如何在C ++中创建“包装器”？

Question

Update Below

I am trying to create this wrapper to contain pointers to all the other classes. I've hit this issue (example):

main.cpp

struct wrap {
  Game* game;
  Player* player;
  Map* map;
};

game.h

class Game {
  private:
    wrap* info;
}

Is there a way around this, wrap needs Game, and Game needs wrap. (I do know wrapper class [this case struct] is not the best practice, but I am needing that info frequently in other classes.)

Now, I have a new problem.

items.h

// top
struct CoreInfo;


void Items::test() {
    struct CoreInfo* b;
    //b->testing = 4;
}

(The struct CoreInfo contains a variable "int testing." And I cannot figure out how to access anything within the items class, normal error: 7 request for member 'testing' in 'b', which is of non-class type 'CoreInfo*'

Answer 1

just forward declare the wrap struct, as shown below:

main.cpp

#include "game.h"

struct wrap {
  Game* game;
  Player* player;
  Map* map;
};

game.h

struct wrap;

class Game {
  private:
    struct wrap* info;
}

edit:

the problem is that you did not make a separation between declaration and definition by taking advantage of compilation units. If you define your class and its members in a compilation unit ( items.cpp ), while declaring it in the header items.h , you'll have no trouble.

Let's make an example to illustrate this:

foo.h

#include "bar.h"

class A {
    B b_instance;
    void do_something(int i, int j);
}

foo.cpp

#include "foo.h"

int A::do_something(int i, int j) {
   return i+j; 
}

bar.h

class B {
    A a_instance;
    void use_a();
}

bar.cpp

#include "foo.h" // which includes bar.h as well

void B::use_a() {
    int k = a_instance.do_something();
}