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C++ Programming: chapter 7 – inheritence

C++ Programming: chapter 7 – inheritence. 2014, Spring Pusan National University Ki-Joune Li http://isel.cs.pnu.edu/~lik. class Student { string name; string ID; short year; string dept; float score; };. class Professor { string name; string ID; shortage; string dept;

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C++ Programming: chapter 7 – inheritence

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  1. C++ Programming: chapter 7 – inheritence 2014, Spring Pusan National University Ki-Joune Li http://isel.cs.pnu.edu/~lik

  2. class Student { string name; string ID; short year; string dept; float score; }; class Professor { string name; string ID; shortage; string dept; string url; }; common 어떻게 효과적으로 처리하는 방법은 ?

  3. class Person { string name; string ID; string dept; }; Superclass Inheritance subclass subclass class Professor : public Person { shortage; string url; }; class Student : public Person { short year; float score; }; common

  4. class Person { string name; string ID; string dept; }; sizeof(person): 12 bytes class Student : public Person { short year; float score; }; sizeof(Student): 12 + (2+4) bytes • Superclass A, Subclass A1, A2 • Superclass의 모든 Attribute와 memberfunction은 Subclass로 상속

  5. #include <iostream> #include <cstring> using namespace std; class Shape { public:   double width;   double height;   void display() {     cout << "Width and height are " <<  width << " and " << height << "\n";   } }; // Triangle is derived from Shape. class Triangle : public Shape { public:   char style[20];   double area() {     return width * height / 2;   }   void showStyle() {     cout << "Triangle is " << style << "\n";   } }; #include <iostream> #include <cstring> using namespace std; class Shape { public:   double width;   double height;   void display() {     cout << "Width and height are " <<  width << " and " << height << "\n";   } }; // Triangle is derived from Shape. class Triangle : public Shape { public:   char style[20];   double area() {     return width * height / 2;   }   void showStyle() {     cout << "Triangle is " << style << "\n";   } };  #include <iostream> #include <cstring> using namespace std; int main() {   Triangle t1;   Triangle t2;   t1.width = 4.0;   t1.height = 4.0;   strcpy(t1.style, "isosceles");   t2.width = 8.0;   t2.height = 12.0;   strcpy(t2.style, "right");   t1.showStyle();   t1.display();   cout << "Area is " << t1.area() << "\n";   t2.showStyle();   t2.display();   cout << "Area is " << t2.area() << "\n";   return 0; }

  6. class Shape { private:  double width;   double height; public:   void display() {     cout << "Width and height are " << width << " and " << height << "\n";   }   // accessor functons   double getWidth() { return width; }   double getHeight() { return height; }   void setWidth(double w) { width = w; }   void setHeight(double h) { height = h; } }; class Shape { private:  double width;   double height; public:   void display() {     cout << "Width and height are " << width << " and " << height << "\n";   }   // accessor functons   double getWidth() { return width; }   double getHeight() { return height; }   void setWidth(double w) { width = w; }   void setHeight(double h) { height = h; } };  // Triangle is derived from Shape. class Triangle : public Shape {   char style[20]; // now private public:   // Constructor for Triangle.   Triangle(char *str, double w, double h) {     setWidth(w);     setHeight(h);     strcpy(style, str);   }   double area() {     return getWidth() * getHeight() / 2;   }   void showStyle() {     cout << "Triangle is " << style << "\n";   } };  int main() {   Triangle t1("isosceles", 4.0, 4.0);   Triangle t2("right", 8.0, 12.0);    t1.showStyle(); t1.display();   cout << "Area is " << t1.area() << "\n";   t2.showStyle(); t2.display();   cout << "Area is " << t2.area() << "\n";   return 0; } Constructor

  7. class Shape { private:  double width;   double height; public:class Shape { private:  double width;   double height; public:   void display() {     cout << "Width and height are " << width << " and " << height << "\n";   }  Shape(double w,double h): width(w),height(h){}   // accessor functons   double getWidth() { return width; }   double getHeight() { return height; }  };  // Triangle is derived from Shape. class Triangle : public Shape {   char style[20]; // now private public:   // Constructor for Triangle.   Triangle(char *str, double w, double h): Shape(w,h) { strcpy(style, str);}   double area() {     return getWidth() * getHeight() / 2;   }   void showStyle() {     cout << "Triangle is " << style << "\n";   } };  int main() {   Triangle t1("isosceles", 4.0, 4.0);   Triangle t2("right", 8.0, 12.0);    t1.showStyle(); t1.display();   cout << "Area is " << t1.area() << "\n";   t2.showStyle(); t2.display();   cout << "Area is " << t2.area() << "\n";   return 0; } private, protected, public and class inheritance

  8. class Shape { protected:  double width;   double height; public:class Shape { protected:  double width;   double height; public:   void display() {     cout << "Width and height are " << width << " and " << height << "\n";   }   // accessor functons };  // Triangle is derived from Shape. class Triangle : public Shape {   char style[20]; // now private public:   // Constructor for Triangle.   Triangle(char *str, double w, double h): Shape(w, h) { strcpy(style, str);}   double area() {     return width * height / 2;   }   void showStyle() {     cout << "Triangle is " << style << "\n";   } };  int main() {   Triangle t1("isosceles", 4.0, 4.0);   Triangle t2("right", 8.0, 12.0);    t1.showStyle(); t1.display();   cout << "Area is " << t1.area() << "\n";   t2.showStyle(); t2.display();   cout << "Area is " << t2.area() << "\n";   return 0; } Subclass에서만 접근 가능 private, protected, public and class inheritance

  9. private, protected, public and class inheritance class base {  int i; // private to basepublic:  int j, k;  void seti(int x) { i = x; }  int geti() { return i; }};class derived: private base {public:  base::j; // make j public again - but not k  base::seti(); // make seti() public  base::geti(); // make geti() public  int a; // public};

  10. int main() { Shapes(4.0, 4.0);   Triangle t("right", 8.0, 12.0);int main() { Shapes(4.0, 4.0);   Triangle t("right", 8.0, 12.0); Right_Triangle r(10.0); t.display(); cout<<“Area: “<<r.area() <<“\n”; cout<<“Area: “<<r.Triangle::area()<<“\n”;  return 0; } class Shape { protected:  double width;   double height; public: Shape(double w, double h): width(w), height(h) {}  void display() { cout << "Width and height are " << width << " and " << height << "\n";}};  // Triangle is derived from Shape. class Triangle : public Shape { string style; // now private public:   // Constructor for Triangle.   Triangle(double w, double h, string s): width(w), height(h), style(s) {}  void display() { cout << ”Style: “<<style<<“Width:”<<width<<“ Height: "<<height << "\n"; } double area() { width*height/2.0; }};  class Regular_Triangle : public Triangle { double side;public:   // Constructor for Triangle. Right_Triangle(double s): Triangle(s, sqrt(3.0)/2.0*s,“regular”), side(s) {}  double area() { side*sqrt(3.0)/4.0; }};  Member function redefinition

  11. class Shape { protected:  double width; double height,double area;public: Shape(double w, double h, double a): width(w), height(h), area(a) {}};  class Rectangle : public Shape { public: Rectangle(double a, double b): Shape(a, b, a*b){} };  // Triangle is derived from Shape. class Triangle : public Shape { protected: double s1, s2, s3;public:   Triangle(double a, double b, string c): s1(a), s2(b), s3(c), Shape(s3,0.0,0.0) { height=s3*sqrt(1-((s3*s3+s1*s1)/2.0*s3*s1)*((s3*s3+s1*s1)/2.0*s3*s1)); area=s3*height/2.0; }};  Member function redefinition

  12. FunctionA(Shape A) {…} int main() { Shapes(4.0, 4.0);   Triangle t("right", 8.0, 12.0); FunctionA(t); // OK ?? FunctionB(s); // OK ?? } FunctionB(Triangle B) {…} Class hierarchy and type conversion

  13. Node: Plus (+) Times (*) Int 10*3+5 + * 5 class Node { protected:int code; public: enum {PLUS, TIME, INT}; Node(int c): code(c) {} int eval(); };  class Plus: public Node { public: Node *left, *right; Plus(Node *l, Node *r): Node(PLUS), left(l), right(r) {} };  10 3 class Times: public Node { public: Node *left, *right; Times(Node *l, Node *r): Node(TIMES), left(l), right(r) {} };  class Int : public Node { public: unsigned int value; Int(int v): Node(INT), value(v) {} };  class hierarchy: example calculator

  14. Node Node Plus Times Int Bop Int Plus Times class hierarchy: example calculator

  15. class Node { protected:const int code; public: enum {PLUS, TIME, INT}; Node(int c): code(c) {} int eval(); };  Node Int Bop int Node::eval() {  switch(code) { case INT: return ((Int *)this)->value; case PLUS: return ((Bop *)this)->left->eval()+((Bop *)this)->right->eval(); case TIMES: return ((Bop *)this)->left->eval()*((Bop *)this)->right->eval(); }}  Plus class Bop: public Node { protected: Node *left, *right; public: Bop(int c, Node *l, Node *r): Node(c), left(l), right(r) {} };  Times class Plus: public Bop { public: Plus(Node *l, Node *r): Bop(PLUS, l, r) {} };  별로 자연스럽지 못한 방법 class Times: public Bop { public: Times(Node *l, Node *r): Bop(TIMES, l, r) {} };  class hierarchy: example calculator

  16. int Node::eval() {  switch(code) { case INT: return ((Int *)this)->value; case PLUS: return ((Bop *)this)->left->eval()+((Bop *)this)->right->eval(); case TIMES: return ((Bop *)this)->left->eval()*((Bop *)this)->right->eval(); }}  무엇이부자연스러운가? int Node::eval() {  switch(code) { case INT: return this->value; // wrong case PLUS: return this->left->eval()+this->right->eval(); // wrong case TIMES: return this->left->eval()*this->right->eval(); // wrong }}  무엇이잘못되었는가?

  17. class Node { protected:const int code; public: enum {PLUS, TIME, INT}; Node(int c): code(c) {} virtual int eval() {return -1;} // -1 means “error” };  eval eval eval Node Bop Int eval class Bop: public Node { protected: Node *left, *right; public: Bop(int c, Node *l, Node *r): Node(c), left(l), right(r) {} };  class Int: public Node {  int value;public: Plus(Node *l, Node *r): Bop(INT, l, r) {} int eval() { return value; } };  Plus class Times: public Bop { public: Times(Node *l, Node *r): Bop(TIMES, l, r) {} int eval() {left->eval()*right->eval();} };  class Plus: public Bop { public: Plus(Node *l, Node *r): Bop(PLUS, l, r) {} int eval() {left->eval()+right->eval();} };  Times 지금까지는 virtual 이 있으나 없으나 비슷함 (없는경우: function redefinition) Virtual function

  18. class Node { protected:const int code; public: enum {PLUS, TIME, INT}; Node(int c): code(c) {} virtual int eval() {return -1;} // -1 means “error” };  class Node { protected:const int code; public: enum {PLUS, TIME, INT}; Node(int c): code(c) {} int eval() {return -1;} // -1 means “error” };  #include <iostream>using namespace std;int main() {  Node* node_ptr=new Node(INT); Int* int1_ptr=new Int(INT, 10); Int* int2_ptr=new Int(INT, 20); Plus* plus_ptr=new Bop(PLUS, int1_ptr, int2_ptr); int flag; cout << “Input flag: ”; cin >> flag; if (flag!=0) node_ptr=plus_ptr; else node_ptr=int1_ptr; cout<<“Evaluation result:” <<node_ptr->eval() << endl;   return 0;} 다른 Function 이 문장으로는 Compile time 때 함수를 결정할 수 없음  Late Binding Virtual function

  19. #include <iostream>using namespace std;int main() {  Node* node_ptr; Int* int1_ptr=new Int(INT, 10); Int* int2_ptr=new Int(INT, 20); Plus* plus_ptr=new Bop(PLUS, int1_ptr, int2_ptr); int flag; cout << “Input flag: ”; cin >> flag; if (flag!=0) node_ptr=plus_ptr; else node_ptr=int1_ptr; cout<<“Evaluation result:” <<node_ptr->eval() << endl;   return 0;} #include <iostream>using namespace std;int main() {  Node node(INT); Int int1(INT, 10); Int int2(INT, 20); Plus plus(PLUS, &int1, &int2); int flag; cout << “Input flag: ”; cin >> flag; if (flag!=0) node=plus; else node=int1; cout<<“Evaluation result:” <<node.eval() << endl;   return 0;} 무슨일이 일어날까? • C++에서 Polymorphism • 객체가 무엇이냐에 따라 서로 다른 동작(또는 함수)이 수행되는 것 • Overriding • 조건: • Pointer (왜??) • Virtual Function

  20. class Node { protected:const int code; public: enum {PLUS, TIME, INT}; Node(int c): code(c) {} virtual int eval()=0; };  class Bop: public Node { protected: Node *left, *right; public: Bop(int c, Node *l, Node *r): Node(c), left(l), right(r) {} };  class Plus: public Bop { public: Plus(Node *l, Node *r): Bop(PLUS, l, r) {} int eval() {left->eval()+right->eval();} };  #include <iostream>using namespace std;int main() {  Node* node_ptr=new Node(INT); // wrong Bop bop(INT, NULL, NULL); // wrong   return 0;} • Pure Virtual Function • Subclass에서만 정의되는 Virtual Function • Pure Virtual Function 을 가지고 있는 Class: Abstract Class • Abstract Class에서는 객체를 생성할 수 없음

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