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; 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), log1p(3), sqrt(3)
COLOPHON
This page is part of release 3.24 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
2008-08-10