[英]Multiple inheritance
我已經從一本名為“ C ++ Primer”的書中閱讀了多重繼承,但是我只收到了書中編寫的示例的頭文件,這使得沒有source.cpp對我來說很難理解。 所以,我的問題是,什么是Endangered
類,我如何定義的成員函數highlight
, cuddle
, onExhibit
等?
該頭文件也可以從此處下載。
// Multiple Inheritance.h
#include <string>
#include <iostream>
class Endangered {
public:
virtual ~Endangered();
virtual std::ostream& print(std::ostream&) const;
virtual void highlight() const;
// ...
};
class ZooAnimal;
extern std::ostream&
operator<<(std::ostream&, const ZooAnimal&);
class ZooAnimal {
public:
ZooAnimal();
ZooAnimal(std::string animal, bool exhibit,
std::string family): nm(animal),
exhibit_stat(exhibit),
fam_name(family) { }
virtual ~ZooAnimal();
virtual std::ostream& print(std::ostream&) const;
virtual int population() const;
// accessors
std::string name() const { return nm; }
std::string family_name() const { return fam_name; }
bool onExhibit() const { return exhibit_stat; }
// ...
protected:
std::string nm;
bool exhibit_stat;
std::string fam_name;
// ...
private:
};
class Bear : public ZooAnimal {
enum DanceType { two_left_feet, macarena, fandango, waltz };
public:
Bear();
Bear(std::string name, bool onExhibit=true,
std::string family = "Bear"):
ZooAnimal(name, onExhibit, family),
ival(0), dancetype(two_left_feet) { }
virtual std::ostream &print(std::ostream&) const;
virtual int toes() const;
int mumble(int);
void dance(DanceType) const;
virtual ~Bear();
private:
int ival;
DanceType dancetype;
};
class Panda : public Bear, public Endangered {
public:
Panda();
Panda(std::string name, bool onExhibit=true);
virtual ~Panda();
virtual std::ostream& print(std::ostream&) const;
void highlight();
virtual int toes();
virtual void cuddle();
// ...
};
Panda::Panda(std::string name, bool onExhibit)
: Bear(name, onExhibit, "Panda") { }
inline
std::ostream& Panda::print(std::ostream &os) const
{
Bear::print(os); // print the Bear part
Endangered::print(os); // print the Endangered part
return os;
}
class PolarBear : public Bear { /* . . . */ };
在要派生的類中具有相同名稱,返回類型,參數編號,常數和參數類型(統稱為函數簽名 )的函數 。
例如,
// Me.h
class Me : public Endangered, public ZooAnimal {
// notice that these don't have virtual before them
std::ostream& print(std::ostream&) const;
void highlight() const;
std::ostream& print(std::ostream&) const;
int population() const;
/* etc */
};
// Me.cpp
std::ostream& Me::print(std::ostream& stream) const { /* stuff */; return stream; }
void Me::highlight() const { /* stuff */ }
/* etc */
請注意,必須為每個類(而不是派生類)定義這些類的析構函數。 所以你需要
ZooAnimal::~ZooAnimal() {
/* stuff */
}
不是Me::~Me
(盡管如果Me
有一個, Me
也需要)。
某處。
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