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include_once() bindet eine angegebene Datei ein und führt sie als PHP-Skript aus. Dieses Verhalten ist identisch zu include(), mit dem einzigen Unterschied, dass die Datei, wenn sie bereits eingebunden wurde, nicht erneut eingebunden wird. Wie der Name schon sagt, wird sie nur einmal eingebunden werden.

include_once() kann beispielsweise benutzt werden, wenn die selbe Datei an mehreren Stellen eingebunden wird, um Problemen durch erneute Definitionen von Funktionen, erneute Zuweisung von Variablen oder ähnliches zu vermeiden.

Für die Funktionsweise der Funktion, siehe die Dokumentation zu include().


Mit PHP 4 wird auf Betriebssystemen, die bei Dateinamen nicht zwischen Groß- und Kleinschreibung unterscheiden (wie Windows), bei _once dennoch zwischen Groß- und Kleinschreibung unterschieden, wie das folgende Beispiel zeigt:

Beispiel #1 include_once() mit einem case-insensitive Betriebssystem und PHP 4

include_once "a.php"// a.php wird eingebunden.
include_once "A.php"// a.php wird nochmal eingebunden! (Nur in PHP 4)

Dieses Verhalten hat sich in PHP 5 geändert, so dass zum Beispiel bei Windows der Pfad zuerst normalisiert wird, sodass C:\PROGRA~1\A.php und C:\Program Files\a.php als das selbe erkannt und nur einmal eingebunden werden.

12 BenutzerBeiträge:
- Beiträge aktualisieren...
22.09.2010 7:06
include_once strtolower($phpFile);
Frankbrennanfilms at yahoo dot com
21.09.2010 22:43
Need some help please. I keep getting this error:

can not include
Fatal error: Cannot redeclare get_postdata()

Here's the solution I was told to put in, but it's  not working

if(!@file_exists('deprecated.php') ) {
'can not include';
} else {

 * @
package WordPress
* @subpackage Deprecated
nospam at freeproxylist dot org
31.03.2009 6:51
I would like to share one very useful tip with include_* statements. For example we have two classes first.class.php and second.class.php both located in the same directory (./classes) and first one uses the second one. So we have:

include_once './second.class.php';

also we have file which uses first.class.php:

include_once './classes/first.class.php';

if you will try to execute your script you will get error. Reason: the current directory is different and the relative path in first.class.php (./second.class.php) will be incorrect.

Here is two possible solution I have found:
include_once dirname(__FILE__).'/second.class.php';



Hope that tip will be useful for some other software developer

Admin of
neil at holcomb dot com
7.01.2009 22:42
Using include_once() in the __autoload() function is redundant.  __autoload() is only called when php can't find your class definition.  If your file containg your class was already included, the class defenition would already be loaded and __autoload() would not be called.  So save a little overhead and only use include() within __autoload()

Neil Holcomb
roach dot scott+spam at googlemail dot com
28.06.2008 2:22
If you include a file that does not exist with include_once, the return result will be false.

If you try to include that same file again with include_once the return value will be true.

(include_once 'fakefile.ext'); // bool(false)
var_dump(include_once 'fakefile.ext'); // bool(true)

This is because according to php the file was already included once (even though it does not exist).
emanuele at rogledi dot com
19.05.2008 2:40
For include_once a file in every paths of application we can do simply this

include_once($_SERVER["DOCUMENT_ROOT"] . "mypath/my2ndpath/myfile.php");
php at metagg dot com
9.08.2007 0:29
If you are like me and make heavy use of the __autoload magic function, always set include paths so you can just instantiate your class, and have multiple locations and name schemes for your custom libraries then you might be frustrated by simple parse errors being supressed when using @include_once('lib.php').

The solution I came up with was:


function __autoload($class){

  $paths = array();
  $paths[] = "{$class}_lib.php";
  $paths[] = "{$class}_inc.php";
  $paths[] = "{$class}.php";

    foreach($paths as &$path){
      if((@include_once $path) !== false){ return; }//if
    // we are not in a production environment so we want to see all errors...
    $include_paths = explode(PATH_SEPARATOR,get_include_path());
    foreach($include_paths as $include_path){
      // go through each of the different class names...
      foreach($paths as $path){
        // attach each class name to the include path...
        $include_file = $include_path.$path;
          if((include_once $include_file) !== false){ return; }//if
  trigger_error("{$class} was not found",E_USER_ERROR);

Now, just make sure you define IN_PRODUCTION_ENV to true or false to get either the slower (with all parse errors shown) or the faster (just suppress everything) autoloading. Hope this helps someone else since it was annoying just having blank screens show up when I had a simple parse error. Thanks to flobee at gmail dot com for providing me with the epiphany on why pages were showing up blank...-Metagg
webmaster AT domaene - kempten DOT de
10.08.2006 14:11
Since I like to reuse a lot of code it came handy to me to begin some sort of library that I stored in a subdir
e.g. "lib"

The only thing that bothered me for some time was that although everything worked all IDEs reported during editing
these useless warnings "file not found" when library files included other library files, since my path were given all relative to the corresponding document-root.

Here is a short workaround that makes that gone:

// Change to your path

if(strpos(__FILE__,'/lib/') != FALSE){
include_once (
// ... or any other include[_once] / require[_once]

just adjust the path and it will be fine - also for your IDE.


29.08.2005 10:52
Dealing with function redefinitions

include_once and require_once are very useful if you have a library of common functions.  If you try to override with - that is define - an identically named local function however, PHP will halt noting that it cannot redeclare functions.  You can allow for this by bracketing (within the include file):
function myUsefulFunc($arg1, $arg2) {
     ... }


if (!function_exists('myUsefulFunc')) {
function myUsefulFunc($arg1, $arg2) {
     ... }}

Top level functions (ie. those not defined within other functions or dependent on code running) in the local file are always parsed first, so within the included/required file is safe - it doesn't matter where the include statements are in the local code.

Csaba Gabor from Vienna
flobee at gmail dot com
26.05.2005 16:55
i already had a discussion with several people about "not shown errors"
error reporting and all others in php.ini set to: "show errors" to find problems:
the answer i finally found:
if you have an "@include..." instead of "include..." or "require..('somthing') in any place in your code
all following errors are not shown too!!!

so, this is actually a bad idea when developing because paser errors will be droped too:
if(!@include_once('./somthing') ) {
'can not include';

if(!@file_exists('./somthing') ) {
'can not include';
} else {
17.03.2005 23:17
Inlude_once can slower your app, if you include to many files.

You cann use this wrapper class, it is faster than include_once


bioster at peri dot csclub dot uwaterloo dot ca
29.10.2004 0:06
Something to be wary of:  When you use include_once and the data that you include falls out of scope, if you use include_once again later it will not include despite the fact that what you included is no longer available.

So you should be wary of using include_once inside functions.

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