Worm copy construction operator overload

Class 6 Default member functions

If there are no members in a class , It is called empty class for short . Is there nothing in the empty class ？ It's not ,== Any class we don't write , Will automatically generate the following 6 Default member functions ==

copy constructor

Constructors ： Only a single parameter , The formal parameter is a reference to an object of this type ( Commonly used const modification ), Automatically called by the compiler when creating a new object with an existing class type object .

features

== copy constructor == It is also a special member function , Its characteristics are as follows ：

1. The copy constructor is == An overloaded form of constructor ==.
2. Copy constructor == There is only one parameter == And == Reference must be used to pass parameters ==, Use == The value passing method will cause infinite recursive calls ==.

3. == If no definition is displayed , The system generates the default copy constructor ==. The default copy constructor object is stored in memory == Complete the copy in byte order ==, This copy is called == Shallow copy ==, Or copy .

== But this will cause some problems ==

== When there is a resource point, you can't use shallow copy ==

Assignment operator overload

Operator overloading

==C++ In order to enhance the readability of the code, operator overloading is introduced , Operator overloading is a function with a special function name ,== It also has its return value type , Function name and parameter list , Its return value type and parameter list are similar to ordinary functions .

== The function name is ： keyword operator Followed by operator symbols that need to be overloaded ==.
== The function prototype ： return type operator The operator ( parameter list )==

Be careful ：

1. Cannot pass == Connect other symbols == To create a new operator ： such as [email protected]
2. The overload operator must have an operand of class type or enumeration type
3. Operators for built-in types , Its meaning cannot be changed , for example ： Built in integer +, No Can change its meaning
4. When overloading a function as a member of a class , Its parameters look less than the operands 1 The operator of a member function has a default formal parameter this, Limited to the first parameter
5. .* 、:: 、sizeof 、?: 、. Pay attention to the above 5 Operators cannot be overloaded . This often appears in multiple-choice questions in written tests

== Implementation of operator overloading ==

// Date class class  Date{public:	// Constructor does not write , The compiler automatically generates constructors , So the constructor is also the default member function 	Date(int year = 2022, int month = 1, int day = 1)	{		_year = year;		_month = month;		_day = day;	}	// We don't write copy constructs , The compiler will automatically generate a default copy construct 	// Copy structure 	/*Date(const Date& d) { _year = d._year; _month = d._month; _day = d._day; }*/	void Print()	{		cout << _year << "-" << _month << "-" << _day << endl;		}		// Judge whether the dates are equal 	bool operator==(Date x2)	{		return _year == x2._year			&& _month == x2._month			&& _day == x2._day;	}	// Judge whether the left is smaller than the right 	bool operator<(Date x2)	{		if (_year < x2._year)			return true;		else if(_year == x2._year)		{			if (_month < x2._month)				return true;			else if(_month == x2._month)			{				if (_day < x2._day)					return true;			}		}		return false;	}	// Date plus days   The returned date is still 	Date operator+(int day)	{	}	// Date minus days   The returned date is still 	Date operator-(int day)	{	}	// Date minus date   Days returned 	int operator-(Date d2)	{	}private:	int _year;	int _month;	int _day;};int main(){	Date d1(2022, 1, 1);	Date d2(2022, 1, 1);	cout << (d1 == d2) << endl;	cout << (d1 < d2) << endl;		return 0;}