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FP_NORMAL, FP_SUBNORMAL, FP_ZERO, FP_INFINITE, FP_NAN

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)

Example

#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

fpclassify (C++11)	categorizes the given floating-point value (function)
C documentation for `FP_categories`

FP_NORMAL, FP_SUBNORMAL, FP_ZERO, FP_INFINITE, FP_NAN

Example

See also