Base Class pointers to Derived Classes calling functions.

[bgold]

Hey. I have a base class (SPRITE), and using this base class I have
derived a large number of derived classes (PERSON, BULLET, MISSILE,
etc.). Now, at a certain point in my program, I have a pair of
pointers, where each is a pointer to the base class (each is a SPRITE
*). I know that each of these pointers actually points to one of the
derived classes, even though the type of the pointer is SPRITE *, but
I don't know which derived class it points to. I would like to write a
set of functions that do something different depending on what
combination of derived classes the two pointers point to (i.e. I want
one function for a PERSON * and BULLET *, a second function for a
PERSON * and MISSILE *, a third for BULLET * and MISSILE *, etc.).

How can I write these functions, and how do I call them, so that the
correct function is called given the two pointers?

I hope this is clear...

[Rahul]

On Dec 31, 7:05 pm, Ron Natalie <r...@spamcop.n etwrote:

Rahul wrote:

dynamic_cast would work only with classes having virtual functions,
typeid operator would
be more appropriate...

typeid has the same restrictions. If the class isn't polymorphic
(virtual) functions, the runtime typing info ain't there.

I meant the compilation error, one gets with dynamic_cast for the
following cases,

class A
{
};

class B : public A
{
};

int main()
{
B *ptr1;
A *ptr2 = new B();
ptr1 = dynamic_cast<B* >(ptr2); // gives a compilation
error
if(ptr1 == NULL)
printf("fail\n" );
else
printf("success \n");
return(0);
}

but typeid doesn't give any such error,

A *ptr = new B();
cout<<typeid(pt r).name()<<endl ;
cout<<typeid(*p tr).name()<<end l; // Yes this would give A
without any virtual functions in A, but atleast works...

[Ron Natalie]

Rahul wrote:

On Dec 31, 7:05 pm, Ron Natalie <r...@spamcop.n etwrote:

>Rahul wrote:

>>dynamic_cas t would work only with classes having virtual functions,
typeid operator would
be more appropriate...

typeid has the same restrictions. If the class isn't polymorphic
(virtual) functions, the runtime typing info ain't there.

I meant the compilation error, one gets with dynamic_cast for the
following cases,

ptr1 = dynamic_cast<B* >(ptr2); // gives a compilation
error

If your compiler gives a compilation error there it is seriously busted.
Dynamic cast has a whole slew of cases that apply EVEN if the classes
aren't polymorphic.

A warning perhaps, but the program is well formed.

[James Kanze]

On Dec 31 2007, 5:20 pm, Ron Natalie <r...@spamcop.n etwrote:

Rahul wrote:

On Dec 31, 7:05 pm, Ron Natalie <r...@spamcop.n etwrote:

Rahul wrote:

>dynamic_cast would work only with classes having virtual functions,
typeid operator would
be more appropriate...
typeid has the same restrictions. If the class isn't polymorphic
(virtual) functions, the runtime typing info ain't there.

I meant the compilation error, one gets with dynamic_cast for the
following cases,

ptr1 = dynamic_cast<B* >(ptr2); // gives a compilation
error

If your compiler gives a compilation error there it is
seriously busted. Dynamic cast has a whole slew of cases that
apply EVEN if the classes aren't polymorphic.

True, but pointer to base to pointer to derived isn't one of
them. The above code should result in a compiler error.
(Remember that ptr2 has type A*, and that A is a base class of
B.)

The reverse, of course, should work.

--
James Kanze (GABI Software) email:ja******* **@gmail.com
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