Reference to value of STL map element?

Question

Is it OK to pass to function a reference to the value of map element, and to modify it there?

foo(string & s)
{
    s = "xyz";
}

map<int, string> m;
m[1] = "abc";
foo(m[1]); // <-- Is it ok? Will m[1] be "xyz" after this call?

Thank you.

Answer 1

The answer is Yes.

(operator [] returns a reference)

Answer 2

Yes, we can.
And it also works with std::vectors (and since it looks like you're using numeric keys, you may consider using them instead).

Answer 3

Yes.

This is no different to typing m[1] = "xyz". The compiler will reduce it all to about the same thing once its finished with it.

Answer 4

A word of advice: You might want to pass it as a pointer rather than a reference. I do that to make it more obvious to the casual reader that it will be changed.

It's all about communicating clearly with the next guy comming down the pike, who has to maintain this code.

But other than that, yeah, it's completely legal code!