[fpc-devel] new string - question on usage

[Hans-Peter Diettrich]

Paul Ishenin schrieb:
> 13.10.2011 9:13, Hans-Peter Diettrich wrote:
>> Sven Barth schrieb:
>>
>>> http://svn.freepascal.org/cgi-bin/viewvc.cgi/trunk/rtl/inc/astrings.inc?revision=19444&view=markup 
>>>
>>>
>>
>> I don't understand the use of encoding 0 and CP_NONE in FPC. Can
>> somebody explain?
> 
> DefaultSystemCodepage is used When the paticular encoding must be known 
> both for 0 and CP_NONE codepages.

What's CP_NONE? Value and purpose?

>> Furthermore I suspect that the implementation of
>>
>> Function Pos(Const Substr : RawByteString; Const Source : RawByteString)
>> : SizeInt;
>>
>> is wrong. The comparison must take into account the encodings of both
>> strings.
>>
>>
>> Function Pos(c : AnsiChar; Const s : RawByteString) : SizeInt;
>> is questionable at all, when the encoding of the arguments is unknown or
>> ignored (as is).
> 
> Did you run some tests in delphi for these functions?
> 
> Please run the next program to be sure:
> 
> {$apptype console}
> 
> type
>   T866Sting = type AnsiString(866);
>   T1251String = type AnsiString(1251);
> var
>   s866: T866Sting;
>   s1251: T1251String;
> begin
>   s866 := 'привет';
>   writeln(s866);
>   s1251 := 'рив';
>   writeln(s1251);
>   writeln(pos(s1251, s866));
> end.

I've a problem, because my console only supports the OEM font.
The output (pasted as Ansi) looks like
»a¿óÑG
=FG
0

With the strings replaced the output is
abcdef
bcd
2

Now we have 2 problems. Pos() expects Unicode arguments, i.e. the 
strings should be converted before comparison. Then something is 
obviously wrong with the cyrillic strings, result=0 :-(

I tested again, assigning the strings to "string" variables before Pos, 
and now
»a¿óÑG
=FG
0
2 //using Unicode strings

It turned out that the result only is correct when at least one of the 
strings is an UnicodeString. Otherwise Pos seems to end up in a 
RawByteString compare, with the encoding ignored.

I think that I have to ask in a Delphi group.


>> I have the bad impression that the implementors didn't understand the
>> purpose and correct use of RawByteString, or try to implement something
>> incompatible with Delphi :-(
> 
> Do you base your impression on paticular knowlege of how delphi RTL 
> works or only on your ideas of how it should work?

In my understanding Pos() et al. should respect the encoding, and should 
not do a binary compare of AnsiStrings of different encodings.

What do you think, is it okay when the result of the same function 
depends on the argument type, i.e.
   writeln(pos(s1251, s866)); //returns 0
   writeln(pos(string(s1251), s866)); //returns 2
???

Thanks for your interesting example :-)

DoDi