从多重继承中的二义性 到 虚基类（摘抄自谭浩强c++）

一个多重继承的程序

#include<iostream>
using namespace std;

class Teacher
{
public:
    Teacher(string nam,int a,string t):name(nam),age(a),title(t){}
    void display()
    {
        cout << "name:" << name << endl;
        cout << "age:" << age << endl;
        cout << "title:" << title << endl;
    }
protected:
    string name;
    int age;
    string title;
};

class student
{
public:
    student(string nam,char a,float sco):name(nam),sex(a),score(sco){}
    void display()
    {
        cout << "name:" << name << endl;
        cout << "sex:" << sex << endl;
        cout << "score:" << score << endl;
    }
protected:
    string name;
    char sex;
    float score;
};

class Graduate:public Teacher,public student
{
public:
    Graduate(string nam,int a,char s,string t,float sco,float w):Teacher(nam,a,t),student(nam,s,sco),wage(w){}
    void show()
    {
        cout << "name:" << name << endl;
        //cout << "name:" << Teacher::name << endl;
        cout << "age:" << age << endl;
        cout << "sex:" << sex << endl;
        cout << "score:" << score << endl;
        cout << "title:" << title << endl;
        cout << "wages:" << wage << endl;
    }
private:
    float wage;
};

int main()
{
    Graduate grad1("Wang -li",24,'f',"assistant",89.5,1234.5);
    grad1.show();
    return 0;
}

编译错误，

C:\Users\Administrator\Desktop\test - cpp\test.cpp||In member function 'void Graduate::show()':|
C:\Users\Administrator\Desktop\test - cpp\test.cpp|42|error: reference to 'name' is ambiguous|
C:\Users\Administrator\Desktop\test - cpp\test.cpp|31|error: candidates are: std::string student::name|
C:\Users\Administrator\Desktop\test - cpp\test.cpp|15|error:                 std::string Teacher::name|
||=== Build failed: 3 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|

 reference to 'name' is ambiguous   研究生的两个基类都有同名的成员 name，导致二义性。

作程序中被注释掉的修改后，程序可以继续运行。Teacher::name

尝试用同名覆盖来解决这个问题：

#include<iostream>
using namespace std;


class Teacher
{
public:
    Teacher(string nam,int a,string t):name(nam),age(a),title(t){}
    void display()
    {
        cout << "name:" << name << endl;
        cout << "age:" << age << endl;
        cout << "title:" << title << endl;
    }
protected:
    string name;
    int age;
    string title;
};


class student
{
public:
    student(string nam,char a,float sco):name(nam),sex(a),score(sco){}
    void display()
    {
        cout << "name:" << name << endl;
        cout << "sex:" << sex << endl;
        cout << "score:" << score << endl;
    }
protected:
    string name;
    char sex;
    float score;
};


class Graduate:public Teacher,public student
{
public:
    Graduate(string nam,int a,char s,string t,float sco,float w):Teacher(nam,a,t),student(nam,s,sco),name(nam),wage(w){}
    void show()
    {
        cout << "name:" << name << endl;
        //cout << "name:" << Teacher::name << endl;
        cout << "age:" << age << endl;
        cout << "sex:" << sex << endl;
        cout << "score:" << score << endl;
        cout << "title:" << title << endl;
        cout << "wages:" << wage << endl;
    }
//private:
public:
    string name;
    float wage;
};


int main()
{
    Graduate grad1("Wang -li",24,'f',"assistant",89.5,1234.5);
    grad1.show();
    cout << endl;
    cout << "Graduate's name:" << grad1.name;
    return 0;
}

只是给Graduate类增加了一个name成员变量，然后利用同名覆盖解决了问题。

用虚基类来解决问题：

#include<iostream>
using namespace std;

class Person
{
public:
    Person(string nam,char s, int a):name(nam),sex(s),age(a){}
protected:
    string name;
    char sex;
    int age;
};

class Teacher:virtual public Person
{
public:
    Teacher(string nam,char s,int a,string t):Person(nam,s,a),title(t){}
    void display()
    {
        cout << "name:" << name << endl;
        cout << "sex:" << sex << endl;
        cout << "age:" << age << endl;
    }
protected:
    string title;
};

class student:virtual public Person
{
public:
    student(string nam,char s,int a,float t):Person(nam,s,a),score(t){}
    void display()
    {
        cout << "name:" << name << endl;
        cout << "sex:" << sex << endl;
        cout << "age:" << age << endl;
        cout << "score:" << score << endl;
    }
protected:
    float score;
};

class Graduate:public Teacher,public student
{
public:
    Graduate(string nam,char s,int a,string t,float sco,float w):Person(nam,s,a),Teacher(nam,s,a,t),student(nam,s,a,sco),wage(w){}
    void show()
    {
        cout << "name:" << name << endl;
        //cout << "name:" << Teacher::name << endl;
        cout << "age:" << age << endl;
        cout << "sex:" << sex << endl;
        cout << "score:" << score << endl;
        cout << "title:" << title << endl;
        cout << "wages:" << wage << endl;
    }
//private:
public:
    float wage;
};

int main()
{
    Graduate grad1("Wang -li",'f',24,"assistant",89.5,1234.5);
    grad1.show();
    cout << endl;
    student srm("srm",'b',25,1234.5);
    srm.display();
    return 0;
}

使用了虚基类的办法，Gradute类只保留了一份person类的数据，需要注意的是gradute类的构造函数中，实际上是只由gradute类的构造函数完成person类的初始化。