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下面的代码部分可能存在错误，主要是理解继承的思想。

普通公有派生#include 
   
    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#include 
   
    #include 
    
     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 
   
    #include 
    
     class Point{   private:    double x， 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-axispublic:    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;}```cpp多继承#include 
     
      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 
   
    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 
   
    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()}
   

私有继承#include 
   
    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 directlyint 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#include 
   
    // THE POINT CLASSclass 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 Pointclass 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 pointostream &operator<<(ostream &os, Circle &aCircle){       cout << "Circle:radius:" << aCircle.radius;    os << aCircle.x << "/n";    os << aCircle.y << "/n";    return os;}// THE CYLINDER CLASSclass 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访问控制属性在继承的意义#include 
   
    // THE POINT CLASSclass 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 Pointclass 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 pointostream &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 assignmentsvoid 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 
   
    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 
   
    #include 
    
     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;}