How to generate a new GUID?

You can try the following:

function GUID()
{
    if (function_exists('com_create_guid') === true)
    {
        return trim(com_create_guid(), '{}');
    }

    return sprintf('%04X%04X-%04X-%04X-%04X-%04X%04X%04X', mt_rand(0, 65535), mt_rand(0, 65535), mt_rand(0, 65535), mt_rand(16384, 20479), mt_rand(32768, 49151), mt_rand(0, 65535), mt_rand(0, 65535), mt_rand(0, 65535));
}

Source - com_create_guid

As an alternative to the above options:

$guid = bin2hex(openssl_random_pseudo_bytes(16));

It gives a string like 412ab7489d8b332b17a2ae127058f4eb

According to Is there any difference between a GUID and a UUID?

GUID is Microsoft's implementation of the UUID standard.

So, here's a link to libraries, that let's you create UUIDs of the following types:

• version 1 (time-based)
• version 3 (name-based and hashed with MD5)
• version 4 (random)
• version 5 (name-based and hashed with SHA1)

https://github.com/search?p=1&q=uuid+php&ref=cmdform&type=Repositories

I don't know exactly, which one C# is using, but that's at least something you can use if you're writing some piece of software and want to have universal unique identifiers.

My perfered choice was https://github.com/fredriklindberg/class.uuid.php because it is just a simple PHP file and the most rated one (https://github.com/ramsey/uuid) had to much dependencies on other libraries, but his may change soon (see https://github.com/ramsey/uuid/issues/20).

But if you really need a GUID (according to the Microsoft standard), they have a different generation process than these 4122. Wikipedia claims that

GUIDs and RFC 4122 UUIDs should be identical when displayed textually

http://en.wikipedia.org/wiki/Globally_Unique_Identifier#Binary_encoding

In most cases, you should be fine by going for one of the PHP libs for UUIDs. I don't think you're meddling with Microsoft Component Object Model (COM), don't you?

<?php
function guid(){
if (function_exists('com_create_guid') === true)
    return trim(com_create_guid(), '{}');

$data = openssl_random_pseudo_bytes(16);
$data[6] = chr(ord($data[6]) & 0x0f | 0x40);
$data[8] = chr(ord($data[8]) & 0x3f | 0x80);
return vsprintf('%s%s-%s-%s-%s-%s%s%s', str_split(bin2hex($data), 4));
}
?>

GUID Generator