类中的结构

Question

I have two questions.

1. I know it is possible to declare class objects in structs. But is it ethical to do that from design point of view?

2. In my scenario I have a structure with a huge number of member elements and I want to include a class object too. Here I have another question. If I memset() the whole struct the class handle is also reset. So, I check the size of the rest of the struct without the class object and subtract it while I call memset(), to get rid of this problem. (Please note that I am using STL class 'queue' here. And I cannot use sizeof() operator on the object, since it is not overloaded.)

But is this totally an unacceptable way to do that? Can you suggest some solution to this problem?

Answer 1

• struct = class (except for default visibility).

• If you have a “huge number of members” you are probably doing something wrong, change your design, otherwise it becomes intractable.

• It is absolutely fine to nest classes and / or structs, where it makes sense. For instance, it's common to define nested classes for implementation details (so a linked_list class could have a node member class).

• There's no such thing as a “class object”, and it's not clear what you mean by that.

• Don't use memset – you probably don't need it, just use normal constructors and assignment.

• And I cannot use sizeof() operator on the object

  Wrong, you can use it.

Answer 2

The solution is to avoid memset with classes and structures, and use constructors. In C++11 you can use initialization lists too under various conditions.

Answer 3

There is no much functional difference between classes and structs in c++. Structs exisist in c++ only for backward compatibility with C. So it is ok to have a class objects in structs. However I generally prefer structs that have only member variables with getter and setter. I dont use any functions inside struct that manupulate the data. If i need that then i will use class.