[fpc-devel] TFieldDef.Size vs TField.Size

[michael.vancanneyt at wisa.be]

On Thu, 24 Feb 2011, LacaK wrote:

> Hi,
> I am writting here to discuss bug 
> http://bugs.freepascal.org/view.php?id=17268
> (I do not want reopen bug and writte there because I am not sure about my 
> arguments)
>
> IMHO root of problem is in different definition of TFieldDef.Size and 
> TField.Size
> Documentation says, that
> 1. TFieldDef.Size should be "For string and byte fields, *Size* is the number 
> of bytes reserved "
>   http://docwiki.embarcadero.com/VCL/en/DB.TFieldDef.Size
> 2. TField.Size should be "the maximum number of characters in the string" 
> (for ftString and I guess that also for ftWideString)
>   http://docwiki.embarcadero.com/VCL/en/DB.TField.Size
>   http://docwiki.embarcadero.com/VCL/en/DB.TStringField.Size
>
> And now let's go look into fields.inc:
> 1. Function TFieldDef.CreateField copies Result.Size:=FSize (so 
> TField.Size:=TFieldDef.Size)
> 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

Correct, if you assume 1 char = 1 byte.

> (so documentation is wrong in this case ... also fast test in Delphi shows, 
> that FieldDef.Size=Field.Size=number of characters)

Your story is confusing to me. Where do you see a problem ?

Do you see an implementation problem or a documentation problem ?

Note that nowhere in the documentation pages you mention, widestrings are
mentioned (which is convenient, since that's where 1 char <> 1 byte).

Michael.