Contructor and Destructor in C ++

Class Contructor in C ++

A contructor class is a special member function of a class that is executed whenever we create new objects of that class.

A constructor will have the same name as the class and it does not have any return type, including void type.Constructors can be very useful for setting initialization values ​​for specific member variables.

The following example explains the concept of constructor in C ++:

 #include using namespace  std ; class Line { public : void  setChieuDai ( double  dai  ); double  layChieuDai ( void ); Line (); // Day la constructor private : double  chieudai ; }; // phan dinh nghia cac ham thanh vien, bao gom ca constructor Line :: Line ( void ) {  cout  << "Doi tuong da duoc tao!" <<  endl ; } void Line :: setChieuDai ( double  dai  ) {  chieudai  =  dai ; } double Line :: layChieuDai ( void ) { return  chieudai ; } // Ham main cua chuong trinh int  main ( ) { Line  line ; // thiet lap chieu dai cua line  line . setChieuDai ( 6.0 );  cout  << "Chieu dai cua duong la: " <<  line . layChieuDai () << endl ; return 0 ; } 

Compiling and running the above C ++ program will produce the following results:

The constructor is parameterized in C ++

A default constructor in C ++ does not have any parameters, but if you need it, a constructor can have parameters. This helps you assign the initial value to an object at the time of creating it, as in the following example:

 #include using namespace  std ; class Line { public : void  setChieuDai ( double  dai  ); double  layChieuDai ( void ); Line ( double  dai ); // Day la phan khai bao constructor private : double  chieudai ; }; // phan dinh nghia cac ham thanh vien, bao gom constructor Line :: Line ( double  dai ) {  cout  << "Doi tuong dang duoc tao, chieudai = " <<  dai  <<  endl ;  chieudai  =  dai ; } void Line :: setChieuDai ( double  dai  ) {  chieudai  =  dai ; } double Line :: layChieuDai ( void ) { return  chieudai ; } // ham main cua chuong trinh int  main ( ) { Line  line ( 10.0 ); // lay chieu dai da duoc khoi tao ban dau.  cout  << "Chieu dai cua line la: " <<  line . layChieuDai () << endl ; // thiet lap chieu dai mot lan nua  line . setChieuDai ( 6.0 );  cout  << "Chieu dai cua line la: " <<  line . layChieuDai () << endl ; return 0 ; } 

Compiling and running the above C ++ program will produce the following results:

Use the initialization list for initialization fields

In case the constructor is parameterized, you can use the following syntax to initialize fields.

 Line :: Line ( double  dai ):  chieudai ( dai ) {  cout  << "Doi tuong dang duoc tao, chieudai = " <<  dai  <<  endl ; } 

The above syntax is equivalent to the following syntax:

 Line :: Line ( double  dai ) {  cout  << "Doi tuong dang duoc tao, chieudai = " <<  dai  <<  endl ;  chieudai  =  dai ; } 

If with a class in C, you have multiple X, Y, Z, . fields to be initialized, then you can use the same syntax and distinguish the fields by commas, as follows:

 C :: C ( double  a , double  b , double  c ):  X ( a ),  Y ( b ),  Z ( c ) { . } 

Destructor class in C ++

A destructor is a special member function of a class that is executed whenever an object of that class is out of scope or whenever the delete expression is applied to a pointer to the object of the class. there.

A destructor will have the same name as the class and be preceded by the ~ symbol and it can: not return a value and not receive any parameters. Destructor can be very useful to free resources before exiting the program, for example: closing files, freeing memory .

The following example explains the concept of destructor in C ++:

 #include using namespace  std ; class Line { public : void  setChieuDai ( double  dai  ); double  layChieuDai ( void ); Line (); // Day la phan khai bao constructor  ~ Line (); // Day la phan khai bao destructor private : double  chieudai ; }; // phan dinh nghia ham thanh vien, bao gom constructor va destructor Line :: Line ( void ) {  cout  << "Doi tuong dang duoc tao" <<  endl ; } Line ::~ Line ( void ) {  cout  << "Doi tuong dang bi xoa!" <<  endl ; } void Line :: setChieuDai ( double  dai  ) {  chieudai  =  dai ; } double Line :: layChieuDai ( void ) { return  chieudai ; } // ham main cua chuong trinh int  main ( ) { Line  line ; // Thiet lap chieu dai cua line  line . setChieuDai ( 6.0 );  cout  << "Chieu dai cua line la: " <<  line . layChieuDai () << endl ; return 0 ; } 

Compiling and running the above C ++ program will produce the following results:

According to Tutorialspoint

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