A detailed explanation of how PHP generates a unique ID

PHP generated a unique ID, the web looked down, there are many ways

1, MD5 (Time (). Mt_rand (1,1000000));

This method has a certain probability that there will be repetition

2. PHP built-in function uniqid ()

The Uniqid () function generates a unique ID based on the current time in microseconds.

W3school Reference Manual There is a sentence: "Due to system time, the ID generated by this function is not optimal." To generate an absolutely unique ID, use the MD5 () function.

The following method returns the result similar to: 5ddb650f-4389-f4a9-a100-501ef1348872 more please refer to my blog: php instance

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. The random number sowing, 4.2.0 not need after. $charid = Strtoupper (MD5 (Uniqid (rand (), true)); Generates a unique ID based on the current time (in microseconds). $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,//.CHR);//"}" return $uuid;}    }

Com_create_guid () is a PHP self-generated unique ID method, which seems to have gone php5.
3, the official uniqid () reference manual has the user-provided method, the result is similar: {E2DFFFB3-571E-6CFC-4B5C-9FEDAAF2EFD7}

public function create_guid ($namespace = ') {static $guid = '; $uid = Uniqid ("" , true); $data = $namespace; $data. = $_server[' request_time '); $data. = $_server[' http_user_agent ']; $data. = $_server[' Local_addr ']; $data. = $_server[' Local_port '); $data. = $_server[' remote_addr ']; $data. = $_server[' Remote_port ']; $hash   = Strtoupper (hash (' ripemd128 ', $uid. $guid. MD5 ($DATA))); $guid = ' {'.             substr ($hash, 0, 8).            '-'. substr ($hash, 8, 4).            '-'. substr ($hash, 12, 4).            '-'. substr ($hash, 16, 4).            '-'. substr ($hash, 20, 12).  '} '; return $guid; }