构造函数
构造函数是特殊的成员函数，名字虽然叫做构造，但他不是用来开空间的，而是来完成初始化工作的。当实例化对象完成后，就会调用构造函数来对成员变量进行初始化。
构造函数的特点：
（1）函数名与类名相同。
（2）无返回值（返回值什么都不写，void也不写）
（3）对象实例化时系统会自动调用构造函数
（4）构造函数可以重载
代码语言：javascript
AI代码解释
class Date { public: //构造函数可以重载 Date()//无参构造函数 { _year = 1; _month = 1; _day = 1; } Date(int year,int month,int day)//带参构造函数，全缺省 { _year = year; _month = month; _day = day; } void print() { cout << _year << "年" << _month << "月" << _day << "日" << endl; } private: int _year; int _month; int _day; }; int main() { Date d1;//调用无参的构造函数 d1.print(); Date d2(2024, 7, 26);//调用带参的构造函数 d2.print(); return 0; }（5）如果类中没有显示定义构造函数，那么c++编译器会自动生成一个无参的默认构造函数。
如果类中定义了，编译器将不会再生成。
代码语言：javascript
AI代码解释
class Date { public://调用编译器自动生成的构造函数 void print() { cout << _year << "年" << _month << "月" << _day << "日" << endl; } private: int _year; int _month; int _day; }; int main() { Date d1;//调用无参的构造函数 d1.print(); return 0; }（6）无参构造函数，全缺省构造函数，和我们不写时编译器自动生成构造函数，都叫做默认的构造函数。但这三个函数不能同时存在，不然调用的时候会存在歧义。
说明： c++中，把类型分为内置类型和自定义类型。内置类型就是语言提供的原生数据类型，如int,double等，自定义类型就是我们使用class/struct等关键字自己定义的类型。
（7）我们不写时，编译器自动生成的构造函数，对内置类型成员变量没有要求，是否初始化取决于编译器。而对于自定义类型成员变量，要求调用这个成员变量的默认构造函数，若是没有默认构造函数，编译器就会报错。
3，析构函数
析构函数与构造函数的功能相反，它完成的不是对对象本身的销毁，不如局部对象是存在栈帧的，函数结束栈帧销毁，它就释放了，不需要我们管。c++规定，在对象销毁时，会调用析构函数，完成对象中资源清理释放工作。
析构函数的特点：
（1）析构函数名是在类名前加上~
（2）无参数，无返回值
（3）一个类只能有一个析构函数，若是未显示定义，系统会自动生成默认的析构函数。
（4）对象生命周期结束时，系统会自动调用析构函数。
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