log, logf, logl - natural logarithmic function

Attributes

       For an explanation of the terms used in this section, see attributes(7).
       ┌─────────────────────────────────────────────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                                                                   │ Attribute     │ Value   │
       ├─────────────────────────────────────────────────────────────────────────────┼───────────────┼─────────┤
       │ log(), logf(), logl()                                                       │ Thread safety │ MT-Safe │
       └─────────────────────────────────────────────────────────────────────────────┴───────────────┴─────────┘

Bugs

       In glibc 2.5 and earlier, taking the log() of a NaN produces a bogus invalid floating-point  (FE_INVALID)
       exception.

Description

       These functions return the natural logarithm of x.

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.

History

       C99, POSIX.1-2001.

       The variant returning double also conforms to SVr4, 4.3BSD, C89.

Library

       Math library (libm, -lm)

Name

       log, logf, logl - natural logarithmic function

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.

Standards

       C11, POSIX.1-2008.

Synopsis

#include<math.h>doublelog(doublex);floatlogf(floatx);longdoublelogl(longdoublex);

   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