include_once()

La funciÃ³n include_once() incluye y evalua el fichero especificado durante la ejecuciÃ³n del script. Se comporta de manera similar a include(), con la Ãºnica diferencia que si el cÃ³digo ha sido ya incluido, no se volverÃ¡ a incluir.

include_once() deberÃa de usarse en casos en los que, un mismo fichero puede ser incluido y evaluado mÃ¡s de una vez durante la ejecuciÃ³n de un script, y se quiere estar seguro que se incluye una sola vez para evitar problemas con redefiniciones de funciones, valores de funciones, etc.

Para consultar ejemplos que usen include_once() e require_once(), ver el cÃ³digo de PEAR incluido con las Ãºltimas versiones de PHP.

Nota: include_once() fue incorporado en PHP 4.0.1pl2

Nota: El comportamiento de de include_once() y require_once() puede que no sea el esperado en sistemas operativos en los que mayÃºsculas y minÃºsculas se traten igual (como en Windows)
Ejemplo 16-9. Con include_once() no importan las mayÃºsculas y minÃºsculas en Windows

<?php include_once("a.php"); // this will include a.php include_once("A.php"); // this will include a.php again on Windows! ?>

Aviso

Versiones de PHP para Windows anteriores a 4.3.0, no soportan el acceso remoto a archivos para esta funciÃ³n, no funcionarÃ¡ ni activando siquiera allow_url_fopen.

Ver tambiÃ©n include(), require(), require_once(), get_required_files(), get_included_files(), readfile(), y virtual().

add a note User Contributed Notes
include_once

webmaster AT domaene - kempten DOT de
10-Aug-2006 05:11


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:



<?php

// Change to your path



if(strpos(__FILE__,'/lib/') != FALSE){

    chdir("..");

}

include_once ('./lib/other_lib.inc');

// ... or any other include[_once] / require[_once]

?>



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



greetings

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.

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MANUAL DE PHP

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include_once()