求挑错 stringstream operator<< 应用.该怎么解决

求挑错 stringstream operator<< 应用.

C/C++ code

#include <iostream>#include <string>#include <sstream>using namespace std;int main(){    string fmtStr = "1234 5678";    stringstream io(fmtStr);    string num1, num2;    io.seekg(0);    io >>num1 >>num2;    io.seekp(0);    io <<num2 <<num1;        cout <<io.str() <<endl;         // 输出的还是 1234 5678, 我认为应该是 5678 1234. 不知错在哪里了.    return 0;}

C/C++ code

int main(){    string fmtStr = "1234 5678";    stringstream io(fmtStr);    string num1, num2;    io.seekg(0);    io >>num1 >>num2;    io.clear();//这儿错了    io.seekp(0);    io <<num2<<" "<<num1;//这儿    cout <<io.str() <<endl;    return 0;}