On Thu, 24 Feb 2011, LacaK wrote:
See please
http://svn.freepascal.org/cgi-bin/viewvc.cgi/trunk/packages/fcl-db/src/sqldb/odbc/odbcconn.pas?r1=16094&r2=16988
And look at ftWideString, ftFixedWideChar cases
What happens if we have NVARCHAR(20) column on MS SQL Server (uses UCS-2
1char=2bytes):
1. in AddFieldDefs method is created TFieldDef object with Size=20*2 (because
FieldSize:=ColumnSize*sizeof(Widechar))
2. later when TField objects are created in TFieldDef.CreateField method,
TWideString object is created with Size=40 (because Size is copied from
TFieldDef object) ... and this is wrong, because:
2.1 TWideString.Size should IMO return max.number of characters ... Size is
used for example in data-aware controls to limit MaxLength
2.2 TWideStringField.GetDataSize will return 82, which is also wrong
(because (40+1)*2)
2.3 in record buffer will be allocated also 82 bytes (because of
TCustomBufDataset.GetFieldSize)
So IMO correct will be in step 1 FieldSize:=ColumnSize not
FieldSize:=ColumnSize*sizeof(WideChar)
(like in my original fix in bug report)
This seems correct, yes.
Note also, that Size is used (also in Delphi) to limit the number of
characters in data-aware controls (for ftString, ftWideString), so it must be
number of characters in both cases.
Do you see an implementation problem or a documentation problem ?
Implementation problem at first
but also Documentation is confusing, because do not clearly says about
menaing of TWideStringField.Size (only indirect guess can be done, that it is
inherited from TStringField.Size, so it is number of characters)
See, that also other users are confusing by it
https://forums.embarcadero.com/thread.jspa?messageID=188792
Yes, but that is an embarcadero bug :-)
Note that nowhere in the documentation pages you mention, widestrings are
mentioned (which is convenient, since that's where 1 char <> 1 byte).
Yes, but in Delphi6 help is for TWideStringField.DataSize:
"Inspect DataSize to determine the number of bytes required to store the
fields value. Use DataSize to determine the size needed for a buffer when
working with the GetData and SetData methods.
For wide string fields, DataSize is the value of the Size property plus one
(for the trailing NULL character), multiplied by two."
So we can estimate, that Size is number of characters, while
DataSize=(Size+1)*2
Indeed.
Michael.
_______________________________________________
fpc-devel maillist - fpc-devel@lists.freepascal.org
http://lists.freepascal.org/mailman/listinfo/fpc-devel
