System Namespace


.NET Framework Class Library
Guid Structure

Represents a globally unique identifier (GUID).

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)
Syntax
Visual Basic (Declaration) 
<SerializableAttribute> _
<ComVisibleAttribute(True)> _
Public Structure Guid _
    Implements IFormattable, IComparable, IComparable(Of Guid),  _
    IEquatable(Of Guid)
Visual Basic (Usage) 
Dim instance As Guid
C# 
[SerializableAttribute]
[ComVisibleAttribute(true)]
public struct Guid : IFormattable, IComparable, 
    IComparable<Guid>, IEquatable<Guid>
Visual C++ 
[SerializableAttribute]
[ComVisibleAttribute(true)]
public value class Guid : IFormattable, IComparable, 
    IComparable<Guid>, IEquatable<Guid>
JScript 
JScript supports the use of structures, but not the declaration of new ones.
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 code sample demonstrates how to attach and read a Guid object as an attribute on a user-defined class or interface.

Visual Basic 
Imports System
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 MyTestClass
    Implements IMyInterface

    ' Run regasm on this assembly to create .reg and .tlb files.
    ' Reg file can be used to register this coclass in the registry.
    ' Tlb file will be used to do interop.
    Public Sub MyMethod() Implements IMyInterface.MyMethod
    End Sub

    Public Shared Sub Main()
        ' Example addresses the following in System.Runtime.InterOpServices.GuidAttribute.
        ' How to specify the attribute on interface/coclass.
        ' Retrieve the GuidAttribute from an interface/coclass.
        ' Value property on GuidAttribute class.
        ' Example addresses the following in System.Guid.
        ' Constructor Guid(string).
        ' Constructor Guid(ByteArray).
        ' Equals.
        ' Operator ==.
        ' CompareTo.
        Dim IMyInterfaceAttribute As Attribute = Attribute.GetCustomAttribute(GetType(IMyInterface), GetType(GuidAttribute))

        ' The Value property of GuidAttribute returns a string. 
        System.Console.WriteLine("IMyInterface Attribute: " + CType(IMyInterfaceAttribute, GuidAttribute).Value)

        ' 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
            System.Console.WriteLine("myGuid1 equals myGuid2")
        Else
            System.Console.WriteLine("myGuid1 not equals myGuid2")
        End If 
        ' Equality operator can also be used to determine if two guids have same value.
        If myGuid1.ToString() = myGuid2.ToString() Then
            System.Console.WriteLine("myGuid1 == myGuid2")
        Else
            System.Console.WriteLine("myGuid1 != myGuid2")
        End If
        ' CompareTo returns 0 if the guids have same value.
        If myGuid1.CompareTo(myGuid2) = 0 Then
            System.Console.WriteLine("myGuid1 compares to myGuid2")
        Else
            System.Console.WriteLine("myGuid1 does not compare to myGuid2")
        End If 

        System.Console.ReadLine()

        'Output:
        'IMyInterface Attribute: F9168C5E-CEB2-4faa-B6BF-329BF39FA1E4
        'myGuid1 equals myGuid2
        'myGuid1 == myGuid2
        'myGuid1 compares to myGuid2
    End Sub
End Class
C# 
using System;
using System.Runtime.InteropServices;

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

// Guid for the coclass MyTestClass.
[Guid("936DA01F-9ABD-4d9d-80C7-02AF85C822A8")]
public class MyTestClass : IMyInterface
{
    // Run regasm on this assembly to create .reg and .tlb files.
    // Reg file can be used to register this coclass in the registry.
    // Tlb file will be used to do interop.

    public void MyMethod() {}

    public static void Main( string []args )
    {
        // Example addresses the following in System.Runtime.InterOpServices.GuidAttribute.
        // How to specify the attribute on interface/coclass.
        // Retrieve the GuidAttribute from an interface/coclass.
        // Value property on GuidAttribute class.

        // Example addresses the following in System.Guid.
        // Constructor Guid(string).
        // Constructor Guid(ByteArray).
        // Equals.
        // Operator ==.
        // CompareTo.

        Attribute IMyInterfaceAttribute = Attribute.GetCustomAttribute( typeof( IMyInterface ), typeof( GuidAttribute ) );

        // The Value property of GuidAttribute returns a string. 
        System.Console.WriteLine( "IMyInterface Attribute: " + ((GuidAttribute)IMyInterfaceAttribute).Value );    

        // 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 ) )
            System.Console.WriteLine( "myGuid1 equals myGuid2" );
        else
            System.Console.WriteLine( "myGuid1 not equals myGuid2" );

        // Equality operator can also be used to determine if two guids have same value.
        if ( myGuid1 == myGuid2 )
            System.Console.WriteLine( "myGuid1 == myGuid2" );
        else
            System.Console.WriteLine( "myGuid1 != myGuid2" );

        // CompareTo returns 0 if the guids have same value.
        if ( myGuid1.CompareTo( myGuid2 ) == 0 )
            System.Console.WriteLine( "myGuid1 compares to myGuid2" );
        else
            System.Console.WriteLine( "myGuid1 does not compare to myGuid2" );

        System.Console.ReadLine();

        //Output.
        //IMyInterface Attribute: F9168C5E-CEB2-4faa-B6BF-329BF39FA1E4
        //myGuid1 equals myGuid2
        //myGuid1 == myGuid2
        //myGuid1 compares to myGuid2
    }
}
Visual C++ 
using namespace System;
using namespace System::Runtime::InteropServices;

// Guid for the interface IMyInterface.

[Guid("F9168C5E-CEB2-4faa-B6BF-329BF39FA1E4")]
public interface class IMyInterface
{
public:
   void MyMethod();
};


// Guid for the coclass MyTestClass.

[Guid("936DA01F-9ABD-4d9d-80C7-02AF85C822A8")]
public ref class MyTestClass: public IMyInterface
{
public:

   // Run regasm on this assembly to create .reg and .tlb files.
   // Reg file can be used to register this coclass in the registry.
   // Tlb file will be used to do interop.
   virtual void MyMethod(){}
};

int main()
{
   // Example addresses the following in System.Runtime.InterOpServices.GuidAttribute.
   // How to specify the attribute on interface/coclass.
   // Retrieve the GuidAttribute from an interface/coclass.
   // Value property on GuidAttribute class.
   // Example addresses the following in System.Guid.
   // Constructor Guid(string).
   // Constructor Guid(ByteArray).
   // Equals.
   // Operator ==.
   // CompareTo.
   Attribute^ IMyInterfaceAttribute = Attribute::GetCustomAttribute( IMyInterface::typeid, GuidAttribute::typeid );

   // The Value property of GuidAttribute returns a string. 
   System::Console::WriteLine( String::Concat(  "IMyInterface Attribute: ", (dynamic_cast<GuidAttribute^>(IMyInterfaceAttribute))->Value ) );

   // Using the string to create a guid.
   Guid myGuid1 = Guid(dynamic_cast<GuidAttribute^>(IMyInterfaceAttribute)->Value);

   // Using a byte array to create a guid.
   Guid myGuid2 = Guid(myGuid1.ToByteArray());

   // Equals is overridden and so value comparison is done though references are different.
   if ( myGuid1.Equals( myGuid2 ) )
      System::Console::WriteLine(  "myGuid1 equals myGuid2" );
   else
      System::Console::WriteLine(  "myGuid1 not equals myGuid2" );

   // Equality operator can also be used to determine if two guids have same value.
   if ( myGuid1 == myGuid2 )
      System::Console::WriteLine(  "myGuid1 == myGuid2" );
   else
      System::Console::WriteLine(  "myGuid1 != myGuid2" );

   // CompareTo returns 0 if the guids have same value.
   if ( myGuid1.CompareTo( myGuid2 ) == 0 )
      System::Console::WriteLine(  "myGuid1 compares to myGuid2" );
   else
      System::Console::WriteLine(  "myGuid1 does not compare to myGuid2" );

   //Output.
   //IMyInterface Attribute: F9168C5E-CEB2-4faa-B6BF-329BF39FA1E4
   //myGuid1 equals myGuid2
   //myGuid1 == myGuid2
   //myGuid1 compares to myGuid2
}
JScript 
import System;
import System.Runtime.InteropServices;

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

// Guid for the coclass MyTestClass.
public Guid("936DA01F-9ABD-4d9d-80C7-02AF85C822A8") class MyTestClass implements IMyInterface
{
    // Run regasm on this assembly to create .reg and .tlb files.
    // Reg file can be used to register this coclass in the registry.
    // Tlb file will be used to do interop.

    public function MyMethod() {}

    public static function Main()
    {
        // Example addresses the following in System.Runtime.InterOpServices.GuidAttribute.
        // How to specify the attribute on interface/coclass.
        // Retrieve the GuidAttribute from an interface/coclass.
        // Value property on GuidAttribute class.

        // Example addresses the following in System.Guid.
        // Constructor Guid(string).
        // Constructor Guid(ByteArray).
        // Equals.
        // Operator ==.
        // CompareTo.

        var IMyInterfaceAttribute : Attribute = Attribute.GetCustomAttribute(Type.GetType("IMyInterface"), GuidAttribute);

        // The Value property of GuidAttribute returns a string. 
        System.Console.WriteLine( "IMyInterface Attribute: " + (GuidAttribute(IMyInterfaceAttribute)).Value );    

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

        // Equals is overridden and so value comparison is done though references are different.
        if ( myGuid1.Equals( myGuid2 ) )
            System.Console.WriteLine( "myGuid1 equals myGuid2" );
        else
            System.Console.WriteLine( "myGuid1 not equals myGuid2" );

        // Equality operator can also be used to determine if two guids have same value.
        if ( myGuid1 == myGuid2 )
            System.Console.WriteLine( "myGuid1 == myGuid2" );
        else
            System.Console.WriteLine( "myGuid1 != myGuid2" );

        // CompareTo returns 0 if the guids have same value.
        if ( myGuid1.CompareTo( myGuid2 ) == 0 )
            System.Console.WriteLine( "myGuid1 compares to myGuid2" );
        else
            System.Console.WriteLine( "myGuid1 does not compare to myGuid2" );

        System.Console.ReadLine();

        //Output.
        //IMyInterface Attribute: F9168C5E-CEB2-4faa-B6BF-329BF39FA1E4
        //myGuid1 equals myGuid2
        //myGuid1 == myGuid2
        //myGuid1 compares to myGuid2
    }
}

MyTestClass.Main();
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.
Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
Version Information

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0
See Also

Reference

Guid Members
System Namespace
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Community Content

CSharpUniversity.com
Don't try to create your own unique identifier-use a GUID
If you are developing an application and you need to ensure that something like a filename is unique, use a GUID. Don't try to come up with your own unique identifier. You can even use a GUID appended with another string that makes sense in your application. To see an example where a GUID is used to create a unique image file name on the web server when a file is uploaded please see:
http://www.csharpuniversity.com/2009/03/05/uploading-files-and-validating-them-using-the-aspnet-fileupload-and-customvalidator-controls/

Tags : contentbug

jmiller_2308
XML Serializing a guid
This class serializes beutifully with output that includes a microsoft.com.wsdl.types.xsd file complete with restrictions on a simpleType based off an xsd:string. How do they do that?

I would like to do the same for other types of restricted simpleTypes but when I create a ref class in C++/CLI it results in a complexType being serialized out. Clearly I am missing something. Is there example code that shows exactly how guid does this? Perhaps, is there even guid code available to look at?
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