php生成唯一id方法

下面方法返回结果类似：5DDB650F-43-F4A9-A100-501EF1348872

function uuid() {
 if (function_exists ( 'com_create_guid' )) {
 return com_create_guid ();
 } else {
 mt_srand ( ( double ) microtime () * 10000 ); //optional for php 4.2.0 and up.随便数播种，4.2.0以后不需要了。
 $charid = strtoupper ( md5 ( uniqid ( rand (), true ) ) ); //根据当前时间（微秒计）生成唯一id.
 $hyphen = chr ( 45 ); // "-"
 $uuid = '' . //chr(123)// "{"
substr ( $charid, 0, 8 ) . $hyphen . substr ( $charid, 8, 4 ) . $hyphen . substr ( $charid, 12, 4 ) . $hyphen . substr ( $charid, 16, 4 ) . $hyphen . substr ( $charid, 20, 12 );
 //.chr(125);// "}"
 return $uuid;
 }
}

2，md5(time() . mt_rand(1,1000000));

这种方法有一定的概率会出现重复