某发票（lnvoice）由抬头（Head）部分、正文部分和脚注（Foot）部分构成。现采用装饰（Decorator）模式实现打印发票的功能，得到如图5-1所示的类图。
【C++代码】
#include
using namespace std;
class Invoice{
public:
（1）{
cout＜＜"This is the content of the invoice!"＜＜endl;
}
};
class Decorator:public Invoice{
Invoice*ticket;
public:
Decorator(lnvoice*t){ticket=t;}
void printInvoice（ ）{
if(ticket!=NULL)
（2）;
}
};
class HeadDecorator:public Decorator{
public:
HeadDecorator(lnvoice*t):Decorator(t){}
void printInvoice（ ）{
cout＜＜"This is the header of the invoice!"＜＜endl;
（3）;
}
};
class FootDecorator:public Decorator{
public:
FootDecorator(Invoice*t):Decorator(t){}
void printlnvoice（ ）{
（4）;
cout＜＜"This is the footnote of the invoice!"＜＜endl;
}
};
int main(void){
Invoice t;
FootDecorator f(&t);
HeadDecorator h(&f);
h.printInvoice（ ）;
cout＜＜”------------------------”＜＜endl;
FootDecorator a(NULL);
HeadDecorator b(（5）);
b.printInvoice（ ）;
return 0;
}
程序的输出结果为：
This is the header of the invoice!
This is the content of the invoice!
This is the footnote of the invoice!
----------------------------
This is the header of the invoice!
This is the footnote of the invoice!
正确答案及解析
正确答案
解析
（1）virtual void printInvoice()
（2）ticket->printInvoice()
（3）Decorator::printInvoice()
（4）Decorator::printInvoice()
（5）&a
1.Invoice类下，定义虚函数，按类图，函数名是printInvoice。
2.前面定义对象名是ticket，那么在ticket不为空的时候调用函数printInvoice。
3.这部分填写发票的抬头，看类图应该实现函数printInvoice，Decorator装饰模式使用该方法。
4.这部分是发票的脚注，看类图应该实现函数printInvoice，Decorator装饰模式使用该方法。
5.FootDecorator a(NULL)；脚步的装饰参数是a，调用a参数。
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