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Class pointers

Started by Zoot Jun 30, 2002 at 12:32 PM 10 replies 1.1k views

Original Post

Jun 30, 2002 at 12:32 PM

I am playing some with classes and i am trying to make a list of all my classes: class *classlist[128] int usedclasses = 0; void ADD_CLASS(class *pClass) { classlist[usedclasses] = pClass; usedclasses++; } class CBajs { public: int test; char classname[128]; }; ADD_CLASS(CBajs); But this isn´t working... any ideas?

LordShade

Jun 30, 2002 at 12:38 PM

You have to instantiate the class first. A class name is a type.

Thus,

ADD_CLASS(CFoo)

will not work cause your passing a type.

CFoo* pFoo = new CFoo;
ADD_CLASS(pFoo);

This will work.

NuffSaid

Jun 30, 2002 at 12:40 PM

  
class *classlist[128];

is that even legal? (I''m away from my work PC, hence I can''t compile it to find out

)

Zoot

Author

Zoot

Jun 30, 2002 at 12:50 PM

NuffSaid, i want to create instantiate of the class later using the classlist.

Yes, LordShade class *classlist[128]; is legal.

dalleboy

Jun 30, 2002 at 12:56 PM

You may want to look up on how MFC does it with their RUNTIME_CLASS, DECLARE_DYNAMIC and DECLARE_DYNCREATE. You may find it interesting.

Oluseyi

526

Oluseyi

Jun 30, 2002 at 1:35 PM

quote:
Original post by Zoot
Yes, LordShade class *classlist[128]; is legal.

No, Zoot, class * classlist[128]; isn''t legal - at least, not in the sense you think.


class *classlist[128];
class T
{
public:
  T() { cout << typeid( *this ).name() << endl;
};
 
int main()
{
  T * t = new T;
  classlist[0] = t;
  return 0;
}

error C2440: ''='' : cannot convert from ''class T *'' to ''class $S1 *''
                   Types pointed to are unrelated; conversion requires reinterpret_cast,
                   C-style cast or function-style cast

George2

Jun 30, 2002 at 2:34 PM

Derive all classes from one base class
and store them in a linked list of pointer''s to the base class

Oluseyi

526

Oluseyi

Jun 30, 2002 at 3:34 PM

quote:
Original post by George2
Derive all classes from one base class and store them in a linked list of pointer''s to the base class

Only do this if the classes are actually related (ie, don''t introduce inheritance and polymorphism merely for convenience of reference). It''s an obvious indication of poor design.

(It probably goes without saying that concepts and generic algorithms are beyond your ken, so I''ll save that discussion for some other time).

dalleboy

Jun 30, 2002 at 5:56 PM

  
class CBase
{
};

class CDerived1 : public CBase
{
public:
   static CBase* CreateObject()
   {
      return new CDerived1;
   }
};

class CDerived2 : public CBase
{
public:
   static CBase* CreateObject()
   {
      return new CDerived2;
   }
};

typedef CBase* (*CreateObjectFunc)();

int main()
{
   CreateObjectFunc  pCreateObjectFuncs[2];

   pCreateObjectFuncs[0] = CDerived1::CreateObject;
   pCreateObjectFuncs[1] = CDerived2::CreateObject;

   CBase*   pBase1 = pCreateObjectFuncs[0]();
   CBase*   pBase2 = pCreateObjectFuncs[1]();

   return 0;
}

This could work as you intend. You could expand it further to send init-parameters to the constructors.

LordShade

Dec 31, 2002 at 1:50 AM

quote:
Original post by Zoot
NuffSaid, i want to create instantiate of the class later using the classlist.

Yes, LordShade class *classlist[128]; is legal.

I should have read the first post more closely. You will have to do runtime typing.

Also, I believe "class" is a keyword that ultimately compiles out to mean structure. Thus,

class* classlist[128]

is compiled out to

structure* classlist[128]

which means you don''t have a type defined so the compiler has no idea what type you are asking to store. Sure it can allocate the storage, a pointer is a pointer no matter what, but trying to assign something to it, well now, that''s when the compiler sits up and goes, "HUH!?"

Fruny

203

Fruny

Dec 31, 2002 at 2:47 AM

Zoot - C++ supports (currently ? Oh, please! Please! *beg* *grovel* Gimme! Please! )neither reflexion nor metaclasses. You can, however implement an abstract factory. See also this link in the C++ FAQ-Lite.

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