log(3M) Mathematical Library Functions log(3M)NAME
log, logf, logl - natural logarithm function
SYNOPSIS
c99 [ flag... ] file... -lm [ library... ]
#include <math.h>
double log(double x);
float logf(float x);
long double logl(long double x);
DESCRIPTION
These functions compute the natural logarithm of their argument x,
log(e)(x).
RETURN VALUES
Upon successful completion, log() returns the natural logarithm of x.
If x is ±0, a pole error occurs and log(), logf(), and logl() 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 occurs and a NaN is returned.
If x is NaN, a NaN is returned.
If x is 1, +0 is returned.
If x is +Inf, x is returned.
For exceptional cases, matherr(3M) tabulates the values to be returned
by log() as specified by SVID3 and XPG3.
ERRORS
These functions will fail if:
Domain Error The finite value of x is negative, or x is -Inf.
If the integer expression (math_errhandling &
MATH_ERREXCEPT) is non-zero, the invalid floating-point
exception is raised.
The log() function sets errno to EDOM if the value of x
is negative.
Pole Error The value of x is 0.
If the integer expression (math_errhandling &
MATH_ERREXCEPT) is non-zero, the divide-by-zero float‐
ing-point exception is raised.
USAGE
An application wanting to check for exceptions should call feclearex‐
cept(FE_ALL_EXCEPT) before calling these functions. On return, if
fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is
non-zero, an exception has been raised. An application should either
examine the return value or check the floating point exception flags to
detect exceptions.
An application can also set errno to 0 before calling log(). On return,
if errno is non-zero, an error has occurred. The logf() and logl()
functions do not set errno.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Standard │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │MT-Safe │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOexp(3M), feclearexcept(3M), fetestexcept(3M), isnan(3M), log10(3M),
log1p(3M), math.h(3HEAD), matherr(3M), attributes(5), standards(5)SunOS 5.11 12 Jul 2006 log(3M)
