Teach Yourself Borland C++ in 14 Days - portal

104 Day 4
NOTE
use in all functions of the class. Depending on the data member’s access level, it might be
visible outside the class as well. Private and protected data members, for instance, are private
to the class and cannot be seen outside the class. Public data members, however, can be
accessed from outside the class, but only through an object. Take the Rect class declared
previously, for example. It has no public data members. You could try the following, but
you’d get a compiler error:
Rect rect(10, 10, 200, 200);
int x = rect.left; // compiler error!
The compiler error will say Rect::left is not accessible. The compiler is telling you that
left is a private data member and you can’t get to it. If left were in the public section of the
class declaration, this code would compile.
You can use getters and setters to change private data members. That is, getters are functions
that get the value of a private data member, and setters are functions that set the value of a
private data member. Both getters and setters are public member functions that act on private
data members.
To illustrate, let’s say that for the Rect class you had the following getters and setters for the
left data member:
int Rect::GetLeft()
{
return left;
}
void Rect::SetLeft(int newLeft)
{
left = newLeft;
}
Now, when you want to obtain the value of the left member of the Rect class, use this:
TRect rect;
int x = rect.GetLeft();
In some cases this is overkill. Setters have one main advantage, though—they allow you to
validate input. By validating input, you can control the values your data members contain.
Some OOP extremists say that data members should never be public.
They would say that you should use getters and setters to access all data
members. On the other end of the spectrum is the group that says to
make all your data members public. The truth lies somewhere in
between. Some data members are noncritical and may be left public if
it is more convenient. Other data members are critical to the way the
class operates and should not be made public. If you are going to err, it
is better to err on the side of making data members private.