Name
signbit - test sign of a real floating-point numberLibrary
Math library ( libm ", " -lm )Synopsis
"#include <math.h>"
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 signbit(-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; otherwise it returns zero.Errors
No errors occur.Attributes
For an explanation of the terms used in this section, see attributes(7).| Interface | Attribute | Value |
| T} | 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)