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Guid Structure

.NET Framework 4

Other Versions

Represents a globally unique identifier (GUID).

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

Syntax

C++

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

The Guid type exposes the following members.

Constructors

	Name	Description
	Guid(Byte())	Initializes a new instance of the Guid structure using the specified array of bytes.
	Guid(String)	Initializes a new instance of the Guid structure using the value represented by the specified string.
	Guid(Int32, Int16, Int16, Byte())	Initializes a new instance of the Guid structure 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 structure using the specified integers and bytes.
	Guid(UInt32, UInt16, UInt16, Byte, Byte, Byte, Byte, Byte, Byte, Byte, Byte)	Initializes a new instance of the Guid structure using the specified unsigned 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 that indicates 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 it 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 structure.
	Parse	Converts the string representation of a GUID to the equivalent Guid structure.
	ParseExact	Converts the string representation of a GUID to the equivalent Guid structure, 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 structure, according to the provided format specifier and culture-specific format information.
	TryParse	Converts the string representation of a GUID to the equivalent Guid structure.
	TryParseExact	Converts the string representation of a GUID to the equivalent Guid structure, 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	Indicates 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 structure whose value is all zeros.

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Explicit Interface Implementations

	Name	Description
	IFormattable.ToString	Returns a string representation of the value of this instance, according to the provided format specifier and culture-specific format information.

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

C++

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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
{
    public void MyMethod() {}

    public static void Main( string []args )
    {
        GuidAttribute IMyInterfaceAttribute = (GuidAttribute) Attribute.GetCustomAttribute(typeof(IMyInterface), typeof(GuidAttribute));

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

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

        // Equals is overridden to perform a value comparison.
        if (myGuid1.Equals(myGuid2))
            System.Console.WriteLine("myGuid1 equals myGuid2");
        else
            System.Console.WriteLine("myGuid1 does not equal 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" );
    }
}
// The example displays the following output:
//       IMyInterface Attribute: F9168C5E-CEB2-4faa-B6BF-329BF39FA1E4
//       myGuid1 equals myGuid2
//       myGuid1 == myGuid2

Note that the GuidAttribute is typically used in an application to expose a type to COM. If you compile this example, you can run Regasm.exe on the generated assembly to create .reg file and .tlb files. The .reg file can be used to register the coclass in the registry, and the .tlb file can provide metadata for COM interop.

Version Information

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Platforms

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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.

Reference

System Namespace

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FAQ

Desperate need of validity check method!

Checking to see if a GUID is valid is a major hassle:

' Very, very roundabout way to test if DeviceInterfaceGUIDvalue is a valid GUID, thanks MS. I have to 
' convert the GUID back to string, specifying the format, then parse it back to a GUID, just to see if
' it started off as a GUID. GUID class should contain a validity method, punto y se acabo.
If Not (Guid.TryParseExact(DeviceInterfaceGUIDvalue.ToString("B"), "B", DeviceInterfaceGUIDvalue)) Then
   Return -1
End If

There should be a method that checks validity and uses the format specifiers of TryParseExact and ToString: "N", "D", "B", "P", or "X". I would probably add "A" for 'All'.

This is a basic function, that should already be part of the GUID class!

More Information, Please!

I'm sure I'm misunderstanding something, so it would be helpful if you can provide more information about your scenario. All of the GUID validation routines that I know of attempt to determine whether a string is a valid GUID, and most commonly a regular expression is used for this purpose. Guid.TryParse should perform this function as effectively and offer better performance. More specifically, what I don't understand is why, if you're starting out with a GUID value, you would want to convert it to a string in order to determine whether it is a valid GUID. I would think that (and here I may well be misunderstanding something) if it is a GUID value, it ipso facto must be a valid GUID, unless its value is GUID.Empty. What are some examples of GUIDs that fail to validate?

Thanks.

--Ron Petrusha
Common Language Runtime User Education
Microsoft Corporation

Why the Cast?

The cast or conversion is necessary in this example because the Attribute.GetCustomAttribute method returns an Attribute instance, and we want to access the Value property, which is a property that is implemented by the GuidAttribute class and is not derived from Attribute.

It would have been somewhat more efficient, though, to perform the cast or conversion only once, in the definition of IMyInterfaceAttribute, rather than twice. We'll revise the example slightly for the next online documentation refresh.

--Ron Petrusha
Common Language Runtime User Education
Microsoft Corporation

History

10/15/2011
simpletense

10/17/2011
R Petrusha - MSFT