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(C++) + (inheritance) = little problem

Started by BlueChip Mar 3, 2003 at 11:26 AM 8 replies 250+ views

Original Post

Mar 3, 2003 at 11:26 AM

Hi folks... while I coding my game, I''ve meet a problem... It''s not a big problem, but I''m onlooker of to know if exist a solution that doesn''t obligate me to remake all... This is my problem... I''ve a class A that inherits from classes B and C.... Class C has a struct XXX, and this struct has a pointer to class A object... That give me some problems because a base class can''t to have an attribute of her superclass ... the files inclusions would be redundant... There are solutions? Or must I remake the logical structure? goodbye and thanks to your time...

Zipster

Mar 3, 2003 at 11:34 AM

Why does class C need a pointer to type A? If A is derived from C, then C should be able to hold a C pointer, and it can point to derived objects. If you need to call A-class-only functions from that C pointer, then there''s some design issues.

smart_idiot

Mar 3, 2003 at 11:34 AM

class A* C::XXX::Pointer;

[edit: smilies]

[edited by - smart_idiot on March 3, 2003 12:35:25 PM]

flangazor

Mar 3, 2003 at 11:36 AM

I suggest an attempt to re-order your type hierarchy more like a tree structure.

Circular references are /usually/ indicative of a flawed design. I have no metrics, however, to back up this assertion.

civguy

Mar 3, 2003 at 11:37 AM

I think you''ll need to forward declare A before C:

  
class B {};

class A; //forward declaration

class C { A* a };

class A : public B, public C {};

Was this the problem? I''m not sure

Qw3r7yU10p!

Mar 3, 2003 at 11:42 AM

Pointers to classes are fine. Just forward declare the class before its name is made use of

ie

  #include <string>

class Cat;
class Truck;

class Dog {
public:
     Dog(const std::string& name);
     bool Chase(Cat*);
     bool Chase(Truck*);
private:
    std::string name_;
};

[edited by - petewood on March 3, 2003 12:45:43 PM]

Zipster

Mar 3, 2003 at 11:51 AM

Do direct pointers to derived classes contained within a base class still count as composite structure, or does it have to be a base class pointer as well? While we''re on the subject just thought I''d ask

BlueChip

Mar 3, 2003 at 1:53 PM

hi ... I'll try to explain my problem better

    
//****************

//class_b.h

//****************

class b
{........
.........
.........
}

-----------------------------------------
//****************

//class_c.h

//****************

#include "class_a.h" <--- to define newstruct

struct newstruct
{.....
.......
a* trallallero
}

class c
{........
.........
newstruct* XXX
}

-----------------------------------------
//****************

//class_a.h

//****************

#include "class_b.h"
#include "class_c.h"

class a: public b, c
{........
.........
.........
}

all right... that's all.
I'll remake type hierarchy, but before I would want to know how do you would arrange it.
I love to know other people's ideas.... it help me to improve =)

Ps: I don't want put "newstruct* XXX" in class_a.h because semantically it must to be in class_c.h

[edited by - BlueChip on March 3, 2003 2:55:40 PM]

civguy

Mar 3, 2003 at 2:05 PM

Hmm, I think you''re lacking header guards too.

But the problem you have now can be solved like this:

  
//****************

//class_c.h

//****************


class a; //THIS IS A FORWARD DECLARATION


struct newstruct
{.....
.......
a* trallallero
};

class c
{........
.........
newstruct* XXX
};

BlueChip

Mar 4, 2003 at 6:45 AM

ok, from the moment that I have already demonstrated my ignorance I can continue.............

I''ve used forward declaration, but another problem is born...
in class_c.cpp I must use this call:

(newstruct* XXX)->(Get a* trallallero) -> (method Class_b.h)

I can do it, because all class_b method are inherit by class_a, but to do this, I must include in bottom class_c.h the class_a header...... otherwise the compiler tell me that class A hasn''t (Get a* trallallero) method....

but if I put the header..... I recall to start point ^__^

I am becoming crazy O_o

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