tabLink').live('click', function() {
    $('#modal ul.tabs li').removeClass("current"); //Remove any "current" class
    $(this).parent().addClass("current"); //Add "current" class to selected tab
    $('#modal div#testTab1 .tabContent').hide();
    return false;
$('#testTab2 .tabLink').live('click', function() {
    $('#modal ul.tabs li').removeClass("current"); //Remove any "current" class
    $(this).parent().addClass("current"); //Add "current" class to selected tab
    $('#modal div#testTab2 .tabContent').hide();
    return false;

Here is the HTML..

<div id="tabView1" style="display:none;">
  <!-- start: the code for tabView 1 -->
  <div id="testTab1" style="width:1080px; height:640px; position:relative;">
    <h1 class="Bold_Gray_45px">Modal Header</h1>
    <div class="tabBleed"></div>
    <ul class="tabs">
      <li class="current"> <a href="#" class="tabLink" id="link1">Tab Title Link</a>
        <div class="tabContent" id="tabContent1-1">
          <div class="modalCol">
            <p>Your Tab Content</p>
            <p><a href="#" class="tabShopLink">tabBased Anchor Link</a> </p>
          <div class="tabsImg"> </div>
      <li> <a href="#" class="tabLink" id="link2">Tab Title Link</a>
        <div class="tabContent" id="tabContent1-2">
          <div class="modalCol">
            <p>Your Tab Content</p>
            <p><a href="#" class="tabShopLink">tabBased Anchor Link</a> </p>
          <div class="tabsImg"> </div>

Of course you can repeat that pattern..with more LI's

What is a monad?

Actually, contrary to common understanding of Monads, they have nothing to do with state. Monads are simply a way to wrapping things and provide methods to do operations on the wrapped stuff without unwrapping it.

For example, you can create a type to wrap another one, in Haskell:

data Wrapped a = Wrap a

To wrap stuff we define

return :: a -> Wrapped a
return x = Wrap x

To perform operations without unwrapping, say you have a function f :: a -> b, then you can do this to lift that function to act on wrapped values:

fmap :: (a -> b) -> (Wrapped a -> Wrapped b)
fmap f (Wrap x) = Wrap (f x)

That's about all there is to understand. However, it turns out that there is a more general function to do this lifting, which is bind:

bind :: (a -> Wrapped b) -> (Wrapped a -> Wrapped b)
bind f (Wrap x) = f x

bind can do a bit more than fmap, but not vice versa. Actually, fmap can be defined only in terms of bind and return. So, when defining a monad.. you give its type (here it was Wrapped a) and then say how its return and bind operations work.

The cool thing is that this turns out to be such a general pattern that it pops up all over the place, encapsulating state in a pure way is only one of them.

For a good article on how monads can be used to introduce functional dependencies and thus control order of evaluation, like it is used in Haskell's IO monad, check out IO Inside.

As for understanding monads, don't worry too much about it. Read about them what you find interesting and don't worry if you don't understand right away. Then just diving in a language like Haskell is the way to go. Monads are one of these things where understanding trickles into your brain by practice, one day you just suddenly realize you understand them.

Explicit vs implicit SQL joins

Performance wise, it should not make any difference. The explicit join syntax seems cleaner to me as it clearly defines relationships between tables in the from clause and does not clutter up the where clause.

Java Delegates?

Depending precisely what you mean, you can achieve a similar effect (passing around a method) using the Strategy Pattern.

Instead of a line like this declaring a named method signature:

// C#
public delegate void SomeFunction();

declare an interface:

// Java
public interface ISomeBehaviour {
   void SomeFunction();

For concrete implementations of the method, define a class that implements the behaviour:

// Java
public class TypeABehaviour implements ISomeBehaviour {
   public void SomeFunction() {
      // TypeA behaviour

public class TypeBBehaviour implements ISomeBehaviour {
   public void SomeFunction() {
      // TypeB behaviour

Then wherever you would have had a SomeFunction delegate in C#, use an ISomeBehaviour reference instead:

// C#
SomeFunction doSomething = SomeMethod;
doSomething = SomeOtherMethod;

// Java
ISomeBehaviour someBehaviour = new TypeABehaviour();
someBehaviour = new TypeBBehaviour();

With anonymous inner classes, you can even avoid declaring separate named classes and almost treat them like real delegate functions.

// Java
public void SomeMethod(ISomeBehaviour pSomeBehaviour) {


SomeMethod(new ISomeBehaviour() { 
   public void SomeFunction() {
      // your implementation

This should probably only be used when the implementation is very specific to the current context and wouldn't benefit from being reused.

And then of course in Java 8, these do become basically lambda expressions:

// Java 8
SomeMethod(() -> { /* your implementation */ });

C# switch statement limitations - why?

Microsoft finally heard you!

Now with C# 7 you can:

case Circle c:
    WriteLine($"circle with radius {c.Radius}");
case Rectangle s when (s.Length == s.Height):
    WriteLine($"{s.Length} x {s.Height} square");
case Rectangle r:
    WriteLine($"{r.Length} x {r.Height} rectangle");
    WriteLine("<unknown shape>");
case null:
    throw new ArgumentNullException(nameof(shape));

Can someone explain __all__ in Python?

I'm just adding this to be precise:

All other answers refer to modules. The original question explicitely mentioned __all__ in files, so this is about python packages.

Generally, __all__ only comes into play when the from xxx import * variant of the import statement is used. This applies to packages as well as to modules.

The behaviour for modules is explained in the other answers. The exact behaviour for packages is described here in detail.

In short, __all__ on package level does approximately the same thing as for modules, except it deals with modules within the package (in contrast to specifying names within the module). So __all__ specifies all modules that shall be loaded and imported into the current namespace when us use from package import *.

The big difference is, that when you omit the declaration of __all__ in a package's, the statement from package import * will not import anything at all (with exceptions explained in the documentation, see link above).

On the other hand, if you omit __all__ in a module, the "starred import" will import all names (not starting with an underscore) defined in the module.

How would you make a comma-separated string from a list of strings?

Don't you just want:


Obviously it gets more complicated if you need to quote/escape commas etc in the values. In that case I would suggest looking at the csv module in the standard library:

VB.NET Empty String Array

Not sure why you'd want to, but the C# way would be

string[] newArray = new string[0];

I'm guessing that VB won't be too dissimilar to this.

If you're building an empty array so you can populate it with values later, you really should consider using


and converting it to an array (if you really need it as an array) with


Reading Email using Pop3 in C#

I just tried SMTPop and it worked.

  1. I downloaded this.
  2. Added smtpop.dll reference to my C# .NET project

Wrote the following code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;    
using SmtPop;

namespace SMT_POP3 {

    class Program {
        static void Main(string[] args) {
            SmtPop.POP3Client pop = new SmtPop.POP3Client();
            pop.Open("<hostURL>", 110, "<username>", "<password>");

            // Get message list from POP server
            SmtPop.POPMessageId[] messages = pop.GetMailList();
            if (messages != null) {

                // Walk attachment list
                foreach(SmtPop.POPMessageId id in messages) {
                    SmtPop.POPReader reader= pop.GetMailReader(id);
                    SmtPop.MimeMessage msg = new SmtPop.MimeMessage();

                    // Read message
                    if (msg.AddressFrom != null) {
                        String from= msg.AddressFrom[0].Name;
                        Console.WriteLine("from: " + from);
                    if (msg.Subject != null) {
                        String subject = msg.Subject;
                        Console.WriteLine("subject: "+ subject);
                    if (msg.Body != null) {
                        String body = msg.Body;
                        Console.WriteLine("body: " + body);
                    if (msg.Attachments != null && false) {
                        // Do something with first attachment
                        SmtPop.MimeAttachment attach = msg.Attachments[0];

                        if (attach.Filename == "data") {
                           // Read data from attachment
                           Byte[] b = Convert.FromBase64String(attach.Body);
                           System.IO.MemoryStream mem = new System.IO.MemoryStream(b, false);

                           //BinaryFormatter f = new BinaryFormatter();
                           // DataClass data= (DataClass)f.Deserialize(mem); 

                        // Delete message
                        // pop.Dele(id.Id);

Add alternating row color to SQL Server Reporting services report

I think this trick is not discussed here. So here it is,

In any type of complex matrix, when you want alternate cell colors, either row wise or column wise, the working solution is,

If you want a alternate color of cells coloumn wise then,

  1. At the bottom right corner of a report design view, in "Column Groups", create a fake parent group on 1 (using expression), named "FakeParentGroup".
  2. Then, in the report design, for cells that to be colored alternatively, use following background color expression

=IIF(RunningValue( Fields![ColumnGroupField].Value, countDistinct, "FakeParentGroup" ) MOD 2, "White", "LightGrey")

Thats all.

Same for the alternate color row wise, just you have to edit solution accordingly.

NOTE: Here, sometimes you need to set border of cells accordingly, usually it vanishes.

Also dont forget to delete value 1 in report that came into pic when you created fake parent group.

How do I get the current location of an iframe?

I like your server side idea, even if my proposed implementation of it sounds a little bit ghetto.

You could set the .innerHTML of the iframe to the HTML contents you grab server side. Depending on how you grab this, you will have to pay attention to relative versus absolute paths.

Plus, depending on how the page you are grabbing interacts with other pages, this could totally not work (cookies being set for the page you are grabbing won't work across domains, maybe state is being tracked in Javascript... Lots of reasons this might not work.)

I don't believe that tracking the current state of the page you are trying to mirror is theoretically possible, but I'm not sure. The site could track all sorts of things server side, you won't have access to this state. Imagine the case where on a page load a variable is set to a random value server-side, how would you capture this state?

Do these ideas help with anything?

-Brian J. Stinar-

Differences in string compare methods in C#

Using .Equals is also a lot easier to read.

Extending the User model with custom fields in Django

New in Django 1.5, now you can create your own Custom User Model (which seems to be good thing to do in above case). Refer to 'Customizing authentication in Django'

Probably the coolest new feature on 1.5 release.

Truncate (not round) decimal places in SQL Server

I think we can go much easier with simpler example solution found in Hackerrank:

Problem statement: Query the greatest value of the Northern Latitudes (LAT_N) from STATION that is less than 137.2345. Truncate your answer to 4 decimal places.

WHERE LAT_N < 137.23453;

Solution Above gives you idea how to simply make value limited to 4 decimal points. If you want to lower or upper the numbers after decimal, just change 4 to whatever you want.

Changing the default title of confirm() in JavaScript?

This is not possible, as you say, from a security stand point. The only way you could simulate it, is by creating a modeless dialog window.

There are many third-party javascript-plugins that you could use to fake this effect so you do not have to write all that code.

How to concatenate strings of a string field in a PostgreSQL 'group by' query?

How about using Postgres built-in array functions? At least on 8.4 this works out of the box:

SELECT company_id, array_to_string(array_agg(employee), ',')
FROM mytable
GROUP BY company_id;

How SID is different from Service name in Oracle tnsnames.ora

what is a SID and Service name

please look into oracle's documentation at

In case if the above link is not accessable in future, At the time time of writing this answer, the above link will direct you to, "Database Service and Database Instance Identification" topic in Connectivity Concepts chapter of "Database Net Services Administrator's Guide". This guide is published by oracle as part of "Oracle Database Online Documentation, 10g Release 2 (10.2)"

When I have to use one or another? Why do I need two of them?

Consider below mapping in a RAC Environment,

bob1    bob
bob2    bob
bob3    bob
bob4    bob

if load balancing is configured, the listener will 'balance' the workload across all four SIDs. Even if load balancing is configured, you can connect to bob1 all the time if you want to by using the SID instead of SERVICE_NAME.

Please refer,

How to convert a date String to a Date or Calendar object?

In brief:

DateFormat formatter = new SimpleDateFormat("MM/dd/yy");
try {
  Date date = formatter.parse("01/29/02");
} catch (ParseException e) {

See SimpleDateFormat javadoc for more.

And to turn it into a Calendar, do:

Calendar calendar = Calendar.getInstance();

How do I style (css) radio buttons and labels?

For any CSS3-enabled browser you can use an adjacent sibling selector for styling your labels

input:checked + label {
    color: white;

MDN's browser compatibility table says essentially all of the current, popular browsers (Chrome, IE, Firefox, Safari), on both desktop and mobile, are compatible.

How to find the mime type of a file in python?

In Python 3.x and webapp with url to the file which couldn't have an extension or a fake extension. You should install python-magic, using

pip3 install python-magic

For Mac OS X, you should also install libmagic using

brew install libmagic

Code snippet

import urllib
import magic
from urllib.request import urlopen

url = "http://...url to the file ..."
request = urllib.request.Request(url)
response = urlopen(request)
mime_type = magic.from_buffer(response.readline())

alternatively you could put a size into the read

import urllib
import magic
from urllib.request import urlopen

url = "http://...url to the file ..."
request = urllib.request.Request(url)
response = urlopen(request)
mime_type = magic.from_buffer(

Can I write native iPhone apps using Python?

I think it was not possible earlier but I recently heard about PyMob, which seems interesting because the apps are written in Python and the final outputs are native source codes in various platforms (Obj-C for iOS, Java for Android etc). This is certainly quite unique. This webpage explains it in more detail.

I haven't given it a shot yet, but will take a look soon.

Comparing two byte arrays in .NET

User gil suggested unsafe code which spawned this solution:

// Copyright (c) 2008-2013 Hafthor Stefansson
// Distributed under the MIT/X11 software license
// Ref:
static unsafe bool UnsafeCompare(byte[] a1, byte[] a2) {
  if(a1==a2) return true;
  if(a1==null || a2==null || a1.Length!=a2.Length)
    return false;
  fixed (byte* p1=a1, p2=a2) {
    byte* x1=p1, x2=p2;
    int l = a1.Length;
    for (int i=0; i < l/8; i++, x1+=8, x2+=8)
      if (*((long*)x1) != *((long*)x2)) return false;
    if ((l & 4)!=0) { if (*((int*)x1)!=*((int*)x2)) return false; x1+=4; x2+=4; }
    if ((l & 2)!=0) { if (*((short*)x1)!=*((short*)x2)) return false; x1+=2; x2+=2; }
    if ((l & 1)!=0) if (*((byte*)x1) != *((byte*)x2)) return false;
    return true;

which does 64-bit based comparison for as much of the array as possible. This kind of counts on the fact that the arrays start qword aligned. It'll work if not qword aligned, just not as fast as if it were.

It performs about seven timers faster than the simple for loop. Using the J# library performed equivalently to the original for loop. Using .SequenceEqual runs around seven times slower; I think just because it is using IEnumerator.MoveNext. I imagine LINQ-based solutions being at least that slow or worse.

T-SQL stored procedure that accepts multiple Id values

Yeah, your current solution is prone to SQL injection attacks.

The best solution that I've found is to use a function that splits text into words (there are a few posted here, or you can use this one from my blog) and then join that to your table. Something like:

SELECT d.[Name]
FROM Department d
    JOIN dbo.SplitWords(@DepartmentIds) w ON w.Value = d.DepartmentId

How do I calculate a trendline for a graph?

Given that the trendline is straight, find the slope by choosing any two points and calculating:

(A) slope = (y1-y2)/(x1-x2)

Then you need to find the offset for the line. The line is specified by the equation:

(B) y = offset + slope*x

So you need to solve for offset. Pick any point on the line, and solve for offset:

(C) offset = y - (slope*x)

Now you can plug slope and offset into the line equation (B) and have the equation that defines your line. If your line has noise you'll have to decide on an averaging algorithm, or use curve fitting of some sort.

If your line isn't straight then you'll need to look into Curve fitting, or Least Squares Fitting - non trivial, but do-able. You'll see the various types of curve fitting at the bottom of the least squares fitting webpage (exponential, polynomial, etc) if you know what kind of fit you'd like.

Also, if this is a one-off, use Excel.

Easy way to write contents of a Java InputStream to an OutputStream

you can use this method

public static void copyStream(InputStream is, OutputStream os)
     final int buffer_size=1024;
         byte[] bytes=new byte[buffer_size];
           int, 0, buffer_size);
           os.write(bytes, 0, count);
     catch(Exception ex){}

Algorithm to randomly generate an aesthetically-pleasing color palette

I would use a color wheel and given a random position you could add the golden angle (137,5 degrees)

in order to get different colours each time that do not overlap.

Adjusting the brightness for the color wheel you could get also different bright/dark color combinations.

I've found this blog post that explains really well the problem and the solution using the golden ratio.

UPDATE: I've just found this other approach:

It's called RYB(red, yellow, blue) method and it's described in this paper:

as "Paint Inspired Color Compositing".

The algorithm generates the colors and each new color is chosen to maximize its euclidian distance to the previously selected ones.

Here you can find a a good implementation in javascript:


The Sciences Po Medialb have just released a tool called "I want Hue" that generate color palettes for data scientists. Using different color spaces and generating the palettes by using k-means clustering or force vectors ( repulsion graphs) The results from those methods are very good, they show the theory and an implementation in their web page.

How do you get the index of the current iteration of a foreach loop?

Ian Mercer posted a similar solution as this on Phil Haack's blog:

foreach (var item in Model.Select((value, i) => new { i, value }))
    var value = item.value;
    var index = item.i;

This gets you the item (item.value) and its index (item.i) by using this overload of LINQ's Select:

the second parameter of the function [inside Select] represents the index of the source element.

The new { i, value } is creating a new anonymous object.

Heap allocations can be avoided by using ValueTuple if you're using C# 7.0 or later:

foreach (var item in Model.Select((value, i) => ( value, i )))
    var value = item.value;
    var index = item.i;

You can also eliminate the item. by using automatic destructuring:

foreach ((MyType value, Int32 i) in Model.Select((value, i) => ( value, i )))
    <li id="item_@i">@value</li>

How to get the last day of the month?

Here is a long (easy to understand) version but takes care of leap years.

cheers, JK

def last_day_month(year, month):
    leap_year_flag = 0
    end_dates = {
        1: 31,
        2: 28,
        3: 31,
        4: 30,
        5: 31,
        6: 30,
        7: 31,
        8: 31,
        9: 30,
        10: 31,
        11: 30,
        12: 31

    # Checking for regular leap year    
    if year % 4 == 0:
        leap_year_flag = 1
        leap_year_flag = 0

    # Checking for century leap year    
    if year % 100 == 0:
        if year % 400 == 0:
            leap_year_flag = 1
            leap_year_flag = 0

    # return end date of the year-month
    if leap_year_flag == 1 and month == 2:
        return 29
    elif leap_year_flag == 1 and month != 2:
        return end_dates[month]
        return end_dates[month]

Best way to get identity of inserted row?

  • @@IDENTITY returns the last identity value generated for any table in the current session, across all scopes. You need to be careful here, since it's across scopes. You could get a value from a trigger, instead of your current statement.

  • SCOPE_IDENTITY() returns the last identity value generated for any table in the current session and the current scope. Generally what you want to use.

  • IDENT_CURRENT('tableName') returns the last identity value generated for a specific table in any session and any scope. This lets you specify which table you want the value from, in case the two above aren't quite what you need (very rare). Also, as @Guy Starbuck mentioned, "You could use this if you want to get the current IDENTITY value for a table that you have not inserted a record into."

  • The OUTPUT clause of the INSERT statement will let you access every row that was inserted via that statement. Since it's scoped to the specific statement, it's more straightforward than the other functions above. However, it's a little more verbose (you'll need to insert into a table variable/temp table and then query that) and it gives results even in an error scenario where the statement is rolled back. That said, if your query uses a parallel execution plan, this is the only guaranteed method for getting the identity (short of turning off parallelism). However, it is executed before triggers and cannot be used to return trigger-generated values.

How do you rotate a two dimensional array?

For i:= 0 to X do For j := 0 to X do graphic[j][i] := graphic2[X-i][j]

X is the size of the array the graphic is in.

How do you get the footer to stay at the bottom of a Web page?

If you don't want it using position fixed, and following you annoyingly on mobile, this seems to be working for me so far.

html {
    min-height: 100%;
    position: relative;

#site-footer {
    position: absolute;
    bottom: 0;
    left: 0;
    width: 100%;
    padding: 6px 2px;
    background: #32383e;

Just set the html to min-height: 100%; and position: relative;, then position: absolute; bottom: 0; left: 0; on the footer. I then made sure the footer was the last element in the body.

Let me know if this doesn't work for anyone else, and why. I know these tedious style hacks can behave strangely among various circumstances I'd not thought of.

function declaration isn't a prototype

Quick answer: change int testlib() to int testlib(void) to specify that the function takes no arguments.

A prototype is by definition a function declaration that specifies the type(s) of the function's argument(s).

A non-prototype function declaration like

int foo();

is an old-style declaration that does not specify the number or types of arguments. (Prior to the 1989 ANSI C standard, this was the only kind of function declaration available in the language.) You can call such a function with any arbitrary number of arguments, and the compiler isn't required to complain -- but if the call is inconsistent with the definition, your program has undefined behavior.

For a function that takes one or more arguments, you can specify the type of each argument in the declaration:

int bar(int x, double y);

Functions with no arguments are a special case. Logically, empty parentheses would have been a good way to specify that an argument but that syntax was already in use for old-style function declarations, so the ANSI C committee invented a new syntax using the void keyword:

int foo(void); /* foo takes no arguments */

A function definition (which includes code for what the function actually does) also provides a declaration. In your case, you have something similar to:

int testlib()
    /* code that implements testlib */

This provides a non-prototype declaration for testlib. As a definition, this tells the compiler that testlib has no parameters, but as a declaration, it only tells the compiler that testlib takes some unspecified but fixed number and type(s) of arguments.

If you change () to (void) the declaration becomes a prototype.

The advantage of a prototype is that if you accidentally call testlib with one or more arguments, the compiler will diagnose the error.

(C++ has slightly different rules. C++ doesn't have old-style function declarations, and empty parentheses specifically mean that a function takes no arguments. C++ supports the (void) syntax for consistency with C. But unless you specifically need your code to compile both as C and as C++, you should probably use the () in C++ and the (void) syntax in C.)

How do I handle newlines in JSON?

I guess this is what you want:

var data = '{"count" : 1, "stack" : "sometext\\n\\n"}';

(You need to escape the "\" in your string (turning it into a double-"\"), otherwise it will become a newline in the JSON source, not the JSON data.)

How do I get the difference between two Dates in JavaScript?

function dayDiff()
     var start = document.getElementById("datepicker").value;
     var end= document.getElementById("date_picker").value;
     var oneDay = 24*60*60*1000; 
     var firstDate = new Date(start);
     var secondDate = new Date(end);    
     var diffDays = Math.round(Math.abs((firstDate.getTime() - secondDate.getTime())/(oneDay)));
    document.getElementById("leave").value =diffDays ;
<input type="text" name="datepicker"value=""/>
<input type="text" name="date_picker" onclick="function dayDiff()" value=""/>
<input type="text" name="leave" value=""/>

How do I download code using SVN/Tortoise from Google Code?

Create a folder where you want to keep the code, and right click on it. Choose SVN Checkout... and type into the URL of repository field.

You can also run

svn checkout

from the command line in the folder you want to keep it (svn.exe has to be in your path, of course).

How do you properly use namespaces in C++?

Namespaces are packages essentially. They can be used like this:

namespace MyNamespace
  class MyClass

Then in code:

MyNamespace::MyClass* pClass = new MyNamespace::MyClass();

Or, if you want to always use a specific namespace, you can do this:

using namespace MyNamespace;

MyClass* pClass = new MyClass();

Edit: Following what bernhardrusch has said, I tend not to use the "using namespace x" syntax at all, I usually explicitly specify the namespace when instantiating my objects (i.e. the first example I showed).

And as you asked below, you can use as many namespaces as you like.

Use of var keyword in C#

I'm fairly new in the C# world, after a decade as a Java professional. My initial thought was along the lines of "Oh no! There goes type safety down the drain". However, the more I read about var, the more I like it.

1) Var is every bit as type safe as an explicitly declared type would be. It's all about compile time syntactic sugar.

2) It follows the principle of DRY (don't repeat yourself). DRY is all about avoiding redundancies, and naming the type on both sides is certainly redundant. Avoinding redundancy is all about making your code easier to change.

3) As for knowing the exact type .. well .. I would argue that you always have a general idea is you have an integer, a socket, some UI control, or whatever. Intellisense will guide you from here. Knowing the exact type often does not matter. E.g. I would argue that 99% of the time you don't care if a given variable is a long or an int, a float or a double. For the last 1% of the cases, where it really matters, just hover the mouse pointer above the var keyword.

4) I've seen the ridiculous argument that now we would need to go back to 1980-style Hungarian warts in order to distinguish variable types. After all, this was the only way to tell the types of variables back in the days of Timothy Dalton playing James Bond. But this is 2010. We have learned to name our variables based upon their usage and their contents and let the IDE guide us as to their type. Just keep doing this and var will not hurt you.

To sum it up, var is not a big thing, but it is a really nice thing, and it is a thing that Java better copy soon. All arguments against seem to be based upon pre-IDE fallacies. I would not hesitate to use it, and I'm happy the R# helps me do so.

How can I add reflection to a C++ application?

You can achieve cool static reflection features for structs with BOOST_HANA_DEFINE_STRUCT from the Boost::Hana library.
Hana is quite versatile, not only for the usecase you have in mind but for a lot of template metaprogramming.

I get a "An attempt was made to load a program with an incorrect format" error on a SQL Server replication project

I've found the solution. I've recently upgraded my machine to Windows 2008 Server 64-bit. The SqlServer.Replication namespace was written for 32-bit platforms. All I needed to do to get it running again was to set the Target Platform in the Project Build Properties to X86.

Checking if a list is empty with LINQ

The second option is much quicker if you have multiple items.

  • Any() returns as soon as 1 item is found.
  • Count() has to keep going through the entire list.

For instance suppose the enumeration had 1000 items.

  • Any() would check the first one, then return true.
  • Count() would return 1000 after traversing the entire enumeration.

This is potentially worse if you use one of the predicate overrides - Count() still has to check every single item, even it there is only one match.

You get used to using the Any one - it does make sense and is readable.

One caveat - if you have a List, rather than just an IEnumerable then use that list's Count property.

Dynamic LINQ OrderBy on IEnumerable<T> / IQueryable<T>

I guess it would work to use reflection to get whatever property you want to sort on:

IEnumerable<T> myEnumerables
var query=from enumerable in myenumerables
          where some criteria
          orderby GetPropertyValue(enumerable,"SomeProperty")
          select enumerable

private static object GetPropertyValue(object obj, string property)
    System.Reflection.PropertyInfo propertyInfo=obj.GetType().GetProperty(property);
    return propertyInfo.GetValue(obj, null);

Note that using reflection is considerably slower than accessing the property directly, so the performance would have to be investigated.

Java and SQLite

The wiki lists some more wrappers:

WCF Service Returning "Method Not Allowed"

It sounds like you're using an incorrect address:

To access the Service I enter http://localhost/project/myService.svc/FileUpload

Assuming you mean this is the address you give your client code then I suspect it should actually be:


How to generate a random alpha-numeric string

public static String getRandomString(int length) {
    char[] chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRST".toCharArray();

    StringBuilder sb = new StringBuilder();
    Random random = new Random();
    for (int i = 0; i < length; i++) {
        char c = chars[random.nextInt(chars.length)];
    String randomStr = sb.toString();

    return randomStr;

Find in Files: Search all code in Team Foundation Server

In my case, writing a small utility in C# helped. Links that helped me -

How to list files of a team project using tfs api?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.TeamFoundation.Client;
using Microsoft.TeamFoundation.VersionControl.Client;
using Microsoft.TeamFoundation.Framework.Client;
using System.IO;

namespace TFSSearch
class Program
    static string[] textPatterns = new[] { "void main(", "exception", "RegisterScript" };  //Text to search
    static string[] filePatterns = new[] { "*.cs", "*.xml", "*.config", "*.asp", "*.aspx", "*.js", "*.htm", "*.html", 
                                           "*.vb", "*.asax", "*.ashx", "*.asmx", "*.ascx", "*.master", "*.svc"}; //file extensions

    static void Main(string[] args)
            var tfs = TfsTeamProjectCollectionFactory
             .GetTeamProjectCollection(new Uri("http://{tfsserver}:8080/tfs/}")); // one some servers you also need to add collection path (if it not the default collection)


            var versionControl = tfs.GetService<VersionControlServer>();

            StreamWriter outputFile = new StreamWriter(@"C:\Find.txt");
            var allProjs = versionControl.GetAllTeamProjects(true);
            foreach (var teamProj in allProjs)
                foreach (var filePattern in filePatterns)
                    var items = versionControl.GetItems(teamProj.ServerItem + "/" + filePattern, RecursionType.Full).Items
                                .Where(i => !i.ServerItem.Contains("_ReSharper"));  //skipping resharper stuff
                    foreach (var item in items)
                        List<string> lines = SearchInFile(item);
                        if (lines.Count > 0)
                            outputFile.WriteLine("FILE:" + item.ServerItem);
                            outputFile.WriteLine(lines.Count.ToString() + " occurence(s) found.");
                        foreach (string line in lines)
                        if (lines.Count > 0)
        catch (Exception e)
            string ex = e.Message;
            Console.WriteLine("!!EXCEPTION: " + e.Message);
            Console.WriteLine("Continuing... ");

    // Define other methods and classes here
    private static List<string> SearchInFile(Item file)
        var result = new List<string>();

            var stream = new StreamReader(file.DownloadFile(), Encoding.Default);

            var line = stream.ReadLine();
            var lineIndex = 0;

            while (!stream.EndOfStream)
                if (textPatterns.Any(p => line.IndexOf(p, StringComparison.OrdinalIgnoreCase) >= 0))
                    result.Add("=== Line " + lineIndex + ": " + line.Trim());

                line = stream.ReadLine();
        catch (Exception e)
            string ex = e.Message;
            Console.WriteLine("!!EXCEPTION: " + e.Message);
            Console.WriteLine("Continuing... ");

        return result;

How to Automatically Start a Download in PHP?

Send the following headers before outputting the file:

header("Content-Disposition: attachment; filename=\"" . basename($File) . "\"");
header("Content-Type: application/octet-stream");
header("Content-Length: " . filesize($File));
header("Connection: close");

@grom: Interesting about the 'application/octet-stream' MIME type. I wasn't aware of that, have always just used 'application/force-download' :)

Execute a large SQL script (with GO commands)

Use SQL Server Management Objects (SMO) which understands GO separators. See my blog post here:

Sample code:

public static void Main()    
  string scriptDirectory = "c:\\temp\\sqltest\\";
  string sqlConnectionString = "Integrated Security=SSPI;" +
  "Persist Security Info=True;Initial Catalog=Northwind;Data Source=(local)";
  DirectoryInfo di = new DirectoryInfo(scriptDirectory);
  FileInfo[] rgFiles = di.GetFiles("*.sql");
  foreach (FileInfo fi in rgFiles)
        FileInfo fileInfo = new FileInfo(fi.FullName);
        string script = fileInfo.OpenText().ReadToEnd();
        using (SqlConnection connection = new SqlConnection(sqlConnectionString))
            Server server = new Server(new ServerConnection(connection));

If that won't work for you, see Phil Haack's library which handles that:

How should I cast in VB.NET?

I prefer the following syntax:

Dim number As Integer = 1
Dim str As String = String.TryCast(number)

If str IsNot Nothing Then

Hah you can tell I typically write code in C#. 8)

The reason I prefer TryCast is you do not have to mess with the overhead of casting exceptions. Your cast either succeeds or your variable is initialized to null and you deal with that accordingly.

What is the best way to give a C# auto-property an initial value?

private string name;
public string Name 
        if(name == null)
            name = "Default Name";
        return name;
        name = value;

How do I size a UITextView to its content?

I found out a way to resize the height of a text field according to the text inside it and also arrange a label below it based on the height of the text field! Here is the code.

UITextView *_textView = [[UITextView alloc] initWithFrame:CGRectMake(10, 10, 300, 10)];
NSString *str = @"This is a test text view to check the auto increment of height of a text view. This is only a test. The real data is something different.";
_textView.text = str;

[self.view addSubview:_textView];
CGRect frame = _textView.frame;
frame.size.height = _textView.contentSize.height;
_textView.frame = frame;

UILabel *lbl = [[UILabel alloc] initWithFrame:CGRectMake(10, 5 + frame.origin.y + frame.size.height, 300, 20)];
lbl.text = @"Hello!";
[self.view addSubview:lbl];

How to show all shared libraries used by executables in Linux?

I found this post very helpful as I needed to investigate dependencies from a 3rd party supplied library (32 vs 64 bit execution path(s)).

I put together a Q&D recursing bash script based on the 'readelf -d' suggestion on a RHEL 6 distro.

It is very basic and will test every dependency every time even if it might have been tested before (i.e very verbose). Output is very basic too.

#! /bin/bash

recurse ()
# Param 1 is the nuumber of spaces that the output will be prepended with
# Param 2 full path to library
#Use 'readelf -d' to find dependencies
dependencies=$(readelf -d ${2} | grep NEEDED | awk '{ print $5 }' | tr -d '[]')
for d in $dependencies; do
   echo "${1}${d}"
   #libstdc++ hack for the '+'-s
   # /lib /lib64 /usr/lib and /usr/lib are searched
   children=$(locate ${d} | grep -E "(^/(lib|lib64|usr/lib|usr/lib64)/${nm1})")
   #at least locate... didn't fail
   if [ ${rc} == "0" ] ; then
      #we have at least one dependency
      if [ ${#children[@]} -gt 0 ]; then
         #check the dependeny's dependencies
         for c in $children; do
          recurse "  ${1}" ${c}
         echo "${1}no children found"
      echo "${1}locate failed for ${d}"
# Q&D -- recurse needs 2 params could/should be supplied from cmdline
recurse "" !!full path to library you want to investigate!!

redirect the output to a file and grep for 'found' or 'failed'

Use and modify, at your own risk of course, as you wish.

Comparing two collections for equality irrespective of the order of items in them

In the case of no repeats and no order, the following EqualityComparer can be used to allow collections as dictionary keys:

public class SetComparer<T> : IEqualityComparer<IEnumerable<T>> 
where T:IComparable<T>
    public bool Equals(IEnumerable<T> first, IEnumerable<T> second)
        if (first == second)
            return true;
        if ((first == null) || (second == null))
            return false;
        return first.ToHashSet().SetEquals(second);

    public int GetHashCode(IEnumerable<T> enumerable)
        int hash = 17;

        foreach (T val in enumerable.OrderBy(x => x))
            hash = hash * 23 + val.GetHashCode();

        return hash;

Here is the ToHashSet() implementation I used. The hash code algorithm comes from Effective Java (by way of Jon Skeet).

How to pass password to scp?

Here's a poor man's Linux/Python/Expect-like example based on this blog post: Upgrading simple shells to fully interactive TTYs. I needed this for old machines where I can't install Expect or add modules to Python.


    echo 'scp [email protected]:./ .'
    sleep 5
    echo 'scp-passwd'
    sleep 5
    echo 'exit'
) |

python -c 'import pty; pty.spawn("/usr/bin/bash")'


scp [email protected] .
bash-4.2$ scp [email protected] .
Password:                                 100%   15KB 236.2KB/s   00:00    
bash-4.2$ exit

Really killing a process in Windows

When ntsd access is denied, try:

ZeroWave was designed to be a simple tool that will provide a multilevel termination of any kind of process.

ZeroWave is also a easy-to-use program due to its simple installation and its very friendly graphical interface.

ZeroWave has three termination modes and with the "INSANE" mode can terminate any kind of process that can run on Windows.

It seems that ZeroWave can't kill avp.exe

Count a list of cells with the same background color

I just created this and it looks easier. You get these 2 functions:

=GetColorIndex(E5)  <- returns color number for the cell

from (cell)

=CountColorIndexInRange(C7:C24,14) <- returns count of cells C7:C24 with color 14

from (range of cells, color number you want to count)

example shows percent of cells with color 14

=ROUND(CountColorIndexInRange(C7:C24,14)/18, 4 )

Create these 2 VBA functions in a Module (hit Alt-F11)

open + folders. double-click on Module1

Just paste this text below in, then close the module window (it must save it then):

Function GetColorIndex(Cell As Range)
  GetColorIndex = Cell.Interior.ColorIndex
End Function

Function CountColorIndexInRange(Rng As Range, TestColor As Long)
  Dim cnt
  Dim cl As Range
  cnt = 0

  For Each cl In Rng
    If GetColorIndex(cl) = TestColor Then
      Rem Debug.Print ">" & TestColor & "<"
      cnt = cnt + 1
    End If

  CountColorIndexInRange = cnt

End Function

What is the difference between UNION and UNION ALL?

UNION ALL also works on more data types as well. For example when trying to union spatial data types. For example:

select a.SHAPE from tableA a
select b.SHAPE from tableB b

will throw

The data type geometry cannot be used as an operand to the UNION, INTERSECT or EXCEPT operators because it is not comparable.

However union all will not.

How do we control web page caching, across all browsers?

The use of the pragma header in the response is a wives tale. RFC2616 only defines it as a request header

Git ignore file for Xcode projects

Based on this guide for Mercurial my .gitignore includes:




I've also chosen to include:


which, according to this Apple mailing list post, are "user-specific project settings".

And for Xcode 4:


How do I export (and then import) a Subversion repository?

rsvndump worked great for me migrating a repository from to an Ubuntu server that I control.

How to install and use rsvndump on Ubuntu:

  1. Install missing dependencies ("APR" and Subversion libraries)

    sudo apt-get install apache2-threaded-dev
    sudo apt-get install libsvn-dev
  2. Install rsvndump

    tar xvfz rsvndump-0.5.5.tar.gz
    cd rsvndump-0.5.5
    sudo make install
  3. Dump the remote SVN repository to a local file

    rsvndump > old_repo_dump
  4. Create a new repository and load in the local dump file

    sudo svnadmin create /opt/subversion/my_new_rep
    sudo svnadmin load --force-uuid /opt/subversion/my_new_repo < old_repo_dump

How do I create a MessageBox in C#?

Also you can use a MessageBox with OKCancel options, but it requires many codes. The if block is for OK, the else block is for Cancel. Here is the code:

if (MessageBox.Show("Are you sure you want to do this?", "Question", MessageBoxButtons.OKCancel, MessageBoxIcon.Question) == DialogResult.OK)
    MessageBox.Show("You pressed OK!");
    MessageBox.Show("You pressed Cancel!");

You can also use a MessageBox with YesNo options:

if (MessageBox.Show("Are you sure want to doing this?", "Question", MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes)
    MessageBox.Show("You are pressed Yes!");
    MessageBox.Show("You are pressed No!");

How can I make an EXE file from a Python program?


py2exe is a Python Distutils extension which converts Python scripts into executable Windows programs, able to run without requiring a Python installation.

How do I write a for loop in bash

for ((i = 0 ; i < max ; i++ )); do echo "$i"; done

Prefer composition over inheritance?

My general rule of thumb: Before using inheritance, consider if composition makes more sense.

Reason: Subclassing usually means more complexity and connectedness, i.e. harder to change, maintain, and scale without making mistakes.

A much more complete and concrete answer from Tim Boudreau of Sun:

Common problems to the use of inheritance as I see it are:

  • Innocent acts can have unexpected results - The classic example of this is calls to overridable methods from the superclass constructor, before the subclasses instance fields have been initialized. In a perfect world, nobody would ever do that. This is not a perfect world.
  • It offers perverse temptations for subclassers to make assumptions about order of method calls and such - such assumptions tend not to be stable if the superclass may evolve over time. See also my toaster and coffee pot analogy.
  • Classes get heavier - you don't necessarily know what work your superclass is doing in its constructor, or how much memory it's going to use. So constructing some innocent would-be lightweight object can be far more expensive than you think, and this may change over time if the superclass evolves
  • It encourages an explosion of subclasses. Classloading costs time, more classes costs memory. This may be a non-issue until you're dealing with an app on the scale of NetBeans, but there, we had real issues with, for example, menus being slow because the first display of a menu triggered massive class loading. We fixed this by moving to more declarative syntax and other techniques, but that cost time to fix as well.
  • It makes it harder to change things later - if you've made a class public, swapping the superclass is going to break subclasses - it's a choice which, once you've made the code public, you're married to. So if you're not altering the real functionality to your superclass, you get much more freedom to change things later if you use, rather than extend the thing you need. Take, for example, subclassing JPanel - this is usually wrong; and if the subclass is public somewhere, you never get a chance to revisit that decision. If it's accessed as JComponent getThePanel() , you can still do it (hint: expose models for the components within as your API).
  • Object hierarchies don't scale (or making them scale later is much harder than planning ahead) - this is the classic "too many layers" problem. I'll go into this below, and how the AskTheOracle pattern can solve it (though it may offend OOP purists).


My take on what to do, if you do allow for inheritance, which you may take with a grain of salt is:

  • Expose no fields, ever, except constants
  • Methods shall be either abstract or final
  • Call no methods from the superclass constructor


all of this applies less to small projects than large ones, and less to private classes than public ones

How do I implement a callback in PHP?

For those who don't care about breaking compatibility with PHP < 5.4, I'd suggest using type hinting to make a cleaner implementation.

function call_with_hello_and_append_world( callable $callback )
     // No need to check $closure because of the type hint
     return $callback( "hello" )."world";

function append_space( $string )
     return $string." ";

$output1 = call_with_hello_and_append_world( function( $string ) { return $string." "; } );
var_dump( $output1 ); // string(11) "hello world"

$output2 = call_with_hello_and_append_world( "append_space" );
var_dump( $output2 ); // string(11) "hello world"

$old_lambda = create_function( '$string', 'return $string." ";' );
$output3 = call_with_hello_and_append_world( $old_lambda );
var_dump( $output3 ); // string(11) "hello world"

How do I list loaded plugins in Vim?

:set runtimepath?

This lists the path of all plugins loaded when a file is opened with Vim.

How do I create a foreign key in SQL Server?

You can also name your foreign key constraint by using:

CONSTRAINT your_name_here FOREIGN KEY (question_exam_id) REFERENCES EXAMS (exam_id)

How do I position one image on top of another in HTML?

It may be a little late but for this you can do:

enter image description here


<!-- html -->
<div class="images-wrapper">
  <img src="images/1" alt="image 1" />
  <img src="images/2" alt="image 2" />
  <img src="images/3" alt="image 3" />
  <img src="images/4" alt="image 4" />


// In _extra.scss
$maxImagesNumber: 5;

.images-wrapper {
  img {
    position: absolute;
    padding: 5px;
    border: solid black 1px;

  @for $i from $maxImagesNumber through 1 {
    :nth-child(#{ $i }) {
      z-index: #{ $maxImagesNumber - ($i - 1) };
      left: #{ ($i - 1) * 30 }px;

Getting the ID of the element that fired an event

You can use (this) to reference the object that fired the function.

'this' is a DOM element when you are inside of a callback function (in the context of jQuery), for example, being called by the click, each, bind, etc. methods.

Here is where you can learn more:

How can you find out which process is listening on a TCP or UDP port on Windows?

For Windows, if you want to find stuff listening or connected to port 1234, execute the following at the cmd prompt:

netstat -na | find "1234"

Generating (pseudo)random alpha-numeric strings

function generateRandomString($length = 10) {
    $characters = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
    $charactersLength = strlen($characters);
    $randomString = '';
    for ($i = 0; $i < $length; $i++) {
        $randomString .= $characters[rand(0, $charactersLength - 1)];
    return $randomString;
echo generateRandomString();

Select N random elements from a List<T> in C#

From Dragons in the Algorithm, an interpretation in C#:

int k = 10; // items to select
var items = new List<int>(new[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 });
var selected = new List<int>();
double needed = k;
double available = items.Count;
var rand = new Random();
while (selected.Count < k) {
   if( rand.NextDouble() < needed / available ) {

This algorithm will select unique indicies of the items list.

How do you set, clear, and toggle a single bit?

I use macros defined in a header file to handle bit set and clear:

/* a=target variable, b=bit number to act upon 0-n */
#define BIT_SET(a,b) ((a) |= (1ULL<<(b)))
#define BIT_CLEAR(a,b) ((a) &= ~(1ULL<<(b)))
#define BIT_FLIP(a,b) ((a) ^= (1ULL<<(b)))
#define BIT_CHECK(a,b) (!!((a) & (1ULL<<(b))))        // '!!' to make sure this returns 0 or 1

/* x=target variable, y=mask */
#define BITMASK_SET(x,y) ((x) |= (y))
#define BITMASK_CLEAR(x,y) ((x) &= (~(y)))
#define BITMASK_FLIP(x,y) ((x) ^= (y))
#define BITMASK_CHECK_ALL(x,y) (!(~(x) & (y)))
#define BITMASK_CHECK_ANY(x,y) ((x) & (y))

round() doesn't seem to be rounding properly

You can switch the data type to an integer:

>>> n = 5.59
>>> int(n * 10) / 10.0
>>> int(n * 10 + 0.5)

And then display the number by inserting the locale's decimal separator.

However, Jimmy's answer is better.

Objective-C for Windows

You can use Objective C inside the Windows environment. If you follow these steps, it should be working just fine:

  1. Visit the GNUstep website and download GNUstep MSYS Subsystem (MSYS for GNUstep), GNUstep Core (Libraries for GNUstep), and GNUstep Devel
  2. After downloading these files, install in that order, or you will have problems with configuration
  3. Navigate to C:\GNUstep\GNUstep\System\Library\Headers\Foundation1 and ensure that Foundation.h exists
  4. Open up a command prompt and run gcc -v to check that GNUstep MSYS is correctly installed (if you get a file not found error, ensure that the bin folder of GNUstep MSYS is in your PATH)
  5. Use this simple "Hello World" program to test GNUstep's functionality:

    #include <Foundation/Foundation.h>
    int main(void)
        NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
        NSLog(@"Hello World!.");
        [pool drain];
  6. Go back to the command prompt and cd to where you saved the "Hello World" program and then compile it:2

    gcc -o helloworld.exe <HELLOWORLD>.m -I /GNUstep/GNUstep/System/Library/Headers -L /GNUstep/GNUstep/System/Library/Libraries -std=c99 -lobjc -lgnustep-base -fconstant-string-class=NSConstantString
  7. Finally, from the command prompt, type helloworld to run it

All the best, and have fun with Objective-C!


  1. I used the default install path - adjust your command line accordingly
  2. Ensure the folder path of yours is similar to mine, otherwise you will get an error

How do you clear the SQL Server transaction log?

Most answers here so far are assuming you do not actually need the Transaction Log file, however if your database is using the FULL recovery model, and you want to keep your backups in case you need to restore the database, then do not truncate or delete the log file the way many of these answers suggest.

Eliminating the log file (through truncating it, discarding it, erasing it, etc) will break your backup chain, and will prevent you from restoring to any point in time since your last full, differential, or transaction log backup, until the next full or differential backup is made.

From the Microsoft article onBACKUP

We recommend that you never use NO_LOG or TRUNCATE_ONLY to manually truncate the transaction log, because this breaks the log chain. Until the next full or differential database backup, the database is not protected from media failure. Use manual log truncation in only very special circumstances, and create backups of the data immediately.

To avoid that, backup your log file to disk before shrinking it. The syntax would look something like this:

BACKUP LOG MyDatabaseName 
TO DISK='C:\DatabaseBackups\MyDatabaseName_backup_2013_01_31_095212_8797154.trn'

DBCC SHRINKFILE (N'MyDatabaseName_Log', 200)

How to convert a string to a date in sybase

102 is the rule of thumb, convert (varchar, creat_tms, 102) > '2011'

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

You can if your processor is 64-bit and Virtualization Technology (VT) extension is enabled (it can be switched off in BIOS). You can't do it on 32-bit processor.

To check this under Linux you just need to look into /proc/cpuinfo file. Just look for the appropriate flag (vmx for Intel processor or svm for AMD processor)

egrep '(vmx|svm)' /proc/cpuinfo

To check this under Windows you need to use a program like CPU-Z which will display your processor architecture and supported extensions.