C++奇迹之旅：赋值运算符重载与隐式类型转换

文章目录

• 赋值运算符重载
• 运算符重载
• • 特性
  • 赋值运算符重载
  • 传值返回：
  • 传引用赋值：
  • • 两种返回选择
    • 赋值运算符只能重载成类的成员函数不能重载成全局函数
    • 总结

      ---

      赋值运算符重载

      运算符重载

      运算符重载是C++中的一个重要特性，他允许我们为自定义的类型定义自己的运算符行为。通过运算符重载，我们可以使用与内置数据类型相同的语法来操作自定义类型，从而提高代码的可读性和可维护性。

      还是我们熟悉的日期函数：

      class Date{public:Date(int year, int month, int day){_year = year;_month = month;_day = day;}void Print(){cout Date d1(2024, 2, 17);Date d2(2024, 6, 27);return 0;}public:Date(int year, int month, int day){_year = year;_month = month;_day = day;}bool isSame(const Date& d){return _year == d._year&& _month == d._month&& _day == d._day;}private:int _year;int _month;int _day;};int main(){Date d1(2024, 2, 17);Date d2(2024, 6, 27);if (d1.isSame(d2)){cout cout public:Date(int year, int month, int day){_year = year;_month = month;_day = day;}bool isSame(const Date& d){return _year == d._year&& _month == d._month&& _day == d._day;}//private:int _year;int _month;int _day;};// 这里会发现运算符重载成全局的就需要成员变量是公有的，那么问题来了，封装性如何保证？// 这里其实可以用我们后面学习的友元解决，或者干脆重载成成员函数。bool operator==(const Date& d1,const Date& d2){return d1._year == d2._year&& d1._month == d2._month&& d1._day == d2._day;}int main(){Date d1(2024, 2, 17);Date d2(2024, 6, 27);//d1.isSame(d2)if (d1 == d2){cout cout Date d1(2024, 2, 17);Date d2(2024, 6, 27);// 显式调用operator==(d1, d2);// 直接写，装换调用，编译会转换成operator==(d1, d2);d1 == d2;return 0;}public:    Date(int year = 1900, int month = 1, int day = 1)    {        _year = year;        _month = month;        _day = day;    }    int GetYear() { return _year; }    int GetMonth() { return _month; }    int GetDay() { return _day; }    void SetYear(int year) { _year = year; }    void SetMonth(int month) { _month = month; }    void SetDay(int day) { _day = day; }    bool operator==(const Date& d) const    {        return _year == d._year && _month == d._month && _day == d._day;    }private:    int _year;    int _month;    int _day;};    friend bool operator==(const Date& d1, const Date& d2);public:    Date(int year = 1900, int month = 1, int day = 1)    {        _year = year;        _month = month;        _day = day;    }private:    int _year;    int _month;    int _day;};bool operator==(const Date& d1, const Date& d2){    return d1._year == d2._year    && d1._month == d2._month     && d1._day == d2._day;}public:    Date(int year = 1900, int month = 1, int day = 1)    {        _year = year;        _month = month;        _day = day;    }        // bool operator==(Date* this, const Date& d2)    // 这里需要注意的是，左操作数是this，指向调用函数的对象    bool operator==(const Date& d)     {        return _year == d._year         && _month == d._month         && _day == d._day;    }private:    int _year;    int _month;    int _day;};Date d1(2024, 2, 17);Date d2(2024, 6, 27);//显示调用d1.operator==(d2);//转换调用，等价与d1.operator==(d2);d1 == d2;cout public:void func(){cout //函数指针//void(*ptr)();//成员函数要加&才能取到函数指针ptrFunc fp = &OB::func;//定义函数指针fp指向funcOB temp;//定义OB类对象temp(temp.*fp)();return 0;}_year = d._year;_month = d._month;_day = d._day;return *this;}public:Date(int year = 1900, int month = 1, int day = 1){_year = year;_month = month;_day = day;}Date(const Date& d){cout _year = d._year;_month = d._month;_day = d._day;return *this;}private:int _year;int _month;int _day;};int main(){Date d1(2024, 4, 14);// 拷贝构造// 一个已经存在的对象，拷贝给另一个要创建初始化的对象Date d2(d1);Date d3 = d1;Date d4(2024, 5, 1);// 赋值拷贝/赋值重载// 一个已经存在的对象，拷贝赋值给另一个已经存在的对象d1 = d4;d1 = d2 = d4;return 0;}_year = d._year;_month = d._month;_day = d._day;return *this;}if (this != &d)//使用的是地址判断{_year = d._year;_month = d._month;_day = d._day;}return *this;}Date d(2024, 4, 14);return d;}int main(){const Date& ref = func();return 0;}public:Date(int year = 1900, int month = 1, int day = 1){_year = year;_month = month;_day = day;}Date(const Date& d){cout if (this != &d){_year = d._year;_month = d._month;_day = d._day;}return *this;}void Print(){cout cout Date d(2024, 4, 14);return d;}int main(){const Date ref = func();return 0;}Date d(2024, 4, 14);return d;}int main(){const Date& ref = func();return 0;}public:Date(int year = 1900, int month = 1, int day = 1){_year = year;_month = month;_day = day;}int _year;int _month;int _day;};// 赋值运算符重载成全局函数，注意重载成全局函数时没有this指针了，需要给两个参数Date& operator=(Date& left, const Date& right){if (&left != &right){left._year = right._year;left._month = right._month;left._day = right._day;}return left;}public:Time(){_hour = 1;_minute = 1;_second = 1;}Time& operator=(const Time& t){if (this != &t){_hour = t._hour;_minute = t._minute;_second = t._second;}return *this;}private:int _hour;int _minute;int _second;};class Date{private:// 基本类型(内置类型)int _year = 1970;int _month = 1;int _day = 1;// 自定义类型Time _t;};int main(){Date d1;Date d2;d1 = d2;return 0;}public:Stack(size_t capacity = 10){_array = (DataType*)malloc(capacity * sizeof(DataType));if (nullptr == _array){perror("malloc申请空间失败");return;}_size = 0;_capacity = capacity;}void Push(const DataType& data){// CheckCapacity();_array[_size] = data;_size++;}~Stack(){if (_array){free(_array);_array = nullptr;_capacity = 0;_size = 0;}}private:DataType* _array;size_t _size;size_t _capacity;};int main(){Stack s1;s1.Push(1);s1.Push(2);s1.Push(3);s1.Push(4);Stack s2;s2 = s1;return 0;}