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.
注: include_once() was added in PHP 4.0.1pl2
注: 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).
範例 12-9. include_once() is case sensitive
include_once("a.php"); // this will include a.php include_once("A.php"); // this will include a.php again on Windows!
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See also include(),
require(), require_once(),
get_required_files(),
get_included_files(),
readfile(), and virtual().