[Rd] Standalone Mathlib, C++ and ISNAN()

Martyn Plummer plummer at iarc.fr
Thu Jan 6 12:16:51 CET 2005

On Thu, 2005-01-06 at 08:29 +1100, Bill Northcott wrote:
> On 06/01/2005, at 6:53 AM, Thomas Lumley wrote:
> >
> > I believe (with a little Googling) the suggested C++ approach is to 
> > use std::isnan if <cmath> is included.
> >
> I tried that too, but without any success.  I even tried 
> __gnu_cxx::isnan.
> It was suggested by one of the gcc people, but I could find no 
> documentation about it.  The ISO C++ docs do not include isnan as a 
> symbol provided by cmath within the std namespace.  I looked at the gcc 
> source code and could see no reason why it should work.

I think the workaround is supposed to look like this:

#define _GLIBCPP_USE_C99 1
#include <cmath>
#undef _GLIBCPP_USE_C99
#include <iostream>

using __gnu_cxx::isnan;

I don't know whether this solves the problem on MacOs X but it is valid
on Linux.  But do you really want to write code that is specific to gcc?
I don't.


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