From: Luis Lavena <luislavena@...>
Date: 2010-01-19T12:15:06+09:00
Subject: Re: ffi: How to use wchar_t strings?

On Jan 18, 2:06 pm, Marvin Gülker <sutn...@gmx.net> wrote:
> Hello,
>
> I'm trying to use the ffi gem to work with some WinAPI functions. Till
> now, I've used the win32-api gem which worked quite well, but I'd like
> to try out something new (and maybe easier ;-) ). So, here's my
> question: How do I send a Unicode string (encoded in UTF-16LE) to a
> WinAPI function?
>
> This my code:
> -------------------------------------
> #Encoding: UTF-8
> require "ffi"
>
> module Test
>   extend FFI::Library
>
>   ffi_lib "user32"
>   ffi_convention :stdcall
>
>   attach_function :message_box, :MessageBoxW, [:long, :string, :string,
> :int], :int
> end
>
> module Test2
>   extend FFI::Library
>
>   CP_UTF8 = 65001
>   MB_PRECOMPOSED = 0x00000001
>
>   ffi_lib "kernel32"
>   ffi_convention :stdcall
>
>   attach_function :get_last_error, :GetLastError, [], :long
>   attach_function :multi_byte_to_wide_char, :MultiByteToWideChar,
> [:uint, :int, :string, :int, :buffer_out, :int], :int
> end
>
> buffer = "\0" * 100_000
>
> #I know, I could use Rubies built-in encoding functions
> #and I WILL do so, but for now this is to ensure
> #everything is 100% correct as MS it expects.
> ret = Test2.multi_byte_to_wide_char(Test2::CP_UTF8, 0, "Test",
> "Test".length, buffer, buffer.length)
>
> buffer.force_encoding("UTF-16LE")
> puts buffer.encode("ISO-8859-1").rstrip #Everything correct
>
> #The following line causes the error:
> Test.message_box(0, buffer, buffer, 0)
> -------------------------------------
>
> This is the error message:
> -------------------------------------
> t2.rb:32:in `message_box': string contains null byte (ArgumentError)
>   from t2.rb:32:in `<main>'
> -------------------------------------
>
> An UTF-16LE encoded string *contains* NUL bytes, I know--but I want to
> use Unicode functions, so: How to do that?
>

I think because :string definition is expecting a Ruby string, not a
memory buffer as you're trying to send.

wchar_t should be defined as a new type and a proper memory pointer
and buffer should be used to marshal the string from Ruby to the C
realm :-)

I suggest also bring this topic to FFI group:

http://groups.google.com/group/ruby-ffi

Where you could get better pointers than my vague description.

Cheers,
--
Luis Lavena