/*當建立一個對象時，首先調用基類的構造函數，然后調用下一個派生類的
構造函數，依次類推，直至到達派生類次數最多的派生次數最多的類的構造函數為止。
簡而言之，對象是由“底層向上”開始構造的。因為，構造函數一開始構造時，總是
要調用它的基類的構造函數，然后才開始執行其構造函數體，調用直接基類構造函數時，
如果無專門說明，就調用直接基類的默認構造函數。在對象析構時，其順序正好相反。
下面的這個程序說明這個問題*/
//-------------------------------------------------
#include <iostream>
using namespace std;
class Shape
{
public:
void Draw() {cout<<"Base::Draw()"<<endl;}
void Erase() {cout<<"Base::Erase()"<<endl;}
Shape() {Draw();} //基類構造函數，調用上面的Draw函數體
virtual ~Shape() {Erase();}//基類析構函數，調用上面的Erase函數體
};
//-------------------------------------------------
class Polygon:public Shape
{
public:
Polygon() {Draw();}
void Draw() {cout<<"Polygon::Draw()"<<endl;}
void Erase() {cout<<"Polygon Erase()"<<endl;}
~Polygon() {Erase();}
};
//--------------------------------------------------
class Rectangle:public Polygon
{
public:
Rectangle() {Draw();}
void Draw() {cout<<"Rectangle::Draw()"<<endl;}
void Erase() {cout<<"Rectangle Erase()"<<endl;}
~Rectangle() {Erase();}
};
//--------------------------------------------------
class Square:public Rectangle
{
public:
Square() {Draw();}
void Draw() {cout<<"Square::Draw()"<<endl;}
void Erase() {cout<<"Square Erase()"<<endl;}
~Square() {Erase();}
};
//--------------------------------------------------
int main()
{
Polygon c;
Rectangle s;
Square t;
cout<<"------------------------------------------"<<endl;
return 0;
}
//------------------------------------------
運行結果：
Base::Draw()
Polygon::Draw()
Base::dRAW()
Polygon::Draw()
Rectangle::Draw()
Base::dRAW()
Polygon::Draw()
Rectangle::Draw()
Square::Draw()
------------------------------------------
Square Erase()
Rectangle Erase()
Polygon Erase()
Base::Erase()
Rectangle Erase()
Polygon Erase()
Base::Erase()
Polygon Erase()
Base::Erase()
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