C++Primer15.5节练习

news2025/10/31 17:26:23

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：