Re: Different Objects in Array

From:

Michael Doubez <michael.doubez@free.fr>

Newsgroups:

comp.lang.c++

Date:

Fri, 8 Jan 2010 05:21:29 -0800 (PST)

Message-ID:

<a74795c1-c95b-43b2-ac18-d46a2de90e05@b2g2000yqi.googlegroups.com>

On 8 jan, 04:51, Immortal Nephi <Immortal_Ne...@hotmail.com> wrote:

On Jan 7, 8:21 pm, Victor Bazarov <v.Abaza...@comAcast.net> wrote:

Immortal Nephi wrote:

I thought that you might find an interesting code. Perhaps,=

you have

seen this before. I created two classes of A and B. Two classes=

have

different objects. The class Obj has a relationship to class A and
class B which is called composition.
The class Obj has one variable which is a pointer to member fu=

nction

in array. You can't bind member function of both class A and class=

because they do not belong to class Obj. I use reinterpret_cast to
convert from class A to class Obj before pointer to member function i=

invoked.
I believe that my code is the alternative replacement so I don=

't use

inheritance and polymorphism. It is easier to extract class. Wh=

at do

you think?

Your code has undefined behaviour, not to mention that the compiler tha=

is supposed to compile your 'reinterpret_cast' will exhibit undefined
behaviour (most likely). Aside from that, you're good...

Hi Victor,

How did you say undefined behavior? I played with debugging. I foun=

out that reinterpret_cast array did assign memory address correctly,
but *this* pointer in class A and class B assigns to the wrong memory
address.

For example:

class ....
{
int a;
int b;
int c;

}

*this* pointer should always assigns to data member as a, but it did
assigns to either data member as b or c. The data was misplaced from
a to b like memory misalignment.

I guess there is no alternative replacement to undefined
reinterpret_cast array, but switch block is the answer to each class'
member function.

Do you know if there is another way? What about template array?

You can use union:

class Obj
{
public:
        void Run()
        {
                this->*(pO[0].runA)();
                this->*(pO[1].runB)();
        }

private:
        A a;
        B b;
        union To
        {
          void A::*runA();
          void B::*runB();
        };
        static To const pO[2];

};

// not sure about initialisation - perhaps only possible in C99
Obj::To const Obj::pO[2] =
{
        {&A::Run},
        {&B::Run}
};

--
Michael