[C ++ Basics] 021 _ shallow copy and deep copy

Shallow copy: A pointer member variable exists in the class. During the copy, only the pointer variable is copied, but the address block pointed to by the pointer variable is not copied.

Instance code:

1 # include <iostream> 2 using namespace STD; 3 4 class tree {5 public: 6 // copy constructor 7 tree (const Tree & tree) {8 This-> num = tree. num; 9} 10 // constructor 11 Tree () {12 num = new int (10); 13} 14 // destructor 15 ~ Tree () {16 Delete num; 17} 18 // normal print member variable Content Function 19 void printnum () {20 cout <* (this-> num) <Endl; 21} 22 private: 23 int * num; 24}; 25 26 int main () {27 // generate an object 28 tree * tree1 = new tree () in the heap (); 29 tree1-> printnum (); 30 31 // The copy constructor functions 32 tree tree2 (* tree1); 33 tree2.printnum (); 34 35 // destroy the tree1 object 36 Delete tree1; 37 // at this time, the num pointer is 38 tree2.printnum (); 39 40 system ("pause"); 41 return 0; 42}

 

Deep copy: If a pointer variable exists during object copying, the memory block pointed to by the pointer variable is also copied.

Instance code:

1 # include <iostream> 2 using namespace STD; 3 4 class tree {5 public: 6 // copy constructor (deep copy) 7 tree (const Tree & tree) {8 This-> num = new int (); 9 * (this-> num) = * (tree. num); 10} 11 // constructor 12 tree () {13 num = new int (10); 14} 15 // destructor 16 ~ Tree () {17 Delete num; 18} 19 // normal print member variable content function 20 void printnum () {21 cout <* (this-> num) <Endl; 22} 23 public: // For convenience, declare the member variable as public. In fact, you should write a 24 int * num; 25} function to get the member variable }; 26 27 int main () {28 // generate an object in the heap 29 tree * tree1 = new tree (); 30 tree1-> printnum (); 31 32 // The copy constructor functions 33 tree tree2 (* tree1); 34 tree2.printnum (); 35 36 // destroys the tree1 object 37 Delete tree1; 38 // at this time, num is a floating pointer with 39 tree2.printnum (); 40 41 system ("pause"); 42 return 0; 43}