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2009.05.20 (00:39:56)

Nullable이란?


어떠한 자료형 선언문에서 자료형 후미에 ?(물음표)가 붙어져서 선언하는 경우를 볼 수 있다.


한가지의 예로.. bool을 들어보겠다.

bool의 경우는 True와 False의 두가지 경우만이 올 수가 있다. 또한 bool의 경우 처음 생성하고나서 True나 False등으로 초기화를 해주는 것이 일반적이다. 그런데 bool을 사용하고 싶지만 초기화가 되지 않은 상태도 알고 싶다면 어떻할까?

아마도 이러한 호기심에서 만들어지게된 형식이 아닐까 생각한다.


bool 형식의 경우는 True와 False만이 설정이 가능하지만 bool?와 같은 형식은 True와 False뿐만 아니라 Null의 값도 넣을 수가 있다. Null이 사용 가능해짐으로써 초기 설정 상태를 점검 해볼 수 있고 변수의 사용에 대해 조금 더 명확하게 알 수 있게 될 것이다. 물론 이러한 특성을 이용해서 사용하기에는 개발자의 역량에 따라 다를 것이다. :)


다음은 MSDN에서 가져온 정보이다.


nullable 형식은 System.Nullable(T) 구조체의 인스턴스입니다. nullable 형식은 내부 값 형식의 올바른 값 범위뿐 아니라 null 값도 나타낼 수 있습니다. 예를 들어 Nullable<Int32>("Int32의 nullable"이라고 읽음)에는 -2147483648에서 2147483647까지의 모든 값을 할당하거나 null 값을 할당할 수 있습니다. Nullable<bool>에는 true, false 또는 null 값을 할당할 수 있습니다. 숫자 및 부울 형식에 null 값을 할당할 수 있는 기능은 특히 값이 할당되지 않을 수 있는 요소를 포함하는 데이터베이스 및 기타 데이터 형식을 다룰 때 유용합니다. 예를 들어 데이터베이스의 Boolean 필드는 true 또는 false 값을 저장할 수도 있고, 정의되지 않을 수도 있습니다.




class NullableExample
{
    static void Main()
    {
        int? num = null;
        if (num.HasValue == true)
        {
            System.Console.WriteLine("num = " + num.Value);
        }
        else
        {
            System.Console.WriteLine("num = Null");
        }

        // y is set to zero
        int y = num.GetValueOrDefault();

        // num.Value throws an InvalidOperationException if num.HasValue is false
        try
        {
            y = num.Value;
        }
        catch (System.InvalidOperationException e)
        {
            System.Console.WriteLine(e.Message);
        }
    }
}


이 예제는 다음 출력을 표시합니다.
num = Null
Nullable object must have a value.




이 글의 테그에 포함되는 게시물 목록
  1. [2008/11/09] 하늘공원의 길 by 시크리트 (16764)
profile


삶이란 자신을 망치는 것과 싸우는 일이다
마음을 폐가로 만드는 모든 것과 싸운다

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