Calculates logarithms.
double log( double x );
double log10( double x );
| Routine | Required Header | Compatibility |
| log | <math.h> | ANSI, Win 95, Win NT |
| log10 | <math.h> | ANSI, Win 95, Win NT |
For additional compatibility information, see Compatibility in the Introduction.
Libraries
| LIBC.LIB | Single thread static library, retail version |
| LIBCMT.LIB | Multithread static library, retail version |
| MSVCRT.LIB | Import library for MSVCRT.DLL, retail version |
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