Question

Is it more efficient to use PHP’s include_once or require_once instead of using a C-like include with a header guard?

I.e,

include_once 'init.php';

versus

include 'init.php';

//contents of init.php
if (!defined('MY_INIT_PHP')) {
  define('MY_INIT_PHP', true);
  ...
}

Answer 1

“require_once” and “include_once” are generally a bit slower that just “require” and “include” because they perform a check wether the file has already been loaded before.

But the difference only matters in really complex applications where you should do autoloading anyway and by that would not need require_once/include_once, if your autoloader is well coded.

In most simple applications, it’s better to use the require_once/include_once for convenience reasons.

The header guard approach is just messy code that should be avoided. Just imagine, if you forgot that check in one of many files. Debugging that could be a nightmare.

Just use autoloading if your application is suitable for it. It’s fast and the most convenient and clean way.