difference between a pointer and reference parameter?

c++ pointers reference object-slicing
criddell picture criddell · Mar 6, 2009 · Viewed 38.9k times · Source

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

shoosh picture shoosh · Mar 6, 2009

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.

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