[DUG] Upgrading to XE - Unicode strings questions

[Jolyon Smith]

Colin, the for C in loop and the for i := 1 to Length() loops are
functionally identical!  The only difference is that the “for in” version
incurs the slight overhead of the enumerator framework invoked by the
compiler and runtime magic to support that syntax.

 

But in neither case will the loop itself help detect/respond to surrogate
pairs (a single “WideChar” is potentially only ½ the data required to form a
complete “character”).  The only way to reduce an iterator over a string to
a simple char-wise loop, whether explicit or using enumerators, is to first
convert to UTF32, the facilities for which in the Delphi RTL are <cough>
rudimentary, to put it politely.  Non-existent may be nearer the mark.

 

The precise mechanics of the loop construct used is not material to that
problem.

 

 

However, just as before Unicode when most people didn’t care and just wrote
code that assumed ANSI==ASCII, these days people won’t care and will write
code that assumes that Unicode==BMP (Basic Multilingual Plane), ignoring
surrogate pairs just as they used to ignore extended ASCII and ANSI
characters.

 

And for most people, that will probably actually work.

 

J

 

 

From: delphi-bounces at delphi.org.nz [mailto:delphi-bounces at delphi.org.nz] On
Behalf Of Colin Johnsun
Sent: Tuesday, 23 November 2010 14:31
To: NZ Borland Developers Group - Delphi List
Subject: Re: [DUG] Upgrading to XE - Unicode strings questions

 

I won't answer everything but just on this one question:

On 23 November 2010 11:04, John Bird <johnkbird at paradise.net.nz> wrote:

Extra question:

It looks like code like

   for i:=1 to length(string1) do
   begin
           DoSomethingWithOneChar(string1[i]);
   end;

cannot be used reliably.   The problems are that length(string1) looks like
it cannot be safely used - as unicode characters may include 2 codepoints
and length(string1) highlights that there is a difference between the number
of unicode characters in a string and the number of codepoints.   Still
figuring out what is the best practice here, as I have quite a lot of string
routines.   Should be be OK as long as the unicode text actually is ASCII.

 

 

you can use something like this:

 

var

  C: Char;

...

  for C in String1 do

  begin

    DoSomethingWithOneChar(C);

  end;

 

In this case you don't need to know the index of each character, you just
get the char using the for..in..do loop.

 

 

 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://listserver.123.net.nz/pipermail/delphi/attachments/20101123/ba45fc58/attachment.html