求一个例子代码,说明派生类到基类的向上转换.

[fly2008_fly1314]

编写一个程序,说明派生类到基类的向上转换.用static_cast执行此向上转换.
这是书上的原题,不懂啊,什么是向上转换,能写个例子说明下吗,谢谢了.

[effective_person]

#include <iostream>
#include <bitset>
using namespace std;
class B
{
public:
	virtual void show()
	{
		cout<<"B"<<endl;
	}
};
class D:public B
{
public:
	void show()
	{
		cout<<"D"<<endl;
	}
};
int main()
{
	B *b=new B;
	D *d=new D;
	b->show();
	d->show();
	delete b;
	b=dynamic_cast<B*>(d);
	b->show();
	delete b;
	return 1;
}
/*
dynamic_cast   用于多态类型间的转换。包括继承类间的转换和兄弟类间的转换。
static_cast   用于非多态类型的转换。既不具有继承关系的类型间的转换。

*/

[fly2008_fly1314]

/*class B{...};
    class C:public B{...};
    class D:public C{...};

    viod f(D *pd)
    {
C *pc = dynamic_cast<C *>(pd);//正确:C是D的直接派生类
B *pb = dynamic_cast<B *>(pd);//正确:B是D的间接派生类
...
     }*/
#include <iostream>
using namespace std;

class B {                           
	int x;
protected:
	int y;
public:
	int z;
	B( int a = 0, int b = 0, int c = 0 ): x( a ), y( b ), z( c ) { }
	void Setx( int a ) { x = a; }
	void Sety( int a ) { y = a; }
	int Getx() { return x; }
	int Gety() { return y; }
	void ShowB()
	{ cout << "x = " << x << '\t' << "y = " << y << '\t' << "z = " << z << '\n'; }
};

class C: public B {
	int xc;
public:
	C( int a = 0, int b = 0, int c = 0, int d = 0 ): B( a, b, c ), xc( d ) { }
	void Setxc( int a ) { xc = a; }
	int Getxc() { return xc; }
	void ShowC()
	{ cout << "x = " << Getx() << '\t' << "y = " << y << '\t' << "z = " << z << '\t';
	  cout << "xc = " << xc << endl;
	}
};

class D: public C {
	int xd;
public:
	D( int a = 0, int b = 0, int c = 0, int d = 0, int e = 0 ): C( a, b, c, d ), xd( e ) { }
	void setxd( int a ) { xd = a; }
	int Getxd() { return xd; }
	void ShowD()
	{ cout << "x = " << Getx() << '\t' << "y = " << y << '\t' << "z = " << z << '\t';
	  cout << "xc = " << Getxc() << '\t' << "xd = " << xd << endl;
	}
};

int main()
{
	B b, *pb;
	C c, *pc;
	D d, *pd;
	pd = &d;
	pb = static_cast< B* >( pd );
	pc = static_cast< C* >( pd );
	pb -> ShowD();    //这个为什么不能调用了.地址还是                                        
	
	return 0;         
}
	

照书上写的,最上面的注释找的网上的,
1.static_cast和dynamic_cast运算符什么区别,
2.向上转换是不是就是一个规则,表示派生类指针是可以转换为基类指针的?
3.派生类指针被转成基类指针了是不是,用这个指针在去调用派生类自己的个性函数就不行了啊?

[effective_person]

class B
{
public:
	virtual void show()
	{
		cout<<"B"<<endl;
	}
};
class D:public B
{
public:
	void show()
	{
		cout<<"D"<<endl;
	}
};
int main()
{
	B *b=new B;
	D *d=new D;
	b->show();
	d->show();
	delete b;
	b=static_cast<B*>(d);
	b->show();
	delete b;
	return 1;
}
/*
I'am sorry !  我刚才放一个小错误！static_cast 向上转换是安全的。向下是不安全的。
我想歪了。但是
dynamic_cast也可以用于类层次间的上行转换和下行转换，还可以用于类之间的交叉转换。

*/

//msdn examples
// static_cast_Operator.cpp
// compile with: /LD
class B {};

class D : public B {};

void f(B* pb, D* pd) {
   D* pd2 = static_cast<D*>(pb);   // not safe, pb may
                                   // point to just B

   B* pb2 = static_cast<B*>(pd);   // safe conversion
}

////////////////////
// dynamic_cast_2.cpp
// compile with: /c /GR
class A {virtual void f();};
class B {virtual void f();};

void f() {
   A* pa = new A;
   B* pb = new B;
   void* pv = dynamic_cast<void*>(pa);
   // pv now points to an object of type A

   pv = dynamic_cast<void*>(pb);
   // pv now points to an object of type B
}

[fly2008_fly1314]

谢谢,我好好消化下先..

[effective_person]

class B {                           
    int x;
protected:
    int y;
public:
    int z;
    B( int a = 0, int b = 0, int c = 0 ): x( a ), y( b ), z( c ) { }
    void Setx( int a ) { x = a; }
    void Sety( int a ) { y = a; }
    int Getx() { return x; }
    int Gety() { return y; }
    void ShowB()
    { cout << "x = " << x << '\t' << "y = " << y << '\t' << "z = " << z << '\n'; }
};

class C: public B {
    int xc;
public:
    C( int a = 0, int b = 0, int c = 0, int d = 0 ): B( a, b, c ), xc( d ) { }
    void Setxc( int a ) { xc = a; }
    int Getxc() { return xc; }
    void ShowC()
    { cout << "x = " << Getx() << '\t' << "y = " << y << '\t' << "z = " << z << '\t';
      cout << "xc = " << xc << endl;
    }
};

class D: public C {
    int xd;
public:
    D( int a = 0, int b = 0, int c = 0, int d = 0, int e = 0 ): C( a, b, c, d ), xd( e ) { }
    void setxd( int a ) { xd = a; }
    int Getxd() { return xd; }
    void ShowD()
    { cout << "x = " << Getx() << '\t' << "y = " << y << '\t' << "z = " << z << '\t';
      cout << "xc = " << Getxc() << '\t' << "xd = " << xd << endl;
    }
};

int main()
{
    B b, *pb;
    C c, *pc;
    D d, *pd;
    pd = &d;
    pb = static_cast< B* >( pd );
    pc = static_cast< C* >( pd );
  //  pb -> ShowD();    //这个指针始终没有变啊！一直是指向B类的啊！
	//你进行转换时也没有换成pd啊；
	//
	//你要想吧B 转换成D时就要用下面的语句。
	pd=static_cast<D*>(pb);
	pd->ShowD();
    
    return 0;         
}
    

[meiZiNick]

不会,帮顶

[red64321]

不会，学习学习

[pathuang68]

static_cast和c中的最普通的转型差不多。

参考：
区别：static _cast、dynamic _cast、reinterpret_cast和const_cast