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# Constructor

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### Constructor

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