|
class Head
{
public:
void Look(void) { m_eye.Look(); }
void Smell(void) { m_nose.Smell(); }
void Eat(void) { m_mouth.Eat(); }
void Listen(void) { m_ear.Listen(); }
private:
Eye m_eye;
Nose m_nose;
Mouth m_mouth;
Ear m_ear;
}; | Head由Eye、Nose、Mouth、Ear组合而成。假如答应Head从Eye、Nose、Mouth、Ear派生而成，那么Head将自动具有Look、Smell、Eat、Listen这些功能。程序十分简短并且运行正确，但是下面这种设计方法却是不对的。
class Head : public Eye, public Nose, public Mouth, public Ear
{
};
|
面试例题3:Find the defects in each of the following programs, and explain why it is incorrect.(找出下面程序的错误，并解释它为什么是错的。)[德国某闻名软件咨询企业2005年面试题]
class base{
private: int i;
public: base(int x){i=x;}
};
class derived: public base{
private: int i;
public: derived(int x, int y) {i=x;}
void printTotal() {int total = i base::i;}
}; |
解析:要在子类中设定初始成员变量，把derived(int x, int y)改成derived(int x, int y) : base(x)。
答案:
代码如下:
class base
{
protected: //这里的访问属性需要改变
int i;
public:
base(int x){i=x;}
};
class derived: public base
{
private:
int i;
public:
derived(int x, int y) : base(x) //以前没有初始化基类的成员变量
{
i=y;
}
void printTotal()
{
int total = i base::i;
}
}; |
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