float logf( float arg );
(1) (since C99)double log( double arg );
(2)long double logl( long double arg );
(3) (since C99)#define log( arg )
(4) (since C99)1-3) Computes the natural (base e) logarithm of arg.
4)Type-generic macro: If
arghas type
long double,
logl
is called. Otherwise, if
arghas integer type or the type
double,
log
is called. Otherwise,
logf
is called. If
argis complex or imaginary, then the macro invokes the corresponding complex function (
clogf,
clog,
clogl).
[edit] Parameters arg - floating-point value [edit] Return valueIf no errors occur, the natural (base-e) logarithm of arg (ln(arg) or loge(arg)) is returned.
If a domain error occurs, an implementation-defined value is returned (NaN where supported).
If a pole error occurs, -HUGE_VAL, -HUGE_VALF, or -HUGE_VALL is returned.
Errors are reported as specified in math_errhandling.
Domain error occurs if arg is less than zero.
Pole error may occur if arg is zero.
If the implementation supports IEEE floating-point arithmetic (IEC 60559),
#include <errno.h>
#include <fenv.h>
#include <float.h>
#include <math.h>
#include <stdio.h>
// #pragma STDC FENV_ACCESS ON
int main(void)
{
printf("log(1) = %f\n", log(1));
printf("base-5 logarithm of 125 = %f\n", log(125) / log(5));
// special values
printf("log(1) = %f\n", log(1));
printf("log(+Inf) = %f\n", log(INFINITY));
// error handling
errno = 0; feclearexcept(FE_ALL_EXCEPT);
printf("log(0) = %f\n", log(0));
if (errno == ERANGE)
perror(" errno == ERANGE");
if (fetestexcept(FE_DIVBYZERO))
puts(" FE_DIVBYZERO raised");
}
Output:
log(1) = 0.000000
base-5 logarithm of 125 = 3.000000
log(1) = 0.000000
log(+Inf) = inf
log(0) = -inf
errno == ERANGE: Numerical result out of range
FE_DIVBYZERO raised[edit] References
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