#include <string>

 #include <cctype>

 #include <algorithm>

 #include <iostream>

 #include <list>

 using namespace std;

 class Base{

 public:

         int data;

         Base(int y):data(y){}

 };

 Base *pt(int x){

         Base *tmp = new Base(x);

         return tmp;

 }

 int main()

 {

         string str("this is a test");

         char rpV = '^';

         string::size_type pos = ;

         while((pos = str.find(" ")) != string::npos){

                 //replace(pos, nct1, nct2, ch); 用重复n次的c字符替换从指定位置pos长度为len的内容

                 str.replace(pos,,, rpV);

                 cout << str << endl;

         }

 }