php生成唯一识别码uuid

/*生成唯一标志
*标准的UUID格式为：xxxxxxxx-xxxx-xxxx-xxxxxx-xxxxxxxxxx(8-4-4-4-12)
*/

function  uuid()  
{  
    $chars = md5(uniqid(mt_rand(), true));  
    $uuid = substr ( $chars, 0, 8 ) . '-'
            . substr ( $chars, 8, 4 ) . '-' 
            . substr ( $chars, 12, 4 ) . '-'
            . substr ( $chars, 16, 4 ) . '-'
            . substr ( $chars, 20, 12 );  
    return $uuid ;  
}  
 
echo  uuid();  //Returns like 'dba5ce3e-430f-cf1f-8443-9b337cb5f7db'