LOG
Section: Linux Programmer's Manual (3)
Updated: 20100920
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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 floatingpoint exception
(FE_INVALID)
is raised.
 Pole error: x is zero

errno
is set to
ERANGE.
A dividebyzero floatingpoint exception
(FE_DIVBYZERO)
is raised.
CONFORMING TO
C99, POSIX.12001.
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 floatingpoint
(
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
manpages
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/manpages/.
Index
 NAME

 SYNOPSIS

 DESCRIPTION

 RETURN VALUE

 ERRORS

 CONFORMING TO

 BUGS

 SEE ALSO

 COLOPHON
