NAME

std::fpclassify - std::fpclassify

Synopsis

Defined in header <cmath>
int fpclassify( float arg ); (1) (since C++11)
(constexpr since C++23)
int fpclassify( double arg ); (2) (since C++11)
(constexpr since C++23)
int fpclassify( long double arg ); (3) (since C++11)
(constexpr since C++23)
int fpclassify( IntegralType arg ); (4) (since C++11)
(constexpr since C++23)

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