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isunordered - cppreference.com

From cppreference.com

#define isunordered(x, y) /* implementation defined */

 (since C99)

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.

Parameters

x - floating point value
y - floating point value

Return value

Nonzero integral value if either x or y is NaN, 0 otherwise.

Example

#include <math.h>
#include <stdio.h>
 
int main(void)
{
    printf("isunordered(NAN,1.0) = %d\n", isunordered(NAN, 1.0));
    printf("isunordered(1.0,NAN) = %d\n", isunordered(1.0, NAN));
    printf("isunordered(NAN,NAN) = %d\n", isunordered(NAN, NAN));
    printf("isunordered(1.0,0.0) = %d\n", isunordered(1.0, 0.0));
 
    return 0;
}

Possible output: 

isunordered(NAN,1.0) = 1
isunordered(1.0,NAN) = 1
isunordered(NAN,NAN) = 1
isunordered(1.0,0.0) = 0

References

  • C23 standard (ISO/IEC 9899:2024):
  • 7.12.14.6 The isunordered macro (p: TBD)
  • F.10.11 Comparison macros (p: TBD)
  • C17 standard (ISO/IEC 9899:2018):
  • 7.12.14.6 The isunordered macro (p: TBD)
  • F.10.11 Comparison macros (p: TBD)
  • C11 standard (ISO/IEC 9899:2011):
  • 7.12.14.6 The isunordered macro (p: 261)
  • F.10.11 Comparison macros (p: 531)
  • C99 standard (ISO/IEC 9899:1999):
  • 7.12.14.6 The isunordered macro (p: 242)

See also