# isless

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< c‎ | numeric‎ | math

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

Run this code

    #include <stdio.h>
    #include <math.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

- 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)

### See also

isgreater (C99) | checks if the first floating-point argument is greater than the second (function)
C++ documentation for isless

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