'<< 오퍼레이터, >> 오퍼레이터' 오버로딩

'<< 오퍼레이터, >> 오퍼레이터' 오버로딩

<< 연산자의 이름이 double shift라고 막연히 생각했는데, insertion operator 라는 충격적인 사실을 알게 되었다. 마찬가지로 >> 도 extraction operator라는 이름을 가지고 있었다. 

# C++의 표준 입출력 스트림 객체와 함께 사용되는 연산자  >> , <<

1) >> operator :  extraction operator

2) << operator :  insertion operator 

이를 위해, msdn 의 차료를 참고해서 공부를 해보자.

1. >> operator  오버로딩(Input stream - extraction operator)

---

Input streams use the extraction (>>) operator for the standard types. You can write similar extraction operators for your own types; your success depends on using white space precisely.

Here is an example of an extraction operator for the Date class presented earlier:

istream& operator>> ( istream& is, Date& dt )  
{  
   is >> dt.mo >> dt.da >> dt.yr;  
   return is;  
}  

이 경우에는 return by address를 통해서 istream 객체를 반환하여 chaining을 지원하여 1) is >> dt.mo, 2) is > >dt.da , 3) is >> dt.yr 순으로 실행된다.

2. << operator  오버로딩

---

Output streams use the insertion (<<) operator for standard types. You can also overload the << operator for your own classes.

예제

The write function example showed the use of a Date structure. A date is an ideal candidate for a C++ class in which the data members (month, day, and year) are hidden from view. An output stream is the logical destination for displaying such a structure. This code displays a date using the cout object:

Date dt( 1, 2, 92 );  
cout << dt;  

To get cout to accept a Date object after the insertion operator, overload the insertion operator to recognize an ostream object on the left and a Date on the right. The overloaded << operator function must then be declared as a friend of class Date so it can access the private data within a Date object.

// overload_date.cpp  
// compile with: /EHsc  
#include <iostream>  
using namespace std;  
  
class Date  
{  
    int mo, da, yr;  
public:  
    Date(int m, int d, int y)  
    {  
        mo = m; da = d; yr = y;  
    }  
    friend ostream& operator<<(ostream& os, const Date& dt); // friend 키워드를 통해 directly access data 가능  
};  
  
ostream& operator<<(ostream& os, const Date& dt) // 오퍼레이터 오버로딩
{  
    os << dt.mo << '/' << dt.da << '/' << dt.yr;  // 예를 들면 5/6/92 와 같이 출력
    return os;  
}  
  
int main()  
{  
    Date dt(5, 6, 92);  
    cout << dt;  
}  

5/6/92

설명

The overloaded operator returns a reference to the original ostream object, which means you can combine insertions:

cout << "The date is" << dt << flush;  

https://msdn.microsoft.com/ko-kr/library/1z2f6c2k.aspx