joshyfun at gmail.com
Sun Sep 4 14:29:07 CEST 2016
El 04/09/2016 a las 14:04, Michael Van Canneyt escribió:
>> The second powerful reason is that I was not aware about TBufStream :)
> It's even documented.
Sure :) But I'm not aware about all the gems in fpc code :)
>> TBufStream does support seek ? And SetSize ?
> Seek: yes. Setsize not.
I was asking looking at code:
function TWriteBufStream.Seek(const Offset: Int64; Origin: TSeekOrigin):
if (Offset=0) and (Origin=soCurrent) then
Result := FTotalPos
Maybe I'm missing something ?
On the SetSize side I think there is a missing check, SetSize can make
the file smaller, so think in a 1 Kb file, you read the first byte so
the buffer will be filled with the 1 Kb data, now you SetSize to 1 byte
and read another byte, this read will return 1 byte success read which
is out of the bounds of the file.
I know this is a terrible border case and the solution could be just
invalidate buffer when a SetSize is called.
> The TBufStream class has 2 descendents: one for reading, one for writing.
> This means the implementation is much more simple, and for most
> usecases, this is sufficient.
That's more or less what I was using in other programs, with my own
class (I should read more docs).
>> My code like TBufStream inherits from TStream. Which is the advantage
>> of inherit from TOwnerStream ?
> TOwnerStream is only useful if you have a second stream which you use as a
> source. It will free it for you. This is useful when chaining streams.
Oh! I see, I'm using the typical Create(Stream,Owned=true)
> I will add your implementation to the bufstream unit. It offers more
> functionality, but works only on files.
> It's - as usual - a tradeoff.
Not exactly, it is possible to add my original implementation
TCacheStream which works over any TStream and create a
TBufferedFileStream (for Delphi compat.) inheriting from it, but it will
not have the same inheritance chain.
What's the best for fpc ? A generic stream cache, a inheritance
compatible TBufferedFileStream ? Or maybe both ? Or None ? :)
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