IOS CFStringTransform and Đ

Question

I am working on an iOS application in which I have to list and sort the names of people. I have a problem with a special character.

I need to clarify Martin R's answer on https://stackoverflow.com/a/312960/

You can use the CoreFoundation CFStringTransform function, which performs almost all the conversions from your list. Only "đ" and "Đ" need to be processed separately:

Why exactly this letter? Where does this come from? Where can I find the documentation?

Thank you very much.

Answer 1

I'm not 100% sure, but I think it can be seen from the Unicode database http://www.unicode.org/Public/6.2.0/ucd/UnicodeData.txt .

For example, the entry for "à" is

  00E0; LATIN SMALL LETTER A WITH GRAVE; Ll; 0; L; 0061 0300 ;;;; N; LATIN SMALL LETTER A GRAVE ;; 00C0 ;; 00C0

where field # 6 is the “Decomposition Display” in “a” + U + 0300 (COMBINED DISTRIBUTION), Therefore

CFStringTransform(..., kCFStringTransformStripCombiningMarks, ...) 

converts "a" to "a".

The entries for "Đ" and "đ" are

  0110; LATIN CAPITAL LETTER D WITH STROKE; Lu; 0; L ;;;;; N; LATIN CAPITAL LETTER D BAR ;;; 0111;
 0111; LATIN SMALL LETTER D WITH STROKE; Ll; 0; L ;;;;; N; LATIN SMALL LETTER D BAR ;; 0110 ;; 0110

where field # 6 is empty, so these characters are not decomposed into “base character” and “combining character”.

So the question remains: what standard defines that the "normalized form" of "đ / Đ" is equal to "d / D"?