Does PHP require, require_once, or include automatically read the file at page load?

Question

I have several pages which use the include or require language constructs within PHP. Many of these lie within IF, ELSE statements.

I do realize that a page will not load at all if a require'd file is missing but the main purpose of including this way is to:

1) reduce code clutter on the page

2) not load the file unless a statement is met.

Does issuing an include or require statement load the file regardless (and thus eliminating the benefits I was trying to achieve by placing within the if/else statement?

Brief example:

<?php


$i = 1

if($i ==1) {

      require_once('somefile.php');

} else {

     require_once('otherfile.php');
}

?>

At page load, are both files checked AND loaded?

Answer 1

If you place an include/require statement in the body of an if (or else), it'll be executed if the if's condition is true.

if ($a == 10) {
    // your_first_file.php will only be loaded if $a == 10
    require 'your_first_file.php';
} else {
    // your_second_file.php will only be loaded if $a != 10
    require 'your_second_file.php';
}

And, if you want, you can test this pretty easily.
This first example :

if (true) {
    require 'file_that_doesnt_exist';
}

will get you :

Warning: require(file_that_doesnt_exist) [function.require]: failed to open stream: No such file or directory
Fatal error: require() [function.require]: Failed opening required 'file_that_doesnt_exist'

i.e. the require is executed -- and fails, as the file doesn't exist.

While this second example :

if (false) {
    require 'file_that_doesnt_exist';
}

Will not get you any error : the require is not executed.