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Does anyone here know when PHP executes include and include_once calls?

I'm wondering because I come from a Flash and Desktop development background where you have to import your classes at the beginning of each class.

But now that I am starting to build more complex PHP code, it seems like it would be better to just include classes when I actually need them to save on loading time. For example, look at the following psuedo code:

if (I_need_to_check_login)
 { 
   include_once "Class.class.php";
   $C = new Class();
 }

If I do this, is the file Class.class.php going to be included everytime the code is run or only when I execute the include_once.

I'm a bit of a Class freak and usually build a class for just about any functionality used by my apps, so I often have lots of class files.

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    You may want to look into an autoloader strategy. It's more efficient than using include_once/require_once and simplifies your code Commented Aug 26, 2011 at 1:14

4 Answers 4

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include, include_once are standard PHP instructions. This means the interpreter executes each include, include_once when he finds one in the flow of the program. If a control structure avoids to execute a piece of code which has an include instruction, this one won't be executed.

In your example, the include_once, will be executed if, and only if, I_need_to_check_login is true.

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4

Includes are only performed if interpreter ever gets there. eg:

$variable = false;
if ($variable) {
    include 'a.php';
} else {
    include 'b.php';
}

In this case only b.php would be included.

For more on its behavior: PHP Manual - include

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4 Comments

Sorry, based on what section of the manual page is it stated that the code will be included conditionally at runtime? It certainly get executed conditionally, but as I stated below in my comment, it can easily be proven that php parses files that aren't executed.
@gview No, and you are demonstrably wrong. See this and this; it's the same script - but you get to pick which file to include. In the first case everything works fine. In the 2nd case, it tries to include a file that has a syntax error in it, and fails upon including it - entirely contradicting what you said in your comment.
Yes, I was wrong on this -- my test case had a silly error in it. The manual page does not contain anything about this that I could find however, but I understand that is not why you included a link to it.
@gview I believe it's somewhere in the manual but I can't find it right now.
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Yes, every time you have to call: $C = new Class(); you will have to require or include the file. Now what you can do instead of include_once is:

if (!class_exists('MyClass')) {
    include("Class.class.php");
}

which mean you might not have you include it again, if you already included it before. This will also improve performance since include is faster to execute than include_once.

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2 Comments

what's wrong with using include_once with class_exists check?
class_exists will check if the class is already loaded (for example you already included it in other files) - now include_once will have to check your code if he already included the file. Read stackoverflow.com/questions/4326435/… for more info. (I recommend to run an STRACE to see how it's working).
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Files are actually included only if you perform include_once command.

So if that I_need_to_check_login evaluates to false - file will not be included at all

It can be easily checked by yourself with adding echo "I've been included"; exit; to the first line of that file.

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5 Comments

include_once simply does a check to see if the target file has already been included. Otherwise it will simply load the source again, and depending on the contents this could be a problem.
@gview: correct, but what did you try to say to me? The question I answered is "If I do this, is the file Class.class.php going to be included everytime the code is run or only when I execute the include_once." and the short answer is "it runs only when include_once is executed". Cannot get how it is related to your notice.
what I'm saying is that the way I read your response, I believe your answer is incorrect. There are many things that can be included but not executed. If i have an include file that declares a bunch of functions that aren't used, they are included, but not executed.
@gview: you're cheating - included file has been parsed anyway. you're using executed term in confusing way. Again, please read the original question: "If I do this, is the file Class.class.php going to be included everytime the code is run or only when I execute the include_once."
@zerk He/she is confused about how include works in PHP. See his/her answer and comments on this question and its answers.

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