include, include_once, require和require_once

include() and require() are identical in every way except how they handle failure.
They both produce a warning, requrie() results in a fatal error.


The
[url=mk:@MSITStore:D:\gelf\学习资料\php\php_manual_en.chm::/en/function.include-once.html]include_once()[/url]
is a behavior similar to the
[url=mk:@MSITStore:D:\gelf\学习资料\php\php_manual_en.chm::/en/function.include.html]include()[/url]
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.

The require_once() is a behavior similar to the require() 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 required just once.