натуральная логарифмическая функция (natural logarithmic function)
Имя (Name)
log, logf, logl - natural logarithmic function
Синопсис (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 <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
Описание (Description)
These functions return the natural logarithm of x.
Возвращаемое значение (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.
Ошибки (Error)
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.
Атрибуты (Attributes)
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│log(), logf(), logl() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
Стандарты (Conforming to)
C99, POSIX.1-2001, POSIX.1-2008.
The variant returning double also conforms to SVr4, 4.3BSD, C89.
Ошибки (баги) (Bugs)
In glibc 2.5 and earlier, taking the log() of a NaN produces a
bogus invalid floating-point (FE_INVALID) exception.
Смотри также (See also)
cbrt(3), clog(3), log10(3), log1p(3), log2(3), sqrt(3)
