uuid

    /**
     * 生成GUID
     * @param bool $opt
     * @return string
     */
    public static function guid($opt = true ){       //  Set to true/false as your default way to do this.

        if( function_exists('com_create_guid') ){
            if($opt){
                return com_create_guid();
            }
            else {
                return trim(com_create_guid(), '{}');
            }
        }
        else {
            mt_srand((double)microtime() * 10000 );    // optional for php 4.2.0 and up.
            $charid = strtoupper(md5(uniqid(rand(), true)));
            $hyphen = chr( 45 );    // "-"
            $left_curly = $opt ? chr(123) : "";     //  "{"
            $right_curly = $opt ? chr(125) : "";    //  "}"

            $uuid = substr( $charid, 0, 8 ) . $hyphen
                . substr( $charid, 8, 4 ) . $hyphen
                . substr( $charid, 12, 4 ) . $hyphen
                . substr( $charid, 16, 4 ) . $hyphen
                . substr( $charid, 20, 12 );
//            $uuid = $left_curly
//                . substr( $charid, 0, 8 ) . $hyphen
//                . substr( $charid, 8, 4 ) . $hyphen
//                . substr( $charid, 12, 4 ) . $hyphen
//                . substr( $charid, 16, 4 ) . $hyphen
//                . substr( $charid, 20, 12 )
//                . $right_curly;
            return $uuid;// 00000000-0000-0000-0000-000000000001
        }
    }