ffi: How to use wchar_t strings?


M

Marvin Gülker

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?

My ruby version: ruby 1.9.1p243 (2009-07-16 revision 24175)
[i386-mingw32]
My OS: Windows Vista Home Premium SP2 (32 bit)

Marvin
 
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L

Luis Lavena

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)

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,
 
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M

Marvin Gülker

Luis said:
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 :)
Maybe true. I'm new to ffi, so I'll have to look how to define my own
type.
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.
I've done so:
http://groups.google.com/group/ruby-ffi/browse_thread/thread/ada0ea99600b7fa1

Marvin
 

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