Is Returning by Reference Useless?

Question

Coming from a C# background, I was more or less puzzled by the seemly weird behavior of returning method handling in C++. My concern now is for a method in C++, returning by reference is not a very useful technique, this is because-- unlike C#--any variable declared inside a method body will go out of scope once the the control exit the method.

So, in C++, this cannot even compile ( but an equivalent version in C# can):

int& DoubleValue(int nX)
{
    int nValue = nX * 2;
    return nValue; // return a reference to nValue here
} // nValue goes out of scope here

The only time where returning by reference is useful is when you are returning a reference to an existing data member in a class, or you are returning a reference to an element inside a parameter of the method. But in both cases there is really no need to return anything; as the returned reference is already freely available to the caller of the method.

So, my conclusion is, there is no need to use return by reference at all. Am I right?

Answer 1

Operations like std::vector<>::operator[] return references to elements obtained by dereferencing a pointer (and adding offsets to it). The pointer in that case is a private member internal to the vector, and so not something the user could have obtained themselves without breaking the abstraction of the class.