map<string, int> M;
for (auto E: M) 
{ 
    cout << E.first << ": " << E.second << endl; 
    F << E.first << ": " << E.second << endl; 
};

我正在学习c++，我对auto感到困惑。我正在尝试将上面的代码转换为下面的代码（上面的代码与auto一起工作正常）

map<string, int> M;
for (map<string, int> :: iterator p = begin(M); p != end(M); p ++ )
{
    cout << p.first << ": " << p.second << endl;
    F << p.first << ": " << p.second << endl;
}

出现以下错误：

error: ‘std::map<std::basic_string<char>, int>::iterator’ has no member named ‘first’
     cout << p.first << ": " << p.second << endl;
 error: ‘std::map<std::basic_string<char>, int>::iterator’ has no member named ‘second’
     cout << p.first << ": " << p.second << endl;
 error: ‘std::map<std::basic_string<char>, int>::iterator’ has no member named ‘first’
     F << p.first << ": " << p.second << endl;
 error: ‘std::map<std::basic_string<char>, int>::iterator’ has no member named ‘second’
     F << p.first << ": " << p.second << endl;

为什么它不工作？