log3
Natural logarithmic function
Usage
#include <math.h>
double log(double x); float logf(float x); long double logl(long double x);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
logf(), logl():
_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
Library
Math library (libm, -lm)
Overview
These functions return 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.
Attributes
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
| log(), logf(), logl() | Thread safety | MT-Safe |
Releases
19 releases since Debian 1.1 (Buzz); the text changed 13 times.