There still seems to be some confusion surrounding these rather simple functions. So here is a quick explanation.
Include()
The include function simply includes a file, and that is all. If the file isn’t found a warning is raised, but the script will continue to execute.
Require()
Require has very similar functionality to include(). However, if a file is not found a warning will be raised and the script will halt completely.
Include_Once() and Require_Once()
You should use these functions if you do not want to include a file multiple times (which can cause errors with functions and classes).
e.g.
file1.php includes file2.php and file3.php.
file2.php also includes file3.php
Without the _once() functions file3 will be included twice, but with the _once() function it will only be included once.
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April 5th, 2007 at 4:49 pm
I was just adding an rss feed with magpie (something I’ve done several times), and was wondering why they used require_once() in one of their examples. Thanks very much for this clear, and to the point explanation of something that I’ve been meaning to learn for a while now.
April 5th, 2007 at 6:33 pm
Good to hear it helped you out, if you need help with anything else feel free to contact me.
By the way: you have a nice site
August 10th, 2008 at 7:15 pm
Are there different memory consumptions for these 4 different techniques? If there is a “most efficient” method of including I would rely on that more often….
August 10th, 2008 at 7:53 pm
I haven’t looked at the memory footprint - but I’d assume include and require use virtually the same amount of memory. The only the extra thing require does is halt the script - but that is only executed if the “if a warning is generated” if statement is triggered in the function itself. Without a doubt the _once functions are the least efficient in almost every way.
August 23rd, 2008 at 4:17 am
Here are execution times and memory consumption…
http://www.raditha.com/wiki/Readfile_vs_include
August 23rd, 2008 at 9:50 am
Hi, thanks for the list, however I must disagree with it completely.
For starters the benchmark does not accommodate the fact that require_once really shows it’s sluggishness when you use it all the time - which many people do. Anyone who has done php work for more than a few years knows what I mean when I say if you use any of the _once constructs more than a few times per script it becomes sluggish - much more than the .00003 second difference that be benchmark claims.
For example, here’s the results before/after wikia switched from include_once/require_once to include/require:
http://www.techyouruniverse.com/include_test/ab_output.txt
I’ll run some tests later today and publish my results.