Include, include_once, require

[wombax]

Hey there

Could anyone please explain to me the differences, advantages, and disadvantages of the functions include(), require() and include_once(). I plan to "include" 2 files onto all the pages of my site - one containing simple functions and one containing configuration variables (database names/passwords, error email, that sort of thing) for the site.

Which finction(s) should i use for each file and why?

Thanks in advance!

--ben

[tomhath]

The manual has pretty good discussion of them all. All of what follows is taken right out of the php manual, available as a free download:

... in an inclusion chain, the use of require_once() will assure that the code is added to your script only once, and avoid clashes with variable values or function names that can happen

Unlike include(), require() will always read in the target file, even if the line it's on never executes. If you want to conditionally include a file, use include(). The conditional statement won't affect the require(). However, if the line on which the require() occurs is not executed, neither will any of the code in the target file be executed.

Similarly, looping structures do not affect the behaviour of require(). Although the code contained in the target file is still subject to the loop, the require() itself happens only once.

This means that you can't put a require() statement inside of a loop structure and expect it to include the contents of a different file on each iteration. To do that, use an include() statement.