php openssl_random_pseudo_bytes() 生成随机数

function getRandomString($length = 6)
{
        /*
         * Use OpenSSL (if available)
         */
        if (function_exists('openssl_random_pseudo_bytes')) {
            $bytes = openssl_random_pseudo_bytes($length * 2);
 
            if ($bytes === false)
                throw new RuntimeException('Unable to generate a random string');
 
            return substr(str_replace(['/', '+', '='], '', base64_encode($bytes)), 0, $length);
        }
 
        $pool = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';
 
        return substr(str_shuffle(str_repeat($pool, 5)), 0, $length);
}

注意 :

1. 需要安装openssl扩展