Constructors and Destructors

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ConstructorsandDestructors
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Private Members

• Mutator routines

• Sets the value of a private data member

• E.g. getData (), setData (), setCount ()

• Accessor routines

• Returns the value of private data member

• E.g. putData ()

• Some people uses the name getData () as an
  accessor routine

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Initializing Private Members

• Used mutator functions to initialize private
  data members.

• E.g. x.getData ( 100, 75.4 )

• Can be invoked only via an already created
  object.

• Cannot be used to initialize members while
  creating an object.

• Not agree with C philosophy.

• E.g. Initializing built-in data types
• int i 24
• float x 5.25

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Constructors

• Enables an object to initialize itself when it
  is created.

• Special member function whose task is to
  initialize objects.

• Name is same as the class name.

• Invoked automatically whenever an object is
  created.

• No need to call like normal member functions.

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Constructors
class Complex float x, y public Complex (
void ) //constructor declared
//constructor defined Complex Complex ( void )
x 0.0 y 0.0
Complex z1
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Constructors

• If the programmer does not supply a default
  constructor, compiler provides a default
  constructor.

• Should be in the public section.

• No return types.

• Cannot be inherited.

• Can have default arguments.

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Parameterized Constructors

• Default constructor Complex () initializes
  only data members to zero.

• May be needed to initialize to various values
  for different objects.

• Soln Parameterized constructors.

• Pass arguments to constructors when the
  objects are created.

• Can have more than one parameterize
  constructors for a one class.

• However, they should have different signatures.

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Parameterized Constructors
class Complex float x, y public //parameteri
zed constructor Complex ( float a, float b
)
Complex Complex ( float a, float b ) x a
y b
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Parameterized Constructors

• Complex z1 //Illegal

• We must pass the initial values as arguments
  to the parameterized constructor.

• Two ways

• By calling the constructor explicitly.
• E.g. Complex z1 Complex ( 3.0, 4.0 )

• By calling the constructor implicitly.
• E.g. Complex z1 ( 3.0, 4.0 )

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Multiple Constructors in a class
class Complex int x, y public Complex ( )
//default constructor x 0.0 y
0.0 Complex ( float a, float b )
//parameterized constructor x a y
b Complex ( Complex z ) //copy
constructor x z.x y z.y
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Multiple Constructors

• Compiler invoke the correct version depends on

• number of arguments.

• types of the arguments.

• Complex z1 //invoke default constructor
• Complex z2 ( 23.5, 34.5 ) / invoke
  parameterized constructor /
• Complex z3 ( z2 ) //invoke copy constructor

• Constructor overloading

• Once you define a constructor include a
  default constructor too.

• Cannot create objects without arguments.

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Constructors with default args
class Complex int x, y public Complex ( )
//default constructor x 0.0 y
0.0 Complex ( float a, float b 0.0 )
//parameterized constructor x a y
b Complex ( Complex z ) //copy
constructor x z.x y z.y
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Default arguments

• Complex z ( 3.4 ) // x 3.4, y 0.0

• Complex z ( 2.3, 5.7 ) // x 2.3, y 5.7

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Copy Constructor

• Used to declare and initialize an object from
  another.

• Complex z3 ( z2 )

• Other situations where copy constructor calls

• When you pass an object by value, the
  constructor initializes the corresponding
  formal argument.

• When you have a function return an object, the
  constructor initializes a temporary object used
  to convey the objects values to the calling
  program.

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Destructor

• Used to destroy the objects.

• Same as the class name but is preceded by a
  tilde ().

• E.g.
• Complex ()

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Destructor

• A destructor never takes any arguments nor
  returns a value.

• Invoked by the compiler upon exit from the
  program (or block or function as the case may
  be) to clean up storage that is no longer
  accessible.

• It is a good practice to declare destructors
  in a program since it releases the memory space
  for future use.