log(3) Library Functions Manual log(3) log, logf, logl - (libm -lm) #include double log(double x); float logf(float x); long double logl(long double x); glibc ( feature_test_macros(7)): logf() logl(): _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE x. x. x (NaN) NaN. x 1 +0. x . x (pole error) -HUGE_VAL -HUGE_VALF -HUGE_VALL . x ( ) NaN ( ). math_error(7) . : : x errno EDOM. (FE_INVALID). : x errno ERANGE. (FE_DIVBYZERO). attributes(7). +------------+------------------------------------+--------------------+ || | | +------------+------------------------------------+--------------------+ |log() | | MT-Safe | |logf() | | | |logl() | | | +------------+------------------------------------+--------------------+ C11, POSIX.1-2008. C99 POSIX.1-2001. double SVr4 4.3BSD C89. glibc 2.5 log() NaN (FE_INVALID). cbrt(3) clog(3) log10(3) log1p(3) log2(3) sqrt(3) 3 . . : . 6.18 8 2026 log(3)