std::fpclassify (3) - Linux Manuals

std::fpclassify: std::fpclassify

NAME

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