Copy constructor in C ++

Copy constructor is a constructor that creates an object by initializing it with an object of the same class, which was created earlier. Copy constructor is used to:

Initialize an object from another object with the same type.

Copy an object to pass it as a parameter to a function.

Copy an object to return it from a function.

If a copy constructor is not defined in a class, the compiler will automatically define a copy of the constructor. If the class has pointer variables and there are some dynamic memory allocations, then it is a necessity to have a copy of the constructor. The most common form of copy constructor in C ++ is:

 ten_lop  ( const  ten_lop  & obj ) { // phan than cua constructor } 

Here, obj is a reference to an object that is being used to initialize another object.

 #include using namespace  std ; class Line { public : int  layChieuDai ( void ); Line ( int  dai  ); // Day la mot constructor don gian Line ( const Line & obj ); // Day la copy constructor ~ Line (); // Day la destructor private : int * contro ; }; // Phan dinh nghia cac ham thanh vien, bao gom constructor, copy constructor, destructor Line :: Line ( int  dai ) {  cout  << "Constructor: cap phat bo nho cho con tro contro" <<  endl ; // cap phat bo nho cho con tro  contro  = new int ; * contro  =  dai ; } Line :: Line ( const Line & obj ) {  cout  << "Copy constructor: cap phat bo nho cho con tro contro" <<  endl ;  contro  = new int ; * contro  = * obj . contro ; // sao chep gia tri } Line ::~ Line ( void ) {  cout  << "Giai phong bo nho!" <<  endl ; delete  contro ; } int Line :: layChieuDai ( void ) { return * contro ; } void  hienThi ( Line  obj ) {  cout  << "Chieu dai cua line la: " <<  obj . layChieuDai () << endl ; } // ham main cua chuong trinh int  main ( ) { Line  line ( 50 );  hienThi ( line ); return 0 ; } 

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

You follow the same example above with a small change to create another object using an object that already exists with the same type.

 #include using namespace  std ; class Line { public : int  layChieuDai ( void ); Line ( int  dai  ); // Day la mot constructor don gian Line ( const Line & obj ); // Day la copy constructor ~ Line (); // Day la destructor private : int * contro ; }; // Phan dinh nghia cac ham thanh vien, bao gom constructor, copy constructor, destructor Line :: Line ( int  dai ) {  cout  << "Constructor: cap phat bo nho cho con tro contro" <<  endl ; // cap phat bo nho cho con tro  contro  = new int ; * contro  =  dai ; } Line :: Line ( const Line & obj ) {  cout  << "Copy constructor: cap phat bo nho cho con tro contro" <<  endl ;  contro  = new int ; * contro  = * obj . contro ; // sao chep gia tri } Line ::~ Line ( void ) {  cout  << "Giai phong bo nho!" <<  endl ; delete  contro ; } int Line :: layChieuDai ( void ) { return * contro ; } void  hienThi ( Line  obj ) {  cout  << "Chieu dai cua line la: " <<  obj . layChieuDai () << endl ; } // Ham main cua chuong trinh int  main ( ) { Line  line1 ( 45 ); Line  line2  =  line1 ; // Lenh nay cung goi copy constructor  hienThi ( line1 );  hienThi ( line2 ); return 0 ; } 

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

According to Tutorialspoint

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