C++ Primer Plus 第6版第13章编程练习答案-优快云博客

本文链接：https://blog.youkuaiyun.com/Anna_L/article/details/119930526

本文介绍了C++中派生类的构造与析构，探讨了为什么构造函数不应是虚函数的原因，以及赋值操作符是否应该为虚函数的讨论。通过经典音乐CD类的实例，解释了如何处理字符串存储，并提醒读者赋值操作符的虚函数特性可能导致混淆。同时，提到了友元函数`operator<<()`不能声明为虚函数的情况。

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1. 以下面的类声明为基础：

class Cd {
private:
   char performers[50];
   char label[20];
   int selections;
   double playtime;
public:
   Cd(char* s1, char* s2, int n, double x);
   Cd(const Cd& d);
   Cd();
   ~Cd();
   void Report() const; // 显示此CD信息
   Cd& operator=(const Cd& d);
};

派生出一个Classic类，并添加一组char成员，用于存储指出CD中主要作品的字符串。修改上述声明，使基类的所有函数都是虚的。如果上述定义声明的某个方法并不需要，则请删除它。使用下面的程序测试您的产品：

#include <iostream>
#include "classic.h"
using namespace std;
void Bravo(const Cd& disk);

int main() {
   Cd c1("Beatles", "Capitol", 14, 35.5);
   Classic c2 = Classic("Piano Sonata in B flat, Fantasia in C", "Philips", 2, 57.17, "Alfred Brendel");

   Cd* pcd = &c1;

   cout << "Using object directly:\n";
   c1.Report();
   c2.Report();

   cout << "Using type cd* pointer to objects:\n";
   pcd->Report();
   pcd = &c2;
   pcd->Report();

   cout << "Calling a function with a Cd reference argument:\n";
   Bravo(c1);
   Bravo(c2);

   cout << "Testing assignment: ";
   Classic copy;
   copy = c2;
   copy.Report();

   return 0;
}

void Bravo(const Cd& disk) {
   disk.Report();
}

解答：

#pragma once
// classic.h
#ifndef CLASSIC_H_
#define CLASSIC_H_

class Cd {
private:
	char performers[50];
	char label[20];
	int selections;
	double playtime;
public:
	Cd(const char* s1, const char* s2, int n, double x);
//	Cd(const Cd& d);
	Cd();
//	virtual ~Cd();
	virtual void Report() const;   // 显示此CD信息
//	Cd& operator=(const Cd& d);
};

class Classic : public Cd {
private:
	char primary_work[50];
public:
	Classic(const char* s1, const char* s2, int n, double x, const char* s3);
	Classic();
	virtual void Report() const;
//	virtual ~Classic();
};

#endif // !CLASSIC_H_

// cd.cpp
#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstring>
#include "classic.h"
using std::strncpy;
using std::strcpy;
using std::cout;
using std::endl;

Cd::Cd(const char* s1, const char* s2, int n, double x) {
	strncpy(performers, s1, 49);
	performers[49] = '\0';
	strncpy(label, s2, 19);
	label[19] = '\0';
	selections = n;
	playtime = x;
}

Cd::Cd() {
	strcpy(performers, "None");
	strcpy(label, "No label");
	selections = 0;
	playtime = 0.0;
}

void Cd::Report() const {
	cout << "Performers: " << performers << endl;
	cout << "Label: " << label << endl;
	cout << "Selections: " << selections << endl;
	cout << "Playtime: " << playtime << endl;
}

Classic::Classic(const char* s1, const char* s2, int n, double x, const char* s3): Cd(s1, s2, n, x) {
	strncpy(primary_work, s3, 49);
	primary_work[49] = '\0';
}

Classic::Classic(): Cd() {
	strcpy(primary_work, "None");
}

void Classic::Report() const {
	Cd::Report();
	cout << "Primary work: " << primary_work << endl;
}

// 13-1
#include <iostream>
#include "classic.h"
using namespace std;
void Bravo(const Cd& disk);

int main() {
	Cd c1("Beatles", "Capitol", 14, 35.5);
	Classic c2 = Classic("Piano Sonata in B flat, Fantasia in C", "Philips", 2, 57.17, "Alfred Brendel");

	Cd* pcd = &c1;

	cout << "Using obje