function
log
<cmath>
double log ( double x );
float log ( float x );
long double log ( long double x );
Compute natural logarithm
Returns the natural logarithm of
x.
The natural logarithm is the base-e logarithm, the inverse of the natural exponential function (
exp). For base-10 logarithms, a specific function
log10 exists.
In C++, this function is overloaded in
<complex> and
<valarray> (see
complex log and
valarray log).
Parameters
- x
- Floating point value.
If the argument is negative, a domain error occurs, setting the global variable errno to the value EDOM.
If it is zero, the function returns a negative HUGE_VAL and sets the value of the global variable errno to the ERANGE value.
Return Value
Natural logarithm of
x.
Portability
In C, only the
double version of this function exists with this name.
Example
1 2 3 4 5 6 7 8 9 10 11 12
|
/* log example */
#include <stdio.h>
#include <math.h>
int main ()
{
double param, result;
param = 5.5;
result = log (param);
printf ("ln(%lf) = %lf\n", param, result );
return 0;
}
|
Output:
See also
- log10
- Compute common logarithm (function)
- exp
- Compute exponential function (function
)
- pow
- Raise to power (function
)