Re: Using rand_r

[Greg Chicares <gchicares at sbcglobal dot net>]

On 2009-05-14 05:49Z, Nicholas Sherlock wrote:
> David Billinghurst wrote:
>  > Nicholas Sherlock wrote:
>  >> Hey everyone,
>  >>
>  >> I'm trying to use the function rand_r with gcc-4 in Cygwin 1.7, all 
> my packages are up to date. It's supposed to be defined in stdlib.h, and 
> I can see it there. But if I compile a program which uses it, I get:
>  >>
>  >> warning: implicit declaration of function 'rand_r'.
>  >>
>  >> The reason seems to be the check for #ifndef __STRICT_ANSI__ in 
> stdlib.h. Even though I'm compiling with -std=c99, __STRICT_ANSI__ still 
> gets declared, so the definition of rand_r is unavailable. This seems to 
> be the same problem stated here:

'-std=c99' correctly gives a diagnostic because rand_r() is not in C99.

>  > Try -std=gnu99.  It doesn't define __STRICT_ANSI__
>  >
>  > This doesn't answer your question, unfortunately.
> 
> Thanks, that does solve my immediate problem. But I'm really hoping to 
> compile as vanilla C99 as I can manage, since I'll also be using my code 
> with non-GNU compilers.

If you want consistently identical results with different compilers,
then you'll need to write your own routine anyway (which you can do
in strictly-conforming C). See the rationale for myrand() here:
  http://www.opengroup.org/onlinepubs/000095399/functions/rand.html

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