c++继承经典样例
#include <iostream.h>

class Base
{
private:
        int b_number;
public:
        Base( ){}
        Base(int i) : b_number (i) { }
        int get_number( ) {return b_number;}
        void print( ) {cout << b_number << endl;}        
};

 

class Derived : public Base
{
private:
        int d_number;

public:
// constructor, initializer used to initialize the base part of a Derived object.
        Derived( int i, int j ) : Base(i), d_number(j) { };        
        // a new member function that overrides the print( ) function in Base
        void print( ) 
        {
                cout << get_number( ) << " ";        
                // access number through get_number( )
                cout << d_number << endl;
        }
};

int main( )
{
        Base a(2);
        Derived b(3, 4);

        cout << "a is ";
        a.print( );                // print( ) in Base
        cout << "b is ";
        b.print( );                // print( ) in Derived
        cout << "base part of b is "; 
        b.Base::print( );                // print( ) in Base

        return 0;
}

 

---

没有虚析构函数，继承类没有析构
//Example:  non- virtual destructors for dynamically allocated objects.

 

#include <iostream.h>
#include <string.h>

class Thing
{ public:
virtual void what_Am_I( ) {cout << "I am a Thing./n";}
~Thing(){cout<<"Thing destructor"<<endl;}
};

class Animal : public Thing
{  
public:
virtual void what_Am_I( ) {cout << "I am an Animal./n";}
~Animal(){cout<<"Animal destructor"<<endl;}
};

void main( )
{
   Thing *t =new Thing;      
   Animal*x = new Animal;
   Thing* array[2];

   array[0] = t;                                // base pointer
   array[1] = x;               

    for (int i=0; i<2; i++)  array->what_Am_I( ) ;

   delete array[0];
   delete array[1];
   return ;
}

 

---

纯虚函数，多态

#include <iostream.h>
#include <math.h>

class Point
{
private:
        double x;
        double y;
public:
        Point(double i, double j) : x(i), y(j) { } 
        void print( ) const
        { cout << "(" << x << ", " << y << ")"; }
};

class Figure
{
private:
        Point center;
public:
        Figure (double i = 0, double j = 0) : center(i, j) { }         
        
Point& location( )
{
return center;
}                  // return an lvalue
   void move(Point p)
{
center = p;
draw( );
}

        virtual void draw( ) = 0; // draw the figure
        virtual void rotate(double) = 0; 
// rotate the figure by an angle                
};

class Circle : public Figure
{
private:
        double radius;
public:
        Circle(double i = 0, double j = 0, double r = 0) : Figure(i, j), radius(r) { }
        void draw( )
        {
                cout << "A circle with center ";
                location( ).print( );
                cout << " and radius " << radius << endl;
        }
        void rotate(double)
        {
                cout << "no effect./n";
        }        // must be defined
};

class Square : public Figure
{
private:
        double side;        // length of the side
        double angle;        // the angle between a side and the x-axis
public:
        Square(double i = 0, double j = 0, double d = 0, double a = 0)        : Figure(i, j), side(d), angle(a) { }
   void draw( )
        {
                cout << "A square with center ";
                location( ).print( );
                cout << " side length " << side << "./n"  
                << "The angle between one side and the X-axis is " << angle << endl;
        }
        void rotate(double a)
        {
               angle += a;
                cout << "The angle between one side and the X-axis is " << angle << endl;
        }
        void vertices( )
        {
                cout << "The vertices of the square are:/n";
                // calculate coordinates of the vertices of the square
          }
};

int main( )
{
        Circle c(1, 2, 3);
        Square s(4, 5, 6);
   Figure *f = &c, &g = s;

        f -> draw( );
        f -> move(Point(2, 2));

        g.draw( );
          g.rotate(1);
        
s.vertices( );
// Cannot use g here since vertices( ) is not a member of Figure.

        return 0;
}
////////////////////////////////////////////////////////////////////
#include <iostream.h>
#include <string.h>

class Thing
{ 
public:
virtual void what_Am_I( ) {cout << "I am a Thing./n";}

~Thing(){cout<<"Thing destructor"<<endl;}
};

class Animal : public Thing
{ 
public:
virtual void what_Am_I( ) {cout << "I am an Animal./n";}

~Animal(){cout<<"Animal destructor"<<endl;}
};

void main( )
{
   Thing t ; 
        Animal x ;
   Thing* array[2];

   array[0] = &t;                        // base pointer
   array[1] = &x;        
          for (int i=0; i<2; i++)  array->what_Am_I( ) ;

   return ;
}

 

---

 

多继承

#include <iostream.h>

class A
{
private:
        int a;
public:
        A(int i) : a(i) { }
        virtual void print( )        {cout << a << endl;}
        int get_a( ) {return a;}
};

class B
{
private:
        int b;
public:
        B(int j) : b(j) { }
        void print( )        {cout << b << endl;}
        int get_b( ) {return b;}
};

class C : public A, public B
{
        int c;
public:
        C(int i, int j, int k) : A(i), B(j), c(k) { }
        void print( )        {A::print( ); B::print( );}
        // use print( ) with scope resolution
        void get_ab( )        {cout << get_a( ) << " " << get_b( ) << endl;}
        // use get_a( ) and get_b( ) without scope resolution
};

int main( )
{
        C x(5, 8, 10);
        A* ap = &x;
        B* bp = &x;

        ap -> print( );                // use C::print( );
        bp -> print( );                // use B::print( );
//        bp -> A::print( );                // as if x is inherited from B only,
                                                // cannot access A::print( );
        x.A::print( );                // use A::print( );
        x.get_ab( );

        return 0;
}

 

---

 

共同基类的多继承

#include <iostream.h>
class R
{int r;
public:
        R(int anInt){ r = anInt;};
       printOn(){ cout<<"r="<<r<<endl;} ; };

class A : public R
{
int a;
public:
        A(int int1,int int2):R(int2){ a = int1;};};

class B : public R
{
int b;
public:
        B(int int1,int int2):R(int2){ b = int1;};};

class C : public A, public B
{
int c;
public:
C(int int1,int int2, int int3):A(int2,int3), B(int2,int3){ c = int1;}
};

int main( )
{    
  int i;
        R rr(10);      
A aa(20,30);      
B bb (40,50);
        C cc(5, 7, 9);
        rr.printOn();    
aa.printOn();                  //inherits R printOn  
bb.printOn();                   //inherits R printOn
        //cc.printOn();                  //would give error
        return 0;}

 

---

虚基类

 

#include <iostream.h>

class R
{ int r;
public:
        R (int x = 0) : r(x) { }   // constructor in R
        void f( ){ cout<<"r="<<r<<endl;}     
        void printOn(){cout<<"printOn R="<<r<<endl;}
};

class A : public virtual R
{  int a;
public:
        A (int x, int y) : R(x), a(y)  { } // constructor in A
        void f( ){ cout<<"a="<<a<<endl;R::f();}
};

class B : public virtual R
{int b;
public:
        B(int x, int z) : R(x), b(z) { }// constructor in B
        void f( ){ cout<<"b="<<b<<endl;R::f();}
};

class C : public A, public B
{ int c;
public:
// constructor in C, which constructs an R object first
C(int x, int y, int z, int w) : R(x), A(x, y), B(x, z), c(w) { }
        
void f( ){ cout<<"c="<<c<<endl;A::f(); B::f();}
};

void main()
{  R rr(1000);
   A aa(2222,444);
   B bb(3333,111);
   C cc(1212,345,123,45);
   cc.printOn();     //uses R printOn but only 1 R..no ambiguity
   cc.f();                // shows multiple call of the R::f()
}

////////////////////////////////////////

#include <iostream.h>

class R
{ int r;
public:
        R (int x = 0) : r(x) { }   // constructor in R
        void f( ){ cout<<"r="<<r<<endl;}
};

class A : virtual public R
{ int a ;
protected:
        void fA( ){cout<<"a="<<a<<endl;};

public:
        A (int x, int y) : R(x), a(y)  { } // constructor in A
        void f( ) {fA( ); R::f( );}
};

class B : virtual public R
{  int b;
protected:
        void fB( ){cout<<"b="<<b<<endl;};
public:
        B (int x, int y) : R(x), b(y)  { } // constructor in A
        void f( ) {fB( ); R::f( );}
};

class C : public A, public B
{ int c;

protected:
        void fC( ){ cout<<"c="<<c<<endl;};        
public:
C(int x, int y, int z, int w) : R(x), A(x, y), B(x, z), c(w) { }

void f( )
        {  
                   R::f( );                    // acts on R stuff only
                A::fA( );            //acts on A stuff only
                B::fB( );                   // acts on B stuff only
                fC( );                  // acts on C stuff only
        }
};

void main()
{  R rr(1000);
   A aa(2222,444);
   B bb(3333,111);
   C cc(1212,345,123,45);
   cc.f();
}

 

---

 

私有继承

// Access levels

#include <iostream.h>

class Base
{
private:
        int priv;
protected:
        int prot;
        int get_priv( ) {return priv;}
public:
        int publ;
        Base( );
        Base(int a, int b, int c) : priv(a), prot(b), publ(c) { }
        int get_prot( ) {return prot;}
        int get_publ( ) {return publ;}
};

class Derived1 : private Base        // private inheritance
{
public:
        Derived1 (int a, int b, int c) : Base(a, b, c) { }
        int get1_priv( ) {return get_priv( );}
        // priv not accessible directly
        int get1_prot( ) {return prot;}
      int get1_publ( ) {return publ;}
};

class Leaf1 : public Derived1
{
public:
        Leaf1(int a, int b, int c) : Derived1(a, b, c) { }
        void print( )
        {
                cout << "Leaf1 members: " << get1_priv( ) << " "
//                        << get_priv( )        // not accessible
                        << get1_prot( ) << " "
//                        << get_prot( )         // not accessible
//                        << publ         // not accessible
                        << get1_publ( ) << endl;
        }  // data members not accessible.  get_ functions in Base not accessible
};

class Derived2 : protected Base // protected inheritance
{
public:
        Derived2 (int a, int b, int c) : Base(a, b, c) { }
};

class Leaf2 : public Derived2
{
public:
        Leaf2(int a, int b, int c) : Derived2(a, b, c) { }
        void print( )
        {
                cout << "Leaf2 members: " << get_priv( ) << " "
//                        << priv                 // not accessible
                        << prot << " "
                        << publ << endl;
        }  // public and protected data members accessible.  get_ functions in Base accessible. 
};

class Derived3 : public Base  // public inheritance
{
public:
        Derived3 (int a, int b, int c) : Base(a, b, c) { }
};

class Leaf3 : public Derived3
{

public:
        Leaf3(int a, int b, int c) : Derived3(a, b, c) { }
        void print( )
        {
                cout << "Leaf3 members: " << get_priv( ) << " "
                        << prot << " "
                        << publ << endl;
        }  // public and protected data members accessible.  get_ functions in Base accessible
};

int main( )
{
        Derived1 d1(1, 2, 3);
        Derived2 d2(4, 5, 6);
        Derived3 d3(7, 8, 9);

//        cout << d1.publ;                // not accessible
//        cout << d1.get_priv( );        // not accessible
//        cout << d2.publ;                // not accessible
//        cout << d2.get_priv( );        // not accessible
        cout << d3.publ;                // OK
        cout << d3.get_prot( );        // OK

        Leaf1 lf1(1, 2, 3);
        Leaf2 lf2(4, 5, 6);
        Leaf3 lf3(7, 8, 9);

//         cout << lf1.publ << endl;                    // not accessible
//         cout << lf2.publ << endl;                // not accessible
        cout << lf3.publ << endl;                 // OK

        return 0;
}

 

---

 

多级继承

// Point-Circle-Cylinder
#include <iostream.h>

// THE POINT CLASS

class Point
{
friend ostream & operator<<(ostream &,Point &);

public:
        
//  constructor
        Point (double xval =0, double yval=0 )
        { x=xval; y=yval;};  

protected:       // accessed by derived class
        double  x;
        double  y;
};

ostream & operator << (ostream & os,
                              Point &  apoint)
{
cout <<" Point:X:Y: "<<apoint.x << "," 
                      << apoint.y<< "/n";
  return os;  
}

//The Circle class  inherits from class Point

class Circle : public Point
{
friend ostream & operator<<(ostream &,Circle&);

public:
Circle (double r=0,double xval=0,double yval=0) 
                             :Point(xval,yval), radius(r)
{ 
//radius = r;
}

double area()
{ 
return (3.14159* radius *radius);
}

protected:
  double radius;
};

//note casting circle to point
ostream & operator <<(ostream & os, Circle & aCircle)
{
cout<< "Circle:radius:" << aCircle.radius;
os<< aCircle.x << "/n"; 
os<< aCircle.y << "/n";        
return os;      
}

// THE CYLINDER CLASS
class  Cylinder  : public Circle
{
friend ostream & operator << (ostream & ,Cylinder &);

public:
Cylinder (double hv=0,double rv=0, 
                      double xv=0,double yv=0 )
                           : Circle( xv,yv,rv)
{
height = hv;
}        

double  area ( );

protected:     // may have derived classes
        double  height;
};

double Cylinder :: area ( )
{ // Note that cylinder area uses Circle area
return  2.0* Circle::area() + 2.0*3.14159* radius*height;
}

ostream & operator << (ostream & os,
                        Cylinder & acylinder)

{ 
cout << "cylinder dimensions: ";
  cout << "x: " <<acylinder.x;
  cout << "  y: " <<acylinder.y ;
  cout << "  radius: " <<acylinder.radius ;
  cout << "  height: " <<acylinder.height 
                        << endl;
  return os; 
}

int main(void)
{
Point p(2,3);
Circle c(7,6,5);
Cylinder cyl(10,11,12,13);
cout << p;

cout << c;
cout << "area of cirle:" << c.area() << endl;

cout<< cyl;
cout<<"area of cylinder:"<< cyl.area()<<endl ;

cout<<"area of cylinder base is "  
                 << cyl.Circle::area() << endl;

return 0;
}

 

---

 

protected 訪问控制属性在继承的意义

 

//Example of treating derived class object as base class objects. Point------Circle

#include <iostream.h>

// THE POINT CLASS

class Point
{ 
friend ostream & operator<<(ostream &,Circle&);
public:
Point (double xval =0, double yval=0 ) { x=xval; y=yval;};  

public:
void print()
{
cout <<" Point:X:Y: "<<x << "," <<y<< "/n";
}

protected:       // accessed by derived class
double  x;    double  y;
};

ostream & operator << (ostream & os, Point &  apoint)
{
cout <<" Point:X:Y: "<<apoint.x << ","<< apoint.y<< "/n";
  return os;  
}

//The Circle class  inherits from class Point
class Circle : public Point
{

friend ostream & operator<<(ostream &,Circle&);

public:
Circle (double r=0,double xval=0,double yval=0):Point(xval,yval)
{ radius = r;};

void print()
{
cout<< "Circle:radius:" <<radius<<endl;
cout <<" Point:X:Y: "<<x << "," <<y<< "/n";
}

double area()
{ return (3.14159* radius *radius);};

protected:
double radius;
};

//note casting circle to point
ostream & operator <<(ostream & os, Circle & aCircle)
{
cout<< "Circle:radius:" << aCircle.radius;
cout<< (Point) aCircle << "/n";           
return os;      
}

//We will look at a few main programs based on previous class definitions. Casting and assignments

void main (void )
{
Point p(2,3);         cout <<"Point P=  "<< p;

Point pp(0,0);       cout <<"Point PP=  "<< pp;

Circle c(7,6,5);     cout <<"Circle c=  "<< c;        //radius =7

pp = p;             cout <<"Point PP=  "<< pp;    //built in assign =

// a circle is a member of the point class so assign a circle to a point.

pp = c;           //legal; also assignment O.K.
cout <<"Point PP=  "<< pp;

pp= (Point) c;    // but better  use the cast
cout <<"Point PP=  "<< pp;  //note we get only the point part of the Circle

//c = (Circle) pp;   //  illegal Cannot convert ‘class Point‘ to ‘class Circle‘

//c=pp;                 //illegal assignment not defined

Point*  p;
p = &c;

P->print();    //call base class print
((Circle*)p)->print();

Point& r = c;
r.print();
((Circle&)r).print();

}

 

---

类的兼容性规则

 

#include <iostream.h>

class Base
{ 
public:  
void func( ) 
{cout << "Base class function./n";} 
};

class Derived : public Base
{ 
public:  
void func( ) 
{cout << "Derived class function./n";}
};

void foo(Base b)
{ b.func( ); }

int main( )
{
   Derived d;
   Base b;
   Base * p = &d;
   Base& br = d;

   b = d;
   b.func( );
   d.func( );
   p -> func( );
   foo(d);
   br.func( );

   return 0;
}

 

 

---

 
虚析构函数，防止内存泄露

 

 

#include <iostream.h>
#include <string.h>

class Base
{
protected:
        int id;
        char * name;
public:
        // default constructor
        Base(int a = 0, char * s = "") : id(a)
        {
                if (!s) 
{ 
name = NULL; 
}
                else
                {
                        name = new char[strlen(s) + 1];
                        strcpy(name, s);
                }
                cout << "base default constructor/n";
        }
                // copy constructor
        Base(const Base& b) : id(b.id)
        {
                if (!b.name) { name = NULL; }
                else
                { 
                        name = new char[strlen(b.name) + 1];
        strcpy(name, b.name);
}
                    cout << "base copy constructor/n";
        } 
        // destructor
      ~Base( ) 
        {
            if( name != NULL )        delete [ ] name; 
                cout << "base destructor/n";
        }
        const Base& operator= (const Base& b);                
friend ostream& operator << (ostream&, const Base&);
};

const Base& Base:perator= (const Base& b)
{
        if (this != &b)                        // Check if an object is assigned to itself.
        {
             id = b.id;
                delete [ ] name;                //  Destroy the old object.
                if (!b.name) { name = NULL; }
                else
                {
        name = new char[strlen(b.name) + 1];
        strcpy(name, b.name);
                }
        }
            cout << "base assignment operator/n";
        return *this;
}

ostream& operator << (ostream& out, const Base& b)
{
        out << "Base member id = " << b.id << endl;
        out << "Base member name = " << b.name << endl;
        
        return out;
}

class Derived : public Base
{
private:
        float f;
        char * label;
public:
        // default constructor
        Derived(int a = 0, char * s = "", float x = 0, char * t = "") : Base(a, s), f(x)
        {
                if (!t) { label = NULL; }
                else
                {
        label = new char [strlen(t) + 1]; 
        strcpy(label, t);
}
                cout << "derived default constructor/n";
        }
        // copy constructor
        Derived(const Derived& d) : Base(d), f(d.f)
                // d used as an instance of Base
        {
                if(!d.label) { label = NULL; }
                else
                {
                        label = new char [strlen(d.label) + 1];
        strcpy(label, d.label);
}
                cout << "derived copy constructor/n";
        }
        // destructor
        ~Derived( )          
        {
                delete [ ] label; 
                cout << "derived destructor/n";
        }
        const Derived& operator= (const Derived& d);
friend ostream& operator << (ostream&, const Derived&);
};

const Derived& Derived:perator= (const Derived& d)
{
        if (this != &d)
        {
                delete [ ] label;
                Base:perator=(d);        //  Assign the Base part of d to the Base
// part of the object that calls this operator;
f = d.f;
if (!d.label) { label = NULL; }
else
{
        label = new char [strlen(d.label) + 1];
                        strcpy(label, d.label);
                }
                cout << "derived assignment operator/n";
        }
        return *this;
}

ostream& operator << (ostream& out, const Derived& d)
{
        out << (Base)d;                // Convert d to Base object to output Base members.
        out << "Derived member f = " << d.f << endl;
        out << "Derived member label = " << d.label << endl;
        return out;
}

int main( )
{
        Derived d1;
Derived  d2(d1);

        return 0;
}