C# COM client error handling

[definition]

hey guys, im looking for some information on how to handle exceptions within a C# client from a C++ COM server. I'm use to error handling in C++ and am not quite sure what to do with being able to say SUCCEEDED or have the HRESULT available to me. how do i manage this in C#? anyone know?

p.s sorry if this should be in the C# section, but it is a bit of both worlds.

[Siddhartha]

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Regards,
Siddhartha

[darwen]

If an HRESULT returns an error code then a COMException is thrown. The property ErrorCode on this exception gives the error code.

e.g.


uint hResult = 0;

try
{
// make COM call here
}
catch (COMException exception)
{
hResult = exception.ErrorCode;
}

return hResult;


I'm unsure if it throws this exception if S_FALSE is returned : you'll have to try it out.

Alternatively, you can do your own COM interop as shown in my article.

http://www.codeguru.com/Csharp/Csharp/cs_misc/com/article.php/c9065/

Define [PreserveSig] on each method and an exception will not be thrown : the HRESULT will be passed back.

e.g.


[Guid("----")]
[InterfaceType(ComInterfaceType.InterfaceIsIDispatch)]
public interface ITestInterface
{
[PreserveSig] uint MyMethod();
}


Darwen.

[Siddhartha]

S_FALSE, S_OK, and S_* in general are success return codes.
E_FAIL, E_POINTER, and E_* in general are error return codes.

An Error returned by a Native C++ COM Server will throw an exception in the C# client.
Success (even if S_FALSE) will not.

Attached is a sample ATL C++ COM Server accessed by a C# client.

Should you return E_FAIL in CDialogInterface::Show (exposed via IDialogInterface), you will get an unhandled exception - one that needs to be handled via the technique in the previous post.

In general, the sample displays a Dialog implemented in a C++ COM Server invoked via a C-Sharp client.

Detailed explanation of the sample is in my post here (http://www.codeguru.com/forum/showthread.php?p=1233999#post1233999).
(Ah, it seems that you have already seen it!)

On a side note - in C++, the macro SUCCEEDED returns TRUE for S_FALSE as well - reason being that S_FALSE is also a return code implying SUCCESS.