PreserveSigAttribute Class
Indicates that the HRESULT or retval signature transformation that takes place during COM interop calls should be suppressed.
Assembly: mscorlib (in mscorlib.dll)
The PreserveSigAttribute type exposes the following members.
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PreserveSigAttribute | Initializes a new instance of the PreserveSigAttribute class. |
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Equals | Infrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.) |
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Finalize | Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.) |
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GetHashCode | Returns the hash code for this instance. (Inherited from Attribute.) |
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GetType | Gets the Type of the current instance. (Inherited from Object.) |
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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.) |
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Match | When overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.) |
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MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) |
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ToString | Returns a string that represents the current object. (Inherited from Object.) |
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_Attribute.GetIDsOfNames | Maps a set of names to a corresponding set of dispatch identifiers. (Inherited from Attribute.) |
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_Attribute.GetTypeInfo | Retrieves the type information for an object, which can be used to get the type information for an interface. (Inherited from Attribute.) |
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_Attribute.GetTypeInfoCount | Retrieves the number of type information interfaces that an object provides (either 0 or 1). (Inherited from Attribute.) |
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_Attribute.Invoke | Provides access to properties and methods exposed by an object. (Inherited from Attribute.) |
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, retavl] 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
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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);
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.
