如果执行下面C++代码后，输出的结果是“gesp ccf org cn ”，则横线上应填入哪个代码？（    ）

#include <iostream> 

using namespace std;

int main() {

    string str = "gesp.ccf.org.cn";

    string delimiter = "."; 

    string result=""; 

    string token;

    size_t found = str.find(delimiter); 

    while (found != string::npos) {

        token = str.substr(0, found); 

        result += token;

        result += " ";

        __________// 在此处填入代码

        found = str.find(delimiter);

        }

    //最后一部分result += str;

    result += " ";

    cout << result << endl; return 0;

}