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.
Note: include_once() was added in PHP 4.0.1pl2
Note: 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).
Example 11-9. 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!
?>
| Warning |
Windows versions of PHP prior to PHP 4.3.0 do not support accessing remote files via this function, even if allow_url_fopen is enabled. |
See also include(), require(), require_once(), get_required_files(), get_included_files(), readfile(), and virtual().
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