std::fpclassify

Since C++23

Header: <cmath>

Categorizes floating point value num into the following categories: zero, subnormal, normal, infinite, NAN, or implementation-defined category.The library provides overloads of std::fpclassify for all cv-unqualified floating-point types as the type of the parameter num.(since C++23)

# Declarations

int fpclassify( float num );
int fpclassify( double num );
int fpclassify( long double num );

(since C++11) (until C++23)

constexpr int fpclassify( /* floating-point-type */ num );

(since C++23)

Additional overloads

template< class Integer >
int fpclassify( Integer num );

(since C++11) (constexpr since C++23)

# Parameters

num: floating-point or integer value

# Return value

one of FP_INFINITE, FP_NAN, FP_NORMAL, FP_SUBNORMAL, FP_ZERO or implementation-defined type, specifying the category of num.

# Notes

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their argument num of integer type, std::fpclassify(num) has the same effect as std::fpclassify(static_cast(num)).

# 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';
}