C++PrimerPlus:第十三章类和继承:编程练习3_修改basedma-lacksdma-优快云博客

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例如：修改baseDMA-lacksDMA-hasDMA类的层次，让三个类都从一个ABC派生而来，然后使用于程序清单13.10相类似的程序对结果进行测试，也就是说，它应使用ABC指针素组，并让用户决定要创建的对象类型，在类定义中添加virtual View()方法以处理数据显示

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前言

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修改baseDMA-lacksDMA-hasDMA类的层次，让三个类都从一个ABC派生而来，然后使用于程序清单13.10相类似的程序对结果进行测试，也就是说，它应使用ABC指针素组，并让用户决定要创建的对象类型，在类定义中添加virtual View()方法以处理数据显示

提示：以下是本篇文章正文内容，下面案例可供参考

一、继承

二、使用步骤

1.头文件

直接用dma.h的类做修改，增加一个虚函数virtual void View() const;

代码如下（示例）：

// dma.h  -- inheritance and dynamic memory allocation
#ifndef DMA_H_
#define DMA_H_
#include <iostream>

//  Base Class Using DMA
class baseDMA
{
private:
    char* label;
    int rating;

public:
    baseDMA(const char* l = "null", int r = 0);
    baseDMA(const baseDMA& rs);
    virtual ~baseDMA();
    baseDMA& operator=(const baseDMA& rs);
    friend std::ostream& operator<<(std::ostream& os,
        const baseDMA& rs);
    virtual void View() const;
};

// derived class without DMA
// no destructor needed
// uses implicit copy constructor
// uses implicit assignment operator
class lacksDMA :public baseDMA
{
private:
    enum { COL_LEN = 40 };
    char color[COL_LEN];
public:
    lacksDMA(const char* c = "blank", const char* l = "null",
        int r = 0);
    lacksDMA(const char* c, const baseDMA& rs);
    friend std::ostream& operator<<(std::ostream& os,
        const lacksDMA& rs);
    void View() const;
};

// derived class with DMA
class hasDMA :public baseDMA
{
private:
    char* style;
public:
    hasDMA(const char* s = "none", const char* l = "null",
        int r = 0);
    hasDMA(const char* s, const baseDMA& rs);
    hasDMA(const hasDMA& hs);
    ~hasDMA();
    hasDMA& operator=(const hasDMA& rs);
    friend std::ostream& operator<<(std::ostream& os,
        const hasDMA& rs);
    void View() const;
};

#endif

2 方法

对增加的虚函数进行编写

// dma.cpp --dma class methods
#define _CRT_SECURE_NO_WARNINGS 
#include "pe13-3.h"
#include <cstring>

// baseDMA methods
baseDMA::baseDMA(const char* l, int r)
{
    label = new char[std::strlen(l) + 1];
    std::strcpy(label, l);
    rating = r;
}

baseDMA::baseDMA(const baseDMA& rs)
{
    label = new char[std::strlen(rs.label) + 1];
    std::strcpy(label, rs.label);
    rating = rs.rating;
}

baseDMA::~baseDMA()
{
    delete[] label;
}

baseDMA& baseDMA::operator=(const baseDMA& rs)
{
    if (this == &rs)
        return *this;
    delete[] label;
    label = new char[std::strlen(rs.label) + 1];
    std::strcpy(label, rs.label);
    rating = rs.rating;
    return *this;
}
void baseDMA::View() const
{
    std::cout << "Label: " << label << std::endl;
    std::cout << "Rating: " << rating << std::endl;
}

std::ostream& operator<<(std::ostream& os, const baseDMA& rs)
{
    os << "Label: " << rs.label << std::endl;
    os << "Rating: " << rs.rating << std::endl;
    return os;
}

// lacksDMA methods
lacksDMA::lacksDMA(const char* c, const char* l, int r)
    : baseDMA(l, r)
{
    std::strncpy(color, c, 39);
    color[39] = '\0';
}

lacksDMA::lacksDMA(const char* c, const baseDMA& rs)
    : baseDMA(rs)
{
    std::strncpy(color, c, COL_LEN - 1);
    color[COL_LEN - 1] = '\0';
}

void lacksDMA::View() const
{
    baseDMA::View();
    std::cout << "Color: " << color << std::endl;

}

std::ostream& operator<<(std::ostream& os, const lacksDMA& ls)
{
    os << (const baseDMA&)ls;
    os << "Color: " << ls.color << std::endl;
    return os;
}

// hasDMA methods
hasDMA::hasDMA(const char* s, const char* l, int r)
    : baseDMA(l, r)
{
    style = new char[std::strlen(s) + 1];
    std::strcpy(style, s);
}

hasDMA::hasDMA(const char* s, const baseDMA& rs)
    : baseDMA(rs)
{
    style = new char[std::strlen(s) + 1];
    std::strcpy(style, s);
}

hasDMA::hasDMA(const hasDMA& hs)
    : baseDMA(hs)  // invoke base class copy constructor
{
    style = new char[std::strlen(hs.style) + 1];
    std::strcpy(style, hs.style);
}

hasDMA::~hasDMA()
{
    delete[] style;
}

void hasDMA::View() const
{
    baseDMA::View();
    std::cout << "Style: " << style << std::endl;
}

hasDMA& hasDMA::operator=(const hasDMA& hs)
{
    if (this == &hs)
        return *this;
    baseDMA::operator=(hs);  // copy base portion
    delete[] style;         // prepare for new style
    style = new char[std::strlen(hs.style) + 1];
    std::strcpy(style, hs.style);
    return *this;
}

std::ostream& operator<<(std::ostream& os, const hasDMA& hs)
{
    os << (const baseDMA&)hs;
    os << "Style: " << hs.style << std::endl;
    return os;
}

3.测试函数

代码如下（示例）：
测试函数这里暂用usebrass2.cpp的基础上进行修改，这里作业留给大家

// usebrass2.cpp -- polymorphic example
// compile with brass.cpp
#include <iostream>
#include <string>
#include "brass.h"
const int CLIENTS = 4;

int main()
{
   using std::cin;
   using std::cout;
   using std::endl;

   Brass * p_clients[CLIENTS];
   std::string temp;
   long tempnum;
   double tempbal;
   char kind;

   for (int i = 0; i < CLIENTS; i++)
   {
       cout << "Enter client's name: ";
       getline(cin,temp);
       cout << "Enter client's account number: ";
       cin >> tempnum;
       cout << "Enter opening balance: $";
       cin >> tempbal;
       cout << "Enter 1 for Brass Account or "
            << "2 for BrassPlus Account: ";
       while (cin >> kind && (kind != '1' && kind != '2'))
           cout <<"Enter either 1 or 2: ";
       if (kind == '1')
           p_clients[i] = new Brass(temp, tempnum, tempbal);
       else
       {
           double tmax, trate;
           cout << "Enter the overdraft limit: $";
           cin >> tmax;
           cout << "Enter the interest rate "
                << "as a decimal fraction: ";
           cin >> trate;
           p_clients[i] = new BrassPlus(temp, tempnum, tempbal,
                                        tmax, trate);
        }
        while (cin.get() != '\n')
            continue;
   }
   cout << endl;
   for (int i = 0; i < CLIENTS; i++)
   {
       p_clients[i]->ViewAcct();
       cout << endl;
   }
              
   for (int i = 0; i < CLIENTS; i++)
   {
       delete p_clients[i];  // free memory
   }
   cout << "Done.\n";         
 /* code to keep window open 
   if (!cin)
      cin.clear();
   while (cin.get() != '\n')
      continue;
*/
   return 0; 
}