在基类中创建派生类的对象
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【中文标题】在基类中创建派生类的对象【英文标题】:Create objects of derived classes in base class 【发布时间】:2020-03-17 19:17:54 【问题描述】:这是我的代码。我正在尝试从基类中的派生类创建对象,但它有一些错误。
#include <iostream>
#include<Windows.h>
#include <string>
#include <ctime>
using namespace std;
class PrgDevice
private:
tm startTime;
tm stopTime;
int choice;
int choice1;
char c;
public:
int dateTime()
cout << "Enter start date and start time: ";
cin >> startTime.tm_mday >> startTime.tm_mon >> startTime.tm_year >> startTime.tm_hour >> startTime.tm_min >> startTime.tm_sec;
cout << "Enter stop date and stop time: ";
cin >> stopTime.tm_mday >> stopTime.tm_mon >> stopTime.tm_year >> stopTime.tm_hour >> stopTime.tm_min >> stopTime.tm_sec;
void mainMenu()
while (choice != 3)
cout << "Main menu options:";
cout << " 1. Select a device to program (contains a submenu)" << endl;
cout << " 2. Display current status of all devices" << endl;
cout << " 3. Exit" << endl;
cout << "Enter your option => ";
cin >> choice;
if (choice == 1)
subMenu();
else if (choice == 2)
cout << choice;
else
system("pause");
void subMenu()
cout << "Select a device:" << endl;
cout << " 1. PVR" << endl;
cout << " 2. Camera DVR" << endl;
cout << " 3. Oven" << endl;
cout << "Enter your option => ";
cin >> choice1;
if (choice1 == 1)
PVR n1;
else if (choice1 == 2)
DVR n2;
else
Oven n3;
void newDevice()
if (c == 'Y' || c == 'y')
subMenu();
else
mainMenu();
;
class PVR : public PrgDevice
private:
int channel;
public:
PVR()
cout << "Select the channel ==> ";
cin >> channel;
cout << endl;
dateTime();
cout << endl;
cout << "Another device to program Y/N ? => ";
newDevice();
;
class DVR : public PrgDevice
private:
string position;
public:
DVR()
cout << "Select the position ==> ";
getline(cin, position);
cout << endl;
dateTime();
cout << endl;
cout << "Another device to program Y/N ? => ";
newDevice();
;
class Oven : public PrgDevice
private:
string food;
public:
Oven()
cout << "What do you want to bake? ==> ";
getline(cin, food);
cout << endl;
dateTime();
cout << endl;
cout << "Another device to program Y/N ? => ";
newDevice();
;
int main()
PrgDevice obj1;
obj1.mainMenu();
system("pause");
return 0;
以下是错误:
错误 C2065:“PVR”:未声明的标识符 错误 C2146:语法错误:缺少“;”在标识符“n1”之前 错误 C2065:“n1”:未声明的标识符 错误 C2065:“DVR”:未声明的标识符 错误 C2146:语法错误:缺少“;”在标识符“n2”之前 错误 C2065:“n2”:未声明的标识符 错误 C2065:“烤箱”:未声明的标识符 错误 C2146:语法错误:缺少“;”在标识符“n3”之前 错误 C2065:“n3”:未声明的标识符 1>完成建设项目“Project1.vcxproj”——失败。 ========== 构建:0 成功,1 失败,0 最新,0 跳过 ==========
请帮助我。谢谢。
【问题讨论】:
你不能使用那里的类,因为在你使用它们时它们还没有被定义。您应该将这些函数的定义从声明中分离出来,并将它们定义在您要使用的类下面。 一个类应该负责一件事。你所有的课程都做得太多了。您正在混合用户输入和逻辑。基类通常不应该知道它的派生类。修复你的代码需要大量的重构,希望你很幸运,并且有人可以在这里看到更大的画面 【参考方案1】:尚不清楚您为什么在这里使用继承。本质上,PVR
DVR
和Oven
这三个对象不需要派生自PrgDevice
。一旦它们没有派生,您可以将它们移动到 PrgDevice
之前,以便您可以在那里使用它们。
class PVR ...
;
class DVR ...
;
class Oven ...
;
class PrgDevice ...
;
因为 PVR
DVR
和 Oven
构造函数都这样做
dateTime();
cout << endl;
cout << "Another device to program Y/N ? => ";
newDevice();
我们可以将它移到PrgDevice::submenu
函数中。
void subMenu() ...
if (choice1 == 1)
PVR n1;
else if (choice1 == 2)
DVR n2;
else
Oven n3;
dateTime();
cout << endl;
cout << "Another device to program Y/N ? => ";
newDevice();
但这并不能解决您的所有问题。你一直在递归:
mainMenu
致电subMenu
submenu
致电newDevice
newDevice
致电submenu
或newDevice
接下来需要修复。新设备真的应该留在submenu
或返回 到主菜单。我们通过添加 do
while
循环来做到这一点
void submenu()
do
cout << "Select a device:" << endl;
...
cout << "Another device to program Y/N ? => ";
cin >> c;
while(c == 'Y' || c == 'y');
我留下了一个看似有效的版本,其中注释掉了 datetime
函数 here
喂
echo -e "1 1 1 y 2 2\n n 3"
输出
Main menu options:
1. Select a device to program (contains a submenu)
2. Display current status of all devices
3. Exit
Enter your option => Select a device:
1. PVR
2. Camera DVR
3. Oven
Enter your option => Select the channel ==>
Another device to program Y/N ? => Select a device:
1. PVR
2. Camera DVR
3. Oven
Enter your option => Select the position ==>
Another device to program Y/N ? => Main menu options:
1. Select a device to program (contains a submenu)
2. Display current status of all devices
3. Exit
Enter your option =>
【讨论】:
【参考方案2】:您需要在使用对象类型之前定义它们。与其在类定义中内联代码,不如在代码顶部(或在包含中)将它们分开,然后当你真正开始使用它们时,编译器就会知道你在做什么。
class A
// Define stuff, but don't inline your methods
class B: public A
// Define stuff, but don't inline your methods
;
void A::subMenu()
// All your code
【讨论】:
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