signbit - test sign of a real floating-point number
#include <math.h>
int signbit(x);
Link with
-lm.
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
signbit():
_ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L
signbit() is a generic macro which can work on all real floating-point
types. It returns a nonzero value if the value of
x has its sign bit
set.
This is not the same as
x < 0.0, because IEEE 754 floating point
allows zero to be signed. The comparison
-0.0 < 0.0 is false, but
signbit(-0.0) will return a nonzero value.
NaNs and infinities have a sign bit.
The
signbit() macro returns nonzero if the sign of
x is negative;
otherwise it returns zero.
No errors occur.
For an explanation of the terms used in this section, see
attributes(7).
| Interface |
Attribute |
Value |
| signbit () |
Thread safety |
MT-Safe |
POSIX.1-2001, POSIX.1-2008, C99. This function is defined in IEC 559 (and the
appendix with recommended functions in IEEE 754/IEEE 854).
copysign(3)