signbit(3) Library Functions Manual signbit(3)
NAME
signbit - test sign of a real floating-point number
LIBRARY
Math library (libm, -lm)
SYNOPSIS
#include <math.h>
int signbit(x);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
signbit():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
DESCRIPTION
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 sign-
bit(-0.0) will return a nonzero value.
NaNs and infinities have a sign bit.
RETURN VALUE
The signbit() macro returns nonzero if the sign of x is negative; oth-
erwise it returns zero.
ERRORS
No errors occur.
ATTRIBUTES
For an explanation of the terms used in this section, see attrib-
utes(7).
┌───────────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├───────────────────────────────────────────┼───────────────┼─────────┤
│ signbit() │ Thread safety │ MT-Safe │
└───────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
C11, POSIX.1-2008.
HISTORY
POSIX.1-2001, C99.
This function is defined in IEC 559 (and the appendix with recommended
functions in IEEE 754/IEEE 854).
SEE ALSO
copysign(3)
Linux man-pages 6.7 2023-10-31 signbit(3)
Generated by dwww version 1.16 on Tue Dec 16 14:49:36 CET 2025.