# log, logf, log10, log10f

Visual Studio .NET 2003

Calculates logarithms.

```double log(
double x
);
float log(
float x
);  // C++ only
long double log(
long double x
);  // C++ only
float logf(
float x
);
double log10(
double x
);
float log10(
float x
);  // C++ only
long double log10(
long double x
);  // C++ only
float log10f (
float x
);
```

#### Parameter

x
Value whose logarithm is to be found.

#### Return Value

The log functions return the logarithm of x if successful. If x is negative, these functions return an indefinite, by default. If x is 0, they return INF (infinite).

Input SEH Exception Matherr Exception
± QNAN,IND none _DOMAIN
± 0 ZERODIVIDE _SING
x < 0 INVALID _DOMAIN

log and log10 has an implementation that uses Streaming SIMD Extensions 2 (SSE2). See _set_SSE2_enable for information and restrictions on using the SSE2 implementation.

#### Remarks

C++ allows overloading, so you can call overloads of log and log10. In a C program, log and log10 always take and return a double.

#### Requirements

log, logf, log10, log10f <math.h> ANSI, Win 98, Win Me, Win NT, Win 2000, Win XP

For additional compatibility information, see Compatibility in the Introduction.

Libraries

All versions of the C run-time libraries.

#### Example

```// crt_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>

int 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
```