signbit

Determines if the given floating point number arg is negative. The macro returns an integral value.

Parameters

Return value

Nonzero integral value if arg is negative, ​0​ otherwise.

Notes

This macro detects the sign bit of zeroes, infinities, and NaNs. Along with copysign, this macro is one of the only two portable ways to examine the sign of a NaN.

Example

#include <stdio.h>
#include <math.h>
 
int main(void)
{
    printf("signbit(+0.0) = %d\n", signbit(+0.0));
    printf("signbit(-0.0) = %d\n", signbit(-0.0));
}

signbit(+0.0) = 0
signbit(-0.0) = 128

References