c++设计一个类层次，基类为Date，从Date分别派生出ShortE、MediumDate和LongDate.他们各自有成员函数print()，输出当前日期。 Date输出日期格式为：04-14-2018 ShortE输出日期格式为：14-04-2018 MediumDate输出日期格式为：Apr.14,2018 LongDate输出日期格式为：April 14, 2018

好的，你的问题是关于设计一个类层次的。基类是 `Date`，从 `Date` 分别派生出 `ShortE`、`MediumDate` 和 `LongDate`，它们各自有成员函数 `print()`，用于输出当前日期。其中，`Date` 输出日期格式为 `04-14-2018`，`ShortE` 输出日期格式为 `14-04-2018`，`MediumDate` 输出日期格式为 `Apr.14,2018`，`LongDate` 输出日期格式为 `April 14, 2018`。下面是具体实现的代码：

#include <iostream>
#include <string>

class Date {
protected:
    int m_month;
    int m_day;
    int m_year;

public:
    Date(int month, int day, int year) : m_month(month), m_day(day), m_year(year) {}

    virtual void print() {
        std::cout << m_month << "-" << m_day << "-" << m_year;
    }
};

class ShortE : public Date {
public:
    ShortE(int month, int day, int year) : Date(month, day, year) {}

    virtual void print() {
        std::cout << m_day << "-" << m_month << "-" << m_year;
    }
};

class MediumDate : public Date {
public:
    MediumDate(int month, int day, int year) : Date(month, day, year) {}

    virtual void print() {
        std::string month_str;

        switch (m_month) {
            case 1:
                month_str = "Jan.";
                break;
            case 2:
                month_str = "Feb.";
                break;
            case 3:
                month_str = "Mar.";
                break;
            case 4:
                month_str = "Apr.";
                break;
            case 5:
                month_str = "May";
                break;
            case 6:
                month_str = "Jun.";
                break;
            case 7:
                month_str = "Jul.";
                break;
            case 8:
                month_str = "Aug.";
                break;
            case 9:
                month_str = "Sep.";
                break;
            case 10:
                month_str = "Oct.";
                break;
            case 11:
                month_str = "Nov.";
                break;
            case 12:
                month_str = "Dec.";
                break;
            default:
                month_str = "Invalid month";
        }

        std::cout << month_str << m_day << "," << m_year;
    }
};

class LongDate : public Date {
public:
    LongDate(int month, int day, int year) : Date(month, day, year) {}

    virtual void print() {
        std::string month_str;

        switch (m_month) {
            case 1:
                month_str = "January";
                break;
            case 2:
                month_str = "February";
                break;
            case 3:
                month_str = "March";
                break;
            case 4:
                month_str = "April";
                break;
            case 5:
                month_str = "May";
                break;
            case 6:
                month_str = "June";
                break;
            case 7:
                month_str = "July";
                break;
            case 8:
                month_str = "August";
                break;
            case 9:
                month_str = "September";
                break;
            case 10:
                month_str = "October";
                break;
            case 11:
                month_str = "November";
                break;
            case 12:
                month_str = "December";
                break;
            default:
                month_str = "Invalid month";
        }

        std::cout << month_str << " " << m_day << "," << m_year;
    }
};

int main() {
    Date d(4, 14, 2018);
    d.print();
    std::cout << std::endl;

    ShortE se(4, 14, 2018);
    se.print();
    std::cout << std::endl;

    MediumDate md(4, 14, 2018);
    md.print();
    std::cout << std::endl;

    LongDate ld(4, 14, 2018);
    ld.print();
    std::cout << std::endl;

    return 0;
}

注意，如果您计划使用此代码，请使用自己的日期类进行适当修改和归因。