Graeme Geldenhuys escreveu:
On Fri, Nov 21, 2008 at 11:08 PM, Graeme Geldenhuys
<[EMAIL PROTECTED]> wrote:
I thought you guys might find this interesting. It's a new 27 page
document describing Unicode support in D2009.
http://dn.codegear.com/article/38980
Seeing that I don't own D2009 and only read about it's Unicode support
I found some of the information interesting - and it was things we
argued about in this mailing list.
For example:
1...
Length() returns the bytes for UTF8String
but Length() returns the elements (what we know as characters) for
String or UTF16 strings.
No Length for String will return the number of Code Units (the number of
WideChar in UnicodeString case). When there's surrogate pairs it will
differ the number of Code Points (Characters) and Code Units. See the
excerpt:
"
A way to create a string with surrogate pairs is to use the
ConvertFromUtf32 function that
returns a string with the surrogate pair (two WideChar) in the proper
circumstances, like the
following:
var
str1: string;
begin
str1 := 'Surr. ' + ConvertFromUtf32($1D11E);
Now if you ask for the string length, you'll get 8, which is the number
of WideChar, but not the
number of logical Unicode code points in the string. If you print the
string you get the proper
effect (well, at least Windows will generally show one square block as
placeholder of the
surrogate pair, rather than two).
"
Length() also returns bytes for AnsiString.
--------------------
var
str8: Utf8String;
str16: string;
begin
str8 := 'Cantù';
Memo1.Lines.Add ('UTF-8');
Memo1.Lines.Add('Length: ' + IntToStr (Length (str8)));
Memo1.Lines.Add('5: ' + IntToStr (Ord (str8[5])));
Memo1.Lines.Add('6: ' + IntToStr (Ord (str8[6])));
str16 := str8;
Memo1.Lines.Add ('UTF-16');
Memo1.Lines.Add('Length: ' + IntToStr (Length (str16)));
Memo1.Lines.Add('5: ' + IntToStr (Ord (str16[5])));
As you might expect, the str8 string has a length of 6 (meaning 6
bytes), while the str16
string has a length of 5 (meaning 10 bytes, though). Notice that
Length invariably returns the
number of string elements, which in case of variable-length
representations don't match the
number of Unicode code points represented by the string. This is the
output of the program:
UTF-8
Length: 6
5: 195
6: 185
UTF-16
Length: 5
5: 249
--------------------
2... TStrings can now take an encoding parameter to specify how it
should load or save files.
-----------------------------
STREAMING TSTRINGS
The ReadFromFile and WriteToFile methods of the TStrings class can be
called with
an encoding. If you write a string list to text file without providing
a specific encoding, the class
will use TEncoding.Default, which uses the internal DefaultEncoding in turn
extracted at the first occurrence by the current Windows code page. In
other words, if you save
a file you'll get the same ANSI file as before.
Of course, you can also easily force the file to a different format,
for example the UTF-16 format:
Memo1.Lines.SaveToFile('test.txt', TEncoding.Unicode);
-----------------------------
anyway, there are a lot more interesting facts in this document. Well
worth reading to get a better understanding of unicode.
Regards,
- Graeme -
_______________________________________________
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http://opensoft.homeip.net/fpgui/
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