Man Pages

LOG


NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
ATTRIBUTES
CONFORMING TO
BUGS
SEE ALSO
COLOPHON

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():

_BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 600 || _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L;
or cc -std=c99

DESCRIPTION

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).

CONFORMING TO

C99, POSIX.1-2001, POSIX.1-2008.

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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