функция натурального логарифма (natural logarithm function)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
log, logf, logl — natural logarithm function
Синопсис (Synopsis)
#include <math.h>
double log(double x);
float logf(float x);
long double logl(long double x);
Описание (Description)
The functionality described on this reference page is aligned
with the ISO C standard. Any conflict between the requirements
described here and the ISO C standard is unintentional. This
volume of POSIX.1‐2017 defers to the ISO C standard.
These functions shall compute the natural logarithm of their
argument x, loge(x).
An application wishing to check for error situations should set
errno to zero and call feclearexcept(FE_ALL_EXCEPT) before
calling these functions. On return, if errno is non-zero or
fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW |
FE_UNDERFLOW) is non-zero, an error has occurred.
Возвращаемое значение (Return value)
Upon successful completion, these functions shall return the
natural logarithm of x.
If x is ±0, a pole error shall occur and log(), logf(), and
logl() shall return -HUGE_VAL, -HUGE_VALF, and -HUGE_VALL,
respectively.
For finite values of x that are less than 0, or if x is -Inf, a
domain error shall occur, and either a NaN (if supported), or an
implementation-defined value shall be returned.
If x is NaN, a NaN shall be returned.
If x is 1, +0 shall be returned.
If x is +Inf, x shall be returned.
Ошибки (Error)
These functions shall fail if:
Domain Error
The finite value of x is negative, or x is -Inf.
If the integer expression (math_errhandling &
MATH_ERRNO) is non-zero, then errno shall be set to
[EDOM]. If the integer expression (math_errhandling
& MATH_ERREXCEPT) is non-zero, then the invalid
floating-point exception shall be raised.
Pole Error The value of x is zero.
If the integer expression (math_errhandling &
MATH_ERRNO) is non-zero, then errno shall be set to
[ERANGE]. If the integer expression
(math_errhandling & MATH_ERREXCEPT) is non-zero, then
the divide-by-zero floating-point exception shall be
raised.
The following sections are informative.
Примеры (Examples)
None.
Использование в приложениях (Application usage)
On error, the expressions (math_errhandling & MATH_ERRNO) and
(math_errhandling & MATH_ERREXCEPT) are independent of each
other, but at least one of them must be non-zero.
Обоснование (Rationale)
None.
Будущие направления (Future directions)
None.
Смотри также (See also)
exp(3p), feclearexcept(3p), fetestexcept(3p), isnan(3p),
log10(3p), log1p(3p)
The Base Definitions volume of POSIX.1‐2017, Section 4.20,
Treatment of Error Conditions for Mathematical Functions,
math.h(0p)
