String.GetHashCode Method (System) (2024)

Source:: String.Comparison.cs

Source:: String.Comparison.cs

Source:: String.Comparison.cs

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

Returns

Int32

A 32-bit signed integer hash code.

Examples

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*/

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

Remarks

The behavior of GetHashCode is dependent on its implementation, which might change from one version of the common language runtime to another. A reason why this might happen is to improve the performance of GetHashCode.

Important

If two string objects are equal, the GetHashCode method returns identical values. However, there is not a unique hash code value for each unique string value. Different strings can return the same hash code.

The hash code itself is not guaranteed to be stable. 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 some cases, they can even differ by application domain. This implies that two subsequent runs of the same program may return different hash codes.

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.

Finally, don't use the hash code instead of a value returned by a cryptographic hashing function if you need a cryptographically strong hash. For cryptographic hashes, use a class derived from the System.Security.Cryptography.HashAlgorithm or System.Security.Cryptography.KeyedHashAlgorithm class.

For more information about hash codes, see Object.GetHashCode.

In .NET Framework desktop apps, you can use the <UseRandomizedStringHashAlgorithm> element to generate unique hash codes on a per-application domain basis. This can reduce the number of collisions and improve the overall performance of insertions and lookups that use hash tables. The following example shows how to use the <UseRandomizedStringHashAlgorithm> element. It defines a DisplayString class that includes a private string constant, s, whose value is "This is a string." 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()); }}

open Systemtype 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 SubEnd ModulePublic 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 SubEnd Class

When you run the example without supplying a configuration file, it displays output similar to the following. Note that the hash codes for the string are identical in the two application domains.

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

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>

When the configuration file is present, the example displays the following output:

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

Important

Hash codes are used to insert and retrieve keyed objects from hash tables efficiently. However, hash codes don't uniquely identify strings. Identical strings have equal hash codes, but the common language runtime can also assign the same hash code to different strings. In addition, hash codes can vary by version of .NET, by platform within a single version, and by application domain. 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.

For additional information about the use of hash codes and the GetHashCode method, see Object.GetHashCode.

Notes to Callers

The value returned by GetHashCode() is platform-dependent. It differs on the 32-bit and 64-bit versions of .NET Framework. It also can differ between versions of .NET Framework and .NET Core.

Applies to