多重继承

Question

我已经从一本名为“C++ Primer”的书中读过多重继承，但是我只收到了书中示例中的头文件，这使得我在没有source.cpp的情况下理解它变得很困难。所以，我的问题是，什么是Endangered类，我如何定义成员函数highlight，cuddle,onExhibit等？

该头文件也可以从here下载。

// 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 { /* . . . */ }; 

Answer 1

只是具有相同的名称，返回类型，参数号，常量性和参数类型（统称为函数签名）在你的类，你获得的功能。

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 */ 

注意，对于这些类的析构函数必须为每个类派生的类来定义，而不是。所以，你需要

ZooAnimal::~ZooAnimal() { 
    /* stuff */ 
} 

不Me::~Me（虽然你需要的是太多，如果Me有一个）。

某处。