c++ std::stack content will not be free when leaving function

Question

I think in function err_fun, the stack em will be free when leave err_fun(), so the content of em will be free in the same time, and why i can still get right answer in main function with stack st?

Thanks.

#include <stack>

stack<int> st;

void err_fun() {
    stack<int> em;
    st.swap( em );
}

int main() {
    err_fun();

    //... some operation with stack st.
    return 0;
}

Answer 1

The content of em will be copied over as that's what you asked for when you did swap . Since st is global in scope it's not destroyed.