[fpc-devel] TFieldDef.Size vs TField.Size
lacak at zoznam.sk
Thu Feb 24 08:02:20 CET 2011
I am writting here to discuss bug
(I do not want reopen bug and writte there because I am not sure about
IMHO root of problem is in different definition of TFieldDef.Size and
Documentation says, that
1. TFieldDef.Size should be "For string and byte fields, *Size* is the
number of bytes reserved "
2. TField.Size should be "the maximum number of characters in the
string" (for ftString and I guess that also for ftWideString)
And now let's go look into fields.inc:
1. Function TFieldDef.CreateField copies Result.Size:=FSize (so
2. function TStringField.GetDataSize returns for ftString ... Size+1
3. function TWideStringField.GetDataSize returns for ftWideString ...
(Size + 1) * 2
Points 2,3 are clear Size is expected to be number of characters,
DataSize number of bytes.
But point 1 says, that TFieldDef.Size and TField.Size should be the same
And now let's go look into bufdataset.pas:
4. function TCustomBufDataset.GetFieldSize works with TFieldDef and
returns number of bytes needed in record buffer
case FieldDef.DataType of
ftString, ftGuid, ftFixedChar: result := FieldDef.Size + 1;
ftFixedWideChar, ftWideString:result := (FieldDef.Size + 1)*2;
So also here we can see, that FieldDef.Size is expected to be number of
characters not bytes.
So IMHO logical conclusion will be say, that TFieldDef.Size for string
fields has same menaing as Field.Size, so it is number of characters
(so documentation is wrong in this case ... also fast test in Delphi
shows, that FieldDef.Size=Field.Size=number of characters)
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