-1

I want to know a right and maybe elegant way in C++ to detect whether a floating point number is ordinary. By "ordinary floating point numbers", I mean those of double/float/long double type except NAN or INF.

iikkoo
  • 2,681
  • 6
  • 34
  • 37
zell
  • 8,807
  • 8
  • 50
  • 99
  • 1
    @Drew That makes sense. My apologies. – zell Jan 13 '15 at 03:41
  • 2
    In addition to the good answers, finite floating-point numbers are exactly those that make the condition `x - x == 0` true, for when you have good reasons to avoid including a header. Specialists will read it as an idiom but non-specialists will be annoyed, so use with care. – Pascal Cuoq Jan 13 '15 at 12:23

2 Answers2

3

You could check out Boost.Math. It defines all of these:

template <class T>
bool isfinite(T z); // Neither infinity nor NaN.

template <class T>
bool isinf(T t); // Infinity (+ or -).

template <class T>
bool isnan(T t); // NaN.

template <class T>
bool isnormal(T t); // isfinite and not denormalised.

Since C++11, these are in <cmath> too: std::isnan, std::isinf, std::isfinite, and std::isnormal.

Barry
  • 267,863
  • 28
  • 545
  • 906
3

std::isfinite() will return true for values that are not INF or NaN.

(Edited to reflect a question edit)

Drew Dormann
  • 54,920
  • 13
  • 119
  • 171