C++ header file problem - is this a bug?

[Bill Northcott]

On 05/01/2005, at 6:27 AM, Dave Korn wrote:
>   Did you notice that you're writing C++, and ***NOT*** C?
>
>   As such, you should use the C++ library functions and headers, not 
> the C
> library functions and headers, since they're for a different 
> programming
> language.
>
>   Why aren't you using the std::isnan() function?

I can't find any documentation, and if I try to use it I get the 
following:
error: `isnan' undeclared  in namespace `std'
which is unsurprising since it does not appear to be declared or 
defined in any header in /usr/include except math.h, which gets stuffed 
by cmath.

Would those be adequate reasons not to use it?

Just how is one expected to get isnan() functionality in a C++ program?

Bill Northcott