log(3)                     Library Functions Manual                     log(3)

NAME
       log, logf, logl - natural logarithmic function

LIBRARY
       Math library (libm, -lm)

SYNOPSIS
       #include <math.h>

       double log(double x);
       float logf(float x);
       long double logl(long double x);

   Feature Test Macro Requirements for glibc (see 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

DESCRIPTION
       These functions return the natural logarithm of x.

RETURN VALUE
       On success, these functions return the natural logarithm of x.

       If x is a NaN, a NaN is returned.

       If x is 1, the result is +0.

       If x is positive infinity, positive infinity is returned.

       If x is zero, then a pole error occurs, and the functions return
       -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.

       If x is negative (including negative infinity), then a domain error
       occurs, and a NaN (not a number) is returned.

ERRORS
       See math_error(7) for information on how to determine whether an error
       has occurred when calling these functions.

       The following errors can occur:

       Domain error: x is negative
              errno is set to EDOM.  An invalid floating-point exception
              (FE_INVALID) is raised.

       Pole error: x is zero
              errno is set to ERANGE.  A divide-by-zero floating-point
              exception (FE_DIVBYZERO) is raised.

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       +--------------------------------------------+---------------+---------+
       |Interface                                   | Attribute     | Value   |
       +--------------------------------------------+---------------+---------+
       |log (), logf (), logl ()                    | Thread safety | MT-Safe |
       +--------------------------------------------+---------------+---------+
STANDARDS
       C11, POSIX.1-2008.

HISTORY
       C99, POSIX.1-2001.

       The variant returning double also conforms to SVr4, 4.3BSD, C89.

BUGS
       In glibc 2.5 and earlier, taking the log() of a NaN produces a bogus
       invalid floating-point (FE_INVALID) exception.

SEE ALSO
       cbrt(3), clog(3), log10(3), log1p(3), log2(3), sqrt(3)

Linux man-pages 6.7               2023-10-31                            log(3)