Re: [PATCH] Add example to rand.3

[Alejandro Colomar <alx.manpages@gmail.com>]

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Hi Jonny,

On 12/27/22 22:37, Jonny Grant wrote:
> Hi Alex
> 
> On 26/12/2022 22:29, Alejandro Colomar wrote:
>> Hi Jonny,
>>
>> On 12/26/22 22:50, Jonny Grant wrote:
>>> Hi Alejandro
>>
>> Please send also to my email.
>>
>>> Please find below a patch.
>>>
>>> 2022-12-26  Jonathan Grant <jg@jguk.org>
>>>      * man3/rand.3: Add example to rand.3 seed with time(NULL)
>>>
>>>
>>>   From 2d4501354ea6c465173fe6c089dfbcc80393a644 Mon Sep 17 00:00:00 2001
>>> From: Jonathan Grant <jg@jguk.org>
>>> Date: Mon, 26 Dec 2022 21:48:17 +0000
>>> Subject: [PATCH] add rand.3 example
>>>
>>> Signed-off-by: Jonathan Grant <jg@jguk.org>
>>
>> time(NULL) is not too good.  If you call it several times per second, you'll find that it only changes the seed every second.  There are better ways to produce a good seed.
>>
>> However, I prefer suggesting arc4random() rather than workarounding rand(3) to get good results.
>>
>> Florian, did you already merge arc4random() to glibc?
> 
> Hopefully arc4random will come soon. Maybe rand.3 could then be updated to SEE ALSO that. >
> I would only mention to call srand once to seed, but you're right there are lots of other ways to get a seed.
> Jonny

But consider the following case:

You're testing some program with random data in a loop.  And the program 
executes in less than a second.  Then srand(3) will be called several times per 
second with the same seed, and you'll get useless results.  I faced that exact 
situation a few years ago :)

Cheers,

Alex


-- 
<http://www.alejandro-colomar.es/>

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