# log10(), log10f(), log10l()

Compute the logarithm (base 10) of a number

## Synopsis:

```#include <math.h>

double log10( double x );

float log10f( float x );

long double log10l( long double x );
```

## Arguments:

x
The number that you want to compute the log of.

## Library:

libm

Use the -l m option to qcc to link against this library.

## Description:

These functions compute the base 10 logarithm of x:

log10 x

To check for error situations, use feclearexcept() and fetestexcept(). For example:

• Call feclearexcept(FE_ALL_EXCEPT) before calling log10(), log10f(), or log10l().
• On return, if fetestexcept(FE_ALL_EXCEPT) is nonzero, then an error has occurred.

## Returns:

The base 10 logarithm of x.

If x is: These functions return: Errors:
x is ±0.0 -Inf FE_DIVBYZERO
1.0 +0.0
Less than 0.0 and finite, or -Inf NaN FE_INVALID
Inf Inf
NaN NaN

These functions raise FE_INEXACT if the FPU reports that the result can't be exactly represented as a floating-point number.

## Examples:

```#include <stdio.h>
#include <math.h>
#include <fenv.h>
#include <stdlib.h>

int main( void )
{
int except_flags;

feclearexcept(FE_ALL_EXCEPT);

printf( "%f\n", log10(.5) );

except_flags = fetestexcept(FE_ALL_EXCEPT);
if(except_flags) {
/* An error occurred; handle it appropriately. */
}

return EXIT_SUCCESS;
}
```

produces the output:

```-0.301030
```

## Classification:

Safety:
Cancellation point No
Interrupt handler No
Signal handler No