std::isunordered(3)

NAME
std::isunordered - std::isunordered

Synopsis
   Defined in header <cmath>
   bool isunordered( float x, float y );
                        (since C++11)
   bool isunordered( double x, double y ); (until C++23)
   bool isunordered( long double x, long double y );
   constexpr bool isunordered( /* floating-point-type
   */ x, (1) (since C++23)
                        /* floating-point-type
   */ y );
   Additional overloads
   Defined in header <cmath>
   template< class Arithmetic1, class Arithmetic2 > (A) (since C++11)
   bool isunordered( Arithmetic1 x, Arithmetic2 y ); (constexpr since C++23)
   1) 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)
   A) Additional overloads are provided for all other combinations of arithmetic types.

Parameters
   x, y - floating-point or integer values

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

Notes
   The additional overloads are not required to be provided exactly as (A). 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 (until C++23)
       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)).
   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, (since C++23)
   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.

Example
// Run this code
 #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);
 }

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

See also
   fpclassify categorizes the given floating-point value
   (C++11) (function)
   isnan checks if the given number is NaN
   (C++11) (function)
   C documentation for
   isunordered