Teach Yourself Borland C++ in 14 Days - portal

Totally Immersed: C++ Classes and Object-Oriented Programming
HOUSE RULES: CLASS MEMBER FUNCTIONS
■ Make public only those functions that users will need in order to properly utilize
the class.
■ Make private any functions that users do not need to know about.
■ Make protected any functions that derived classes may need access to but that
users do not need to know about.
■ Use static member functions only under special circumstances.
■ Declare any class member functions that have to be executed quickly as inline
functions. Remember to keep inline functions short.
■ Place any code duplicated more than twice in a function.
What’s this?
All classes have a hidden data member called this. this is a pointer to the instance of
NEW TERM
the class in memory. (A discussion on the this pointer quickly starts to look like a
“Who’s on First?” comedy sketch, but I’ll try anyway.)
Obviously this (pun intended) will require some explanation. First, let’s take a look at how
the Rect class would look if this were not a hidden data member:
class Rect {
public:
Rect();
Rect(int _left, int _top, int _bottom, int _right);
~Rect();
int GetWidth();
int GetHeight();
void SetRect(int _left, int _top, int _bottom, int _right);
private:
Rect* this; // if ‘this’ were not invisible
int left;
int top;
int bottom;
int right;
char* text;
};
This is effectively what the Rect class looks like to the compiler. When a class object is created,
the this pointer automatically gets initialized to the address of the class in memory:
TRect* rect = new TRect(20, 20, 100, 100);
// now ‘rect’ and ‘rect->this’ have the same value
// because both point to the object in memory
107
4