There are two ways to do this.  The first is to specify the header in your php code.  This is great if you want to programatically adjust the expiry time.  For example a wiki could set a longer expires time for a page which is not edited very often.  

    header(&#39;Expires: &#39;.gmdate(&#39;D, d M Y H:i:s \G\M\T&#39;, time() + (60 * 60))); // 1 hour

Your second choice is to create an **.htaccess** file or modify your httpd config.  In a shared hosting environment, modifying your .htaccess file is quite common.  In order to do this, you need to know if your server supports **mod\_expires**, **mod\_headers** or both.  The easiest way is simply trial and error, but some Apache servers are configured to let you view this information via the /server-info page.  If your server has both mod\_expires and mod\_headers, and you want to set the expiry on static resources, try putting this in your .htaccess file:

    # Turn on Expires and set default to 0
    ExpiresActive On
    ExpiresDefault A0
 
    # Set up caching on media files for 1 year (forever?)
    &lt;FilesMatch &quot;\.(flv|ico|pdf|avi|mov|ppt|doc|mp3|wmv|wav)$&quot;&gt;
    ExpiresDefault A29030400
    Header append Cache-Control &quot;public&quot;
    &lt;/FilesMatch&gt;

For other combinations and more examples see: http://www.askapache.com/htaccess/speed-up-your-site-with-caching-and-cache-control.html



This Apache module might be of help:
http://httpd.apache.org/docs/2.0/mod/mod_expires.html

Did you try something like?

    &lt;?php
    header(&quot;Expires: Sat, 26 Jul 1997 05:00:00 GMT&quot;);
    ?&gt;

I was looking at the `www.google.com` in Firebug and noticed something odd: The Google logo is centered using a center tag.

So I went and checked the page with the [W3C validator][1] and it found 48 errors. Now, I know there are times when you can&#39;t make a page valid, especially when we&#39;re talking about something like `www.google.com` and you want it to be as small as possible, but can someone please explain why they use the center tag? 

[1]: http://validator.w3.org/check?uri=http://www.google.com/&amp;charset=(detect+automatically)&amp;doctype=Inline&amp;group=0

Why does the Google homepage use deprecated HTML (ie. is not valid HTML5)?

I have a table with three fields, FirstName, LastName and Email.

Here&#39;s some dummy data:

    FirstName | LastName | Email
    Adam        West       adam@west.com
    Joe         Schmoe     NULL

Now, if I do:

    SELECT CONCAT(FirstName, LastName, Email) as Vitals FROM MEMBERS

Vitals for Joe is null, as there is a single null field. How do you overcome this behaviour? Also, is this the default behaviour in MS SQL Server?



CONCAT&#39;ing NULL fields

How can I setup expires headers in PHP + Apache? I&#39;m currently using an auto_prepend to serve resources gzipped but I&#39;d also like to maximise the HTTP cache.

How can I set these up?

Setup HTTP expires headers using PHP and Apache

<p>How can I setup expires headers in PHP + Apache? I'm currently using an auto_prepend to serve resources gzipped but I'd also like to maximise the HTTP cache.</p>
<p>How can I set these up?</p>


How to clear browser cache with php?

How to call a JavaScript function from PHP?

    &lt;?php
    
      jsfunction();
      // or
      echo(jsfunction());
      // or
      // Anything else?

The following code is from *xyz.html* (on a button click) it calls a `wait()` in an external *xyz.js*. This `wait()` calls wait.php.

    function wait() 
    {
      xmlhttp=GetXmlHttpObject();
      var url=&quot;wait.php&quot;; \
      xmlhttp.onreadystatechange=statechanged; 
      xmlhttp.open(&quot;GET&quot;, url, true); 
      xmlhttp.send(null);
    } 
    
    function statechanged()
    { 
      if(xmlhttp.readyState==4) {
           document.getElementById(&quot;txt&quot;).innerHTML=xmlhttp.responseText;
      }
    }

and *wait.php*

    &lt;?php echo &quot;&lt;script&gt; loadxml(); &lt;/script&gt;&quot;; 

where `loadxml()` calls code from another PHP file the same way. 

The `loadxml()` is working fine otherwise, but it is not being called the way I want it.

How to call a JavaScript function from PHP?

What type of hash does WordPress use?  
Here is an example of a WordPress hash: 

&gt; $P$Bp.ZDNMM98mGNxCtHSkc1DqdRPXeoR.

What type of hash does WordPress use?

When I open a MySQL connection in PHP with just PHP&#39;s built-in MySQL functions, I do the following:

    $link = mysql_connect($servername, $username, $password);
    mysql_select_db($dbname);
    //queries etcetera
    mysql_close($link);

When I open a connection with PDO, it looks like this:

    $link = new PDO(&quot;mysql:dbname=$dbname;host=$servername&quot;,$username,$password);
    //prepare statements, perform queries

Do I have to explicitly close the connection like I do with `mysql_connect()` and `mysql_close()`?  If not, how does PHP know when I&#39;m done with my connection?

TIA.

Do SQL connections opened with PDO in PHP have to be closed

I have checked my PHP ini file (`php.ini`) and `display_errors` is set and also error reporting is `E_ALL`. I have restarted my Apache webserver.

I have even put these lines at the top of my script, and it doesn&#39;t even catch simple parse errors. For example, I declare variables with a `&quot;$&quot;` and I don&#39;t close statements` &quot;;&quot;`. But all my scripts show a blank page on these errors, but I want to actually see the **errors** in my browser output. 

```
error_reporting(E_ALL);
ini_set(&#39;display_errors&#39;, 1);
```

What is left to do?



How do I get PHP errors to display?

I don&#39;t know if this is true, but when I was reading FAQ on one of the problem providing sites, I found something, that poke my attention:

&gt; Check your input/output methods. In C++, using cin and cout is too slow. Use these, and you will guarantee not being able to solve any problem with a decent amount of input or output. Use printf and scanf instead.

Can someone please clarify this? Is really using *scanf()* in C++ programs faster than using *cin &gt;&gt; something* ? If yes, that is it a good practice to use it in C++ programs? I thought that it was C specific, though I am just learning C++...

Using scanf() in C++ programs is faster than using cin?

Given these two commands

A:

    $ java -Xms10G -Xmx10G myjavacode input.txt

B:

    $ java -Xms5G -Xmx5G myjavacode input.txt

I have two questions:

 1. Since command A reserves more memory with its parameters, will A run faster than B? 
 2. How do `-Xmx` and `-Xms` affect the running process and the output of my program?

Speed tradeoff of Java&#39;s -Xms and -Xmx options

What is a good random number generator to use for a game in C++?

My considerations are:

1. Lots of random numbers are needed, so speed is good.
2. Players will always complain about random numbers, but I&#39;d like to be able to point them to a reference that explains that I really did my job. 
3. Since this is a commercial project which I don&#39;t have much time for, it would be nice if the algorithm either a) was relatively easy to implement or b) had a good non-GPL implementation available.
4. I&#39;m already using `rand()` in quite a lot of places, so any other generator had better be good to justify all the changes it would require.

I don&#39;t know much about this subject, so the only alternative I could come up with is the [Mersenne Twister][1]; does it satisfy all these requirements? Is there anything else that&#39;s better?

**Edit:** Mersenne Twister seems to be the consensus choice. But what about point #4? Is it really that much better than `rand()`?

**Edit 2:** Let me be a little clearer on point 2: There is no way for players to cheat by knowing the random numbers. Period. I want it random enough that people (at least those who understand randomness) can&#39;t complain about it, but I&#39;m not worried about predictions. 
That&#39;s why I put speed as the top consideration.

**Edit 3:** I&#39;m leaning toward the Marsaglia RNGs now, but I&#39;d still like more input. Therefore, I&#39;m setting up a bounty.

**Edit 4:** Just a note: I intend to accept an answer just before midnight UTC today (to avoid messing with someone&#39;s rep cap). So if you&#39;re thinking of answering, don&#39;t wait until the last minute!  
Also, I like the looks of Marsaglia&#39;s XORshift generators. Does anyone have any input about them?

  [1]: http://en.wikipedia.org/wiki/Mersenne_Twister

What is a good random number generator for a game?

Quite often on SO I find myself benchmarking small chunks of code to see which implemnetation is fastest. 

Quite often I see comments that benchmarking code does not take into account jitting or the garbage collector. 

I have the following simple benchmarking function which I have slowly evolved: 

      static void Profile(string description, int iterations, Action func) {
            // warm up 
            func();
            // clean up
            GC.Collect();

            var watch = new Stopwatch();
            watch.Start();
            for (int i = 0; i &lt; iterations; i++) {
                func();
            }
            watch.Stop();
            Console.Write(description);
            Console.WriteLine(&quot; Time Elapsed {0} ms&quot;, watch.ElapsedMilliseconds);
        }

Usage: 

    Profile(&quot;a descriptions&quot;, how_many_iterations_to_run, () =&gt;
    {
       // ... code being profiled
    });


Does this implementation have any flaws? Is it good enough to show that implementaion X is faster than implementation Y over Z iterations? Can you think of any ways you would improve this? 

**EDIT**
Its pretty clear that a time based approach (as opposed to iterations), is preferred, does anyone have any implementations where the time checks do not impact performance? 


Benchmarking small code samples in C#, can this implementation be improved?

Does anyone with experience with these libraries have any comment on which one they preferred? Were there any performance differences or difficulties in using?

boost serialization vs google protocol buffers?

What are the advantages and disadvantages of using `mod_jk` and `mod_proxy` for fronting a tomcat instance with apache?

I&#39;ve been using mod_jk in production for years but I&#39;ve heard that it&#39;s &quot;the old way&quot; of fronting tomcat. Should I consider changing? Would there be any benefits?

apache to tomcat: mod_jk vs mod_proxy

I have a website that doesn&#39;t seem to redirect from non-www to www.
  
*My Apache configuration is as follows:*

    RewriteEngine On
    ### re-direct to www
    RewriteCond %{http_host} !^www.example.com [nc]
    RewriteRule ^(.*)$ http://www.example.com/$1 [r=301,nc] 

What am I missing?


apache redirect from non www to www

I&#39;m making a website which allows people to upload files, html pages, etc... Now I&#39;m having a problem. I have a directory structure like this:

    -/USERS
        -/DEMO1
        -/DEMO2
        -/DEMO3
        -/etc... (every user has his own direcory here)
    -index.php
    -control_panel.php
    -.htaccess

Now I want to disable PHP, but enable Server-side includes in the direcories and subdirectories inside /USERS

Can this be done (and how :) )? Thanks in advance.

BTW, I use WAMP server

Disable PHP in directory (including all sub-directories) with .htaccess

I am trying to run a process on a web page that will return its output in realtime. For example if I run &#39;ping&#39; process it should update my page every time it returns a new line (right now, when I use exec(command, output) I am forced to use -c option and wait until process finishes to see the output on my web page). Is it possible to do this in php?

I am also wondering what is a correct way to kill this kind of process when someone is leaving the page. In case of &#39;ping&#39; process I am still able to see the process running in the system monitor (what makes sense).


Run process with realtime output in PHP

What is the maximum length of a URL in apache? Where is it documented, and is it configurable?

I&#39;m implementing an openid identity provider, and would like to know the limitations I&#39;m up against. I know about the 2048 byte path limit on Internet Explorer. That can be handled specially using user agent detection. Other browsers have much higher URL limits. 

So what I&#39;m interested in is apache server limits when coding an application. 

What is apache&#39;s maximum url length?

For example in HTTP you send a request and receive a response; is there a noun that describes that request-response pair?

I&#39;d thought of &quot;dialog&quot; or &quot;conversation&quot; however those imply multiple request-response pairs, whereas I&#39;m looking for a word that indicates exactly one.

The reason for asking is that I need to name an object which encapsulates the details of both, and `RequestResponse` seems fairly lame.

What is a request-response pair called?

Use case: user clicks the link on a webpage - boom! load of files sitting in his folder.&lt;br&gt;
I tried to pack files using [multipart/mixed message][1], but it seems to work only for Firefox

This is how my response looks like:

    HTTP/1.0 200 OK
    Connection: close
    Date: Wed, 24 Jun 2009 23:41:40 GMT
    Content-Type: multipart/mixed;boundary=AMZ90RFX875LKMFasdf09DDFF3
    Client-Date: Wed, 24 Jun 2009 23:41:40 GMT
    Client-Peer: 127.0.0.1:3000
    Client-Response-Num: 1
    MIME-Version: 1.0
    Status: 200

    --AMZ90RFX875LKMFasdf09DDFF3 
    Content-type: image/jpeg 
    Content-transfer-encoding: binary 
    Content-disposition: attachment; filename=&quot;001.jpg&quot; 
    
    &lt;&lt; here goes binary data &gt;&gt;--AMZ90RFX875LKMFasdf09DDFF3 
    Content-type: image/jpeg 
    Content-transfer-encoding: binary 
    Content-disposition: attachment; filename=&quot;002.jpg&quot; 
    
    &lt;&lt; here goes binary data &gt;&gt;--AMZ90RFX875LKMFasdf09DDFF3 
    --AMZ90RFX875LKMFasdf09DDFF3--

Thank you&lt;br&gt;

P.S. No, zipping files is not an option

  [1]: http://en.wikipedia.org/wiki/MIME#Multipart_subtypes

How to download multiple files with one HTTP request?

The header `Cache-Control: max-age=0` implies that the content is considered stale (and must be re-fetched) immediately, which is in effect the same thing as `Cache-Control: no-cache`.

What&#39;s the difference between Cache-Control: max-age=0 and no-cache?

Given a URL in a string:

    http://www.example.com/test.xml

What&#39;s the easiest/most succinct way to download the contents of the file from the server (pointed to by the url) into a string in C#?

The way I&#39;m doing it at the moment is:

    WebRequest request = WebRequest.Create(&quot;http://www.example.com/test.xml&quot;);
    WebResponse response = request.GetResponse();
    Stream dataStream = response.GetResponseStream();
    StreamReader reader = new StreamReader(dataStream);
    string responseFromServer = reader.ReadToEnd();

That&#39;s a lot of code that could essentially be one line:

    string responseFromServer = ????.GetStringFromUrl(&quot;http://www.example.com/test.xml&quot;);

Note: I&#39;m not worried about asynchronous calls - this is not production code.



Easiest way to read from a URL into a string in .NET

Due to weird domain/subdomain cookie issues that I&#39;m getting, I&#39;d like to know how browsers handle cookies. If they do it in different ways, it would also be nice to know the differences.

In other words - when a browser receives a cookie, that cookie MAY have a domain and a path attached to it. Or not, in which case the browser probably substitutes some defaults for them. Question 1: what are they?

Later, when the browser is about to make a request, it checks its cookies and filters out the ones it should send for that request. It does so by matching them against the requests path and domain. Question 2: what are the matching rules?
&lt;hr/&gt;
**Added:**

The reason I&#39;m asking this is because I&#39;m interested in some edge cases. Like:

 * Will a cookie for `.example.com` be available for `www.example.com`?
 * Will a cookie for `.example.com` be available for `example.com`?
 * Will a cookie for `example.com` be available for `www.example.com`?
 * Will a cookie for `example.com` be available for `anotherexample.com`?
 * Will `www.example.com` be able to set cookie for `example.com`?
 * Will `www.example.com` be able to set cookie for `www2.example.com`?
 * Will `www.example.com` be able to set cookie for `.com`?
 * Etc.

**Added 2:**

Also, could someone suggest how I should set a cookie so that:

 * It can be set by either `www.example.com` or `example.com`;
 * It is accessible by both `www.example.com` and `example.com`.

Content Type	Original Author	Original Content on Stackoverflow
Question	Tom	View Question on Stackoverflow
Solution 1 - Php	brianegge	View Answer on Stackoverflow
Solution 2 - Php	middus	View Answer on Stackoverflow
Solution 3 - Php	acemtp	View Answer on Stackoverflow

Setup HTTP expires headers using PHP and Apache

Php Problem Overview

Php Solutions

Solution 1 - Php

Solution 2 - Php

Solution 3 - Php

CONCAT'ing NULL fields

Why does the Google homepage use deprecated HTML (ie. is not valid HTML5)?

Attributions