Re: Proposal to extend documentation about interop

From: Robert Jordan (robertj_at_gmx.net)
Date: 10/19/04 

Date: Wed, 20 Oct 2004 00:19:58 +0200

John Allberg wrote:

> Hi!
>
> I think the MSDN docs about interop doesn't state clearly enough that there
> is a character encoding conversion automaticly done from Unicode to the
> characterset for the computer during interop.
>
> This got me really puzzled for a few days.
>
> I've got a legacy C-application (dll) that takes in UTF-8 encoded strings in
> an array of structs. I call that C-dll from C# which works fine, as long as
> I use ansi characters, for example english. When sending in swedish
> characters (where the utf-8 encoding becomes two bytes) such as åäö the
> lowercase works fine, but the uppercase ÅÄÖ simply comes out as invalid
> utf-8 encoding of the character FF.
>
> I solved it by doing the conversion of UTF-8 to bytes and when going back to
> string used the encoder for "Default" and converting those bytes to a
> "unicode-string". That way, when the interop converts the string from
> Unicode to "Default", the UTF-8 once again surfaces.
>
> So my suggestion is to update the MSDN doc to state this conversion clearly
> enough.

The automatic p/invoke conversion can be applied only to those
legacy types:

- LPSTR (ansi encoding, 1 byte)
- LPWSTR (unicode encoding. 2 bytes)
- LPTSTR (platform specific, one of the above)
- BSTR

You cannot properly import UTF-8 because Win32 doesn't support
UTF-8 for the legacy API either.

bye
Rob

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