Error assigning object to pointer c++

Question

Me and my friend are making a text based game in c++ for fun, and to learn a little more. I have been trying to use pointers to classes, but am having no luck, and some errors are occurring which make absolutely no sense to me at all, and am hoping someone can help me.

Code:

    //Map.h
    #include "Player.h"

    class Map
    {
        //Virtual functions
    };

    class StartMap : public Map
    {
        //Code
    }Start;

    class JungleMap : public Map
    {
        //Code
    }Jungle;

    class RiverMap : public Map
    {
        //Code
    }River;


    //Player.h
    #ifndef MAP_H
    #define MAP_H
    #endif

    class Player
    {
        private:
            Map *PlayerMap;
            //Other variables
        public:
            void Initialize()
            {
                //Initialize variables
                PlayerMap = &Start; //This is where the error occurs, says there's a
                                    //<error-type>*Player::PlayerMap. Tried putting
                                    //this->PlayerMap = &Start, didn't help
                                    //There's no error when I make the pointer
            }

            //Bunch of other functions
    }Player;

Okay, here's my code since I decided to add .cpp files:

    //Command.h
    class Command
    {
    private:
    string GameCommand;

    void Trim();

    public:
    Command (string command) {GameCommand = command;}
    Command () {}
    void operator = (string command) {GameCommand = command;}

    void ReadCommand();

    string Print();
    }


    //Command.cpp
    #include <iostream>
    #include <string>
    #include "Command.h"
    #include "Parameter.h"

    using namespace std;

    void Command::Trim()
        {
        int LeadingPos = 0, MidCount = 0, TrailingPos = GameCommand.length()-1, Size = 0;
        string TempCommand = "";
        while (GameCommand[LeadingPos] == ' '){LeadingPos += 1;}
        while (GameCommand[TrailingPos] == ' '){TrailingPos -= 1;}
        Size = ((TrailingPos+1)-LeadingPos);
        for (int loops = 0; loops < Size; loops++)
        {
            if (MidCount > 0 && GameCommand[LeadingPos] == ' ')
            {
                LeadingPos += 1;
            }
            else
            {
                if (GameCommand[LeadingPos] == ' ')
                {
                    MidCount += 1;
                }
                TempCommand += GameCommand[LeadingPos];
                LeadingPos += 1;
            }
        }
        GameCommand = TempCommand;
    }

    void Command::ReadCommand()
    {
        Trim();
        string Parameter;
        if (GameCommand.substr(0,3) == "go ")
        {
            Parameter = GameCommand.substr(3,string::npos);
            CommandParameter.Go(Parameter);
        }
        else if (GameCommand.substr(0,4) == "dig ")
        {
            Parameter = GameCommand.substr(4,string::npos);
            CommandParameter.Dig(Parameter);
        }
        else if (GameCommand.substr(0,4) == "eat ")
        {
            Parameter = GameCommand.substr(4,string::npos);
            CommandParameter.Eat(Parameter);
        }
        else if (GameCommand.substr(0,4) == "exit" || GameCommand.substr(0,4) == "quit")
        {
            exit(0);
        }
        else if (GameCommand.substr(0,4) == "use ")
        {
            Parameter = GameCommand.substr(4,string::npos);
            CommandParameter.Use(Parameter);
        }
        else if (GameCommand.substr(0,5) == "drop ")
        {
            Parameter = GameCommand.substr(5,string::npos);
            CommandParameter.Drop(Parameter);
        }
        else if (GameCommand.substr(0,5) == "grab " || GameCommand.substr(0,5) == "take ")
        {
            Parameter = GameCommand.substr(5,string::npos);
            CommandParameter.Pickup(Parameter);
        }
        else if (GameCommand.substr(0,5) == "help ")
        {
            Parameter = GameCommand.substr(5,string::npos);
            CommandParameter.Help(Parameter);
        }
        else if (GameCommand.substr(0,5) == "look ")
        {
            Parameter = GameCommand.substr(5,string::npos);
            CommandParameter.Look(Parameter);
        }
        else if (GameCommand.substr(0,5) == "sleep")
        {
            CommandParameter.Sleep();
        }
        else if (GameCommand.substr(0,6) == "check ")
        {
            Parameter = GameCommand.substr(6,string::npos);
            CommandParameter.Check(Parameter);
        }
        else if (GameCommand.substr(0,6) == "climb ")
        {
            Parameter = GameCommand.substr(6,string::npos);
            CommandParameter.Climb(Parameter);
        }
        else if (GameCommand.substr(0,6) == "throw ")
        {
            Parameter = GameCommand.substr(6,string::npos);
            CommandParameter.Throw(Parameter);
        }
        else if (GameCommand.substr(0,7) == "attack ")
        {
            Parameter = GameCommand.substr(7,string::npos);
            CommandParameter.Attack(Parameter);
        }
        else if (GameCommand.substr(0,7) == "search ")
        {
            Parameter = GameCommand.substr(7,string::npos);
            CommandParameter.Search(Parameter);
        }
        else
        {
            cout << "Not a valid command.\n";
        }
    }

    string Print()
    {
        return GameCommand;
    }

The string GameCommand is what's not working.

Answer 1

class StartMap : public Map;

is syntactically incorrect. You need

class StartMap : public Map
{
   // Details of class
} Start;

You need to make similar changes to JungleMap and RiverMap.

Answer 2

First thing I noticed was the semi-colon after each inheritance declaration.. class XXXXX : public Map; <-- that semi-colon shouldn't be there..

In the initialize function, I'm fairly certain you mean PlayerMap = new StartMap();

You'll need a destructor to delete it and a copy, move constructor as well as an assignment operator in order to assign, move or copy the class.

You can follow this to make the class conform to RAII: What is the copy-and-swap idiom?

Answer 3

There are lots of problems with your code layout.

This doesn't do anything:

//Player.h
#ifndef MAP_H
#define MAP_H
#endif

I guess you are trying to do an include guard. The proper layout is:

#ifndef PLAYER_H
#define PLAYER_H

// all your code for the header file goes here
class Player 
{ 
// ....
};

#endif    // no more code after this line

The next issue is that Player.h should include Map.h, not the other way around. Imagine you are the compiler. You are processing Player.h. You get down as far as Map *PlayerMap; . But you don't know what Map is because you haven't seen Map.h yet. So you have to give an error and stop compiling.

The map definitions in Map.h should look like:

class StartMap : public Map
{
    //Code
};

The Start; you had on the end is poor style. It would cause undefined behaviour if two different .cpp files included Map.h because there would be two different global variables with the same name.

Moving onto the void Map::Initialize() function. You're supposed to use the constructor for initialization. Either way, my suggestion is that you don't implement this in Player.h. Instead, just have void Initialize();, and then in Map.cpp you could have:

// the global variables
StartMap start_map;
JungleMap jungle_map;

void Map::Initialize()
{
    player_map = &start_map;
}

It's a good idea to use a different naming convention for classes than for variables. So that when someone sees StartMap for example, they know immediately whether it is a class name or a variable name.