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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 <iostream>
#include <cmath>
#include <cfloat>
 
const char* 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