create objects in object passing variables through constructor

Question

Been banging my head against this all day with many trips to google. I have a master object that needs to create several other objects in its constructor the main object gets variables in its constructor that are passed on to the objects it creates.

class WorldManager{
  public:
  WorldManager(int x, int y, int z){
    //do stuff
  }
}

class GameManager{
  public:
  WorldManager world;
  GameManager(int x, int y, int z){
    world(x,y,z);
  }
}

I get error

error: no matching function for call to `GAMEMANAGER::GraphicsManager(HWND__*&, int&, int&)'

it works untill I ask for args in the constructors of the world class

Be careful, your error message and your code seem unrelated. There's no `GraphicsManager` function or class in your code. — J.N., Nov 24 '12 at 05:37
Thinking in terms of "manager" objects and, in general, dominance relationships between parts of the code, will probably cause you worse headaches than this little technicality. — Cheers and hth. - Alf, Nov 24 '12 at 05:42
Move all the creation code into a Factory. Pass a Configuration object to the Factory. Inside the Factory, assemble your object graph from the inside out, passing the config data only to the components that need them. Do not push the config data through the object graph. — Gordon, Nov 24 '12 at 11:38

score 3 · Accepted Answer · edited Nov 24 '12 at 07:16

3

I think that you want:

class GameManager{
public:
    WorldManager world;
    GameManager(int x, int y, int z) : world(x, y, z) { }
};

The weird colon thing is called an initialization list, and it does construction of member objects and parent classes and a bunch of other things.

If you have more than one object that you want to construct, add them to the list:

class GameManager{
public:
    WorldManager world1, world2;
    GameManager(int x, int y, int z) : world1(x, y, z), world2(x, y, z) { }
};

edited Nov 24 '12 at 07:16

juanchopanza

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answered Nov 24 '12 at 05:31

Xymostech

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@billz, I can't see why not, can you elaborate ? – J.N. Nov 24 '12 at 05:32
I have 3 classes I am creating – FreakinaBox Nov 24 '12 at 05:33
@billz I'm fairly certain this is what they're looking for. – Xymostech Nov 24 '12 at 05:34
@FreakinaBox Go look up how initialization lists work, you can initialize multiple objects with them. I'll add to the answer, though. – Xymostech Nov 24 '12 at 05:35
@billz that part of the question (the error message) wasn't there till later on. – J.N. Nov 24 '12 at 05:36
@billz but there's no GAMEMANAGER in the code. Also this definitely solves a problem in the code, if not the problem that FreakinaBox was asking about. – user1610015 Nov 24 '12 at 05:36
I have this class defined in a header file. would I include the initialization list in the header file also? – FreakinaBox Nov 24 '12 at 05:43
@FreakinaBox The initialization list should go wherever your constructor is defined. So, if you have a `.cpp` file, it should probably go there. – Xymostech Nov 24 '12 at 05:44
got some more errors to work out before I can tell if that works. so far the errors from this have disappeared. thanks! – FreakinaBox Nov 24 '12 at 05:46
@FreakinaBox You put the initialization list whereever you implement the constructor, which can be in the header or in the source file. – user1610015 Nov 24 '12 at 05:46

create objects in object passing variables through constructor

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