c++ 交换两个容器（swap）

#include <iostream>
#include <vector>
using namespace std;
int main ()
{
    vector<int> foo (,);   // three ints with a value of 100
    vector<int> bar (,);   // five ints with a value of 200

    foo.swap(bar);

    cout << "foo contains:";
    for (unsigned i=; i<foo.size(); i++)
        cout << ' ' << foo[i];
    cout << '\n';

    cout << "bar contains:";
    for (unsigned i=; i<bar.size(); i++)
        cout << ' ' << bar[i];
    cout << '\n';

    return ;
}