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例如，这是我使用 Haskell 和 gtk2hs 编写的一小段程序：

import System.GIO

foreign import ccall safe "g_type_init"
    g_type_init :: IO ()

main :: IO ()
main = do
    g_type_init
    let file = fileFromParseName "my-file.txt"
    inputStream <- fileRead file Nothing
    ...

该fileRead方法返回一个FileInputStream实例，但我无法在文档中的任何地方找到从中读取的方法。GIO中对应的C方法应该是g_input_stream_read，但是gtk2hs中好像没有实现。

我错过了什么吗？

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1 回答 1

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经过一些实验，我设法编写了自己的g_input_stream_read. 它不是很漂亮，甚至可能不安全，但这将成功打印 main 顶部指定的文件的前 1,024 个字符：

import Control.Monad (liftM)
import Data.Char (chr)
import Data.Word (Word8)
import Foreign
import Foreign.C (CInt)
import System.GIO
import System.GIO.Types (unInputStream, toInputStream)
import System.Glib (glibTypeInit, GError)

foreign import ccall unsafe "g_input_stream_read"
    -- inputStreamRead <stream> <buffer> <count> <cancellable> <error>, returns the number of bytes read
    inputStreamRead :: Ptr InputStream -> Ptr a -> CInt -> Ptr (Maybe Cancellable) -> Ptr GError -> IO (CInt)

addrToChar :: Ptr a -> Int -> IO (Char)
addrToChar p i = do
    let addr = p `plusPtr` i
    val <- peek addr :: IO Word8
    return $ chr (fromIntegral val)

main :: IO ()
main = do
    glibTypeInit
    let file = fileFromParseName "file.txt"
    fileInputStream <- fileRead file Nothing
    let stream = unInputStream $ toInputStream fileInputStream
    allocaBytes 1024 $ \buffer -> do
        alloca $ \err -> do
            bytesRead <- liftM fromEnum $ inputStreamRead (unsafeForeignPtrToPtr stream) buffer 1024 nullPtr err :: IO Int
            result <- mapM (addrToChar buffer) [0..bytesRead]
            putStrLn result

它需要一些工作才能变得简单inputStreamRead :: InputStream -> IO (String)，但至少这是朝着正确方向迈出的一步。

编辑：找到了更好的解决方案。这个应该继续读取，直到读取的字节数等于 0，并且有一个更友好的入口点：

import Control.Monad (liftM)
import Data.Char (chr)
import Data.Word (Word8)
import Foreign
import Foreign.C (CInt)
import System.GIO
import System.GIO.Types
import System.Glib (glibTypeInit, GError)

foreign import ccall unsafe "g_input_stream_read"
    -- inputStreamRead <stream> <buffer> <count> <cancellable> <error>, returns the number of bytes read
    inputStreamRead :: Ptr InputStream -> Ptr a -> CInt -> Ptr Cancellable -> Ptr GError -> IO (CInt)

chunk :: Int
chunk = 4096

bytesToText :: [Word8] -> [Char]
bytesToText [] = []
bytesToText (x:xs) = (chr $ fromEnum x):(bytesToText xs)

readGIOStream :: InputStream -> Maybe Cancellable -> IO ([Word8])
readGIOStream stream cancel = do
    allocaBytes chunk $ \buffer -> do
        alloca $ \err -> do
            case cancel of
                Just c  -> withForeignPtr (unCancellable c) $ \c' -> readChunk buffer c' err streamPtr
                Nothing -> readChunk buffer nullPtr err streamPtr
            where streamPtr = unInputStream stream
                  readChunk b c e s = withForeignPtr s $ \s' -> do
                          bytesRead <- liftM fromEnum $ inputStreamRead s' b (toEnum chunk) c e
                          result <- mapM (\i -> peek $ b `plusPtr` i) [0..(bytesRead-1)]
                          if bytesRead == 0
                              then return result
                              else do rest <- readChunk b c e s
                                      return $ result ++ rest

main :: IO ()
main = do
    glibTypeInit
    let file = fileFromParseName "live-forever.txt"
    fileInputStream <- fileRead file Nothing
    text <- liftM bytesToText $ readGIOStream (toInputStream fileInputStream) Nothing
    putStrLn text
于 2012-10-17T18:40:33.390 回答