生成 n 位数的随机验证码

function random($length = 6 , $numeric = 0) {
	PHP_VERSION < '4.2.0' && mt_srand((double)microtime() * 1000000);
	if($numeric) {
		$hash = sprintf('%0'.$length.'d', mt_rand(0, pow(10, $length) - 1));
	} else {
		$hash = '';
		$chars = 'ABCDEFGHJKLMNPQRSTUVWXYZ23456789abcdefghjkmnpqrstuvwxyz';
		$max = strlen($chars) - 1;
		for($i = 0; $i < $length; $i++) {
			$hash .= $chars[mt_rand(0, $max)];
		}
	}
	return $hash;
}
echo random(6,1);