Teach Yourself Borland C++ in 14 Days - portal

Totally Immersed: C++ Classes and Object-Oriented Programming
The first constructor is a default constructor by virtue of the fact that it takes no parameters.
It simply initializes each data member to 0. The second constructor takes the parameters
passed and assigns them to the corresponding class data members. The variable names in the
parameter list are local to the constructor, so each of the variable names begins with an
underscore to differentiate between the local variables and the class data members.
TIP
NEW TERM
Remember that an uninitialized variable will contain random data.
This is true for class data members as well as other variables. To be safe,
you should set class member variables to some initial value.
Instantiation is the creation of an object, an instance, or a class.
It’s important to understand that you can’t call a constructor directly. So how do you use one
of these constructors over the other? You do that when you create or instantiate an object or
a class. The following code snippet creates two instances of the Rect class. The first uses the
default constructor, and the second uses the second form of the constructor:
Rect rect1; // object created using default constructor
Rect rect2(0, 0, 100, 100); // created using 2nd constructor
You can have as many constructors as you like, but be sure that your constructors don’t have
ambiguous parameter lists (as per the rules on function overloading).
Initializer Lists
NEW TERM
C++ provides a means by which you can initialize class data members in what
is called an initializer list.
The following is the proper way to initialize data members of a class. Rather than trying to
explain how to use an initializer list, let me show you an example. Let’s take the two
constructors for the Rect class and initialize the data members with an initializer list rather
than in the body of the function as I did before. It looks like this:
Rect::Rect() :
left(0),
top(0),
bottom(0),
right(0)
{
}
101
4