Re: [PATCH] Add example to rand.3

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

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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?

Cheers,

Alex

> ---
>   man3/rand.3 | 14 ++++++++++++++
>   1 file changed, 14 insertions(+)
> 
> diff --git a/man3/rand.3 b/man3/rand.3
> index 572471749..c1542fb56 100644
> --- a/man3/rand.3
> +++ b/man3/rand.3
> @@ -164,6 +164,20 @@ when good randomness is needed.
>   .BR random (3)
>   instead.)
>   .SH EXAMPLES
> +
> +A possibly useful seed value would be by calling
> +.BR rand ()
> +with the result of
> +
> +.BR time ()
> +as that varies with every call
> +
> +.EX
> +srand((unsigned int)time(NULL));
> +.EE
> +.in
> +.PP
> +
>   POSIX.1-2001 gives the following example of an implementation of
>   .BR rand ()
>   and

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

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