OS X - how to calculate normalized file name

Question

I need to create a mapping between file names generated on Windows and OS X. I know that OS X "converts all file names to decomposed Unicode" however, "most volume formats do not follow the exact specification for these normal forms"

So, it does not seem a simple matter of converting the Windows name to NFD using a standard UTF8 API and being sure I have the correct OS X name. Is there a way to determine what the actual OS X file name will be without actually creating the file in the file system and then scanning the directory to see what was actually created?

Answer 1

I think the answer is this from TechNote 1150 HFS Plus Volume Format:

Note: The Mac OS Text Encoding Converter provides several constants that let you convert to and from the canonical, decomposed form stored on HFS Plus volumes. When using CreateTextEncoding to create a text encoding, you should set the TextEncodingBase to kTextEncodingUnicodeV2_0, set the TextEncodingVariant to kUnicodeCanonicalDecompVariant, and set the TextEncodingFormat to kUnicode16BitFormat. Using these values ensures that the Unicode will be in the same form as on an HFS Plus volume, even as the Unicode standard evolves.

Answer 2

You're probably looking for -[NSString fileSystemRepresentation] method.

Note that there is no general solution for this task. What is a valid file name depends on filesystem of the volume you're saving on. Not every file name valid for HFS+ is valid for FAT32, for example.

For Mac's “standard” filesystem (currently HFS+), fileSystemRepresentation should give what you need; for other file systems, there is no general way. Think about ones that don't exist but will be introduced in the future, for example :)