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std::fpclassify

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( Integral 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

#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

(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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