multiple linked lists for different objects in c++

Question

consider these classes (simplified)

class Character 
{
public:
char name[20];
    char type[20];
    int strength;
};

class inventoryItem
{
public:
    char name[20];
};
class weapon: public inventoryItem
{
public:
    int magical resistance;
};
class spell: public inventoryItem
{
public:
   int magical power;
};

i have written a class for a linked list (not allowed to use stl list)

class list
{
public:
struct listItem
{
    listItem* objectPointer;
    listItem* pnext;

}*phead;


list()
{
    phead=NULL;

}

bool isEmpty(){ 
if (!phead)
return true;
else
    return false;
}
void addToBack(listItem *itemtoadd)
{
    listItem *ptemp;
    listItem *ppast;
    listItem *pNewItem;

pNewItem=new listItem();

pNewItem->objectPointer=itemtoadd;
pNewItem->pnext=NULL;
if (phead==NULL)
    phead=itemtoadd;
else
{
      ptemp=phead;
      while(ptemp)
      {
     ptemp= ptemp->pnext;

      }
      ptemp->pnext=itemtoadd;

}

}

};

I have cut this down a lot but my question is , is there an easy way to create linked lists for all these using the same list class ? or am I wasting my time ?

every time I have tried it cant convert the pointer from type 'weapon' to type 'listitem'
I need a list of characters and a list of each weapon or spell for that character
I'm still a beginner with OOP and pointers , the program I have now compiles and I have a list of characters working , however the list is not managed by the class its managed within some other functions, I'm hoping there's a way for one class to deal with it all , can anyone help explain it to me ?

You say you're not allowed to use STL, so clearly this is some sort of assignment with restrictions. Are you allowed to use templates / have you learned about them? — svk
– svk, Commented Mar 24, 2013 at 11:14
@svk Yes i've looked into templates briefly, and it doesn't specifically say I cant use them , but I am trying to get my head around how classes work together , and in theory I would have thought it was possible , but I'm struggling . Would you suggest templates are the way to with this? — user1652319
– user1652319, Commented Mar 24, 2013 at 11:22
Yes, templates are the "proper" way to do this. The solution you're not allowed to use is from the STL (the Standard Template Library) and is done with templates. But templates are a fairly advanced part of C++, and you will likely have trouble with them if you're a beginner. By now there are answers which suggest simpler ways, you might want to use one of those. — svk
– svk, Commented Mar 24, 2013 at 11:27
@svk thanks for that! i've just looked into templates and it would seem its the solution — user1652319
– user1652319, Commented Mar 24, 2013 at 11:35

yaakov · Accepted Answer · 2013-03-24 11:19:17Z

1

Take a look at C++ Templates. Using templates you can have one list class in terms of reading/writing code, but you can have a list of weapons, a list of items or a list of anything else without having to write WeaponsList, ItemsList and SomethingElseList classes separately.

answered Mar 24, 2013 at 11:19

yaakov

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john · Accepted Answer · 2013-03-24 11:21:16Z

1

The simple answer is to do this

struct listItem
{
    void* objectPointer;
    listItem* pnext;

}*phead;

A void pointer will allow you to store a pointer to anything. Of course it's then entirely up to you to make sure that you don't lose track of what kind of object you are pointing to. So this approach is risky. The safer approach is templates as has been suggested.

answered Mar 24, 2013 at 11:21

john

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Comments

stevedes · Accepted Answer · 2013-03-24 11:25:47Z

0

You could use:

enum item
{
    WEAPON,SPELL
}

class list {
public:
    struct listItem {
        union {
            weapon *weaponPointer;
            spell *spellPointer
        } object;
        item objType;
        listItem* pnext;

    }*phead;

however the catch is you have to access the type member to determine what type of item you are accessing.

answered Mar 24, 2013 at 11:25

stevedes

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1 Comment

stevedes Over a year ago

you also have to add an additional parameter to your addtoback function specifying item type.

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