std::fpclassify

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fpclassify
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Defined in header <cmath>
(1)
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)
Defined in header <cmath>
template < class Integer >
int fpclassify( Integer num ) ;
(A) (since C++11)
(constexpr since C++23)
1) 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)
A) Additional overloads are provided for all integer types, which are treated as double.

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 < double > (num) )

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

See also

(C++11)
 checks if the given number has finite value
(function)
(C++11)
 checks if the given number is infinite
(function)
(C++11)
 checks if the given number is NaN
(function)
(C++11)
 checks if the given number is normal
(function)
provides an interface to query properties of all fundamental numeric types
(class template)
C documentation for fpclassify
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