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-- !!! file positions (hGetPosn and hSetPosn)
module Main(main) where
import System.IO
import Control.Monad ( sequence )
testPosns :: Handle -> BufferMode -> IO ()
testPosns hdl bmo = do
hSetBuffering hdl bmo
putStrLn ("Testing positioning with buffer mode set to: " ++ show bmo)
testPositioning hdl
bmo_ls = [NoBuffering, LineBuffering, BlockBuffering Nothing,
BlockBuffering (Just 511),BlockBuffering (Just 3), BlockBuffering (Just 11)]
main = do
hdl <- openFile "hSeek003.hs" ReadMode
sequence (zipWith testPosns (repeat hdl) bmo_ls)
hClose hdl
testPositioning hdl = do
hSeek hdl AbsoluteSeek 0 -- go to the beginning of the file again.
ps <- getFilePosns 10 hdl
hSeek hdl AbsoluteSeek 0
putStr "First ten chars: "
ls <- hGetChars 10 hdl
putStrLn ls
-- go to the end
hSeek hdl SeekFromEnd 0
ls <- sequence (map (\ p -> hSetPosn p >> hGetChar hdl) ps)
putStr "First ten chars: "
putStrLn ls
-- position ourselves in the middle.
sz <- hFileSize hdl
hSeek hdl AbsoluteSeek (sz `div` 2)
ls <- sequence (map (\ p -> hSetPosn p >> hGetChar hdl) ps)
putStr "First ten chars: "
putStrLn ls
hGetChars :: Int -> Handle -> IO String
hGetChars n h = sequence (replicate n (hGetChar h))
getFilePosns :: Int -> Handle -> IO [HandlePosn]
getFilePosns 0 h = return []
getFilePosns x h = do
p <- hGetPosn h
hGetChar h
ps <- getFilePosns (x-1) h
return (p:ps)
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