Generate random string ( use to generate a password)

generate_random_str.php

<?php
if(!function_exists('generate_random_str')) {
    function generate_random_str($len = 9, $type=2) {
        $letters = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
        $numbers = '0123456789';
        $special_chars = '!@#$%^&*()-_ []{}<>~`+=,.;:/?|';
        $words = '';
        switch ($type) {
            case 1:
                $words = $letters.$numbers;
                break;
            case 2:
                $words = $letters.$numbers.$special_chars;
                break;
            case 3:
                $words = $letters;
                break;
            case 4:
                $words = $numbers;
                break;
            default:
                $words = $letters.$numbers;
                break;
        }
        $words_len = strlen($words);
        $temp = array();
        for($i = 0; $i < $len; $i++) {
            $temp[] = $words[mt_rand(0, $words_len-1)];
        }
        return join('', $temp);
    }
}