rvalue reference—"An rvalue may be used to initialize an rvalue reference to extend its lifetime until the scope of the reference ends."

Question

The code below is what i used to test the feature. G++ compiled it successfully but something went wrong when running it.

#include <iostream>
#include <vector>

using namespace std;

vector<int> &&ff()
{
    vector<int> AA({1, 2, 4, 
5, 7, 8});
    return std::move(AA);
}

int main(void)
{
    cout << ff()[0] << endl;

    return 0;
}

The output is as follows:

6822576

[Done] exited with code=0 in 0.633 seconds

Answer 1

Lifetime extension rule only works for temporaries; while AA is a local object and would be destroyed when ff returns. Its lifetime won't be extended even it's bound to the return value of ff in the return statement. ff() always returns a dangling reference and ff()[0] leads to UB.