double log (      double x );
      float log (       float x );
long double log ( long double x );

<cmath>

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.

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

Portability

Example

/* 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