Isunordered

Defined in header <cmath>.

Description

Determines if the floating point numbers x and y are unordered, that is, one or both are NaN and thus cannot be meaningfully compared with each other.
​The library provides overloads for all cv-unqualified floating-point types as the type of the parameters x and y  (since C++23).

​Additional Overloads are provided for all other combinations of arithmetic types.

Declarations

C++23

// 1)
constexpr bool isunordered( /* floating-point-type */ x,
                          /* floating-point-type */ y );

Additional Overloads

// 2)
template< class Arithmetic1, class Arithmetic2 >
constexpr bool isunordered( Arithmetic1 x, Arithmetic2 y );

C++11

// 1)
bool isunordered( float x, float y );
// 2)
bool isunordered( double x, double y );
// 3)
bool isunordered( long double x, long double y );

Additional Overloads

// 4)
template< class Arithmetic1, class Arithmetic2 >
bool isunordered( Arithmetic1 x, Arithmetic2 y );

Parameters

x, y - floating-point or integer values

Return value

true if either x or y is NaN, false otherwise.

Notes

The built-in operator >and operator < for floating-point numbers may raise FE_INVALID if one or both of the arguments is NaN. This function is a "quiet" version of the expression x < y || x > y.

The additional overloads are not required to be provided exactly as Additional Overloads. They only need to be sufficient to ensure that for their first argument num1 and second argument num2:

If num1 or num2 has type long double, then
std::isunordered(num1, num2) has the same effect as
​std::isunordered(static_cast<long double>(num1), static_cast<long double>(num2)).

Otherwise, if num1 and/or num2 has type double or an integer type, then
std::isunordered(num1, num2) has the same effect as
​std::isunordered(static_cast<double>(num1), static_cast<double>(num2)).

​Otherwise, if num1 or num2 has type float, then
std::isunordered(num1, num2) has the same effect as
​std::isunordered(static_cast<float>(num1), static_cast<float>(num2)). (until C++23)

If num1 and num2 have arithmetic types, then
std::isunordered(num1, num2) has the same effect as
std::isunordered(static_cast</* common-floating-point-type */>(num1), static_cast</* common-floating-point-type */>(num2)) ,

where /* common-floating-point-type */ is the floating-point type with the greatest floating-point conversion rank and greatest floating-point conversion subrank between the types of num1 and num2, arguments of integer type are considered to have the same floating-point conversion rank as double.

If no such floating-point type with the greatest rank and subrank exists, then overload resolution does not result in a usable candidate from the overloads provided.

Examples

#include <cmath>
#include <iostream>
 
#define SHOW_UNORDERED(x, y) \
    std::cout 
        << std::boolalpha << "isunordered(" \
        << #x << ", " << #y << "): " \
        << std::isunordered(x, y) << '\n'
 
int main()
{
    SHOW_UNORDERED(10, 01);
    SHOW_UNORDERED(INFINITY, NAN);
    SHOW_UNORDERED(INFINITY, INFINITY);
    SHOW_UNORDERED(NAN, NAN);
}

Possible Result

isunordered(10, 01): false
isunordered(INFINITY, NAN): true
isunordered(INFINITY, INFINITY): false
isunordered(NAN, NAN): true