I always used retrieving the Operating system environment, and then get all current include path and then set the include path

<?php
$delim = (PHP_OS == "WIN32" || PHP_OS == "WINNT") ? ';': ':';

ini_set('include_path', ".");
ini_set('include_path', ini_get('include_path') . "my_library");
ini_set('include_path', ini_get('include_path') . "my_library/include");
?>

Here is the code, which simplifies the above logic of detecting OS environment and then to get include_path and appending new one -

<?php
//Set the include path

set_include_path(get_include_path()
. PATH_SEPARATOR . '/my_library'
. PATH_SEPARATOR . '/my_library/include/'
);
?>