Over the past 3 months, I have designed an app for Darwin/Mac OS X using
the POSIX API. I slapped a cocoa interface on it and it's been ported
to most Unixes. Recently I ran into the problem of STRING ENCODING
CONVERSION and have a couple of questions related:
a. My understanding of Darwin is that the File System uses Unicode
16byte strings, correct?
The BSD-level interface to the file system uses canonically decomposed
UTF-8.
b. It is my understanding then that the commands open() and chdir() etc
are all expecting (or at least can handle) Unicode-16 strings under
Darwin?
See above.
c. I am receiving string data over a network encoded in Windows Latin 1
(ANSI codepage 1252) and I need to be sure that it is converted to the
local File System encoding.
- On OSX/Darwin, I have been using CFString functions to read the server
strings as kCFStringEncodingWindowsLatin1, and write them to local as
kCFStringEncodingUTF8. Is this OK? (vice versa going from Local to
server).
(when I tried using kCFStringEncodingUnicode it balked at my straight
ascii strings I sent the conversion function, and when I tried using
kCFStringEncodingASCII things didn't' convert right.) See CFString.h
for definitions.
If you are working in Cocoa, the appropriate thing to do is to create an
NSString and use -[NSString fileSystemRepresentation], or -[NSString
getFileSystemRepresentation:maxLength:], or -[NSFileManager
fileSystemRepresentationWithPath:] to obtain something you can pass to
BSD APIs like open(). (These APIs all do the same thing, just with
slightly different interfaces.) If you have a CFString, you can use it
as an NSString with just a cast from CFStringRef to NSString *, and vice
versa; the two are interchangeable. For the reverse conversion, use
-[NSFileManager stringWithFileSystemRepresentation:length:].
For those who may be working purely in CoreFoundation, my suggestion at
present for this conversion would be (a) create a CFString using
kCFStringEncodingWindowsLatin1, as you have been doing; (b) create a
CFURL using CFURLCreateWithFileSystemPath(); (c) use
CFURLGetFileSystemRepresentation() to get something you can pass to
open(). Then release the intermediate objects. For the reverse
conversion, use CFURLCreateFromFileSystemRepresentation() and
CFURLCopyFileSystemPath().
Douglas Davidson
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