log


function
<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:

ln(5.500000) = 1.704748


See also