log(), logf(), logl()
Compute the natural logarithm of a number
Synopsis:
#include <math.h> double log( double x ); float logf( float x ); long double logl( long double x );
Arguments:
- x
- The number that you want to compute the natural log of.
Description:
The log() and logf() functions compute the natural logarithm (base e) of x:
loge x
A domain error occurs if x is negative. A range error occurs if x is zero.
Returns:
The natural logarithm of x. For finite values of x less than zero, these functions return NaN. The return value when x is -Inf is NaN.
If an error occurs, these functions return 0, but this is also a valid
mathematical result.
If you want to check for errors, set
errno
to 0, call the function, and then check errno again.
These functions don't change errno if no errors occurred.
Examples:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main( void )
{
printf( "%f\n", log(.5) );
return EXIT_SUCCESS;
}
produces the output:
-0.693147
Classification:
| Safety: | |
|---|---|
| Cancellation point | No |
| Interrupt handler | No |
| Signal handler | No |
| Thread | Yes |