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():

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), log10(3), log1p(3), log2(3), sqrt(3)

COLOPHON¶

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