Copyright 1993 David Metcalfe (firstname.lastname@example.org) and Copyright 2008, Linux Foundation, written by Michael Kerrisk <email@example.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting ...
NAMElog, 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)):
_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE ||
_POSIX_C_SOURCE >= 200112L;
or cc -std=c99
DESCRIPTIONThese functions return the natural logarithm of x.
RETURN VALUEOn 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.
ERRORSSee 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.
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
|log(), logf(), logl()||Thread safety||MT-Safe|
CONFORMING TOC99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD, C89.