log, log10

Calculates logarithms.

doublelog(doublex**);**

doublelog10(doublex**);**

For additional compatibility information, see Compatibility in the Introduction.

Libraries

Return Value

The log functions return the logarithm of x if successful. If x is negative, these functions return an indefinite (same as a quiet NaN). If x is 0, they return INF (infinite). You can modify error handling by using the _matherr routine.

Parameter

x

Value whose logarithm is to be found

Example

/* LOG.C: This program uses log and log10
 * to calculate the natural logarithm and
 * the base-10 logarithm of 9,000.
 */

#include <math.h>
#include <stdio.h>

void main( void )
{
   double x = 9000.0;
   double y;

   y = log( x );
   printf( "log( %.2f ) = %f\n", x, y );
   y = log10( x );
   printf( "log10( %.2f ) = %f\n", x, y );
}

Output

log( 9000.00 ) = 9.104980
log10( 9000.00 ) = 3.954243

Floating-Point Support Routines

See Also   exp, _matherr, pow