[hfs-user] Alphabetical order of items in a catalog node
Pierre Duhem <email@example.com>
Tue, 20 Apr 2004 09:51:37 +0200
MD> On Apr 19, 2004, at 5:58 AM, Pierre Duhem wrote:
>> Norton says that the alphabetical order of the items in a node is
>> incorrect. It proposes to fix the matter and does it apprently. When I
>> check in the catalog node, however, I find it put a hidden folder
>> named '0000HFS+ Private Data' (with four null at the beginning of the
>> Unicode string) at the end of the current folder.
>> I thought that alphabetical order problems were a matter of the past
>> (remember the funny order of the accented letters?).
>> Does it make sense for you to put an Unicode character of 0x0000 at
>> the very end of the list?
MD> Yes, it does make sense. It's part of the way HFS Plus handles
MD> case-insensitive comparisons with Unicode. See the Case-Insensitive
MD> String Comparison Algorithm section of Tech Note 1150: HFS Plus Volume
MD> The reason has to do with certain "ignorable" Unicode characters. Some
MD> Unicode code points act as hints, and do not affect the comparison (a
MD> string with these ignorable characters is considered identical to a
MD> string without ignorables). The easy way to handle them in the code
MD> was to map them to 0 during the comparison. But since null (0) is a
MD> valid character in an HFS Plus name, it gets mapped to 0xFFFF (which is
MD> not valid Unicode) during the comparison. That's why nulls sort last
MD> on HFS Plus.
Thanks a lot. I had read this document in the past, and this very
piece, but had not noticed this special treatment for the null
character. I'll correct my code in this sense.
Logiciels & Services Duhem, Paris (France)