LOGSection: Linux Programmer's Manual (3)
Index Return to Main Contents
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)):
DESCRIPTIONThe log() function returns 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.
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.
CONFORMING TOC99, POSIX.1-2001. The variant returning double also conforms to SVr4, 4.3BSD, C89.
BUGSIn glibc 2.5 and earlier, taking the log() of a NaN produces a bogus invalid floating-point (FE_INVALID) exception.
SEE ALSOcbrt(3), clog(3), log1p(3), sqrt(3)
COLOPHONThis page is part of release 3.21 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/.