Use of C# 'ref' keyword compared to C++

Question

I have mainly worked in C++ and I am now using C# at my new job, and after doing some reading on here about the 'ref' keyword and c# value vs reference types I am still finding some confusion with them.

As far as I'm understanding these if you were passing these to a method these would be analogous C++ styles:

Value types:

public void CSharpFunc(value)

and

public void CPlusplusFunc(value)

Reference types:

public void CSharpFunc(reference)

and

public void CPlusPlusFunc(&reference)

'ref' / pointer

public void CSharpFunc(ref bar)

and

public void CPlusPlus(*bar)

Is this a correct analogy?

Answer 1

Is this a correct analogy?

Despite what the other answers say, no. What ref means in terms of C++ actually depends on the type. For value types, your assessment is correct (or close enough). For reference types, a more suitable analogy would be a reference-to-pointer:

public void CPlusPlus(type*& bar)

The whole point about ref is that you can change the reference being passed in. And you can’t do that in C++ by simply passing a pointer:

void f(type* bar) {
    bar = new_address;
}

type* x;
f(x);

This code won’t change the caller’s value of x. If you had passed bar as type*&, on the other hand, it would have changed the value. That is what ref does.

Furthermore, a reference in C# is quite unlike a reference in C++, and much more like a pointer in C++ (in that you can change which object the reference refers to).