include_once()

The include_once() statement includes and evaluates the specified file during the execution of the script. This is a behavior similar to the include() statement, with the only difference being that if the code from a file has already been included, it will not be included again. As the name suggests, it will be included just once.

include_once() should be used in cases where the same file might be included and evaluated more than once during a particular execution of a script, and you want to be sure that it is included exactly once to avoid problems with function redefinitions, variable value reassignments, etc.

For more examples on using require_once() and include_once(), look at the PEAR code included in the latest PHP source code distributions.

Return values are the same as with include(). If the file was already included, this function returns TRUE

Замечание: include_once() was added in PHP 4.0.1pl2

Замечание: Be aware, that the behaviour of include_once() and require_once() may not be what you expect on a non case sensitive operating system (such as Windows).
Пример 16-13. include_once() is case insensitive on Windows

<?php include_once("a.php"); // this will include a.php include_once("A.php"); // this will include a.php again on Windows! (PHP 4 only) ?>
This behaviour changed in PHP 5 - the path is normalized first so that C:\PROGRA~1\A.php is realized the same as C:\Program Files\a.php and the file is included just once.

Внимание

Версии PHP для Windows до PHP 4.3.0 не поддерживают возможность использования удаленных файлов этой функцией даже в том случае, если опция allow_url_fopen включена.

include_once

29-Aug-2005 01:52


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) {

     ... }



with



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 http://php.net/function_exists 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-May-2005 07:55


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:

<?php

if(!@include_once('./somthing') ) {

    echo 'can not include';

}

?>



solution:

<?php

if(!@file_exists('./somthing') ) {

    echo 'can not include';

} else {

   include('./something');

}

?>

Pure-PHP
17-Mar-2005 02:17


Inlude_once can slower your app, if you include to many files.



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



http://www.pure-php.de/node/19



include_once("includeWrapper.class.php")



includeWrapper::includeOnce("Class1.class.php");

includeWrapper::requireOnce("Class1.class.php");

includeWrapper::includeOnce("Class2.class.php")

bioster at peri dot csclub dot uwaterloo dot ca
28-Oct-2004 03:06


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.