LOG(3) manual page
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log, logf, logl - natural logarithmic
function
#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
The log() function returns the natural logarithm
of x.
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.
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.
C99, POSIX.1-2001. The variant
returning double also conforms to SVr4, 4.3BSD, C89.
In glibc 2.5 and
earlier, taking the log() of a NaN produces a bogus invalid floating-point
(FE_INVALID) exception.
cbrt(3)
, clog(3)
, log10(3)
, log1p(3)
, log2(3)
,
sqrt(3)
This page is part of release 3.78 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/.
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