怎么对string 类型的字符串进行增删改查

简单介绍下如何对字符串中的子串进行增删改查，并通过下面实例的伪代码进行简单展示

字符串子串的查找

   string  strfind = "test for find [user] login system";
   string key {"[user]"};
   auto pos = strfind.find(key);
       if(pos != string::npos){  //判断一下是否存在子串
   }

字符串子串的删除

    string strfind = "test for find [user] login system";
    string key{"user"};
    auto pos = strfind.find(key);
    if(pos != string::npos){
        for (int i = pos; i <= strfind.size(); i++)
        {
           cout << strfind[i + key.size()];
           strfind[i] = strfind[i + key.size()];
        }
    }

字符串子串的替换

   string strfind = "test for find [user] login system";
   string key {"[user]"};
   auto pos = strfind.find(key);
   if(pos != string::npos){
       auto rep = strfind.replace(pos, key.size(), "root");
   }

字符串子串增加

    //末尾增加字串
	string strfind = "test for find [user] login system";
	string substr{"user"};
	strfind += substr;