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  <=> operator in MySQL


Have you ever seen "<=>" in a SQL query while using MySQL? Does it mean less and equals to and greater than? Actually if you consider it as the union of <= and =>, great, you are close to it. This is one form of equal operator in MySQL, it has the similar meaning to the = operator with some subtle difference. According to MySQL documentation, <=> is NULL-safe equal. This operator performs an equality comparison like the = operator, but returns 1 rather than NULL if both operand...

   MySQL,NULL safe,<=>     2014-03-24 06:23:22


  A Perl Regular Expression That Matches Prime Numbers


perl -lne '(1x$_) =~ /^1?$|^(11+?)\1+$/ || print "$_ is prime"' Can you figure out how it works? I give an explanation below, but try to figure it out yourself. Here is what happens when you run it: $ perl -lne '(1x$_) =~ /^1?$|^(11+?)\1+$/ || print "$_ is prime"' 1 2 2 is prime 3 3 is prime 4 5 5 is prime 6 7 7 is prime 8 9 10 11 11 is prime Here is how it works. First, the number is converted in its unary representation by (1x$_). For example, the number 5 gets converted into 1x5, which is ...

   Perl,Regex,Regular expression,Prime number,One line     2011-12-26 08:42:00


  C/C++ Pointer Declaration Syntax – It makes sense!


I never really liked the way pointers are declared in C/C++: int *a, *b, *c; // a, b and c are pointers to int The reason is that I am used to reading variable declarations as MyType myVar1, myVar2, myVar3; and I always read “int*” as the type “integer pointer”. I therefore wanted the following int* a, b, c; // a is a pointer to int, b and c are ints to mean that a, b and c all were of type int*, i.e. pointers to int. and I therefore found it slightly annoying to repea...

   C,Pointer,Declaration,Attempt     2012-02-22 05:43:58


  Paint messages will come in as fast as you let them


There is a class of messages which are generated on demand rather than explicitly posted into a message queue. If you call Get­Message or Peek­Message and the queue is empty, then the window manager will look to see if one of these generated-on-demand messages is due, messages like WM_TIMER, WM_MOUSE­MOVE, and WM_PAINT. Neil wonders, "In that program that called Invalidate­Rect 100,000 times, how many paint messages were generated?" The Zen answer to this question is "Yes." A more pra...

   WM_PAINT,paint message,work,Mouse move     2011-12-21 09:37:14


  A Javascript When Function


function when(conditionFunc, execFunc, interval){ if (conditionFunc()){ execFunc(); }else{ setTimeout(function(){ when(conditionFunc, execFunc, interval);}, interval); } } You have some code which should only execute when a condition is true. E.g. You have code which relies on a javascript library but can't be sure the library has loaded yet and don't want the code to execute until it has. This is common if you have a bookmarklet which injects more than one <...

   JavaScript,When,Implementation,When function     2012-02-24 05:08:34


  Turn browser into notepad with one line of code


This is the code shared by Jose on codewall. When you type data:text/html,   into the address bar of the browser and press enter, the browser will turn into a notepad which you can edit. Why it works? This uses Data URI’s format and it tells the browser to render HTML. But contenteditable is a property of HTML5, so this can only work in the web browser which supports this property. Here are some interesting contents. Some people make some changes to the code encouraged by the ide...

   HTML5, Browser editor     2013-01-30 04:20:54


  Bing now supports code search


In programmer's daily life, much time is spent on searching Google or StackOverflow for code snippets which can help them understand how the code works. Now there is one more option. Microsoft's Bing now adds a new feature which support code snippet search. With this new feature, you can search code snippet and execute them directly within the search results. For example, if you type "quick sort java", you will see below search result : This feature now supports a few popular programming langua...

   BING,CODE SEARCH,HACKERRANK     2016-04-09 02:49:25


  Error handling style in C


Following are three error handling styles in C.Which one you like the most? Or you don't like any one?1. /* Problem : Not enough. Easy to be wrong */int foo(int bar){        int return_value = 0;        int doing_okay = 1;        doing_okay = do_something( bar );        if (doing_okay)        { ...

   C,Error handling style,Goto,Nested if     2012-04-24 06:51:00


  2013 Google Code Jam is around the corner


According to Google Code Jam, the registration time of Google Code Jam 2013 will start on 12th March, and the deadline for registration will be 14th April 00:00UTC. This year the champion will get $15,000. Besides the prize and title, the champion will be enrolled in the qualification round in 2014 directly. Since 2003, Google Code Jam attracted many professional and students to solve the hardest algorithm problems in the world. Last year, there were over 35000 programmers participated in this c...

   Google,Code Jam 2013     2013-03-13 05:48:24


  Why you should be careful about optimizations


In one of my current javascript projects, I have to deal with 3D voxel coordinates. And, sometimes, I have floating points coordinates which must be converted to integers in order to convert them into proper array index. Javascript is a wonderful language, really. However, implementations are sometimes weird, and the way to do something can sometimes have very huge impacts on the performances. Worse, sometimes the classical way is more expensive than the tricky one. So, some peo...

   JavaScript,Bitwise,Floor,Trick,Optimization     2012-05-02 11:29:20