#include <iostream>
using namespace std;

class Date {
private:
    int year;
    int month;
    int day;
public:
    Date(int y = 2006, int m = 3, int d = 3) : year(y), month(m), day(d) {
        cout << "Date的默认构造" << endl;
    }
    Date(const Date& tmp) : year(tmp.year), month(tmp.month), day(tmp.day) {
        cout << "Date的复制构造" << endl;
    }
    ~Date() {
        cout << "Date的析构函数" << endl;
    }
    void Show() const {
        cout << year << "-" << month << "-" << day << endl;
    }
    void Set(int y, int m, int d) {
        year = y;
        month = m;
        day = d;
    }
};

class Staff {
private:
    int num;
    string name;
    char gender;
    Date birth;
    string id;
public:
    Staff(int nu = 0, const string& na = "scandi", char g = 'M',
          const Date& d = Date(), const string& i = "100000000000000000")
        : num(nu), name(na), gender(g), birth(d), id(i) {
        cout << "Staff的构造函数" << endl;
    }
    Staff(const Staff& s)
        : num(s.num), name(s.name), gender(s.gender), birth(s.birth), id(s.id) {
        cout << "Staff的复制构造" << endl;
    }
    ~Staff() {
        cout << "Staff的析构函数" << endl;
    }
    inline void Show_Staff() const {
        cout << num << endl;
        cout << name << endl;
        cout << gender << endl;
        birth.Show();
        cout << id << endl;
    }
    inline void Set_Staff(int nu, const string& na, char g, const Date& d, const string& i) {
        num = nu;
        name = na;
        gender = g;
        birth = d;
        id = i;
    }
};

int main() {
    Staff s;
    s.Show_Staff();
    return 0;
}

出错了（流汗。。。

#include <iostream>
#include <cstring>
using namespace std;

class String {
private:
    char* s = nullptr;
public:
    friend istream& operator>> (istream& cin, String& x);
    friend ostream& operator<< (ostream& cout, String& x);
    String() :s(nullptr) {
        cout << "String的构造函数" << endl;
    }
    String(const char* p) {
        s = new char[strlen(p) + 1];
        strcpy(s, p);
    }
    String(const String& x) {
        if (s != nullptr) {
            delete[] s;
        }
        s = new char[strlen(x.s) + 1];
        strcpy(s, x.s);
    }
    ~String() {
        if (s != nullptr) {
            delete[] s;
        }
    }
    String operator+ (const String& x) {
        String tmp;
        if (x.s == nullptr) {
            return *this;
        }
        tmp.s = new char(strlen(x.s) + strlen(s) + 1);
        strcpy(tmp.s, s);
        strcat(tmp.s, x.s);
        return tmp;
    }
    String& operator+= (const String& x) {
        const char* tt = s ? s : "";
        char* tmp = new char[strlen(tt) + strlen(x.s) + 1];
        strcpy(tmp, s);
        strcat(tmp, x.s);
        if (s != nullptr) {
            delete[] s;
        }
        s = tmp;
        return *this;
    }
    char& operator[] (int i) {
        return s[i];
    }
    bool operator== (const String& x) {
        return strcmp(this->s, x.s) == 0;
    }
    bool operator< (const String& x) {
        return strcmp(this->s, x.s) < 0;
    }
    int Length() {
        return strlen(s);
    }
};
istream& operator>> (istream& cin, String& x) {
    string tmp;
    cin >> tmp;
    if (x.s != nullptr) {
        delete[] x.s;
    }
    x.s = new char[tmp.length() + 1];
    strcpy(x.s, tmp.c_str());
    return cin;
}
ostream& operator<< (ostream& cout, String& x) {
    cout << (x.s ? x.s : "");
    return cout;
}

int main(){
    String s1("Help!"), s2("Good!"), s3(s2), s4, s5;
    cout << "s1=" << s1 << endl;
    s3 = "Hello!";
    cout << "s3=" << s3 << endl;
    s3 += s2;
    cout << "s3=" << s3 << endl;
    cin >> s4;
    cout << "s4=" << s4 << endl;
    s5 = s3 + s4;
    cout << "s5=" << s5 << endl;
    s5[0] = 'g';
    cout << "s5=" << s5 << endl;
    cout << "strlen(s5)=" << s5.Length() << endl;
    cout << boolalpha << (s3 == s1) << endl;
    return 0;
}