Performance: Reference vs. value as function parameters

Question

I have got a function which I need to pass a value to for read-only purposes only.

For example:

unsigned short strlen(String str)
{
  short i = 0;
  while(str[i] != '\0')
    i++;
  return i;
}

As you can see, I do not want to change the original value I work with, I only need to read its length. Would it - in terms of performance - be better to replace the parameter String str , which is making a copy of the original variable, by a reference like String &str ?

Answer 1

Would it - in terms of performance - be better to replace the parameter String str, which is making a copy of the original variable, by a reference like String &str?

Yes, it would. Instead of creating a copy, which you do not seem to need here, a reference would be bound. Since you are not modifying the object, a reference to const would be better:

unsigned short strlen(String const& str)
//                           ^^^^^^