PreserveSigAttribute Class

Definition

Namespace:

System.Runtime.InteropServices

Assembly:

System.Runtime.InteropServices.dll

Source:

PreserveSigAttribute.cs

Indicates that the HRESULT signature transformation that takes place during COM interop calls should be suppressed.

public ref class PreserveSigAttribute sealed : Attribute

[System.AttributeUsage(System.AttributeTargets.Method, Inherited=false)]
public sealed class PreserveSigAttribute : Attribute

[<System.AttributeUsage(System.AttributeTargets.Method, Inherited=false)>]
type PreserveSigAttribute = class
    inherit Attribute

Public NotInheritable Class PreserveSigAttribute
Inherits Attribute

Inheritance

Object

Attribute

PreserveSigAttribute

Attributes

AttributeUsageAttribute

Examples

The following example shows how Tlbexp.exe converts a C# method without PreserveSigAttribute when exporting an assembly to a COM type library.

Managed signature:

int DoSomething (long l);  

Unmanaged signature:

HRESULT DoSomething ([in] long l, [out, retval] int * i);  

When you apply PreserveSigAttribute to the same C# method and export the assembly, the method conversion differs from the previous example. Notice that Tlbexp.exe removes the HRESULT and the [out, retval] parameter modifier.

Managed signature:

[PreserveSig] int DoSomething (long l);  

Unmanaged signature:

int DoSomething ([in] long l);  

Remarks

You can apply this attribute to methods.

By default, the Tlbexp.exe (Type Library Exporter) ensures that a call that returns an HRESULT of S_OK is transformed such that the [out, retval] parameter is used as the function return value. The S_OK HRESULT is discarded. For HRESULTs other than S_OK, the runtime throws an exception and discards the [out, retval] parameter. When you apply the PreserveSigAttribute to a managed method signature, the managed and unmanaged signatures of the attributed method are identical.

Preserving the original method signature is necessary if the member returns more than one success HRESULT value and you want to detect the different values. Since most COM member return an HRESULT, by applying the PreserveSigAttribute, you can retrieve an integer representing the success or failure HRESULT. Tlbexp.exe preserves any [out, retval] parameters as out parameters in the managed signature.

The Tlbimp.exe (Type Library Importer) also applies this attribute; it applies the attribute to dispinterfaces when it imports a type library.

Note

Return types of Currency, Guid, and Object are not supported by the PreserveSigAttribute class when interoperation occurs from COM to managed code and the managed code is marked with the PreserveSigAttribute class. When you attempt to use one of these return types with the PreserveSigAttribute class during these conditions, a TypeLoadException is thrown.

Constructors

PreserveSigAttribute()

Initializes a new instance of the PreserveSigAttribute class.

Properties

TypeId

When implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute)

Methods

Equals(Object)	Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute)
GetHashCode()	Returns the hash code for this instance. (Inherited from Attribute)
GetType()	Gets the Type of the current instance. (Inherited from Object)
IsDefaultAttribute()	When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute)
Match(Object)	When overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
ToString()	Returns a string that represents the current object. (Inherited from Object)

See also

• Tlbexp.exe (Type Library Exporter)
• Tlbimp.exe (Type Library Importer)