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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.
Example:
<?php
var_dump(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).
include_once()
A instrução include_once() inclui e avalia o arquivo especificado durante a execução de um script. Seu comportamento é similar a instrução include(), a não ser que o arquivo informado já tenha sido incluído, não refazendo a operação novamente. Como o nome sugere, ele será incluído apenas uma vez.
include_once() pode ser utilizado nos casos em que o mesmo arquivo pode acabar sendo incluído mais de uma vez durante a execução de um script em particular, quando na verdade ele só pode ser incluído apenas uma para evitar problemas com redefinições de funções, alterações nos valores de variáveis, etc.
Para maiores informações utilizando require_once() e include_once(), veja o código do » PEAR incluído nas últimas distribuições do código fonte do PHP.
Nota: include_once() foi acrescentado a partir PHP 4.0.1
Nota: Esteja avisado que o comportamento de include_once() e require_once() pode não ser o que você espera em um sistema operacional insensitivo ao caso (como o Windows).
Este funcionamento mudou no PHP 5 - o caminho é normalizado primeiro, assim C:\PROGRA~1\A.php é realizado como o mesmo que C:\Program Files\a.php e o arquivo é incluído apenas uma vez.Exemplo #1 include_once() não diferencia maiúsculas e minuúsculas no Windows
<?php
include_once "a.php"; // isto irá incluir a.php
include_once "A.php"; // isto irá incluir a.php novamente no Windows! (Apenas PHP 4)
?>
Aviso
A versões Windows do PHP anteriores ao PHP 4.3.0 não suportam acesso a arquivos remotos através desta função, mesmo se allow_url_fopen estiver ativado.
Veja também: include(), require(), require_once(), get_required_files(), get_included_files(), readfile() e virtual().
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User Contributed Notesinclude_once
roach dot scott+spam at googlemail dot com
27-Jun-2008 05:22
27-Jun-2008 05:22
emanuele at rogledi dot com
18-May-2008 05:40
18-May-2008 05:40
For include_once a file in every paths of application we can do simply this
include_once($_SERVER["DOCUMENT_ROOT"] . "mypath/my2ndpath/myfile.php");
php at metagg dot com
08-Aug-2007 03:29
08-Aug-2007 03:29
If you are like me and make heavy use of the __autoload magic function, always set include paths so you can just instantiate your class, and have multiple locations and name schemes for your custom libraries then you might be frustrated by simple parse errors being supressed when using @include_once('lib.php').
The solution I came up with was:
define('IN_PRODUCTION_ENV',FALSE);
function __autoload($class){
$paths = array();
$paths[] = "{$class}_lib.php";
$paths[] = "{$class}_inc.php";
$paths[] = "{$class}.php";
if(IN_PRODUCTION_ENV){
foreach($paths as &$path){
if((@include_once $path) !== false){ return; }//if
}//foreach
}else{
// 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(file_exists($include_file)){
if((include_once $include_file) !== false){ return; }//if
}//if
}//foreach
}//foreach
}//if/else
trigger_error("{$class} was not found",E_USER_ERROR);
}//method
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-Aug-2006 05:11
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
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
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
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.