C++: Return std::string reference from stack memory

Question

I will start by saying I've read this topic: C++ Return reference / stack memory. But there, the question was with an std::vector<int> as object-type. But I though the behavior of std::string was different. Wasn't this class especially made for using strings without having to worry about memory-leaks and wrong usage of memory?

So, I already know this is wrong:

std::vector<t> &function()
{
    vector<t> v;
    return v;
}

But is this wrong as well?

std::string &function()
{
    string s = "Faz";
    s += "Far";
    s += "Boo";
    return s;
}

Thanks

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Extra question (EDIT): So, am I correct when I say returning (by value) an std::string doesn't copy the char sequence, only a pointer to the char * array and an t_size for the length?

If this statement is correct, is this the valid way to create a deep copy of a string (to avoid replacing will alter the string)?

string orig = "Baz";
string copy = string(orig);

Answer 1

It doesn't matter what the type is; this pattern is always completely, 100% wrong for any object type T:

T& f() {
    T x;
    return x;
}   // x is destroyed here and the returned reference is thus unusable

If you return a reference from a function, you must ensure that the object to which it refers will still exist after the function returns. Since objects with automatic storage duration are destroyed at the end of the block in which they are declared, they are guaranteed not to exist after the function returns.