How to set returned value of log10(0)?

Question

Code:

#include <iostream>
#include <math.h>

using namespace std;

int main ()
{
  double result = log10(0.0);
  cout << result;
}

When I execute log10(0) in C++, It prints to me -inf.

Is it fixed for every library/compiler I'll use?

Or could it change in different platforms?

How would you manage the pole error keeping double?

Answer 1

According to cplusplus, it depends on the library what you get for log10(0). However, in general the value of log10(0) is not defined (can be -inf if you like, but it is not a real number). Usually, you should prevent such undefined results (not undefined in the C++ sense of Undefined Behaviour, but in a mathematical sense) before they happen. E.g.

double x;
x = foo();
if ( x <= 0 ) {
    /* handle this case extra */
else {
    y = log10(x);
}

What value you use in the case of log10(0) depends very much on your application. However, I think it is easier to check for 0 before doing the calculation instead of relying on log10(0) returning some particular value (as it might be -inf or something completely different).