是否可以“准备” cin的输入？

cout

streambuf

#include <iostream>
#include <sstream>
using namespace std;

int main(){
        streambuf *coutbuf = cout.rdbuf(cin.rdbuf());
        cout << \"this goes to the input stream\" << endl;
        string s;
        cin >> s;
        cout.rdbuf(coutbuf);
        cout << \"after cour.rdbuf : \" << s;
        return 0;
}

cin

streambuf

#include <iostream>
#include <sstream>

int main()
{
    std::stringstream s(\"32 7.4\");
    std::cin.rdbuf(s.rdbuf());

    int i;
    double d;
    if (std::cin >> i >> d)
        std::cout << i << \' \' << d << \'\\n\';
}

cin

streambuf

#include <iostream>
#include <sstream>
#include <string>
using namespace std;

int main(){
  stringstream ss;
  ss << \"Here be prepared input for cin\";
  streambuf* cin_buf = cin.rdbuf(ss.rdbuf());
  string s;
  while(cin >> s){
    cout << s << \" \";
  }
  cin.rdbuf(cin_buf);
}

cin

streambuf