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c++继承经典例子
#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 Basereturn 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 =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 ; }
#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;}
#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( ); // OKLeaf1 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; // OKreturn 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 访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 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();}
#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;
}
#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;
}转载地址:http://qgjsi.baihongyu.com/