Reference on interface as a parameter

Question

Possible Duplicate:
Pointer vs. Reference

I am wondering if there any benefits in using references instead of pointers on some interface. Being more specific let's consider small example:

struct MyInterface {
   virtual ~MyInterface() {}
   virtual void f() = 0;
};

class MyClass : public MyInterface
{
   virtual void f()
   {
      std::cout << "F()" << std::endl;
   }
};


void myFunction(MyInterface& obj);

int main(int argc, char *argv[])
{
   MyInterface* pObj = new MyClass;

   myFunction(*pObj);

   delete pObj;

   getchar();
   return 0;
}

void myFunction(MyInterface& obj)
{
   obj.f();
}

In myFunction instance of MyClass can be passed as a pointer, what is written in many books. My question is what can be considered as a good practice (pointer or reference) and what is more efficient?

Sorry if this question somehow was asked previously.

With references, you're making it clear to the reader that they can't pass null. There'll be no difference in performance. — avakar, Oct 15 '12 at 08:25
But if 0 is passed as a parameter, this will cause a runtime error, am I wrong? — besworland, Oct 15 '12 at 08:28
@besworland, with references, you can't pass 0 at all. With pointers, yes, the code would likely crash when the first virtual function was called. — avakar, Oct 15 '12 at 08:33

score 3 · Accepted Answer · answered Oct 15 '12 at 08:40

Once a value is passed, passing a reference is, performance wise and semantics wise, the same as passing a pointer. In the example you wrote, you are passing a reference obtained from a pointer, so the limitations imposed by reference-input function are invalidated here. Indeed, if you wrote

MyInterface* pObj = 0;
myFunction(*pObj);

You would get a runtime error. But the error is because you are doing

myFunction( *0 );

i.e., because you are dereferencing a null pointer, not because you are passing the zero value. In fact,

myFunction( 0 );

will give you a compile-time exception (which is great).

score 2 · Answer 2 · answered Oct 15 '12 at 08:57

2

It depends upon your need.

Use pointer:

If there's ever a chance that you could want to pass "no object"
If you want ability to point the passed pointer to different location
If you want to get address of pointer variable for some reason

else use reference. A reference is more like a alias to a variable than a pointer to it. This semantics opens some possible optimizations for the compiler and makes it efficient than pointer.

answered Oct 15 '12 at 08:57

sahaj

822
5
17

Good that you mentioned efficiency! That was exactly what I wanted to hear! +1 Thank you. – besworland Oct 15 '12 at 09:01

Reference on interface as a parameter

2 Answers2