了解php包括路径

Question

I'm trying to understand exactly how php treats include paths on page calls.

Lets say I have index.php in the base directory, functions/functionFile1.php, functions/functionFile2.php and settings/settingFile.php

So the straightforward one is index.php has

include_once("functions/functionsFile1.php"); 
include_once('settings/settingsFile.php');

In the functions1 file:

include_once('settings/settingsFile.php');
include_once('functionsFile2.php);

function DoX()
{
   include("settings/settings.php"); 
   $variableInSettingsPage; 
} 

How is it that this works? The functions1.php file seems to be able to call both files relative to itself (functions2.php) and its calling page (settings/settings.php)? And the function that requires calling the settings file can use a path relative to the calling page, even though it's out of scope and will refuse to use a path relative to its page?

Answer 1

Php use an include path, every path from which a file can be included is stored there. When you try to include a file, php will loop through every path and check if your file is in one of them, if it is, it will stop looping and include it, if it is not, it will keep looping until it eventually reach the end and raise an error.

You can check what's in your include_path, using get_include_path()