Introduction to this pointer

Catalog

brief introduction ：

characteristic ：

give an example ：

Be careful ：

---

brief introduction ：

C++ The compiler gives each “ Non static member functions “ Added a hidden pointer parameter
Count , Let the pointer point to the current object ( The object that the function calls at run time ), Operation of all member variables in the function body , All are accessed through this pointer . But all operations are transparent to users , That is, the user does not need to deliver , Compiler autocompletes

characteristic ：

1. this The type of pointer ： Class types * const
2. Only in “ Member functions ” Internal use of
3. this Pointer is essentially a parameter of a member function , When an object calls a member function , Pass the object address as an argument to this
Shape parameter . So objects don't store this The pointer .
4. this Pointer is the first implied pointer parameter of a member function , Generally, the compiler passes through ecx Register auto transfer , No need for users
Pass on
 

give an example ：

class Data {
public:
	void Printf()
	{
		cout << _year <<" "<<" "<< _month <<" "<< _day << endl;
	}
	void Init(int year=2022,int month=5,int day=25)
	{
		_year = year;
		_month = month;
		_day = day;
	}
private:
	int _year;
	int _month;
	int _day;
};
int main()
{
	Data d1,d2;
	d1.Init(2022,1,1);
	d1.Printf();
	d2.Init(2022,2,2);
	d2.Printf();

	return 0;
}

 

This is a simple date class , So here's a problem , We are using the print function Printf And initialization functions Init When ,d1 and d2 The same function is called , So how does the compiler know that I should set / Print d1 still d2 Well ？

  This is actually used this The pointer

So how does the specific compiler do it ？

void Printf(const* this)// The compiler actually handles 
	{
		cout << this->_year << " " << this->_month << " " << this->_day << endl;
	}
	void Printf()// What we see 
	{
		cout << _year <<" "<<" "<< _month <<" "<< _day << endl;
	}

void Init(const* this,int year=2022,int month=5,int day=25)// The compiler handles 
	{
		this->_year = year;
		this->_month = month;
		this->_day = day;
	}
	void Init(int year = 2022, int month = 5, int day = 25)// What we see 
	{
		_year = year;
		_month = month;
		_day = day;
	}

d1.Init(2022,1,1);// What we see 
	d1.Init(&d1,2022, 1, 1);// The compiler actually handles 

In fact, the Editor takes d1 and d2 Address of function , And passed it on to const*this, In this way, the compiler can automatically print and initialize the corresponding structure .

Be careful ：

We can't add const*this and &, This is what the compiler does , We can't rob the compiler , Even if I did , Compilation will not pass , But we can add

void Printf(const* this)// error 
	{
		cout << _year <<" "<<" "<< _month <<" "<< _day << endl;
	}
void Printf()// Can run , But the compiler will add this->, So we don't need to add , It's okay to add it 
	{
		cout <<this-> _year <<" "<<" "<< this->_month <<" "<< this->_day << endl;
	}