Use of Factory Method pattern in C++

I am looking for an actual example of the use of Factory method pattern in C++. Is there any source code ex开发者_JS百科ample that gives a good illustration.

I like what does Codeproject teaches:

http://www.codeproject.com/KB/architecture/FactoryPattBasics.aspx

class CUIFrameWork 
{
public:
    // Instead of hard coding we write factory methods which
    // perform the task of object creation.
    virtual CDataComponent* MakeDataComp()
    {
        return new CDataComponent(); 
    }

    virtual CUIComponent* MakeUIComp()
    {
        return new CUIComponent();
    } 

    virtual CToolBarComponent* MakeToolBarComp( UINT nID )
    {
        return new CToolBarComponent( nID );
    } 

    CUITemplate* CreateUI()
    {
        CDataComponent* pData = MakeDataComp();
        CUIComponent* pUI = MakeUIComp();
        CToolBarComponent* pTooBar1 = MakeToolBarComp( ID_STANDARD );
        CToolBarComponent* pTooBar2 = MakeToolBarComp( ID_CUSTOM );
        pTooBar2->AddDropDownButton();
        pTooBar2->AddComboBox();

        pUI->AddToolBar(pTooBar1);
        pUI->AddToolBar(pTooBar2);

        return new CUITemplate( pData, pUI );
    }
};

struct pa_diddle { virtual ~pa_diddle(); virtual void diddle() = 0; };

struct bo_diddle : pa_diddle { void diddle() { bo(); }};
struct lee_diddle : pa_diddle { void diddle() { lee(); }};

struct diddle_builder
{
  enum name { BO, LEE };

  pa_diddle * build_diddle(name n)
  {
    switch(n)
    {
    case BO:  return new bo_diddle();
    case LEE: return new lee_diddle();
    }
  }
};

Crud, I totally missed that you were looking for Factory Method, not Abstract Factory. That's what I just gave an example of.

Here's Factory Method:

struct some_abstraction { ... };

struct some_class
{
  ... functions and stuff ...

  struct something_only_some_class_knows_about : some_abstraction {};
  some_abstraction* create_whatnot() const { return new something....about; }
};

Direct example from GoF: (sorry for verbosity)

/*
*/
class Product {};

#ifdef Implementation1
class MyProduct : public Product {};
class YourProduct : public Product {};
class TheirProduct : public Product {};
typedef int ProductId;
const int MINE = 1;
const int YOURS = 2;
const int THEIRS = 2;
/*
*/
class Creator {
public:
    virtual Product* Create(ProductId);
};
/*
*/
Product* Creator::Create (ProductId id) {
    if (id == MINE)  return new MyProduct;
    if (id == YOURS) return new YourProduct;
    // repeat for remaining products...

    return 0;
}
/*
*/
class MyCreator : public Creator {
public:
    virtual Product* Create(ProductId);
};
/*
*/
Product* MyCreator::Create (ProductId id) {
    if (id == YOURS)  return new MyProduct;
    if (id == MINE)   return new YourProduct;
        // N.B.: switched YOURS and MINE

    if (id == THEIRS) return new TheirProduct;

    return Creator::Create(id); // called if all others fail
}
/*
*/
#endif
#ifdef Implementation2
/*
*/
class Creator {
public:
    Product* GetProduct();
protected:
    virtual Product* CreateProduct();
private:
    Product* _product;
};
/*
*/
Product* Creator::GetProduct () {
    if (_product == 0) {
        _product = CreateProduct();
    }
    return _product;
}
/*
*/
#endif
#ifdef Implementation3
/*
*/
class Creator {
public:
    virtual Product* CreateProduct() = 0;
};
/*
*/
template <class TheProduct>
class StandardCreator: public Creator {
public:
    virtual Product* CreateProduct();
};
/*
*/
template <class TheProduct>
Product* StandardCreator<TheProduct>::CreateProduct () {
    return new TheProduct;
}
/*
*/
class MyProduct : public Product {
public:
    MyProduct();
    // ...
};

StandardCreator<MyProduct> myCreator;
/*
*/
#endif
/*
*/
#include "C++/MazeParts.H"
/*
*/
class MazeGame {
public:
    Maze* CreateMaze();
/*
*/
// factory methods:
/*
*/
    virtual Maze* MakeMaze() const
        { return new Maze; }
    virtual Room* MakeRoom(int n) const
        { return new Room(n); }
    virtual Wall* MakeWall() const
        { return new Wall; }
    virtual Door* MakeDoor(Room* r1, Room* r2) const
        { return new Door(r1, r2); }
};
/*
*/
Maze* MazeGame::CreateMaze () {
    Maze* aMaze = MakeMaze();
/*
*/
    Room* r1 = MakeRoom(1);
    Room* r2 = MakeRoom(2);
    Door* theDoor = MakeDoor(r1, r2);
/*
*/
    aMaze->AddRoom(r1);
    aMaze->AddRoom(r2);
/*
*/
    r1->SetSide(North, MakeWall());
    r1->SetSide(East, theDoor);
    r1->SetSide(South, MakeWall());
    r1->SetSide(West, MakeWall());
/*
*/
    r2->SetSide(North, MakeWall());
    r2->SetSide(East, MakeWall());
    r2->SetSide(South, MakeWall());
    r2->SetSide(West, theDoor);
/*
*/
    return aMaze;
}
/*
*/
class BombedMazeGame : public MazeGame {
public:
    BombedMazeGame();
/*
*/
    virtual Wall* MakeWall() const
        { return new BombedWall; }
/*
*/
    virtual Room* MakeRoom(int n) const
        { return new RoomWithABomb(n); }
};
/*
*/
class EnchantedMazeGame : public MazeGame {
public:
    EnchantedMazeGame();
/*
*/
    virtual Room* MakeRoom(int n) const
        { return new EnchantedRoom(n, CastSpell()); }
/*
*/
    virtual Door* MakeDoor(Room* r1, Room* r2) const
        { return new DoorNeedingSpell(r1, r2); }
protected:
    Spell* CastSpell() const;
};
/*
*/

=====================================================================

//Mazeparts.h #included file

#ifndef MazeParts_H
#define MazeParts_H

#include "defs.H"

enum Direction { North, East, South, West };
#ifndef MapSite_H
#define MapSite_H

class MapSite {
public:
    virtual void Enter() = 0;
};

#endif
#ifndef _H
#define _H

class Room : public MapSite {
public:
    Room(int = 0);
    Room(const Room&);

    virtual Room* Clone() const;
    void InitializeRoomNo(int);

    MapSite* GetSide(Direction);
    void SetSide(Direction, MapSite*);

    virtual void Enter();
private:
    MapSite* _sides[4];
    int _roomNumber;
};
#endif
#ifndef Wall_H
#define Wall_H

class Wall : public MapSite {
public:

    Wall();
    Wall(const Wall&);
    virtual Wall* Clone() const;
    virtual void Enter();
};
#endif
#ifndef Door_H
#define Door_H

class Door : public MapSite {
public:
    Door(Room* = 0, Room* = 0);
    Door(const Room&);

    virtual Door* Clone() const;
    void Initialize(Room*, Room*);

    virtual void Enter();
    Room* OtherSideFrom(Room*);
private:
    Room* _room1;
    Room* _room2;
    bool _isOpen;
};
#endif
#ifndef Maze_H
#define Maze_H

class Maze {
public:
    Maze();
    Maze(const Maze&);
    Room* RoomNo(int);
    void AddRoom(Room*);

    virtual Maze* Clone() const;
private:
    // ...
};
#endif
#ifndef BombedWall_H
#define BombedWall_H

class BombedWall : public Wall {
public:
    BombedWall(bool bombed = false);
    BombedWall(const BombedWall&);

    virtual Wall* Clone() const;
    void Intialize(bool);

    virtual void Enter();
private:
    bool _bomb;
};
#endif
#ifndef RoomWithABomb_H
#define RoomWithABomb_H

class RoomWithABomb: public Room {
public:
    RoomWithABomb(int = 0, bool bombed = false);
    RoomWithABomb(const RoomWithABomb&);
    bool HasBomb();
private:
    bool _bomb;
};

#endif
#ifndef EnchantedRoom_H
#define EnchantedRoom_H

class Spell;

class EnchantedRoom : public Room {
public:
    EnchantedRoom(int, Spell* = 0);
    EnchantedRoom(const EnchantedRoom&);
    bool HasSpell();
    Spell PickUpSpell();
private:
    Spell* _spell;
};

#endif
#ifndef DoorNeedingSpell_H
#define DoorNeedingSpell_H

class  DoorNeedingSpell : public Door {
public:
    DoorNeedingSpell(Room*, Room*);
    DoorNeedingSpell(const DoorNeedingSpell&);
    bool TrySpell(Spell);
};
#endif


#endif