chap23.lst

Borland C++ Builder The Complete Reference 例程源代码

listing 1
class X { 
  int i; 
  int j; 
public: 
  void get_ij(); 
  void put_ij(); 
} ; 
 
class Y : public X { 
  int k; 
public: 
  int get_k(); 
  void make_k(); 
} ;

listing 2
class X { 
protected: 
  int i; 
  int j; 
public: 
  void get_ij(); 
  void put_ij(); 
} ; 
 
class Y : public X { 
  int k; 
public: 
  int get_k(); 
  void make_k(); 
} ;

listing 3
class my_class { 
protected: 
  int i; 
  int j; 
public: 
  void f1(); 
  void f2(); 
protected: 
  int a; 
public: 
  int b; 
} ;

listing 4
#include <iostream> 
using namespace std; 
 
class X { 
protected: 
  int i; 
  int j; 
public: 
  void get_ij() { 
    cout << "Enter two numbers: "; 
    cin >> i >> j; 
  } 
  void put_ij() { cout << i << " " << j << "\n"; } 
} ; 
 
// In Y, i and j of X become protected members. 
class Y : public X { 
  int k; 
public: 
  int get_k() { return k; } 
  void make_k() { k = i*j; } 
} ; 
 
/* Z has access to i and j of X, but not to 
   k of Y, since it is private. */ 
class Z : public Y { 
public: 
  void f(); 
} ; 
 
// i and j are accessible here 
void Z::f() 
{ 
  i = 2; // ok 
  j = 3; // ok 
} 
 
int main() 
{ 
  Y var; 
  Z var2; 
 
  var.get_ij(); 
  var.put_ij(); 
 
  var.make_k(); 
  cout << var.get_k(); 
  cout << "\n"; 
 
  var2.f(); 
  var2.put_ij(); 
 
  return 0; 
}

listing 5
#include <iostream> 
using namespace std; 
 
class X { 
protected: 
  int i; 
  int j; 
public: 
  void get_ij() { 
    cout << "Enter two numbers: "; 
    cin >> i >> j; 
  } 
  void put_ij() { cout << i << " " << j << "\n"; } 
} ; 
 
// Now, i and j are converted to private members of Y. 
class Y : private X { 
  int k; 
public: 
  int get_k() { return k; } 
  void make_k() { k = i*j; } 
} ; 
 
/* Because i and j are private in Y, they 
   cannot be inherited by Z. */ 
class Z : public Y { 
public: 
  void f(); 
} ; 
 
// This function no longer works. 
void Z::f() 
{ 
//  i = 2;  i and j are no longer accessible 
//  j = 3; 
} 
 
int main() 
{ 
  Y var; 
  Z var2; 
 
//  var.get_ij();  no longer accessible 
//  var.put_ij();  no longer accessible 
 
  var.make_k(); 
  cout << var.get_k(); 
  cout << "\n"; 
 
  var2.f(); 
//  var2.put_ij();  no longer accessible 
 
  return 0; 
}

listing 6
#include <iostream> 
using namespace std; 
 
class Base { 
public: 
  Base() { cout << "\nBase created\n"; } 
}; 
 
class D_class1 : public Base { 
public: 
  D_class1() { cout << "D_class1 created\n"; } 
}; 
 
int main() 
{ 
  D_class1 d1; 
 
  // do nothing but execute constructors 
  return 0; 
}

listing 7
#include <iostream> 
using namespace std; 
 
class Base { 
public: 
  Base() { cout << "\nBase created\n"; } 
  ~Base() { cout << "Base destroyed\n\n"; } 
}; 
 
class D_class1 : public Base { 
public: 
  D_class1() { cout << "D_class1 created\n"; } 
  ~D_class1() { cout << "D_class1 destroyed\n"; } 
}; 
 
int main() 
{ 
  D_class1 d1; 
 
  cout << "\n"; 
 
  return 0; 
}

listing 8
#include <iostream> 
using namespace std; 
 
class Base { 
public: 
  Base() { cout << "\nBase created\n"; } 
  ~Base() { cout << "Base destroyed\n\n"; } 
}; 
 
class D_class1 : public Base { 
public: 
  D_class1() { cout << "D_class1 created\n"; } 
  ~D_class1() { cout << "D_class1 destroyed\n"; } 
}; 
 
class D_class2 : public D_class1 { 
public: 
  D_class2() { cout << "D_class2 created\n"; } 
  ~D_class2() { cout << "D_class2 destroyed\n"; } 
}; 
 
int main() 
{ 
  D_class1 d1; 
  D_class2 d2; 
 
  cout << "\n"; 
 
  return 0; 
}

listing 9
#include <iostream> 
using namespace std; 
 
class X { 
protected: 
  int a; 
public: 
  void make_a(int i) { a = i; } 
}; 
 
class Y { 
protected: 
  int b; 
public: 
  void make_b(int i) { b = i; } 
} ; 
 
// Z inherits both X and Y 
class Z : public X, public Y { 
public: 
  int make_ab() { return a*b; } 
} ; 
 
int main() 
{ 
  Z i; 
 
  i.make_a(10); 
  i.make_b(12); 
  cout << i.make_ab(); 
 
  return 0; 
}

listing 10
#include <iostream> 
using namespace std; 
 
class X { 
protected: 
  int a; 
public: 
  X() { 
    a = 10; 
    cout << "Initializing X\n"; 
  } 
}; 
 
class Y { 
protected: 
  int b; 
public: 
  Y() { 
    cout << "Initializing Y\n"; 
    b = 20; 
  } 
} ; 
 
// Z inherits both X and Y 
class Z : public X, public Y { 
public: 
  Z() { cout << "Initializing Z\n"; } 
  int make_ab() { return a*b; } 
} ; 
 
int main() 
{ 
  Z i; 
 
  cout << i.make_ab(); 
 
  return 0; 
}

listing 11
#include <iostream> 
using namespace std; 
 
class X { 
protected: 
  int a; 
public: 
  X(int i) { a = i; } 
}; 
 
class Y { 
protected: 
  int b; 
public: 
  Y(int i) { b = i; } 
} ; 
 
// Z inherits both X and Y 
class Z : public X, public Y { 
public: 
  /* Initialize X and Y via Z's constructor. 
     Notice that Z does not actually use x or y 
     itself, but it could, if it so chooses. */ 
  Z(int x, int y) : X(x), Y(y) 
  { 
    cout << "Initializing\n"; 
  } 
  int make_ab() { return a*b; } 
} ; 
 
int main() 
{ 
  Z i(10, 20); 
 
  cout << i.make_ab(); 
 
  return 0; 
}

listing 12
B_class *p;   // pointer to object of type B_class 
B_class B_ob; // object of type B_class 
D_class D_ob; // object of type D_class

listing 13
p = &B_ob; // p points to object of type B_class 
 
p = &D_ob; /* p points to object of type D_class, 
              which is an object derived from B_class. */

listing 14
// Using pointers on derived class objects. 
 
#include <iostream> 
#include <cstring> 
using namespace std; 
 
class B_class { 
  char name[80]; 
public: 
  void put_name(char *s) { strcpy(name, s); } 
  void show_name() { cout << name << " "; } 
} ; 
 
class D_class : public B_class { 
  char phone_num[80]; 
public: 
  void put_phone(char *num) { 
    strcpy(phone_num, num); 
  } 
  void show_phone() { cout << phone_num << "\n"; } 
}; 
 
int main() 
{ 
  B_class *p; 
  B_class B_ob; 
 
  D_class *dp; 
  D_class D_ob; 
 
  p = &B_ob;  // address of base 
 
  // Access B_class via pointer. 
  p->put_name("Thomas Edison"); 
 
  // Access D_class via base pointer. 
  p = &D_ob; 
  p->put_name("Albert Einstein"); 
 
  // Show that each name went into proper object. 
  B_ob.show_name(); 
  D_ob.show_name(); 
  cout << "\n"; 
 
  /* Since put_phone and show_phone are not part of the 
     base class, they are not accessible via the base 
     pointer p and must be accessed either directly, 
     or, as shown here, through a pointer to the 
     derived type. 
  */ 
  dp = &D_ob; 
  dp->put_phone("555 555-1234"); 
  p->show_name(); // either p or dp can be used in this line 
  dp->show_phone(); 
 
  return 0; 
}

listing 15
((D_class *)p)->show_phone();

listing 16
// A short example that uses virtual functions. 
#include <iostream> 
using namespace std; 
 
class Base { 
public: 
  virtual void who() { // specify a virtual function 
    cout << "Base\n"; 
  } 
}; 
 
class first_d : public Base { 
public: 
  void who() { // define who() relative to first_d 
    cout << "First derivation\n"; 
  } 
}; 
 
class second_d : public Base { 
public: 
  void who() { // define who() relative to second_d 
    cout << "Second derivation\n"; 
  } 
}; 
 
int main() 
{ 
  Base base_obj; 
  Base *p; 
  first_d first_obj; 
  second_d second_obj; 
 
  p = &base_obj; 
  p->who();  // access Base's who 
 
  p = &first_obj; 
  p->who(); // access first_d's who 
 
  p = &second_obj; 
  p->who();  // access second_d's who 
 
  return 0; 
}

listing 17
/* Here, a base class reference is used to access 
   a virtual function. */ 
#include <iostream> 
using namespace std; 
 
class Base { 
public: 
  virtual void who() { // specify a virtual function 
    cout << "Base\n"; 
  } 
}; 
 
class first_d : public Base { 
public: 
  void who() { // define who() relative to first_d 
    cout << "First derivation\n"; 
  } 
}; 
 
class second_d : public Base { 
public: 
  void who() { // define who() relative to second_d 
    cout << "Second derivation\n"; 
  } 
}; 
 
// Use a base class reference parameter. 
void show_who(Base &r) { 
  r.who(); 
} 
 
int main() 
{ 
  Base base_obj; 
  first_d first_obj; 
  second_d second_obj; 
 
  show_who(base_obj);   // access Base's who 
  show_who(first_obj);  // access first_d's who 
  show_who(second_obj); // access second_d's who 
 
  return 0; 
}

listing 18
// Derive from first_d, not Base 
class second_d : public first_d { 
public: 
  void who() { // define who() relative to second_d 
    cout << "Second derivation\n"; 
  } 
};

listing 19
#include <iostream> 
using namespace std; 
 
class Base { 
public: 
  virtual void who() { 
    cout << "Base\n"; 
  } 
}; 
 
class first_d : public Base { 
public: 
  void who() { 
    cout << "First derivation\n"; 
  } 
}; 
 
class second_d : public Base { 
// who() not defined 
}; 
 
int main() 
{ 
  Base base_obj; 
  Base *p; 
  first_d first_obj; 
  second_d second_obj; 
 
  p = &base_obj; 
  p->who();  // access Base's who() 
 
  p = &first_obj; 
  p->who(); // access first_d's who() 
 
  p = &second_obj; 
  p->who();  /* access Base's who() because 
                second_d does not redefine it */ 
 
  return 0; 
}

listing 20
#include <iostream> 
using namespace std; 
 
class figure { 
protected: 
  double x, y; 
public: 
  void set_dim(double i, double j) { 
    x = i; 
    y = j; 
  } 
  virtual void show_area() { 
    cout << "No area computation defined "; 
    cout << "for this class.\n"; 
  } 
} ; 
 
class triangle : public figure { 
  public: 
    void show_area() { 
      cout << "Triangle with height "; 
      cout << x << " and base " << y; 
      cout << " has an area of "; 
      cout << x * 0.5 * y << ".\n"; 
    } 
}; 
 
class square : public figure { 
  public: 
    void show_area() { 
      cout << "Square with dimensions "; 
      cout << x << "x" << y; 
      cout << " has an area of "; 
      cout << x *  y << ".\n"; 
    } 
}; 
 
int main() 
{ 
  figure *p;  /* create a pointer to base type */ 
 
  triangle t;  /* create objects of derived types */ 
  square s; 
 
  p = &t; 
  p->set_dim(10.0, 5.0); 
  p->show_area(); 
  p = &s; 
  p->set_dim(10.0, 5.0); 
  p->show_area(); 
 
  return 0; 
}

listing 21
class circle : public figure { 
  public: 
    void show_area() { 
      cout << "Circle with radius "; 
      cout << x; 
      cout << " has an area of "; 
      cout <<  3.14 * x * x; 
    } 
} ;

listing 22
#include <iostream> 
using namespace std; 
 
class figure { 
protected: 
  double x, y; 
public: 
  void set_dim(double i, double j=0) { 
    x = i; 
    y = j; 
  } 
  virtual void show_area() { 
    cout << "No area computation defined "; 
    cout << "for this class.\n"; 
  } 
} ; 
 
class triangle : public figure { 
  public: 
    void show_area() { 
      cout << "Triangle with height "; 
      cout << x << " and base " << y; 
      cout << " has an area of "; 
      cout << x * 0.5 * y << ".\n"; 
    } 
}; 
 
class square : public figure { 
  public: 
    void show_area() { 
      cout << "Square with dimensions "; 
      cout << x << "x" << y; 
      cout << " has an area of "; 
      cout << x *  y << ".\n"; 
    } 
}; 
 
class circle : public figure { 
  public: 
    void show_area() { 
      cout << "Circle with radius "; 
      cout << x; 
      cout << " has an area of "; 
      cout << 3.14 * x * x; 
    } 
} ; 
 
int main() 
{ 
  figure *p;  /* create a pointer to base type */ 
  triangle t;  /* create objects of derived types */ 
  square s; 
  circle c; 
 
  p = &t; 
  p->set_dim(10.0, 5.0); 
  p->show_area(); 
 
  p = &s; 
  p->set_dim(10.0, 5.0); 
  p->show_area(); 
 
  p = &c; 
  p->set_dim(9.0); 
  p->show_area(); 
 
  return 0; 
}

listing 23
class figure { 
  double x, y; 
public: 
  void set_dim(double i, double j=0) { 
    x = i; 
    y = j; 
  } 
  virtual void show_area() = 0; // pure 
} ;

listing 24
/* 
   This program will not compile because the class 
   circle does not override show_area(). 
*/ 
#include <iostream> 
using namespace std; 
 
class figure { 
protected: 
  double x, y; 
public: 
  void set_dim(double i, double j) { 
    x = i; 
    y = j; 
  } 
  virtual void show_area() = 0; // pure 
} ; 
 
class triangle : public figure { 
  public: 
    void show_area() { 
      cout << "Triangle with height "; 
      cout << x << " and base " << y; 
      cout << " has an area of "; 
      cout << x * 0.5 * y << ".\n"; 
    } 
}; 
 
class square : public figure { 
  public: 
    void show_area() { 
      cout << "Square with dimensions "; 
      cout << x << "x" << y; 
      cout << " has an area of "; 
      cout << x *  y << ".\n"; 
    } 
}; 
 
class circle : public figure { 
// no definition of show_area() will cause an error 
}; 
 
int main() 
{ 
  figure *p;  // create a pointer to base type  
  circle c;   // attempt to create an object of type circle -- ERROR 
  triangle t; // create objects of derived types */ 
  square s; 
 
  p = &t; 
  p->set_dim(10.0, 5.0); 
  p->show_area(); 
 
  p = &s; 
  p->set_dim(10.0, 5.0); 
  p->show_area(); 
 
  return 0; 
}