Question

我正试图访问XKB API中的各种位和bob。到目前为止，这是我的测试代码：

{-# LANGUAGE ForeignFunctionInterface #-}
module Main where

import Foreign
import Foreign.C.Types

#include <X11/XKBlib.h>
#let alignment t = "%lu", (unsigned long)offsetof(struct {char x__; t (y__); }, y__)

data XkbDescRec = XkbDescRec   { names  :: Ptr XkbNamesRec } deriving (Show)

data XkbNamesRec = XkbNamesRec { groups :: Ptr Word64 } -- Ignore me

foreign import ccall unsafe "X11/XKBlib.h XkbAllocKeyboard"
  xkbAllocKeyboard :: IO (Ptr XkbDescRec)

instance Storable XkbDescRec where
  sizeOf _    = (#size XkbDescRec)
  alignment _ = (#alignment XkbDescRec)
  peek ptr = do
    names <- (#peek XkbDescRec, names) ptr
    return $ XkbDescRec names 

main = do
  xkbDescPtr <- xkbAllocKeyboard

  print xkbDescPtr           -- (1)
  peek xkbDescPtr >>= print  -- (2)

虽然（1）输出0x0000000001777d80，听起来像是有效地址，但（2）会发出XkbDescRec {names = 0x0000000000000000}。

我不知道我是否以错误的方式使用FFI，或者我是否误解了链接中详述的XkbDescRec结构的结构。

Answer 1

XkbAllocKeyboard生成一个空白的XkbDescRec，由程序员填充。正确的方法是使用XkbGetKeyboard。我做了如下，更改和必要的位：

import Graphics.X11.Xlib (openDisplay, Display(..))

foreign import ccall unsafe "X11/XKBlib.h XkbGetKeyboard"  
xkbGetKeyboard :: Display -> CUInt -> CUInt -> IO (Ptr XkbDescRec)

main = do
  dpy        <- openDisplay ""
  xkbDescPtr <- xkbGetKeyboard dpy 0x7f (#const XkbUseCoreKbd)

XkbDescRep正确填充，0x7f是＆＃34;所有内容的掩码！＆＃34;

使用hsc2hs与XKB API连接

1 个答案: