Compute the natural logarithm of a number
#include <math.h> double log( double x ); float logf( float x ); long double logl( long double x );
Your system requirements will determine how you should work with these libraries:
The log(), logf(), and logl() functions compute the natural logarithm (base e) of x:
log_{e} x
To check for error situations, use feclearexcept() and fetestexcept(). For example:
The natural 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.
#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", log(.5) ); except_flags = fetestexcept(FE_ALL_EXCEPT); if(except_flags) { /* An error occurred; handle it appropriately. */ } return EXIT_SUCCESS; }
produces the output:
-0.693147
Safety: | |
---|---|
Cancellation point | No |
Interrupt handler | Yes |
Signal handler | Yes |
Thread | Yes |