FP_NORMAL, FP_SUBNORMAL, FP_ZERO, FP_INFINITE, FP_NAN
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Defined in header
<cmath>
#define FP_NORMAL /* implementation defined */
(since C++11)
#define FP_SUBNORMAL /* implementation defined */
(since C++11)
#define FP_ZERO /* implementation defined */
(since C++11)
#define FP_INFINITE /* implementation defined */
(since C++11)
#define FP_NAN /* implementation defined */
(since C++11)
The FP_NORMAL, FP_SUBNORMAL, FP_ZERO, FP_INFINITE, FP_NAN macros each represent a distinct category of floating-point numbers. They all expand to an integer constant expression.
Constant
Explanation
FP_NORMAL
indicates that the value is normal, i.e. not an infinity, subnormal, not-a-number or zero
FP_SUBNORMAL
indicates that the value is subnormal
FP_ZERO
indicates that the value is positive or negative zero
FP_INFINITE
indicates that the value is not representable by the underlying type (positive or negative infinity)
FP_NAN
indicates that the value is not-a-number (NaN)
[edit] Example
Run this code
#include <cfloat> #include <cmath> #include <iostream> auto show_classification(double x) { switch (std::fpclassify (x)) { case FP_INFINITE: return "Inf"; case FP_NAN: return "NaN"; case FP_NORMAL: return "normal"; case FP_SUBNORMAL: return "subnormal"; case FP_ZERO: return "zero"; default: return "unknown"; } } int main() { std::cout << "1.0/0.0 is " << show_classification(1 / 0.0) << '\n' << "0.0/0.0 is " << show_classification(0.0 / 0.0) << '\n' << "DBL_MIN/2 is " << show_classification(DBL_MIN / 2) << '\n' << "-0.0 is " << show_classification(-0.0) << '\n' << "1.0 is " << show_classification(1.0) << '\n'; }
Output:
1.0/0.0 is Inf 0.0/0.0 is NaN DBL_MIN/2 is subnormal -0.0 is zero 1.0 is normal
[edit] See also
C documentation for FP_categories