String.GetHashCode String.GetHashCode String.GetHashCode String.GetHashCode Method

Definizione

Overload

GetHashCode(ReadOnlySpan<Char>, StringComparison) GetHashCode(ReadOnlySpan<Char>, StringComparison) GetHashCode(ReadOnlySpan<Char>, StringComparison) GetHashCode(ReadOnlySpan<Char>, StringComparison)
GetHashCode(StringComparison) GetHashCode(StringComparison) GetHashCode(StringComparison) GetHashCode(StringComparison)
GetHashCode(ReadOnlySpan<Char>) GetHashCode(ReadOnlySpan<Char>) GetHashCode(ReadOnlySpan<Char>) GetHashCode(ReadOnlySpan<Char>)
GetHashCode() GetHashCode() GetHashCode() GetHashCode()

Restituisce il codice hash di questa stringa.Returns the hash code for this string.

GetHashCode(ReadOnlySpan<Char>, StringComparison) GetHashCode(ReadOnlySpan<Char>, StringComparison) GetHashCode(ReadOnlySpan<Char>, StringComparison) GetHashCode(ReadOnlySpan<Char>, StringComparison)

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

Parametri

Restituisce

GetHashCode(StringComparison) GetHashCode(StringComparison) GetHashCode(StringComparison) GetHashCode(StringComparison)

public:
 int GetHashCode(StringComparison comparisonType);
public int GetHashCode (StringComparison comparisonType);
override this.GetHashCode : StringComparison -> int
Public Function GetHashCode (comparisonType As StringComparison) As Integer

Parametri

Restituisce

GetHashCode(ReadOnlySpan<Char>) GetHashCode(ReadOnlySpan<Char>) GetHashCode(ReadOnlySpan<Char>) GetHashCode(ReadOnlySpan<Char>)

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

Parametri

Restituisce

GetHashCode() GetHashCode() GetHashCode() GetHashCode()

Restituisce il codice hash di questa stringa.Returns the hash code for this string.

public:
 override int GetHashCode();
public override int GetHashCode ();
override this.GetHashCode : unit -> int
Public Overrides Function GetHashCode () As Integer

Restituisce

Codice hash di un intero con segno a 32 bit.A 32-bit signed integer hash code.

Esempi

Nell'esempio seguente viene illustrato il GetHashCode metodo tramite varie funzionalità di stringhe di input.The following example demonstrates the GetHashCode method using various input strings.

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
*/
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

Commenti

Il comportamento di GetHashCode dipende dalla relativa implementazione, che potrebbe variare da una versione di common language runtime a un altro.The behavior of GetHashCode is dependent on its implementation, which might change from one version of the common language runtime to another. È un motivo per cui questo può verificarsi per migliorare le prestazioni di GetHashCode.A reason why this might happen is to improve the performance of GetHashCode.

Importante

Se due oggetti stringa sono uguali, la GetHashCode metodo restituisce valori identici.If two string objects are equal, the GetHashCode method returns identical values. Tuttavia, non c'è un valore di codice hash univoco per ogni valore di stringa univoco.However, there is not a unique hash code value for each unique string value. Stringhe diverse possono restituire lo stesso codice hash.Different strings can return the same hash code.

Il codice hash non è garantito a essere stabile.The hash code itself is not guaranteed to be stable. I codici hash per stringhe identiche possono differire tra le implementazioni di .NET, tra le versioni di .NET e nelle piattaforme .NET (ad esempio 32 bit e 64 bit) per una singola versione di .NET.Hash codes for identical strings can differ across .NET implementations, across .NET versions, and across .NET platforms (such as 32-bit and 64-bit) for a single version of .NET. In alcuni casi, possono anche differire dal dominio applicazione.In some cases, they can even differ by application domain. Ciò significa che due esecuzioni successive dello stesso programma possono restituire codici hash differenti.This implies that two subsequent runs of the same program may return different hash codes.

Di conseguenza, i codici non devono mai essere usati all'esterno del dominio applicazione in cui sono stati creati, hash non deve mai essere usati come campi di chiave in una raccolta e non deve essere persistente.As a result, hash codes should never be used outside of the application domain in which they were created, they should never be used as key fields in a collection, and they should never be persisted.

Infine, non usare il codice hash anziché un valore restituito da una funzione hash di crittografia se è necessario un hash crittografico.Finally, don't use the hash code instead of a value returned by a cryptographic hashing function if you need a cryptographically strong hash. Per gli hash di crittografia, usare una classe derivata dal System.Security.Cryptography.HashAlgorithm o System.Security.Cryptography.KeyedHashAlgorithm classe.For cryptographic hashes, use a class derived from the System.Security.Cryptography.HashAlgorithm or System.Security.Cryptography.KeyedHashAlgorithm class.

Per altre informazioni sui codici hash, vedere Object.GetHashCode.For more information about hash codes, see Object.GetHashCode.

Nelle App desktop, è possibile usare la <UseRandomizedStringHashAlgorithm > elemento per generare codice hash univoco su una base al dominio dell'applicazione.In desktop apps, you can use the <UseRandomizedStringHashAlgorithm> element to generate unique hash codes on a per application domain basis. Ciò può ridurre il numero di conflitti e migliorare le prestazioni complessive di inserimenti e le ricerche che usano tabelle hash.This can reduce the number of collisions and improve the overall performance of insertions and lookups that use hash tables. Nell'esempio seguente viene illustrato come utilizzare il <UseRandomizedStringHashAlgorithm > elemento.The following example shows how to use the <UseRandomizedStringHashAlgorithm> element. Definisce un DisplayString classe che include una costante di stringa privata, s, il cui valore è "This is a una stringa".It defines a DisplayString class that includes a private string constant, s, whose value is "This is a string." Viene inoltre incluso un metodo ShowStringHashCode tramite cui vengono visualizzati il valore stringa e il codice hash con il nome del dominio applicazione in cui il metodo è in esecuzione.It also includes a ShowStringHashCode method that displays the string value and its hash code along with the name of the application domain in which the method is executing.

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());
   }
}
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

Quando si esegue l'esempio senza fornire un file di configurazione, restituisce un output analogo al seguente.When you run the example without supplying a configuration file, it displays output similar to the following. Si noti che i codici hash per la stringa sono identici nei due domini applicazione.Note that the hash codes for the string are identical in the two application domains.

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

Tuttavia, se si aggiunge il file di configurazione seguente alla directory di esempio e, successivamente, si esegue l'esempio, i codici hash per la stessa stringa risulteranno diversi dal dominio dell'applicazione.However, if you add the following configuration file to the example's directory and then run the example, the hash codes for the same string will differ by application domain.

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

Quando il file di configurazione è presente, l'esempio visualizza il seguente output:When the configuration file is present, the example displays the following output:

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

Importante

I codici hash vengono usati per inserire e recuperare gli oggetti con chiavi da tabelle hash in modo efficiente.Hash codes are used to insert and retrieve keyed objects from hash tables efficiently. Tuttavia, i codici hash non identificano in modo univoco le stringhe.However, hash codes don't uniquely identify strings. Stringhe identiche con codici hash uguali, ma common language runtime può anche assegnare lo stesso codice hash per stringhe diverse.Identical strings have equal hash codes, but the common language runtime can also assign the same hash code to different strings. Inoltre, i codici hash possono variare dalla versione di .NET, platform all'interno di una sola versione e dal dominio applicazione.In addition, hash codes can vary by version of .NET, by platform within a single version, and by application domain. Per questo motivo, è consigliabile non serializzare o mantenere i valori di codice hash, né utilizzarle come chiavi in una tabella hash o un dizionario.Because of this, you should not serialize or persist hash code values, nor should you use them as keys in a hash table or dictionary.

Per altre informazioni sull'uso dei codici hash e il GetHashCode metodo, vedere Object.GetHashCode.For additional information about the use of hash codes and the GetHashCode method, see Object.GetHashCode.

Note per i chiamanti

Il valore restituito da GetHashCode() dipende dalla piattaforma.The value returned by GetHashCode() is platform-dependent. La differenza nelle versioni a 32 e 64 bit di .NET Framework.It differs on the 32-bit and 64-bit versions of the .NET Framework. Anche possibile differiscono tra le versioni di .NET Framework e .NET Core.It also can differ between versions of the .NET Framework and .NET Core.

Vedi anche

Si applica a