给个例子吧，假如把cin重定向到in.txt，把cout重定向到out.txt
#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main()
{
ofstream out("out.txt");
ifstream in("in.txt");
cin.rdbuf(in.rdbuf());
cout.rdbuf(out.rdbuf());
string s;
cin>>s;
cout<<s<<endl;
return 0;
}#i
