ordering of member access operator

**hajimeml** · June 19th, 2009, 11:29 AM

Hello. I have a question about the member access operator ->
I am trying to understand a code of this format: A->B->C->D.
Does it means A->(B->(C->D)) or ((A->B)->C)->D)?
In the former case, I shall try to understand the code which is represented by (C->D) first.
Thanks.

**laserlight** · June 19th, 2009, 11:37 AM

It is the latter case: ((A->B)->C)->D).

**hajimeml** · June 19th, 2009, 07:31 PM

Thanks.

**hajimeml** · June 19th, 2009, 07:50 PM

By the way, what are the advantages of writing the code this way? It seems that the author of the program uses this method to make a pointer (a private member) of one class to point to another class (pointed to by a private member defined in another class).

**JVene** · June 19th, 2009, 08:56 PM

The answer to your question is actually part of the study of C++; there are many tributaries. It's not so much that it's and advantage as it is a technique.

The idea may be that an object needs to 'have' some objects, which in your example, have some object, and that has some objects, too.

Without anything telling me the types of A, B, C or D, all I can say is that it LOOKS like they're pointers (-> can be an operator overload, a function that returns a pointer).

A might be a car. B, which A 'has' and is pointing to in

A->B

Might be a passenger. C might be a wallet, owned by the passenger as indicated by

A->B->C

D might be his credit card.

So, if you want the credit card from passenger B's wallet, you find him in car A with

A->B->C->D

**hajimeml** · June 20th, 2009, 12:01 AM

Thanks for the very interesting example and explaination. I found another variation of the code in the program. Here, the type of A-D are as follows:

A->PGElementPtr()->WPtr()->GetSize()

where PGElementPtr(), WPtr() and GetSize() are respectively B,C,D in the original post.

A is a private member of TFormMain. It points to class C1.
In class C1, there is a member function PGElementPtr().
This function returns a pointer pointing to class C2.
Such pointer is called PGElement which is a private member of class C1.
PGElement in class C1 calls the member function WPtr() of class C2.
WPtr() returns a pointer to class C3. Such pointer is called w, which
is a private member of class C2.
GetSize() is a virtual member function of C3. It has resize(size) in
the function definition which I guess returns the size of class C3.

I am confused by such complicated statement. Do you have an idea what it actually does?
Is the prgrammer trying to get the size of class C3 from TFormMain? I am not sure why he goes through so many steps by using a series of ->. Also, is there a side effect of this statment? I am not sure if he is setting up the links to classes for other parts of the program to use...

**laserlight** · June 20th, 2009, 12:24 AM