Get extension of file if you have only string (filename.ext)

get_file_extension.php

function get_file_extension($filename)
{
    /*
     * "." for extension should be available and not be the first character
     * so position should not be false or 0.
     */
    $last_dot_pos = strrpos($filename, '.');
    if ( !$last_dot_pos ) return false;
    return substr($filename, $last_dot_pos + 1);
}