Question

I have a class A consisting of a bunch of internal data structures (e.g. m_data) and a few objects (e.g. ClassB):

class A
{
public:
      ...
private:
      int m_data[255];
      ClassB B[5];
}

What’s the best way for B to access m_data? I don’t want to pass m_data into B’s function..

// updated:
Many thanks for the responses. Let me provide more contextual info.
I am working on an AI project, where I got some data (e.g. m_data[i]) at each time step. The class A needs to buffer these information (m_data) and uses a list of B’s (example updated) to make inference. Class B itself is actually a base class, where different children derive from it for different purpose so I guess in this context, making B a subclass of A might not be clean (?)..

Answer 1

Ideally, you don’t allow external access the data structure at all. You should rethink your approach, considering more the question “What are the functional requirements / use cases needed for ClassB to access instances of A” rather than offloading the management of the internal members to methods not managed within class A. You will find that restricting management of internal members to the class owning those members will yield cleaner code which is more easily debugged.

However, if for some reason this is not practical for your situation there are a couple possibilities that come to mind:

• You can provide simple get/set accessor methods which, depending upon
  your requirements, can be used to access either a copy of or a
  reference to m_data. This has the disadvantage of allowing everybody
  access, but does so only through well defined interfaces (which can
  be monitored as needed).
• ggPeti mentions use of friend, which may work for you, but it gives ClassB access to all of the internals of A.