Manpage of LOG

LOG

Section: Linux Programmer's Manual (3)
Updated: 2016-03-15
Index
 

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():

_ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
    || /* Since glibc 2.19: */ _DEFAULT_SOURCE
    || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
 

DESCRIPTION

These functions return the natural logarithm of x.  

RETURN VALUE

On success, these functions return the natural logarithm of x.

If xis a NaN, a NaN is returned.

If xis 1, the result is +0.

If xis positive infinity, positive infinity is returned.

If xis zero, then a pole error occurs, and the functions return -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL, respectively.

If xis 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
errnois set to EDOM. An invalid floating-point exception (FE_INVALID) is raised.
Pole error: x is zero
errnois 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).
InterfaceAttributeValue
log(), logf(), logl() Thread safetyMT-Safe
 

CONFORMING TO

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

The variant returning doublealso 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)


 

Index

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

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Time: 22:27:57 GMT, June 20, 2016