Data Hiding

DATA HIDING

•         With data hiding

•         accessing the data is restricted to authorized functions

•         “clients” (e.g., main program) can’t muck with the data directly

•         this is done by placing the data members in the private section

•         and, placing member functions to access & modify that data in the public section

•         So, the public section

•         includes the data and operations that are visible, accessible, and useable by all of the clients that have objects of this class

•         this means that the information in the public section is “transparent”; therefore, all of the data and operations are accessible outside the scope of this class

•         by default, nothing in a class is public!

•         The private section

•         includes the data and operations that are not visible to any other class or client

•         this means that the information in the private section is “opaque” and therefore is inaccessible outside the scope of this class

•         the client has no direct access to the data and must use the public member functions

•         this is where you should place all data to ensure the memory’s integrity

•         The good news is that

•         member functions defined in the public section can use, return, or modify the contents of any of the data members, directly

•         it is best to assume that member functions are the only way to work with private data

•         (there are “friends” but don’t use them this term)

•         Think of the member functions and private data as working together as a team

•         Notice, that the display_all function can access the private my_list and num_of_videos members, directly

•         without an object in front of them!!!

•         this is because the client calls the display_all function through an object

object.display_all();

so the object is implicitly available once we enter “class scope

•         In reality, the previous example was misleading. We don’t place the implementation of functions with this this class interface

•         Instead, we place them in the class implementation, and separate this into its own file

•   Class Interface:              list.h

class list {

public:

int display_all()

•••

};

•         list.h can contain:

•         prototype statements

•         structure declarations and definitions

•         class interfaces and class declarations

include other files