Create linked list of multiple objects

Question

I need help, if I have:

class gameObject{
    public: //get and set;
    private: int x;
    int y;
    string texture;
}

class gun:public gameObject{
    public: //get and set;
    private: int ammo;
}

class armor:public gameObject ... ,
class boots:public gameObject...

How I can create a linked list of multiple derived objects from base class gameObject ? For example user have a menu: [1. Add object 2.Delete object]. If user choose 1 another menu appear [Type: 1-Gun 2-Armor]. After 4 objects added the list will be: 1.Gun 2.Armor 3.Gun 4.Boots. I need an example to understand the concept.

Thanks.

std::list<gameObject*>

NathanOliver
– NathanOliver

2015-06-03 14:14:55 +00:00
Commented Jun 3, 2015 at 14:14 — NathanOliver
– NathanOliver, Commented Jun 3, 2015 at 14:14
std::list<std::unique_ptr<GameObject>>

Quentin
– Quentin

2015-06-03 14:34:49 +00:00
Commented Jun 3, 2015 at 14:34 — Quentin
– Quentin, Commented Jun 3, 2015 at 14:34

sh03 · Accepted Answer · 2015-06-03 14:40:03Z

1

How I can create a linked list of multiple derived objects from base class gameObject ?

You would use std::forward_list (singly linked list) or std::list (doubly linked list) in conjunction with a smart pointer like std::unique_ptr or std::shared_ptr (depending on owning semantic), as demonstrated below:

std::list<std::unique_ptr<gameObject>> list;

and then you would allocate objects using:

list.emplace_back(std::make_unique<gameObject>(...));

answered Jun 3, 2015 at 14:40

sh03

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Comments

Andy Newman · Accepted Answer · 2015-06-03 14:52:08Z

1

Other peoples answers were good, but in case they were answering the wrong question here:

A pointer to the base type (smart or otherwise) can point to any of the derived types too, so you need to make a list of pointers to the base type.

You can't make a list of the base type itself, because the derived types are probably bigger and wouldn't fit. The language won't even let you try.

std::list<GameObject *> is ok.
std::list<GameObject> is not.

answered Jun 3, 2015 at 14:52

Andy Newman

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Comments

Jonathan Mee · Accepted Answer · 2015-06-03 14:55:53Z

0

You'll want to use auto pointers for this.

list<unique_ptr<gameObject>> foo;

foo.push_back(make_unique<gun>());
foo.push_back(make_unique<armor>());

for(auto& i : foo){
    if(dynamic_cast<gun*>(i.get())){
        cout << "gun" << endl;
    }else if(dynamic_cast<armor*>(i.get())){
        cout << "armor" << endl;
    }
}

This example adds a gun and then an armor to foo as unique_ptr<gameObject>s.

In the for-loop we use a dynamic_cast to discern the type. The code will output:

gun
armor

You can see an example of this code here: http://ideone.com/trj9bn

edited Jun 3, 2015 at 14:55

answered Jun 3, 2015 at 14:40

Jonathan Mee

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