I've read and re-read the documentation, but I can't decide whether a UTF-8 character that takes multiple bytes to express counts as one or multiple values in length and sizeof.  Sizeof seems to presume that all entries are the same length, but otherwise it seems to be the property I need.  (I suppose that I could just enter a string that I know is multi-byte chars, but it sure would be better if I could find out from the documentation.)  I'm pretty certain that it just counts as one character for indexing, so length would almost need to also count the number of characters rather than bytes.

Sizeof *should* be the correct property, and I've been assuming that it is, but I'm a bit afraid that I'll run across some unexpected character and it won't act the way I think it should.  And the documentation reads ambiguously.

Does anyone just *know* the answer?  (And if so, could they make the documentation explicit?)

Charles Hixson wrote:
> I've read and re-read the documentation, but I can't decide whether a UTF-8 character that takes multiple bytes to express counts as one or multiple values in length and sizeof.  Sizeof seems to presume that all entries are the same length, but otherwise it seems to be the property I need.  (I suppose that I could just enter a string that I know is multi-byte chars, but it sure would be better if I could find out from the documentation.)  I'm pretty certain that it just counts as one character for indexing, so length would almost need to also count the number of characters rather than bytes.

Strings are just arrays of code units.  Their length is the number of elements (i.e. code units) they contain, just like other arrays.  A code point may comprise multiple code units, and a logical character may comprise multiple code points.  The latter is true even with dchar/utf-32.


-- 
Rainer Deyke - rainerd@eldwood.com

Rainer Deyke wrote:
> Charles Hixson wrote:
>> I've read and re-read the documentation, but I can't decide whether a UTF-8 character that takes multiple bytes to express counts as one or multiple values in length and sizeof.  Sizeof seems to presume that all entries are the same length, but otherwise it seems to be the property I need.  (I suppose that I could just enter a string that I know is multi-byte chars, but it sure would be better if I could find out from the documentation.)  I'm pretty certain that it just counts as one character for indexing, so length would almost need to also count the number of characters rather than bytes.
> 
> Strings are just arrays of code units.  Their length is the number of elements (i.e. code units) they contain, just like other arrays.  A code point may comprise multiple code units, and a logical character may comprise multiple code points.  The latter is true even with dchar/utf-32.
> 
	So, in UTF-8, length is the number of bytes in the string and
sizeof is 8 (on 32-bits systems).

		Jerome
-- 
mailto:jeberger@free.fr
http://jeberger.free.fr
Jabber: jeberger@jabber.fr

On Sun, 01 Nov 2009 11:36:31 -0800, Charles Hixson wrote:

> Does anyone just *know* the answer?  (And if so, could they make the
> documentation explicit?)

I believe the documentation you are looking for is:

http://www.prowiki.org/wiki4d/wiki.cgi?DanielKeep/TextInD

It is more about understanding UTF than it is about learning strings.

Jérôme M. Berger wrote:
> Rainer Deyke wrote:
>> Strings are just arrays of code units.  Their length is the number of elements (i.e. code units) they contain, just like other arrays.  A code point may comprise multiple code units, and a logical character may comprise multiple code points.  The latter is true even with dchar/utf-32.
>>
>     So, in UTF-8, length is the number of bytes in the string and sizeof
> is 8 (on 32-bits systems).

Yes.


-- 
Rainer Deyke - rainerd@eldwood.com

Jesse Phillips wrote:
> I believe the documentation you are looking for is:
> 
> http://www.prowiki.org/wiki4d/wiki.cgi?DanielKeep/TextInD
> 
> It is more about understanding UTF than it is about learning strings.

One thing that page fails to mention is that D has no awareness of
anything higher-level than code points.  In particular:
  - dchar contains a code point, not a logical character.
  - D has no awareness of canonical forms and precomposed/decomposed
characters (at the language level).  (Some characters can be represented
as either one or two code points.  D does not know that these are
supposed to represent the same character.)
  - Although D stops you from outputting an incomplete code point, it
does not stop you from outputting an incomplete logical character.

Also, some D library functions only work on the ASCII subset of utf-8.


-- 
Rainer Deyke - rainerd@eldwood.com

Rainer Deyke wrote:
> Jesse Phillips wrote:
>> I believe the documentation you are looking for is:
>>
>> http://www.prowiki.org/wiki4d/wiki.cgi?DanielKeep/TextInD
>>
>> It is more about understanding UTF than it is about learning strings.
> 
> One thing that page fails to mention is that D has no awareness of
> anything higher-level than code points.  In particular:
>   - dchar contains a code point, not a logical character.
>   - D has no awareness of canonical forms and precomposed/decomposed
> characters (at the language level).  (Some characters can be represented
> as either one or two code points.  D does not know that these are
> supposed to represent the same character.)
>   - Although D stops you from outputting an incomplete code point, it
> does not stop you from outputting an incomplete logical character.
> 
> Also, some D library functions only work on the ASCII subset of utf-8.

Well, it *is* on a Wiki.

Jesse Phillips wrote:
> On Sun, 01 Nov 2009 11:36:31 -0800, Charles Hixson wrote:
>
>> Does anyone just *know* the answer?  (And if so, could they make the
>> documentation explicit?)
>
> I believe the documentation you are looking for is:
>
> http://www.prowiki.org/wiki4d/wiki.cgi?DanielKeep/TextInD
>
> It is more about understanding UTF than it is about learning strings.
Thanks, that does appear to be the answer.

So if a string is too long, and I shorten it by one character, I'd better test it with std.utf.validate(str).  If it doesn't throw an error, it's ok.  Otherwise shorten it again and retry.

I hope I understood this correctly.  (I'm sure there's a more elegant way to do this, but here I'm going for a simple approach, as I should rarely be encountering this problem.)

Charles Hixson <charleshixsn@earthlink.net> wrote:

> Jesse Phillips wrote:
>> On Sun, 01 Nov 2009 11:36:31 -0800, Charles Hixson wrote:
>>
>>> Does anyone just *know* the answer?  (And if so, could they make the
>>> documentation explicit?)
>>
>> I believe the documentation you are looking for is:
>>
>> http://www.prowiki.org/wiki4d/wiki.cgi?DanielKeep/TextInD
>>
>> It is more about understanding UTF than it is about learning strings.
> Thanks, that does appear to be the answer.
> 
> So if a string is too long, and I shorten it by one character, I'd better test it with std.utf.validate(str).  If it doesn't throw an error, it's ok.  Otherwise shorten it again and retry.
> 
> I hope I understood this correctly.  (I'm sure there's a more elegant way to do this, but here I'm going for a simple approach, as I should rarely be encountering this problem.)
> 
> 
As far as I know if you want to shorten a utf8 string you just check the first bit of the last byte to see if its 0. If its 0 go back further until you find a byte that starts with 1, and then remove that byte too.

All characters start with a byte that starts with 1, the number of 1s in the first byte of the character tell you how many bytes in the character.

Hope that helps, but you should find a library that already has a "shorten my string" function.

-Rory

On Tue, Nov 3, 2009 at 2:47 AM, rmcguire <rjmcguire@gmail.com> wrote:
> Charles Hixson <charleshixsn@earthlink.net> wrote:
>
>> Jesse Phillips wrote:
>>> On Sun, 01 Nov 2009 11:36:31 -0800, Charles Hixson wrote:
>>>
>>>> Does anyone just *know* the answer?  (And if so, could they make the
>>>> documentation explicit?)
>>>
>>> I believe the documentation you are looking for is:
>>>
>>> http://www.prowiki.org/wiki4d/wiki.cgi?DanielKeep/TextInD
>>>
>>> It is more about understanding UTF than it is about learning strings.
>> Thanks, that does appear to be the answer.
>>
>> So if a string is too long, and I shorten it by one character, I'd better test it with std.utf.validate(str).  If it doesn't throw an error, it's ok.  Otherwise shorten it again and retry.
>>
>> I hope I understood this correctly.  (I'm sure there's a more elegant way to do this, but here I'm going for a simple approach, as I should rarely be encountering this problem.)
>>
>>
> As far as I know if you want to shorten a utf8 string you just check the first bit of the last byte to see if its 0. If its 0 go back further until you find a byte that starts with 1, and then remove that byte too.
>
> All characters start with a byte that starts with 1, the number of 1s in the first byte of the character tell you how many bytes in the character.
>
> Hope that helps, but you should find a library that already has a "shorten my string" function.

It's explained well in Andrei's book.
0* -- single byte character
11* -- first byte of multi-byte char
10* -- subsequent byte of multi-byte char

--bb