string::replace

 #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;
         }
 }