LOG(3)                              Linux Programmer's Manual                              LOG(3)



NAME
       log, logf, logl - natural logarithmic function

SYNOPSIS
       #include <math.h>

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

       Link with -lm.

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       logf(), logl():
           _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
           _POSIX_C_SOURCE >= 200112L;
           or cc -std=c99

DESCRIPTION
       The log() function returns 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.

CONFORMING TO
       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)

COLOPHON
       This  page  is  part of release 3.74 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at http://www.kernel.org/doc/man-pages/.



                                            2010-09-20                                     LOG(3)