Article
11/18/2011

Guid Structure

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Represents a globally unique identifier (GUID).

Namespace: System
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
<ComVisibleAttribute(True)> _
Public Structure Guid _
    Implements IFormattable, IComparable, IComparable(Of Guid),  _
    IEquatable(Of Guid)

[ComVisibleAttribute(true)]
public struct Guid : IFormattable, IComparable, 
    IComparable<Guid>, IEquatable<Guid>

The Guid type exposes the following members.

Constructors

	Name	Description
	Guid(array<Byte[])	Initializes a new instance of the Guid class using the specified array of bytes.
	Guid(String)	Initializes a new instance of the Guid class using the value represented by the specified string.
	Guid(Int32, Int16, Int16, array<Byte[])	Initializes a new instance of the Guid class using the specified integers and byte array.
	Guid(Int32, Int16, Int16, Byte, Byte, Byte, Byte, Byte, Byte, Byte, Byte)	Initializes a new instance of the Guid class using the specified integers and bytes.

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Methods

	Name	Description
	CompareTo(Guid)	Compares this instance to a specified Guid object and returns an indication of their relative values.
	CompareTo(Object)	Compares this instance to a specified object and returns an indication of their relative values.
	Equals(Guid)	Returns a value indicating whether this instance and a specified Guid object represent the same value.
	Equals(Object)	Returns a value indicating whether this instance is equal to a specified object. (Overrides ValueType.Equals(Object).)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode	Returns the hash code for this instance. (Overrides ValueType.GetHashCode().)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	NewGuid	Initializes a new instance of the Guid class.
	Parse	Converts the string representation of a GUID to the equivalent Guid value.
	ParseExact	Converts the string representation of a GUID to the equivalent Guid value, provided that the string is in the specified format.
	ToByteArray	Returns a 16-element byte array that contains the value of this instance.
	ToString()	Returns a String representation of the value of this instance in registry format. (Overrides ValueType.ToString().)
	ToString(String)	Returns a String representation of the value of this Guid instance, according to the provided format specifier.
	ToString(String, IFormatProvider)	Returns a String representation of the value of this instance of the Guid class, according to the provided format specifier and culture-specific format information.
	TryParse	Converts the string representation of a GUID to the equivalent Guid value.
	TryParseExact	Converts the string representation of a GUID to the equivalent Guid value, provided that the string is in the specified format.

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Operators

	Name	Description
	Equality	Indicates whether the values of two specified Guid objects are equal.
	Inequality	Returns an indication whether the values of two specified Guid objects are not equal.

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Fields

	Name	Description
	Empty	A read-only instance of the Guid class whose value is guaranteed to be all zeroes.

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Remarks

A GUID is a 128-bit integer (16 bytes) that can be used across all computers and networks wherever a unique identifier is required. Such an identifier has a very low probability of being duplicated.

Examples

The following example uses the GuidAttribute class to assign a GUID to a user-defined class and an interface. It retrieves the value of the GUID by calling the Attribute.GetCustomAttribute method and compares it with two other GUIDs to determine whether they are equal.

Imports System.Runtime.InteropServices

' Guid for the interface IMyInterface.
<Guid("F9168C5E-CEB2-4faa-B6BF-329BF39FA1E4")> _
Interface IMyInterface
   Sub MyMethod()
End Interface

' Guid for the coclass MyTestClass.
<Guid("936DA01F-9ABD-4d9d-80C7-02AF85C822A8")> _
Public Class Example
   Implements IMyInterface

   Public Sub MyMethod() Implements IMyInterface.MyMethod
   End Sub

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim IMyInterfaceAttribute As Attribute = Attribute.GetCustomAttribute(GetType(IMyInterface), GetType(GuidAttribute))

      ' The Value property of GuidAttribute returns a string. 
      outputBlock.Text += String.Format("IMyInterface Attribute: " + CType(IMyInterfaceAttribute, GuidAttribute).Value) & vbCrLf

      ' Using the string to create a guid.
      Dim myGuid1 As New Guid(CType(IMyInterfaceAttribute, GuidAttribute).Value)
      ' Using a byte array to create a guid.
      Dim myGuid2 As New Guid(myGuid1.ToByteArray())

      ' Equals is overridden and so value comparison is done though references are different.
      If myGuid1.Equals(myGuid2) Then
         outputBlock.Text &= "myGuid1 equals myGuid2" & vbCrLf
      Else
         outputBlock.Text &= "myGuid1 not equals myGuid2" & vbCrLf
      End If
      ' Equality operator can also be used to determine if two guids have same value.
      If myGuid1.ToString() = myGuid2.ToString() Then
         outputBlock.Text &= "myGuid1 == myGuid2" & vbCrLf
      Else
         outputBlock.Text &= "myGuid1 != myGuid2" & vbCrLf
      End If
   End Sub
End Class
' The example displays the following output:
'       IMyInterface Attribute: F9168C5E-CEB2-4faa-B6BF-329BF39FA1E4
'       myGuid1 equals myGuid2
'       myGuid1 == myGuid2

using System;
using System.Runtime.InteropServices;

// Guid for the interface IMyInterface.
[Guid("F9168C5E-CEB2-4faa-B6BF-329BF39FA1E4")]
interface IMyInterface
{
   void MyMethod();
}

// Guid for MyTestClass.
[Guid("936DA01F-9ABD-4d9d-80C7-02AF85C822A8")]
public class Example : IMyInterface
{
   public void MyMethod() { }

   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      Attribute IMyInterfaceAttribute = Attribute.GetCustomAttribute(typeof(IMyInterface), typeof(GuidAttribute));

      // The Value property of GuidAttribute returns a string. 
      outputBlock.Text += "IMyInterface Attribute: " + ((GuidAttribute)IMyInterfaceAttribute).Value + "\n";

      // Using the string to create a guid.
      Guid myGuid1 = new Guid(((GuidAttribute)IMyInterfaceAttribute).Value);
      // Using a byte array to create a guid.
      Guid myGuid2 = new Guid(myGuid1.ToByteArray());

      // Equals is overridden and so value comparison is done though references are different.
      if (myGuid1.Equals(myGuid2))
         outputBlock.Text += "myGuid1 equals myGuid2" + "\n";
      else
         outputBlock.Text += "myGuid1 not equals myGuid2" + "\n";

      // Equality operator can also be used to determine if two guids have same value.
      if (myGuid1 == myGuid2)
         outputBlock.Text += "myGuid1 == myGuid2" + "\n";
      else
         outputBlock.Text += "myGuid1 != myGuid2" + "\n";
   }
}
// The example displays the following output:
//       IMyInterface Attribute: F9168C5E-CEB2-4faa-B6BF-329BF39FA1E4
//       myGuid1 equals myGuid2
//       myGuid1 == myGuid2

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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