From: Daniel Berger <djberg96@...>
Date: 2008-01-29T14:18:51+09:00
Subject: [OT] JNA Help - LPDWORD

Hi all,

Does anyone happen to know the JNA equivalent of [24].pack('L')? I need 
to pass a LPDWORD (pointer to a long) to a function.

Here's the code snippet I'm trying to make work. I'm pretty sure it's 
failing because 'num' isn't a proper data structure.

require 'java'

Advapi32 = com.sun.jna.NativeLibrary.getInstance('advapi32')
GetUserNameA = Advapi32.getFunction('GetUserNameA')

buf = java.nio.ByteBuffer.allocate(24)
num = [24].pack('L')

p GetUserNameA.invokeInt([buf, num].to_java) # Fails

buf = String.from_java_bytes(buf.array)

p buf.strip             # Empty?
p num.unpack('L').first # Should be length of user

Here's the equivalent win32-api script:

require 'win32/api'
include Win32

GetUserNameA = API.new('GetUserNameA', 'PP', 'I', 'advapi32')
buf = 0.chr * 24
num = [buf.size].pack('L')

p GetUserNameA.call(buf, num)

p buf.strip
p num.unpack('L').firs

Thanks,

Dan