假设有这样一段程序:           
                              
                                     fin.open(file.txt);
                                     string str="abc";
                                     while(fin.find(const &string str) )  //这个函数是猜的不知道有没有啊
                                      {  int count=1;
                                          count++;
                                       }
                    该如何把输入流中的字符"abc"改为jks"啊?