Nullable<T> Struct

Definition

generic <typename T> where T : value classpublic value class Nullable

public struct Nullable<T> where T : struct

[System.Serializable]public struct Nullable<T> where T : struct

type Nullable<'T (requires 'T : struct)> = struct

[<System.Serializable>]type Nullable<'T (requires 'T : struct)> = struct

Public Structure Nullable(Of T)

Type Parameters

Inheritance

Object

ValueType

Nullable<T>

Attributes

SerializableAttribute

Examples

The following code example defines three rows of a table in the Microsoft Pubs sample database. The table contains two columns that are not nullable and two columns that are nullable.

using System;class Sample{    // Define the "titleAuthor" table of the Microsoft "pubs" database.    public struct titleAuthor    {      // Author ID; format ###-##-####      public string au_id;      // Title ID; format AA####      public string title_id;      // Author ORD is nullable.      public short? au_ord;      // Royalty Percent is nullable.      public int? royaltyper;    }    public static void Main()    {      // Declare and initialize the titleAuthor array.      titleAuthor[] ta = new titleAuthor[3];      ta[0].au_id = "712-32-1176";      ta[0].title_id = "PS3333";      ta[0].au_ord = 1;      ta[0].royaltyper = 100;      ta[1].au_id = "213-46-8915";      ta[1].title_id = "BU1032";      ta[1].au_ord = null;      ta[1].royaltyper = null;      ta[2].au_id = "672-71-3249";      ta[2].title_id = "TC7777";      ta[2].au_ord = null;      ta[2].royaltyper = 40;      // Display the values of the titleAuthor array elements, and      // display a legend.      Display("Title Authors Table", ta);      Console.WriteLine("Legend:");      Console.WriteLine("An Author ORD of -1 means no value is defined.");      Console.WriteLine("A Royalty % of 0 means no value is defined.");    }    // Display the values of the titleAuthor array elements.    public static void Display(string dspTitle,                               titleAuthor[] dspAllTitleAuthors)    {      Console.WriteLine("*** {0} ***", dspTitle);      foreach (titleAuthor dspTA in dspAllTitleAuthors) {         Console.WriteLine("Author ID ... {0}", dspTA.au_id);         Console.WriteLine("Title ID .... {0}", dspTA.title_id);         Console.WriteLine("Author ORD .. {0}", dspTA.au_ord ?? -1);         Console.WriteLine("Royalty % ... {0}", dspTA.royaltyper ?? 0);         Console.WriteLine();      }    }}// The example displays the following output://     *** Title Authors Table ***//     Author ID ... 712-32-1176//     Title ID .... PS3333//     Author ORD .. 1//     Royalty % ... 100////     Author ID ... 213-46-8915//     Title ID .... BU1032//     Author ORD .. -1//     Royalty % ... 0////     Author ID ... 672-71-3249//     Title ID .... TC7777//     Author ORD .. -1//     Royalty % ... 40////     Legend://     An Author ORD of -1 means no value is defined.//     A Royalty % of 0 means no value is defined.

open System// Define the "titleAuthor" table of the Microsoft "pubs" database.type titleAuthor =  struct    // Author ID format ###-##-####    val mutable au_id: string    // Title ID format AA####    val mutable title_id: string    // Author ORD is nullable.    val mutable au_ord: Nullable<int16>    // Royalty Percent is nullable.    val mutable royaltyper: Nullable<int>  end// Display the values of the titleAuthor array elements.let display dspTitle (dspAllTitleAuthors: #seq<titleAuthor>) =    printfn $"*** {dspTitle} ***"    for dspTA in dspAllTitleAuthors do        printfn $"Author ID ... {dspTA.au_id}"        printfn $"Title ID .... {dspTA.title_id}"        printfn $"Author ORD .. {dspTA.au_ord.GetValueOrDefault -1s}"        printfn $"Royalty %% ... {dspTA.royaltyper.GetValueOrDefault -1}\n"// Declare and initialize the titleAuthor array.let ta = Array.zeroCreate<titleAuthor> 3ta[0].au_id <- "712-32-1176"ta[0].title_id <- "PS3333"ta[0].au_ord <- Nullable 1sta[0].royaltyper <- Nullable 100ta[1].au_id <- "213-46-8915"ta[1].title_id <- "BU1032"ta[1].au_ord <- Nullable()ta[1].royaltyper <- Nullable()ta[2].au_id <- "672-71-3249"ta[2].title_id <- "TC7777"ta[2].au_ord <- Nullable()ta[2].royaltyper <- Nullable 40// Display the values of the titleAuthor array elements, and// display a legend.display "Title Authors Table" taprintfn "Legend:"printfn "An Author ORD of -1 means no value is defined."printfn "A Royalty %% of 0 means no value is defined."// The example displays the following output://     *** Title Authors Table ***//     Author ID ... 712-32-1176//     Title ID .... PS3333//     Author ORD .. 1//     Royalty % ... 100////     Author ID ... 213-46-8915//     Title ID .... BU1032//     Author ORD .. -1//     Royalty % ... 0////     Author ID ... 672-71-3249//     Title ID .... TC7777//     Author ORD .. -1//     Royalty % ... 40////     Legend://     An Author ORD of -1 means no value is defined.//     A Royalty % of 0 means no value is defined.

Class Sample    ' Define the "titleAuthor" table of the Microsoft "pubs" database.     Public Structure titleAuthor       ' Author ID; format ###-##-####        Public au_id As String        ' Title ID; format AA####        Public title_id As String        ' Author ORD is nullable.        Public au_ord As Nullable(Of Short)        ' Royalty Percent is nullable.        Public royaltyper As Nullable(Of Integer)    End Structure         Public Shared Sub Main()        ' Declare and initialize the titleAuthor array.        Dim ta(2) As titleAuthor        ta(0).au_id = "712-32-1176"        ta(0).title_id = "PS3333"        ta(0).au_ord = 1        ta(0).royaltyper = 100                ta(1).au_id = "213-46-8915"        ta(1).title_id = "BU1032"        ta(1).au_ord = Nothing        ta(1).royaltyper = Nothing                ta(2).au_id = "672-71-3249"        ta(2).title_id = "TC7777"        ta(2).au_ord = Nothing        ta(2).royaltyper = 40               ' Display the values of the titleAuthor array elements, and        ' display a legend.        Display("Title Authors Table", ta)        Console.WriteLine("Legend:")        Console.WriteLine("An Author ORD of -1 means no value is defined.")        Console.WriteLine("A Royalty % of 0 means no value is defined.")    End Sub        ' Display the values of the titleAuthor array elements.    Public Shared Sub Display(ByVal dspTitle As String, _                              ByVal dspAllTitleAuthors() As titleAuthor)         Console.WriteLine("*** {0} ***", dspTitle)        Dim dspTA As titleAuthor        For Each dspTA In dspAllTitleAuthors            Console.WriteLine("Author ID ... {0}", dspTA.au_id)            Console.WriteLine("Title ID .... {0}", dspTA.title_id)            Console.WriteLine("Author ORD .. {0}", dspTA.au_ord.GetValueOrDefault(-1))            Console.WriteLine("Royalty % ... {0}", dspTA.royaltyper.GetValueOrDefault(0))            Console.WriteLine()        Next     End SubEnd Class 'This example displays the following output:'     *** Title Authors Table ***'     Author ID ... 712-32-1176'     Title ID .... PS3333'     Author ORD .. 1'     Royalty % ... 100'     '     Author ID ... 213-46-8915'     Title ID .... BU1032'     Author ORD .. -1'     Royalty % ... 0'     '     Author ID ... 672-71-3249'     Title ID .... TC7777'     Author ORD .. -1'     Royalty % ... 40'     '     Legend:'     An Author ORD of -1 means no value is defined.'     A Royalty % of 0 means no value is defined.

Remarks

For more information about this API, seeSupplemental API remarks for Nullable<T>.

See also

• Nullable
• Nullable Types (C# Programming Guide)
• Nullable Value Types (Visual Basic)