signbit

< c‎ | numeric‎ | math
 
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signbit
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Defined in header <math.h>
#define signbit(arg) /* implementation defined */
 (since C99)

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

Parameters

arg - floating point value

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

Run this code
#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));
}

Possible output: 

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

References

  • C11 standard (ISO/IEC 9899:2011):
  • 7.12.3.6 The signbit macro (p: 237)
  • C99 standard (ISO/IEC 9899:1999):
  • 7.12.3.6 The signbit macro (p: 218)

See also

(C99)(C99)
 computes absolute value of a floating-point value (|x|)
(function)
(C99)(C99)(C99)
 produces a value with the magnitude of a given value and the sign of another given value
(function)