isless

Defined in header `<math.h>`
#define isless(x, y) /* implementation defined */		(since C99)

Determines if the floating-point number x is less than the floating-point number y, without setting floating-point exceptions.

Parameters

x	-	floating-point value
y	-	floating-point value

Return value

Nonzero integral value if x < y, 0 otherwise.

Notes

The built-in 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 operator<.

Example

#include <math.h>
#include <stdio.h>
 
int main(void)
{
    printf("isless(2.0,1.0)      = %d\n", isless(2.0, 1.0));
    printf("isless(1.0,2.0)      = %d\n", isless(1.0, 2.0));
    printf("isless(INFINITY,1.0) = %d\n", isless(INFINITY, 1.0));
    printf("isless(1.0,NAN)      = %d\n", isless(1.0, NAN));
 
    return 0;
}

Possible output:

isless(2.0,1.0)      = 0
isless(1.0,2.0)      = 1
isless(INFINITY,1.0) = 0
isless(1.0,NAN)      = 0

References

C23 standard (ISO/IEC 9899:2024):

7.12.14.3 The isless macro (p: TBD)
F.10.11 Comparison macros (p: TBD)

C17 standard (ISO/IEC 9899:2018):

7.12.14.3 The isless macro (p: TBD)
F.10.11 Comparison macros (p: TBD)

C11 standard (ISO/IEC 9899:2011):

7.12.14.3 The isless macro (p: 260)
F.10.11 Comparison macros (p: 531)

C99 standard (ISO/IEC 9899:1999):

7.12.14.3 The isless macro (p: 241)