Indicates that the HRESULT or retval signature transformation that takes place during COM interop calls should be suppressed.
Assembly: mscorlib (in mscorlib.dll)
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 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 , 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.
The following example shows how Tlbexp.exe converts a C# method without when exporting an assembly to a COM type library.
int DoSomething (long l);
HRESULT DoSomething ([in] long l, [out, retval] int * i);
When you apply 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.
[PreserveSig] int DoSomething (long l);
int DoSomething ([in] long l);
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.