This document discusses constructors and destructors in C++. It explains that constructors initialize objects when they are created and prevent data members from having garbage values, while destructors destroy objects before they go out of scope. The document covers parameterized and copy constructors, constructor overloading, default constructor arguments, and how constructors and destructors are automatically called by the compiler. It also discusses dynamically initializing data members using constructors with pointer arguments.

1. Constructors and
Destructors
UNIT - III
CHAPTER – 9

2. 9.1 Introduction
 When a variable is declared , if it is not initialized it contains a garbage value.
 The programmer has to assign value to the variable.
 Initialization prevents variable from containing garbage value.
 An object holds copies of one or more individual data members.
 When an object is created , its data member contains garbage value.
 Declaring the variable as static allows the programmer to initialize member
variables with desired values.

3. 9.1 Introduction
 Drawback of static members is only one copy of static member is created for
entire class , all objects share same copy and does not provide security.
 If when an object is declared as static , all member variables are initialized to
zero.
 Every static object has its own set of member variables .
 Drawback of static object is , contents of object remains throughout the program
occupying more memory space.
 Eg. Book

4. 9.2 Constructors and Destructors
• A separate member function is used for reading input values for data members.
• By using object ,member functions can be invoked and data members are
initialized.
• C++ provides a pair of built-in functions called Constructor and Destructor .
• Constructor - constructs the objects
• Destructor - destroys the objects
• Compiler automatically executes this functions.
• Programmer does not need to invoke the function.

5. 9.2 Constructors and Destructors
 When an object is created , constructor is executed , programmer can also pass
values to constructor to initialize member variables with values.
 Destructor destroys the object , destructor is executed at the end of the function
when objects are of no use.
 Optional to declare constructor and destructor , if not declared compiler executes
implicit constructor and destructor.
 Constructor , Destructor – special member functions , decides how objects of class
are created , initialized , copied and destroyed.

6. 9.2 Constructors and Destructors
• Names are same to name of class they belong to .
• Only difference is that destructor is preceded by ~(tilde) operator.
• Can declare and define them within the class or declare them within the class and define
them outside.
• Destructor is automatically executed when object goes out of scope.
• Also invoked when delete operator is used to free the memory allocated with class
pointer.
• Class can have only one destructor
•9.3 Characteristics of Constructors and Destructors ( Book)

7. 9.5 Constructors with
Arguments(Parameterized Constructor)
• Also possible to create Constructor with arguments and
such Constructors are called parameterized Constructors.
• For that Constructors values must be passed to the
constructor when an object is created
• Eg. Book

8. 9.6 Overloading Constructors
(Multiple Constructors)
• It is also possible to overload Constructors like functions.
• A Class can have more than one Constructor – this is called as Constructor
Overloading
• All constructors are defined with same name to which the class they belong to.
• All constructors contain different number of arguments, depending upon the
number of arguments , compiler executes appropriate constructor
• Eg. Book

9. 9.8 Constructors with Default Arguments
• Like functions ,possible to declare constructors
with default arguments.
• Eg. Book

10. 9.9 Copy Constructors
•Constructor accepts arguments of any data type including user-defined data types ,exclusive of the
class to which it belongs
•Possible to pass reference of object to the constructor-declaration known as copy constructors

11. 9.9 Copy Constructors
• When we pass object by value into a function , a temporary copy of that object
is created
• Copy constructors require one argument , with reference to an object of
that class
• By using copy constructors , possible to declare and initialize one object
using reference of another object
• Whenever a constructor is called , a copy of an object is created.

12. 9.11 Destructors
• Destructors destroy class objects created by constructors
• Destructors have same name as class preceded by tilde(~)
• Destructor only destroys the object and hence it cannot be overloaded
• It does not require any arguments nor returns any value.
• It is automatically called when object goes out of scope
• Destructor releases memory space occupied by the objects
• Eg. Book

13. 9.12 Calling Constructors and Destructors
• Compiler automatically calls the Constructor and Destructor.
• Can call constructor and destructor like normal user –defined
function.
• Calling methods are different for constructors and destructors.

14. 9.16 Dynamic initialization using
Constructors
• After declaring class data member variables , they can be initialized at the time
of program execution using pointers
• This type of initialization of data is called dynamic initialization
• Advantage of dynamic initialization is , it allows different initialization modes
using overloaded constructors
• Pointer variables are used as arguments for constructors
• Eg. Book