Re: [iPhone] How to create a unique string
Re: [iPhone] How to create a unique string
- Subject: Re: [iPhone] How to create a unique string
- From: Louis Gerbarg <email@hidden>
- Date: Thu, 13 May 2010 11:52:09 -0400
On May 13, 2010, at 11:05 AM, Michael Ash <email@hidden> wrote:
> On Thu, May 13, 2010 at 10:56 AM, Thomas Davie <email@hidden> wrote:
>>
>> On 13 May 2010, at 15:33, Eric Gorr wrote:
>>
>>> So long as it is ok for the string to be unique for the network the user is on only. From the docs:
>>>
>>> The ID includes the host name, process ID, and a time stamp, which ensures that the ID is unique for the network.
>>>
>>> A UUID (Universally Unique Identifier) is entirely unique.
>>
>> No it's not, as can easily be proven by observing that there are only a finite number of 40 character strings. A UUID is probabilistically unique.
>
> CFUUID includes the MAC address, so unless your MAC address is cloned
> or you manage to generate two UUIDs on the same device in the same
> 100ns time interval or the calendar rolls over (which will take about
> 3700 years), they are entirely unique within the universe of CFUUID
> strings.
No, it doesn't use the MAC address. MAC addresses are uses as part of type 1 uuids, CFUUID has generated type 4 (random) uuids by default since Tiger, and has always generated type 4 on iPhone. If you look at the source to CF there is a way to force it to generate type 1 uuids, but I doubt that is supported.
Louis _______________________________________________
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