Question

Are these the same:

int foo(bar* p) {   return p->someInt(); } 

and

int foo(bar& r) {   return r.someInt(); } 

Ignore the null pointer potential. Are these two functions functionally identical no matter if someInt() is virtual or if they are passed a bar or a subclass of bar?

Does this slice anything:

bar& ref = *ptr_to_bar; 

Answer 1

C++ references are intentionally not specified in the standard to be implemented using pointers. A reference is more like a ‘synonym’ to a variable than a pointer to it. This semantics opens some possible optimizations for the compiler when it’s possible to realize that a pointer would be an overkill in some situations.

A few more differences:

• You can’t assign NULL to a reference. This is a crucial difference and the main reason you’d prefer one over the other.
• When you take the address of a pointer, you get the address of the pointer variable. When you take the address of a reference, you get the address of the variable being referred to.
• You can’t reassign a reference. Once it is initialized it points to the same object for its entire life.