1. CS148 Introduction to Programming II
Ayman Abdel-Hamid
Department of Computer Science
Old Dominion University
Lecture 15: 3/21/2003
Lecture 15: 3/21/2003
CS148 Spring 2003

2. Outline C++ Classes Constructors Destructors
Specification and implementation files
Lecture 15: 3/21/2003
CS148 Spring 2003

3. Class Constructors 1/2
A class constructor guarantees the initialization of a class object
Implicitly invoked whenever a class object is created (never invoked using the dot notation)
Has the same name as the class itself
A parameterless constructor is the default constructor
TimeType startTime; //default constructor is invoked
TimeType startTime (10,30,0) //parameterized constructor is invoked
class TimeType {
public:
TimeType(); //default constructor
TimeType (int, int, int); //parameterized constructor
void Increment();
void Write();
private: };
Lecture 15: 3/21/2003
CS148 Spring 2003

4. Class Constructors 2/2 Rules for using constructors
A constructor cannot return a function value (function declared without a return value type)
When a class provides several constructors, and a class object is declared, the compiler chooses the appropriate constructor according to the supplied arguments list
When a class object is declared without an argument list, the effect depends on what constructors the class provides
If the class has no constructors at all, memory is allocated for the class object, but the private data members are in an uninitialized state
If the class does have consructors
The default constructor is invoked if there is one
If no default constructor can be found, a syntax error occurs
Lecture 15: 3/21/2003
CS148 Spring 2003

5. Class destructors Implicitly invoked when a class object is destroyed
A class object is destroyed when the scope it was declared in is exited
Same name as a constructor, except first character is a tilde (~)
Used to performed clean up, e.g., deallocation of dynamic memory allocated within a class
class TimeType {
public:
TimeType(); //default constructor
TimeType (int, int, int); //parameterized constructor
void Increment();
void Write();
~TimeType(); //Destructor
private: };
Lecture 15: 3/21/2003
CS148 Spring 2003

6. Specification/Implementation files
An ADT consists of two parts: a specification and an implementation
The specification describes the behavior of the data type without reference to its implementation
Programming Style
Specification file: a header file (.h) containing only the class declaration
Implementation file: a source file (.cpp) containing functions definitions for the class member functions. Needs to include the specification file.
Client code (.cpp). Uses the class public members. Needs to include the specification file.
Lecture 15: 3/21/2003
CS148 Spring 2003