C++: Performance impact of BIG classes (with a lot of code)

Question

I wonder if and how writing \"almighty\" classes in c++ actually impacts performance.

If I have for example, a class Point, with only uint x

Answer 1

These 2 bits of code are identical:

Point x;
int l=x.getLength();

int l=GetLength(x);

given that the class Point has a non-virtual method getLength(). The first invocation actually calls int getLength(Point &this), an identical signature as the one we wrote in our second example. (*)

This of course wouldn't apply if the methods you're calling are virtual, since everything would go through an extra level of indirection (something akin to the C-style int l=x->lpvtbl->getLength(x)), not to mention that instead of 2 int's for every pixel you'd actually have 3, the extra one being that pointer to the virtual table.

(*) this isn't exactly true, the "this" pointer is passed through one of the cpu registers instead of through the stack, but the mechanism could have easily worked either way.