Constructor
- 2. OBJECTIVES:After this presentation we shall be able to answer following questions: What is a CONSTRUCTOR Function? Characteristics of Constructor Default Constructor Parameterized Constructor Constructor Overloading Constructor with Default Arguments Copy Constructor Guidelines for implementing Constructors Destructor Function
- 3. What is a CONSTRUCTOR Function? Special member function used for initialization of objects (data members). A constructor function is called whenever an object is created. Constructors are also called when an object is created as a part of another object.
- 4. A Constructor is declared and defined as follows: class number { int a, b ; public: number( void); // ** Constructor Function Declared ----- ----- }; number :: number( ) // ** Constructor Function Defined { a=0; b=0; }
- 5. Characteristics of Constructors Constructor Functions have same name as that of class name. They do not have return types, not even void May have parameters C++ has default constructors that are called whenever a class is declared even if no function with the same name exists They should be declared in public section. They are invoked automatically when objects are created.
- 6. C++ The default constructor takes no arguments . If no such constructor is defined, then compiler supplies a default constructor. For Example X x ; The default constructor for class X is X::X( ) The statement X x ; invokes the default constructor of the compiler to create the object x. Default Constructor
- 7. C++ Parameterized Constructor class number { int a, b ; public: number( int x, int y); // Constructor Func. Declared ----- }; number :: number(int x, int y) // Constructor Func Defined { a=x; b=y; } number ob1; // ***** WRONG OBJECT CREATION number ob1( 0,100 ); // ********** * Implicit Call Known as shorthand method Easy to implement and looks better number ob1 = number( 0, 100 ); // ** Explicit Call
- 8. C++ : Constructor Overloading class number { int a, b ; public: number( ){a=0; b=0; } // Constructor 1 number( int x, int y); // Constructor 2 ----- }; number :: number(int x, int y) // Constructor 2 Defined { a=x; b=y; }
- 9. C++ : Constructor with Default Arguments class number { int a, b ; public: number( int x, int y=5 ); // Constructor ----- }; number :: number(int x, int y) // Constructor Defined { a=x; b=y; } number ob1(10); number ob2(0 , 0 );
- 10. Example of Constructor class sum { public: sum(); private: int sum1,sum2; };
- 11. C++ void main () { sum obj1; //constructor is called at this //time cout<<“end of main”<<endl; return; }
- 12. C++ Sample Functions What is the output??
- 13. C++ Functions sum::sum () { sum1=0; sum2=10; cout<<sum1<<“ “<<sum2<<endl; }
- 14. the answer 0 10 end of main
- 15. Example of Constructor withArguments class sum { public: sum(int,int); private: int sum1,sum2; };
- 16. C++ void main () { sum obj1 (10,20); //constructor is // called at this time cout<<“end of main\n”; return; }
- 17. C++ Functions sum::sum (int x,int y)) { sum1=x; sum2=y; cout<<sum1<<“ sum1”; cout<<sum2<<“ sum2”<<endl; }
- 18. C++ Sample Functions sum::sum (int x,int y)) { sum1=x; sum2=y; cout<<sum1<<“ sum1”; cout<<sum2<<“ sum2”<<endl; } 10 sum1 20 sum2 end main What is the output??
- 19. C++ : DESTRUCTOR FUNCTION A special function which also has same name as that of class but is preceded with a tilde (~) sign eg., ~ number( ); Does not have a return type (not even void) Cannot have parameters Called automatically when the class object is destroyed De-allocates storage allocated to a class Should be public (or protected)
- 20. public: ~sum (); // DESTRUCTOR FUNCTION sum::~sum ( ) { close (infile); close (outfile); } C++ DESTRUCTOR FUNCTION