Date: Thu, 6 Mar 1997 07:13:53 -0600 (CST)
From: Andrew Deren <aderen AT eecs DOT uic DOT edu>
To: djgpp <djgpp AT delorie DOT com>
Subject: Re: HELP - need help resolving conundrum with classes
In-Reply-To: <Pine.GSO.3.95.970306003414.21399E-100000@hops.cs.jhu.edu>
Message-ID: <Pine.SUN.3.95.970306071047.12072C-100000@ernie.eecs.uic.edu>
MIME-Version: 1.0
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On Thu, 6 Mar 1997, Michael Phelps wrote:

> On 6 Mar 1997, Graham Howard Wile wrote:
> 
> > 
> > 	How can I declare two different classes, where each class has a member 
> > variable of the other class type. My problem is how to get the compiler to 
> > recognize a variable type before it has been created.
> > 
> > 	EXAMPLE:
> > 
> 
> Put a prototype of the class(es) you will be referring to _before_ the
> class declaration, to inform it that it is a class and will be described
> later.  In your example:
> 

I am not sure if you can do this, because it would lead to a recursive
calling of the class. Let's say in main you would declare 
main()
{
the_owner master;
}
then when this would be created master would have the_cats and each of
those cats would have the_owner and the_owners would have the_cats...
Instead it would be better to use pointers instead of arrays.

I am not sure. Correct me if I am wrong.

> class the_owner;
> 
> > 
> > 
> > class the_cat
> > 	{
> > 	private:
> > 
> > 		int its_age, its_weight;
> > 		char *fur_color;
> > 		the_owner its_owners[3]; //each cat has 3 owners, or people who 
> > 					 //look after it
> > 
> > 					 //I know this is illegal, because the 
> > 					 //class "the_owner" hasn't been
> > 					 //declared yet
> > 
> > 	
> > 	public:
> > 
> > 		//whatever member functions the cat might have
> > 	};
> > 
> > 
> > 
> > class the_owner
> > 	{
> > 	private:
> > 
> > 		the_cat cats_owned[5]   //each owner owns 5 cats
> > 		car *owner_occupation   //what owner does for a living
> > 
> > 	
> > 	public:
> > 
> > 		//whatever member functions the owner might have
> > 	};
> > 
> > 
> > 
> > 	Naturally, this won't work. The class "the_cat" can't declare a 
> > variable of type "the_owner" if the class "the_owner" hasn't been created yet.
> > 
> > 	BUT - I can't reverse the class declarations and have "the_owner" 
> > declared first, or else "the_owner" would not be able to declare any variables 
> > of type "the_cat"
> > 
> > 	Alas, the order of the class declarations shown above will allow me to 
> > have an owner that has 5 cats, but none of the cats can have an owner. In the 
> > other order, I can produce a cat with 3 owners, but none of the owners will be 
> > able to have any cats!
> > 
> > 	Does anyone know how I can declare these two classes so that an owner 
> > can have cats AND the cats have owners too ? I don't need a real long answer 
> > that spells the whole thing out for me. I just need to know what 
> > keywords/concepts I can look up that would likely address this conundrum.
> > 	
> > 
> > 							Thanks, 
> > 								Graham
> > 
> > 
> > 
> > --
> > 
> 
> 
> 						---Michael Phelps
> 						   morphine AT cs DOT jhu DOT edu
> 
> 
>                                CH3
>                                |
>                                N
>                              / |
>                      ______/   |
>                     /      \   CH2
>              _____/         \__|__      
>            //     \\        /  |  \\     
>          //        \\______/___CH2 \\  
>           \        /       \       /
>            \______/         \_____/
>           / ------ \       /      \
>         OH           \   /         OH
>                        O
>  
>                    Morphine
> 
> 
> 
>