Question

In my header file, I have

    typedef map <string, MyClass*> myMap;

    class MainClass {
      myMap map;
    public:
      friend istream& operator>> (istream &is, MainClass &mainc) {
        string name = "Geo";
        MyClass* sample = new MyClass();
        map.insert(myMap::value_type(name, sample) );
        return is; }
    };

During compilation, I get:

line 4: error: invalid use of non-static data member 'MainClass::map'
line 9: error: from this location

I have tried changing myMap map to myMap mapa but I’m getting the same error.

Answer 1

Since your operator>> is a friend to MainClass, it’s not associated with a specific instance of MainClass (i.e., it doesn’t receive a this pointer).

Therefore, when you try to do:

map.insert(myMap::value_type(name, sample) );

The compiler doesn’t know what instance’s map member you want to refer to. Clearly, in this case, you mean:

mainc.map.insert(myMap::value_type(name, sample));

…since mainc is the instance of MainClass whose reference you received as the destination for the data you read.