std::fpclassify (3) Linux Manual Page

std::fpclassify – std::fpclassify

Synopsis

Defined in header <cmath>
int fpclassify( float arg ); (1) (since C++11)
int fpclassify( double arg ); (2) (since C++11)
int fpclassify( long double arg ); (3) (since C++11)
int fpclassify( IntegralType arg ); (4) (since C++11)
1-3) Categorizes floating point value arg into the following categories: zero, subnormal, normal, infinite, NAN, or implementation-defined category.
4) A set of overloads or a function template accepting the from argument of any integral_type. Equivalent to (2) (the argument is cast to double).

Parameters

arg – floating point value

Return value

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

Example

// Run this code

#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

See also

isfinite checks if the given number has finite value
               (function)
(C++11)
isinf checks if the given number is infinite
               (function)
(C++11)
isnan checks if the given number is NaN
               (function)
(C++11)
isnormal checks if the given number is normal
               (function)
(C++11)
               provides an interface to query properties of all fundamental numeric types.
numeric_limits (class template)