为什么我运行代码时会停留在一个循环中？

Question

#include <iostream>
#include <string>
#include <ctime>

using namespace std;

class PVR {
private:
    int channel;
public:
    PVR() {
        cout << "Select the channel ==> ";
        cin >> channel;
        cout << endl;
    }
};

class DVR  {
private:
    string position;
public:
    DVR() {
        cout << "Select the position ==> ";
        cin >> position;
        cout << endl;
    }
};

class Oven {
private:
    string food;
public:
    Oven() {
        cout << "What do you want to bake? ==> ";
        cin >> food;
        cout << endl;
    }
};


class PrgDevice {
private:
    tm startTime;
    tm stopTime;
    int choice;
    int choice1;
    char c;
public:
    void 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: \n";
            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 {
            }
        }
    }
    void subMenu() {
        do {
            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;
            }
            dateTime();
            cout << endl;
            cout << "Another device to program Y/N ? => ";

            cin >> c;
        }
        while(c == 'Y' || c == 'y');
    }
};


int main() {
    PrgDevice obj1;
    obj1.mainMenu();

    system("pause");
    return 0;
}

这是我的输出

Main menu options: 
      1. Select a device to program (contains a submenu)
      2. Display current status of all devices
      3. Exit
Enter your option => 1
Select a device:
         1. PVR
         2. Camera DVR
         3. Oven
Enter your option => 1
Select the channel ==> 23
Enter start date and start time: 12:01:19 20:00:00

当我按下回车键时，我的程序只是进入了一个循环，我不知道为什么会这样。

- brian

---

你没有初始化你的PrgDevice成员变量，它们的值将是不确定的，使用它们将导致未定义的行为。创建一个构造函数来初始化它们。 - Some programmer dude

Answer 1

问题在于您的程序要求用户以空格分隔的方式输入时间和日期，而您却使用冒号分隔这些值。

这意味着：

cin >> startTime.tm_mday >> startTime.tm_mon >> ...

程序会将 12 读入 startTime.tm_mday，但输入中有一个:，这与startTime.tm_mon的类型不匹配。这将导致所有输入停止，让:留在输入缓冲区中等待下一次输入操作。

下一个输入操作是为stopTime准备的，但由于输入缓冲区中有:，因此会立即失败。然后你回到subMenu函数中，这时:会被读入c。由于 ':' 不等于 'Y' 或 'y'，所以循环结束，subMenu 函数返回到 mainMenu，然后再次打印菜单。

- Some programmer dude

Answer 2

我觉得这不像一个无限循环。尝试将开始时间输入为：

12 1 19  20 0 0

cin无法神奇地处理您输入中的“：”字符，因此您可能需要读取整行，并解析出“:”字符。

- robthebloke