signbit(3) Library Functions Manual signbit(3) signbit - (libm -lm) #include int signbit(x); glibc ( feature_test_macros(7)): signbit(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L signbit() . x . x < 0.0 IEEE 754 . -0.0 < 0.0 signbit(-0.0) . NaNs . signbit() x . . attributes(7). +------------+------------------------------------+--------------------+ || | | +------------+------------------------------------+--------------------+ |signbit() | | MT-Safe | +------------+------------------------------------+--------------------+ C11, POSIX.1-2008. POSIX.1-2001 C99. IEC 559 ( IEEE 754/IEEE 854). copysign(3) 3 . . : . 6.18 8 2026 signbit(3)