Wsrtjtyk

I know the following:

• 
  'L' - Long


• 
  'P' - Pointer


• 
  'I' - Integer


• 
  'V' - Void

My problem is that I can't pass a null pointer when I perform an API call. E.g.: ['L', 'P', 'L'] -> api.call(0, nil, 0) :: ArgumentError: Null pointer given. My question is: Are there more parameter types that I don't know about and what should I do to pass a null pointer as a method parameter?

Background

I have been searching the internet for native Ruby programming examples of WinForms-based applications. I have considered the .NET addition to Ruby known as IronRuby for simplicity in coding (trying to avoid wxRuby, and also a .NET fan), but I first want to be able to code explicitly in pure Ruby first.

Now, I have successfully been able to implement most addresses I've tested in the user32.dll object such as:

api = Win32API.new('user32', 'MessageBox', ['L', 'P', 'P', 'L'], 'I')

# or

api = Win32API.new('user32', 'MessageBeep', ['L'], 'I')

..but I cannot perform a CreateWindow Or CreateWindowEx without null parameters.
If it would be of any help, I have found how to do this in Python here (under WinAPI).

Using Win32API: msdn.microsoft.com/en-us/library/ff381397(v=VS.85).aspx

[EDIT]

Well, I think I may have just solved my own problem with this link
(warning: may contain inappropriate content): [link]

I more used that forum as reference and did a bit of fiddling around my self:
createwindow = Win32API.new("user32","CreateWindowEx",'lpplllllllll','l')
showwindow = Win32API.new('user32','ShowWindow',%w(l l),'l')

hWND = createwindow.call((0x00000100|0x00000200),"static", "Window Title",((0x4000000|0x80000000|0)|0x02000000),0,0,600,400,0,0,0,0)
showwindow(hWND, 1)

The only thing that happens after the 'window' is displayed is crash... and that may have been because of some incorrect handling, but, I am happy that I got it to work(for a little bit)! Just need to figure out the rest...

Instead of using Win32API (which I believe is built on top of the obscure and little used DL module), you might find better mileage using the new and improved FFI module.

Here's how:

• (1) Get ffi:
  gem install ffi




• (2) Then try this:

require 'ffi'



module Win32

   extend FFI::Library

   ffi_lib 'user32'

   attach_function :messageBox, 

       :MessageBoxA,[ :pointer, :string, :string, :long ], :int

end



rc = Win32.messageBox(nil, "Hello Ruby user!", "FFI is easy", 0x40)



puts rc

This seems easier than the solution you posted in your edit.

Note: The null pointer instead of Hwnd makes the message box have no owner window.

• 
  Constants to customise your message boxes (dialog box buttons and icon)


• Another example using FFI instead of Win32API
  

I haven't tested this since I'm not on Windows but I think you're intended to use the constant DL::NULL. You can see it in action here (second-to-last line) and it looks similar to your use case. Hope that's helpful!

require 'ffi'



module Win32

  extend FFI::Library

  ffi_lib 'user32'

  attach_function( 

                  :messageBox, 

                    :MessageBoxA,

                      [ :pointer, :string, :string, :long ], 

                      :int

                 )

end



rc = Win32.messageBox(nil, "Hello Ruby user!", "FFI is easy", 0x40)



puts rc