Greetings.
In a C++ program, why can't I use isnan() and all those C99 macros ?
I know I need to define _GLIBCPP_USE_C99, but when I do it, it breaks other
functions. 
Anyway, I found a replacement (isnanf()), but my question is: isn't this non
standard ?
(I know g++ is not fully C99 compliant. I just need a good clarification on
this issue)

Thanks in advance.

-- 
  "Simplicity is the ultimate 
    sophistication." 
    -- Leonardo da Vinci