c++中关于用stringstream进行的类型转化

#include <iostream>
#include <sstream>
using namespace std;
int main()
{
    stringstream ss;
    string s;
    int i=1234;
    ss<<i;
    ss>>s;
    cout<<s<<endl;
    return 0;
}

#include <iostream>
#include <sstream>
using namespace std;
int main()
{
    stringstream ss;
    string s="1234";
    int i;
    ss<<s;
    ss>>i;
    cout<<i<<endl;
    return 0;
}