Making a php library, how to make it independent?

Question

Hi I'm developing a library for guitar chords. In some files on the library I have something like this:

require_once "lib/GuitarChord.php";
require_once "lib/Chord.php";
require_once "lib/Key.php";
require_once "lib/Tuning.php";

How can I make this library so it doesn't need to know where the other library files are?

This way a person could have the library files in any directory?

Edit: Removed second question.

Answer 1

Create autoloaders for all locations where these classes might be.

For Example:

//AUTOLOADER
function class_autoloader($class) {

   // presumes classes are in './classes'
   $folders = array(
     './', './../', './../../'  
   );
   $directories = array(
     'classes','lib',  ''
   );
   $dir = dirname(__FILE__);
   $theClass = '/' . $folderedClass . '.php';


   foreach($folders as $folder){
       foreach($directories as $directory){
           $theInclude = $dir.$folder.$directory.$theClass;

           if (file_exists($theInclude) && include_once($theInclude)) {
              return TRUE;
           } 
       }
   }

  trigger_error("The class '$class' or the file '$theClass' failed to spl_autoload ", E_USER_WARNING);

  return FALSE;
}

spl_autoload_register('class_autoloader');

Then if you want to load the Chord Class and you know it is in your lib folder, the autoloader will do the work for you when you do:

new Chord();

You can attach many different autoloader callbacks with spl_autoload_register

Answer 2

Somewhere you're going to have to include the folder name, if you don't want to include all your classes in one file. You can make it somewhere that the user only has to set once, though:

$lib_folder = "lib";

require_once $lib_folder . "/GuitarChord.php";
require_once $lib_folder . "/Chord.php";
require_once $lib_folder . "/Key.php";
require_once $lib_folder . "/Tuning.php";

As for handling different types of databases, you can make another setting like $db_type that the user either sets to "MYSQL", "FILE", "XML", etc. And where you make calls to the db, use a switch statement to see what database method they're using and change your call accordingly.

Edit: It's also worth looking into PHP's __autoload feature