String.GetHashCode 方法

參考

定義

命名空間:: System

組件:: System.Runtime.dll

組件:: netstandard.dll

組件:: mscorlib.dll

重要

部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。

多載

GetHashCode(ReadOnlySpan<Char>, StringComparison)	使用指定的規則，傳回所提供唯讀字元範圍的雜湊碼。
GetHashCode(StringComparison)	使用指定規則傳回這個字串的雜湊碼。
GetHashCode(ReadOnlySpan<Char>)	傳回所提供唯讀字元範圍的雜湊碼。
GetHashCode()	傳回這個字串的雜湊碼。

GetHashCode(ReadOnlySpan<Char>, StringComparison)

來源:: String.Comparison.cs

來源:: String.Comparison.cs

來源:: String.Comparison.cs

使用指定的規則，傳回所提供唯讀字元範圍的雜湊碼。

public:
 static int GetHashCode(ReadOnlySpan<char> value, StringComparison comparisonType);

public static int GetHashCode (ReadOnlySpan<char> value, StringComparison comparisonType);

static member GetHashCode : ReadOnlySpan<char> * StringComparison -> int

Public Shared Function GetHashCode (value As ReadOnlySpan(Of Char), comparisonType As StringComparison) As Integer

參數

value: ReadOnlySpan<Char>

唯讀的字元範圍。

comparisonType: StringComparison

其中一個列舉值，指定要用於比較的規則。

傳回

Int32

32 位元帶正負號的整數雜湊碼。

適用於

GetHashCode(StringComparison)

來源:: String.Comparison.cs

來源:: String.Comparison.cs

來源:: String.Comparison.cs

使用指定規則傳回這個字串的雜湊碼。

public:
 int GetHashCode(StringComparison comparisonType);

public int GetHashCode (StringComparison comparisonType);

override this.GetHashCode : StringComparison -> int

Public Function GetHashCode (comparisonType As StringComparison) As Integer

參數

comparisonType: StringComparison

其中一個列舉值，指定要用於比較的規則。

傳回

Int32

32 位元帶正負號的整數雜湊碼。

適用於

GetHashCode(ReadOnlySpan<Char>)

來源:: String.Comparison.cs

來源:: String.Comparison.cs

來源:: String.Comparison.cs

傳回所提供唯讀字元範圍的雜湊碼。

public:
 static int GetHashCode(ReadOnlySpan<char> value);

public static int GetHashCode (ReadOnlySpan<char> value);

static member GetHashCode : ReadOnlySpan<char> -> int

Public Shared Function GetHashCode (value As ReadOnlySpan(Of Char)) As Integer

參數

value: ReadOnlySpan<Char>

唯讀的字元範圍。

傳回

Int32

32 位元帶正負號的整數雜湊碼。

適用於

GetHashCode()

來源:: String.Comparison.cs

來源:: String.Comparison.cs

來源:: String.Comparison.cs

傳回這個字串的雜湊碼。

public:
 override int GetHashCode();

public override int GetHashCode ();

override this.GetHashCode : unit -> int

Public Overrides Function GetHashCode () As Integer

傳回

Int32

32 位元帶正負號的整數雜湊碼。

範例

下列範例示範 GetHashCode 使用各種輸入字串的方法。

using namespace System;

void DisplayHashCode( String^ Operand )
{
   int HashCode = Operand->GetHashCode();
   Console::WriteLine( "The hash code for \"{0}\" is: 0x{1:X8}, {1}", Operand, HashCode );
}

int main()
{
   DisplayHashCode( "" );
   DisplayHashCode( "a" );
   DisplayHashCode( "ab" );
   DisplayHashCode( "abc" );
   DisplayHashCode( "abd" );
   DisplayHashCode( "abe" );
   DisplayHashCode( "abcdef" );
   DisplayHashCode( "abcdeg" );
   DisplayHashCode( "abcdeh" );
   DisplayHashCode( "abcdei" );
   DisplayHashCode( "Abcdeg" );
   DisplayHashCode( "Abcdeh" );
   DisplayHashCode( "Abcdei" );
}

/*
This example displays output like the following:
      The hash code for "" is: 0x2D2816FE, 757602046
      The hash code for "a" is: 0xCDCAB7BF, -842352705
      The hash code for "ab" is: 0xCDE8B7BF, -840386625
      The hash code for "abc" is: 0x2001D81A, 536991770
      The hash code for "abd" is: 0xC2A94CB5, -1029092171
      The hash code for "abe" is: 0x6550C150, 1699791184
      The hash code for "abcdef" is: 0x1762906D, 392335469
      The hash code for "abcdeg" is: 0x1763906D, 392401005
      The hash code for "abcdeh" is: 0x175C906D, 391942253
      The hash code for "abcdei" is: 0x175D906D, 392007789
      The hash code for "Abcdeg" is: 0x1763954D, 392402253
      The hash code for "Abcdeh" is: 0x175C954D, 391943501
      The hash code for "Abcdei" is: 0x175D954D, 392009037
*/

using System;

class GetHashCode 
{
    public static void Main() 
    {
        DisplayHashCode( "" );
        DisplayHashCode( "a" );
        DisplayHashCode( "ab" );
        DisplayHashCode( "abc" );
        DisplayHashCode( "abd" );
        DisplayHashCode( "abe" );
        DisplayHashCode( "abcdef" );
        DisplayHashCode( "abcdeg" );
        DisplayHashCode( "abcdeh" );
        DisplayHashCode( "abcdei" );
        DisplayHashCode( "Abcdeg" );
        DisplayHashCode( "Abcdeh" );
        DisplayHashCode( "Abcdei" );
    }

    static void DisplayHashCode( String Operand )
    {
        int     HashCode = Operand.GetHashCode( );
        Console.WriteLine("The hash code for \"{0}\" is: 0x{1:X8}, {1}",
                          Operand, HashCode );
    }
}
/*
      This example displays output like the following:
      The hash code for "" is: 0x2D2816FE, 757602046
      The hash code for "a" is: 0xCDCAB7BF, -842352705
      The hash code for "ab" is: 0xCDE8B7BF, -840386625
      The hash code for "abc" is: 0x2001D81A, 536991770
      The hash code for "abd" is: 0xC2A94CB5, -1029092171
      The hash code for "abe" is: 0x6550C150, 1699791184
      The hash code for "abcdef" is: 0x1762906D, 392335469
      The hash code for "abcdeg" is: 0x1763906D, 392401005
      The hash code for "abcdeh" is: 0x175C906D, 391942253
      The hash code for "abcdei" is: 0x175D906D, 392007789
      The hash code for "Abcdeg" is: 0x1763954D, 392402253
      The hash code for "Abcdeh" is: 0x175C954D, 391943501
      The hash code for "Abcdei" is: 0x175D954D, 392009037
*/

let displayHashCode operand =
    let hashCode = operand.GetHashCode()
    printfn $"The hash code for \"%s{operand}\" is: 0x{1:X8}, {hashCode}"

displayHashCode ""
displayHashCode "a"
displayHashCode "ab"
displayHashCode "abc"
displayHashCode "abd"
displayHashCode "abe"
displayHashCode "abcdef"
displayHashCode "abcdeg"
displayHashCode "abcdeh"
displayHashCode "abcdei"
displayHashCode "Abcdeg"
displayHashCode "Abcdeh"
displayHashCode "Abcdei"

(*
      This example displays output like the following:
      The hash code for "" is: 0x2D2816FE, 757602046
      The hash code for "a" is: 0xCDCAB7BF, -842352705
      The hash code for "ab" is: 0xCDE8B7BF, -840386625
      The hash code for "abc" is: 0x2001D81A, 536991770
      The hash code for "abd" is: 0xC2A94CB5, -1029092171
      The hash code for "abe" is: 0x6550C150, 1699791184
      The hash code for "abcdef" is: 0x1762906D, 392335469
      The hash code for "abcdeg" is: 0x1763906D, 392401005
      The hash code for "abcdeh" is: 0x175C906D, 391942253
      The hash code for "abcdei" is: 0x175D906D, 392007789
      The hash code for "Abcdeg" is: 0x1763954D, 392402253
      The hash code for "Abcdeh" is: 0x175C954D, 391943501
      The hash code for "Abcdei" is: 0x175D954D, 392009037
*)

Module GetHashCode
    Sub Main()
        DisplayHashCode("")
        DisplayHashCode("a")
        DisplayHashCode("ab")
        DisplayHashCode("abc")
        DisplayHashCode("abd")
        DisplayHashCode("abe")
        DisplayHashCode("abcdef")
        DisplayHashCode("abcdeg")
        DisplayHashCode("abcdeh")
        DisplayHashCode("abcdei")
        DisplayHashCode("Abcdeg")
        DisplayHashCode("Abcdeh")
        DisplayHashCode("Abcdei")
    End Sub
       
    Sub DisplayHashCode(Operand As String)
        Dim HashCode As Integer = Operand.GetHashCode()
        Console.WriteLine("The hash code for ""{0}"" is: 0x{1:X8}, {1}", 
                          Operand, HashCode)
    End Sub 
End Module 
' This example displays output like the following:
'       The hash code for "" is: 0x2D2816FE, 757602046
'       The hash code for "a" is: 0xCDCAB7BF, -842352705
'       The hash code for "ab" is: 0xCDE8B7BF, -840386625
'       The hash code for "abc" is: 0x2001D81A, 536991770
'       The hash code for "abd" is: 0xC2A94CB5, -1029092171
'       The hash code for "abe" is: 0x6550C150, 1699791184
'       The hash code for "abcdef" is: 0x1762906D, 392335469
'       The hash code for "abcdeg" is: 0x1763906D, 392401005
'       The hash code for "abcdeh" is: 0x175C906D, 391942253
'       The hash code for "abcdei" is: 0x175D906D, 392007789
'       The hash code for "Abcdeg" is: 0x1763954D, 392402253
'       The hash code for "Abcdeh" is: 0x175C954D, 391943501
'       The hash code for "Abcdei" is: 0x175D954D, 392009037

備註

的行為 GetHashCode 取決於其實作，可能會從一個版本的 Common Language Runtime 變更為另一個版本。原因可能是改善的 GetHashCode效能。

重要

如果兩個字串物件相等，方法 GetHashCode 會傳回相同的值。不過，每個唯一字串值沒有唯一的哈希碼值。不同的字串可以傳回相同的哈希碼。

哈希程式代碼本身不保證穩定。相同字串的哈希碼在 .NET 實作、.NET 版本之間，以及 .NET 平臺 (之間的哈希碼可能會有所不同，例如 32 位和 64 位) 的單一 .NET 版本。在某些情況下，它們甚至可以因應用程式域而有所不同。這表示相同程序的後續兩次執行可能會傳回不同的哈希碼。

如此一來，哈希程式代碼就不應該在建立的應用程式域之外使用，它們不應該當做集合中的索引鍵字段使用，而且絕對不應該保存。

最後，如果您需要密碼編譯強式哈希，請勿使用哈希碼，而不是密碼編譯哈希函式所傳回的值。針對密碼編譯哈希，請使用衍生自或 System.Security.Cryptography.KeyedHashAlgorithm 類別的System.Security.Cryptography.HashAlgorithm類別。

如需哈希碼的詳細資訊，請參閱 Object.GetHashCode。

在 .NET Framework 傳統型應用程式中，您可以使用<UseRandomizedStringHashAlgorithm>元素，根據每個應用程式域產生唯一的哈希碼。這可減少衝突數目，並改善使用哈希表之插入和查閱的整體效能。下列範例示範如何使用 <UseRandomizedStringHashAlgorithm> 元素。它會定義類別 DisplayString ，其中包含私用字串常數， s其值為 “This is a string”。它也包含 ShowStringHashCode 方法，其會顯示字串值及其哈希程式代碼，以及執行方法的應用程式域名稱。

using System;

public class Example
{
   public static void Main()
   {
      // Show hash code in current domain.
      DisplayString display = new DisplayString();
      display.ShowStringHashCode();
      
      // Create a new app domain and show string hash code.
      AppDomain domain = AppDomain.CreateDomain("NewDomain");
      var display2 = (DisplayString) domain.CreateInstanceAndUnwrap(typeof(Example).Assembly.FullName, 
                                                          "DisplayString");   
      display2.ShowStringHashCode();
   }
}

public class DisplayString : MarshalByRefObject
{
   private String s = "This is a string.";
   
   public override bool Equals(Object obj)
   {
      String s2 = obj as String; 
      if (s2 == null)
         return false;
      else
         return s == s2; 
   }

   public bool Equals(String str)
   {
      return s == str;
   }    
   
   public override int GetHashCode()
   {
      return s.GetHashCode();
   }
   
   public override String ToString() 
   {
      return s;
   }

   public void ShowStringHashCode()
   {
      Console.WriteLine("String '{0}' in domain '{1}': {2:X8}",
                        s, AppDomain.CurrentDomain.FriendlyName, 
                        s.GetHashCode());
   }
}

open System

type DisplayString() =
    inherit MarshalByRefObject()
    let s = "This is a string."
   
    override _.Equals(obj) =
        match obj with
        | :? string as s2 -> s = s2
        | _ -> false

    member _.Equals(str) =
        s = str
   
    override _.GetHashCode() =
        s.GetHashCode()
   
    override _.ToString() = 
        s

    member _.ShowStringHashCode() =
        printfn $"String '{s}' in domain '{AppDomain.CurrentDomain.FriendlyName}': {s.GetHashCode():X8}"

// Show hash code in current domain.
let display = DisplayString()
display.ShowStringHashCode()

// Create a new app domain and show string hash code.
let domain = AppDomain.CreateDomain "NewDomain"
let display2 = domain.CreateInstanceAndUnwrap(typeof<DisplayString>.Assembly.FullName, "DisplayString") :?> DisplayString   
display2.ShowStringHashCode()

Module Example
   Public Sub Main()
      ' Show hash code in current domain.
      Dim display As New DisplayString()
      display.ShowStringHashCode()
      
      ' Create a new app domain and show string hash code.
      Dim domain As AppDomain = AppDomain.CreateDomain("NewDomain")
      Dim display2 = CType(domain.CreateInstanceAndUnwrap(GetType(Example).Assembly.FullName, 
                                                          "DisplayString"), DisplayString)   
      display2.ShowStringHashCode()
   End Sub
End Module

Public Class DisplayString : Inherits MarshalByRefObject

   Private s As String = "This is a string."
   
   Public Overrides Function Equals(obj As Object) As Boolean
      Dim s2 As String = TryCast(obj, String)
      If s2 Is Nothing Then
         Return False
      Else
         Return s = s2 
      End If
   End Function

   Public Overloads Function Equals(str As String) As Boolean
      Return s = str
   End Function    
   
   Public Overrides Function GetHashCode() As Integer
      Return s.GetHashCode()
   End Function
   
   Public Overrides Function ToString() As String
      Return s
   End Function

   Public Sub ShowStringHashCode()
      Console.WriteLine("String '{0}' in domain '{1}': {2:X8}",
                        s, AppDomain.CurrentDomain.FriendlyName, 
                        s.GetHashCode())
   End Sub
End Class

當您在沒有提供組態檔的情況下執行此範例，它會顯示類似下列的輸出。請注意，字串的雜湊碼在兩個應用程式定義域中相同。

String 'This is a string.' in domain 'PerDomain.exe': 941BCEAC
String 'This is a string.' in domain 'NewDomain': 941BCEAC

不過，如果您將下列組態檔加入至範例的目錄，然後執行這個範例，相同字串的雜湊碼將會因為應用程式定義域不同而有所不同。

<?xml version ="1.0"?>
<configuration>
   <runtime>
      <UseRandomizedStringHashAlgorithm enabled="1" />
   </runtime>
</configuration>

當組態檔存在時，這個範例會顯示下列輸出：

String 'This is a string.' in domain 'PerDomain.exe': 5435776D
String 'This is a string.' in domain 'NewDomain': 75CC8236

重要

哈希碼可用來有效率地從哈希表插入和擷取索引鍵物件。不過，哈希碼不會唯一識別字串。相同的字串具有相同的哈希碼，但 Common Language Runtime 也可以將相同的哈希程式代碼指派給不同的字串串。此外，哈希碼可能會因 .NET 版本、單一版本內的平臺和應用程式域而有所不同。因此，您不應該串行化或保存哈希碼值，也不應該將它們當做哈希表或字典中的索引鍵使用。

如需使用哈希碼和 GetHashCode 方法的其他資訊，請參閱 Object.GetHashCode。

給呼叫者的注意事項

所 GetHashCode() 傳回的值與平臺相依。其差異在於32位和64位版本的.NET Framework。它也可以在 .NET Framework 和 .NET Core 的版本之間有所不同。

另請參閱

適用於

共用方式為

String.GetHashCode 方法

定義

多載

GetHashCode(ReadOnlySpan<Char>, StringComparison)

參數

傳回

適用於

GetHashCode(StringComparison)

參數

傳回

適用於

GetHashCode(ReadOnlySpan<Char>)

參數

傳回

適用於

GetHashCode()

傳回

範例

備註

給呼叫者的注意事項

另請參閱

適用於

其他資源