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)
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