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PreserveSigAttribute Class

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

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

[ComVisibleAttribute(true)] 
[AttributeUsageAttribute(AttributeTargets.Method, Inherited=false)] 
public sealed class PreserveSigAttribute : Attribute
/** @attribute ComVisibleAttribute(true) */ 
/** @attribute AttributeUsageAttribute(AttributeTargets.Method, Inherited=false) */ 
public final class PreserveSigAttribute extends Attribute
ComVisibleAttribute(true) 
AttributeUsageAttribute(AttributeTargets.Method, Inherited=false) 
public final class PreserveSigAttribute extends Attribute

You can apply this attribute to methods.

By default, the Type Library Exporter (Tlbexp.exe) 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, retavl] parameters as out parameters in the managed signature.

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

NoteNote

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.

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);

System.Object
   System.Attribute
    System.Runtime.InteropServices.PreserveSigAttribute

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

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0

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