Follow-up. Is return reference to x++ defined?

Question

I recently asked the question http://stackoverflow.com/questions/2380803/is-the-behavior-of-return-x-defined

The result was about what I expected, but got me thinking about a similar situation.

If I were to write

class Foo
{   
  ...   
  int x;   
  int& bar() { return x++; }
};

Where bar now returns an int reference, is this behavior defined? If the answer to the previous question is literally true and not just a convenient abstraction of what's going on, it would seem you'd return a reference to a stack variable that would be destroyed as soon as the return was executed.

If it is just an abstraction, I'd be interested to know what behavior is actually guaranteed by a post-increment.

Answer 1

No, you cannot do that, as that would be returning a reference to a temporary.

Answer 2

Your code will result in compilation error. But if you change the post-increment to pre-increment it works. The value of x is incremented and then a reference to this modified x is returned.

The problem with the current code is that you are trying to modify temporary and this is not allowed for the very reason that they are temporary objects.

From this Visual C++ blog article about rvalue references

... C++ doesn't want you to accidentally modify temporaries....