编写程序用不同的格式打印当前日期。要求如下： （1）定一个基类Date； （2）从Date分别派生出ShortE、MediumDate和LongDate.它们各自有成员函数print()，输出当前日期。输出格式如下: 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 （3）在主函数中对每个类及对应的函数进行测试

好的，以下是代码示例：

#include <iostream>
#include <string>
#include <ctime>
using namespace std;

//基类Date
class Date {
protected:
    time_t now;
    struct tm *tm_now;
public:
    Date() {
        now = time(0);
        tm_now = localtime(&now);
    }
    virtual void print() = 0; //虚函数print
};

//派生类ShortE
class ShortE : public Date {
public:
    void print() {
        cout << tm_now->tm_mday << "-" << tm_now->tm_mon + 1 << "-" << tm_now->tm_year + 1900 << endl;
    }
};

//派生类MediumDate
class MediumDate : public Date {
public:
    void print() {
        string month;
        switch (tm_now->tm_mon) {
        case 0:  month = "Jan."; break;
        case 1:  month = "Feb."; break;
        case 2:  month = "Mar."; break;
        case 3:  month = "Apr."; break;
        case 4:  month = "May."; break;
        case 5:  month = "Jun."; break;
        case 6:  month = "Jul."; break;
        case 7:  month = "Aug."; break;
        case 8:  month = "Sep."; break;
        case 9:  month = "Oct."; break;
        case 10: month = "Nov."; break;
        case 11: month = "Dec."; break;
        }
        cout << month << tm_now->tm_mday << "," << tm_now->tm_year + 1900 << endl;
    }
};

//派生类LongDate
class LongDate : public Date {
public:
    void print() {
        string month;
        switch (tm_now->tm_mon) {
        case 0:  month = "January"; break;
        case 1:  month = "February"; break;
        case 2:  month = "March"; break;
        case 3:  month = "April"; break;
        case 4:  month = "May"; break;
        case 5:  month = "June"; break;
        case 6:  month = "July"; break;
        case 7:  month = "August"; break;
        case 8:  month = "September"; break;
        case 9:  month = "October"; break;
        case 10: month = "November"; break;
        case 11: month = "December"; break;
        }
        cout << month << " " << tm_now->tm_mday << ", " << tm_now->tm_year + 1900 << endl;
    }
};

int main() {
    Date *d1, *d2, *d3; //定义基类指针
    ShortE s;
    d1 = &s;
    d1->print(); //调用ShortE的print函数
    MediumDate m;
    d2 = &m;
    d2->print(); //调用MediumDate的print函数
    LongDate l;
    d3 = &l;
    d3->print(); //调用LongDate的print函数
    return 0;
}

输出结果如下：

14-6-2021
Jun.14,2021
June 14, 2021