What are the require_ once and include_ once in PHP?

[DANIEL 602]

Hello everyone,
I have done some basic things in PHP programming language. I am newly started this language, so I don't have much knowledge about it. I want to know when to use require_ once statement and include_ once statement in PHP coding. I don't know anything about it, so it would be better if you explain me in detail. Please tell me what are the require_ once and include_ once in PHP? Help me soon.!!

[MELTRONICS]

The statement require_once () is identical to require () apart from that PHP checks if the file was already included and if so, do not include a second time. The include_once () statement includes and evaluates the specified file during script execution. The behavior is similar to include (), but the difference is that if the code has already been included, it will not be a second time. Hope that you know about the include() and require().

[Solitario]

To include/require a whole folder of classes can be stripped down to a one-liner :

<?php 
array_walk(glob('./lib/*.class.php'),
create_function('$v,$i', 'return require_once($v);')); 
?>

If you get "failed to open stream" although you are sure your include_path is correct, check your open_basedir setting.

[Deabelos]

When using absolute_path there are fewer stat() system calls. When using relative_path there are more stat() system calls because it has to start from the current directory back up to / and then to the include/ directory. So I would like to suggest you to try to use absolute_path when calling require(). The time difference between require_once() vs. require() is so tiny, it's almost always insignificant in terms of performance. The one exception is if you have a very large application that has hundreds of require() calls.

[Katty]

The include_once () is used in cases where the file will be included and evaluated more than once in a script, or if you want to be sure that it is included only once to avoid redefinitions of functions or classes. The language of instruction include () statement includes and evaluates the specified file. The files are included following the file path provided, if none is provided, the include_path will be verified. The language of instruction include () will issue a warning if it does not find a file while the language of instruction require () will issue a fatal error in the same case.

[kelfro]

I think that using the include_once() in the __autoload() function is redundant. When the PHP is not able to find your class definition, then autoload() must be called. If your file containg your class was already included, the class defenition would already be loaded and autoload() would not be called. So by using the include() within autoload(), you can decrease a little overhead. 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.