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Haskell foreign import stdcall on DLL function

Answer 1

+2 A:

ephemient 2009-06-22 16:10:24

ghci dlltest.hs -lhw-driver allowed me to run the main function in ghci, but I'm having issues with compiling in gcc:C:\temp\hs>ghc --make dlltest.hs -lhw-driverLinking dlltest.exe ...C:\ghc\ghc-6.10.3\gcc-lib\ld.exe: cannot find -lhw-drivercollect2: ld returned 1 exit statusThis is very strange to me since it works properly in ghci. I'm going to play around with it some more.

Mark Rushakoff 2009-06-22 16:57:26

GHCi doesn't use ld and implements its own linker instead. More commonly there are situations when a library can be used in compiling but not interactively, without hackish workarounds, but this reverse case seems quite probable too. Can you run with -v and post the intermediate commands that ghc runs?

ephemient 2009-06-22 17:13:02

The -L. option changes my output from "cannot find -lhw-driver" to "undefined reference to 'HW_Init@0'", but neither suggestion got me a successful linking. Found a similar issue at http://www.nabble.com/OpenVG:-Linker-errors-with-ghc---make,-but-not-with-ghci--td22321487.html but no useful answer. Might end up just getting on the GHC mailing lists tomorrow... it is looking like it's just an issue with the linker options somewhere. I am sure I'm not the first person to use ld to link with a DLL.

Mark Rushakoff 2009-06-22 18:54:05

I'm pretty much a Linux-only user, and GHC links with .a and .so flawlessly for me, so any further help will be pure guesswork on my part. Sorry, and hope you find an answer.

ephemient 2009-06-22 19:01:29

I wouldn't be using Windows at all if it wasn't for work :XYou helped me nail down the original question, so I'm accepting your answer, and I'll open a new issue sometime later regarding the weird ld behavior. Thanks.

Mark Rushakoff 2009-06-22 20:06:00

Answer 2

A:

Below is a working example that calls GetComputerName from kernel32.dll:

{-# LANGUAGE ForeignFunctionInterface #-}

module Main where

import Control.Monad
import Foreign.C
import Foreign.Marshal.Alloc
import Foreign.Marshal.Array
import System.Win32.Types

foreign import stdcall "GetComputerNameW"
  win32_getComputerName :: LPTSTR -> LPDWORD -> IO Bool

getComputerName :: IO String
getComputerName = do
  withTString maxBuf $
    \buf -> do
      alloca $ \len -> do
        pokeArray len [fromIntegral maxLength]

        success <- win32_getComputerName buf len
        when (not success) $ fail "GetComputerName failed"

        [len'] <- peekArray 1 len
        peekTStringLen (buf, (fromIntegral len'))
  where
    maxBuf = take maxLength $ repeat 'x'
    maxLength = 15  -- cheating

main :: IO ()
main = getComputerName >>= putStrLn

Build it with

ghc --make compname.hs -lkernel32

Greg Bacon 2009-06-22 17:21:21

That hard-codes the C:\windows\system32 path into the output executable, which I wouldn't consider desirable.

ephemient 2009-06-22 17:23:51

Then please suggest a desirable alternative!

Greg Bacon 2009-06-22 17:30:47

Make sure the library search paths is correct (though that path should already be searched), then use `-lkernel32`.

ephemient 2009-06-22 17:35:17

Thanks for the pointer. With -Lc:/windows/system32, I was getting tons of undefined-reference errors. Omitting the -L argument made everyone happy. KISS, I guess.

Greg Bacon 2009-06-22 18:01:12

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