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C++Primer15.5节练习

news 2025/9/11 2:45:56

练习15.18：

   Base* p = &d1：合法
   p = &d2：不合法，只有当派生类公有地继承基类时，用户代码才能使用派生类向基类的转换
   p = &d3：不合法，只有当派生类公有地继承基类时，用户代码才能使用派生类向基类的转换
   p = &dd1：合法
   p = &dd2：不合法，只有当派生类公有地继承基类时，用户代码才能使用派生类向基类的转换
   p = &dd3：不合法，只有当派生类公有地继承基类时，用户代码才能使用派生类向基类的转换

练习15.19：

对于类Base：合法

对于类Pub_Derv：合法

对于类Prot_Derv：合法

对于类Priv_Derv：合法

对于类Derived_from_Public：合法

对于类Derived_from_Protected：合法

对于类Derived_from_Private：不合法，因为类Derived_from_Private的直接基类Priv_Derv自Base私有继承而来，所以Derived_from_Private的成员无法使用Priv_Derv向Base，也就无法实现Derived_from_Private到Base的转换

练习15.20：

#include <iostream>
#include <string>
#include <errno.h>
using namespace std;class Base {
public:void pub_mem();//正确void memfcn(Base& b) { b = *this; cout << "Base memfcn success" << endl; }
protected:int prot_mem;
private:char priv_mem;
};struct Pub_Derv :public Base {int f() { return prot_mem; }//错误//char g() { return priv_mem; }//正确void memfcn(Base& b) { b = *this; cout << "Pub_Derv memfcn success" << endl;}
};struct Priv_Derv :private Base {int f1()const { return prot_mem; }//正确void memfcn(Base& b) { b = *this; cout << "Priv_Derv memfcn success" << endl;}
};struct Prot_Derv :protected Base {int f1()const { return prot_mem; }//正确void memfcn(Base& b) { b = *this; cout << " Prot_Derv memfcn success" << endl;}
};struct Derived_from_Public :public Pub_Derv {int use_base() { return prot_mem; }//正确void memfcn(Base& b) { b = *this; cout << "Derived_from_Public memfcn success" << endl;}
};struct Derived_from_Protected :public Prot_Derv {int use_base() { return prot_mem; }//正确void memfcn(Base& b) { b = *this; cout << "Derived_from_Protected memfcn success" << endl;}
};struct Derived_from_Private :public Priv_Derv {//错误//int use_base() { return prot_mem; }//不正确//void memfcn(Base& b) { b = *this; }
};//测试
int main()
{Base b1, b2;Pub_Derv d1;Priv_Derv d2;Prot_Derv d3;Derived_from_Public dd1;Derived_from_Private dd2;Derived_from_Protected dd3;Base* p = &d1;//p = &d2;//p = &d3;p = &dd1;//p = &dd2;//p = &dd3;b1.memfcn(b2);d1.memfcn(b2);d2.memfcn(b2);d3.memfcn(b2);dd1.memfcn(b2);dd3.memfcn(b2);system("pause");return 0;
}

结果：