在前一篇文章里，我们讨论了如何利用FileIO从非文本文件中读取数据的问题，本次我们讨论用FileIO编辑现有文件，例如MP3文件上，或是创建新文件，例如从Director 的cast member中输出位图文件。

编辑MP3文件

写二进制文件最简单的例子莫过于编辑MP3文件的标签。这总比新建文件要来得简单，你不必去弄清整个文件结构，只需明白歌曲信息是储存在最后128个字节里。

on writeBinaryFile filePath, byteList, fileStartByte, listStartByte, deleteOriginalFile

result = 0
fileObj = new (xtra "fileIO")
if deleteOriginalFile then
-- It's often "cleaner" to remove the existing file
-- though you obviously wouldn't do this when editing
-- an MP3 file
fileObj.openFile (filePath, 0)
fileObj.delete ()
fileObj.createFile (filePath)
end if
fileObj.openFile (filePath, 2)
-- Attempt to open the file with write-only access

if fileObj.status () = 0 then
listLength = byteList.count
if fileStartByte.voidP then fileStartByte = 1
-- Set default positions if none were supplied via
-- the fileStartByte & listStartByte parameters
if listStartByte.voidP then listStartByte = 1

fileObj.setPosition (fileStartByte-1)
-- Set the write position in the file & begin dumping
-- the list contents into the file

repeat with index = listStartByte to listLength
fileObj.writeChar (numToChar (byteList[index]))
end repeat
result = 1
end if

fileObj.closeFile ()
fileObj = 0
return result
end

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