Re: Normalising file names on macOS
Re: Normalising file names on macOS
- Subject: Re: Normalising file names on macOS
- From: Alastair Houghton <email@hidden>
- Date: Thu, 22 Sep 2016 12:31:19 +0100
On 22 Sep 2016, at 12:04, John Brownie <email@hidden> wrote:
>
> I find that I am in need of dealing with versions of strings that may be turned into file names, and thus I need to be comparing normalised forms. However, according to https://developer.apple.com/library/content/qa/qa1173/_index.html, "For example, HFS Plus (Mac OS Extended) uses a variant of Normal Form D in which U+2000 through U+2FFF, U+F900 through U+FAFF, and U+2F800 through U+2FAFF are not decomposed (this avoids problems with round trip conversions from old Mac text encodings)."
>
> Is there a way to get at this variant? [NSString decomposedStringWithCanonicalMapping] returns "A string made by normalizing the string’s contents using the Unicode Normalization Form D." That seems not to give what I need, but I haven't seen a better option. Is there such a method?
This is rather a hairy problem, actually. You don’t know that the filesystem is actually HFS+. The filename in question could refer to a file on an NTFS volume, or (in future) an APFS volume. It could also be a network filesystem, which could be mounted on a system running a completely different operating system with unknown character encoding behaviour; typically UNIX behaviour, for instance, is to completely ignore the filename encoding problem and treat filenames as a string of bytes (thus you are free to interpret them as UTF-8 if you so wish, but the filesystem will regard U+00E9 as different from U+0065 U+0301, even though the two names will display the same on screen).
Additionally, the version specified in HFS+ was based on a particular version of the Unicode standard (I forget which), but importantly *not* the current version, which is what the NSString APIs will use.
Perhaps we should start by understanding the context of your question. Is there a specific reason you want to match the filesystem behaviour precisely?
Kind regards,
Alastair.
--
http://alastairs-place.net
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