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State/class factory problem

siery (13)
Hello!
I been trying to some kind structure my game data. In the book "Game Programming Gems" I find a Factory Pattern witch I pretty much understand but I can not get the syntax used in the example. The example looks like this:

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BasClass* ClassFactory::CreateObject(int id) {
  BaseClass* pClass = 0;
  switch (id) {
  case 1:
    pClass = new Class1;
    break;
  case 2:
    pClass = new Class2;
    break;
  case 3:
    pClass = new Class3;
    break;
  default:
    assert("*Error! Invalide class ID passed to the factory!");
  };

  // pointed class common initialization
  pClass->Init();

  return pClass;

}


So BasClass* is a type of the CreateObject function. Cool idea, Then I could pass there my "game_state objects" and get initialized date in one place, also share the data between states truth the "BaseState"/"BaseClass". And there is a lot of other benefits of this structure. And I guess I could include all states header into this Factory so it will take care of all initializations.
The think I don't understand is how you make this BaseClass*.

I want it to represent States in my game so I write a simple parent class like:

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class State {
 public:
 State(): id(0) {}
  ~State();

  virtual void Init();

 protected:
  int id;
  
};


And then base for a state will look like:

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class Menu: public State {
 public:
 Menu(): id(1) {}
  ~Menu() {printf("Menu state deleted");}
  
  void Init() {printf("Menu state entered.");}
  
 private:

};


But compiler does not see the "id" entry in children classes, even when I made it public, in the parent class,
../src/menu.h:13:10: error: class ‘Menu’ does not have any field named ‘id’

Am I thinking right about the "BaseClass"? Whats wrong with the code that code? Thank you!
Last edited on
gunnerfunner (2127)
compiler does not see the "id" entry in children classes, even when I made it public

you are using member initialization in the Menu ctor, so the program expects Menu to have a data-member id but it is not declared anywhere in your code and the compiler cannot 'fetch' State's id data-member unless you tell it to. One way to do this would be:
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#include <iostream>

class State {
 public:
 State(int x): id(x) {}//overloading the State ctor 
  ~State();

  virtual void Init();

 public:
  int id;

};
class Menu: public State {
public:
  //  using State::id;
Menu(): State(1) {}
~Menu() {std::cout << "Menu state deleted \n";}

void Init() {std::cout << "Menu state entered \n";}

private:

};

Note you can't just declare anothe data-member id in Menu and expect the complier to know that this is the same as State's id data-member, instead it'll hide/shadow the base class data member and you'd have to use scope resolution (State::id) to make it explicit
how you make this BaseClass*.

just as your book did on line 2, by declaring the variable and initializing it though I'd prefer pClass = nullptr instead
btw printf() is C, not C++
AbstractionAnon (6954)
So BasClass* is a type of the CreateObject function.

No. BasClass is a base class of Class1, Class2, Class3.

Line 14: assert() takes an int value, not a char array.
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