Re: tbufferfile in pyroot

 > I got it working by passing in an array instead, which PyROOT casts as a  > null pointer automatically:

Er, void pointer, of course. :)

Cheers,
Andy

On 11/14/2011 11:57 AM, Andy Mastbaum wrote:
> Wim,
>
> Thanks for the quick reply!
>
> After some further hacking, it turns out the source of my troubles was
> trying to pass a string containing null characters into C. It seems the
> C interface makes null-terminated C strings out of unterminated Python
> strings by stopping at the first zero. Fine for "hello, world!", but a
> real gotcha for buffers!
>
> I got it working by passing in an array instead, which PyROOT casts as a
> null pointer automatically:
>
> msg = socket.recv(copy=False)
> b = array.array('c', msg.bytes)
> buf = ROOT.TBufferFile(ROOT.TBuffer.kRead, len(b), b, False, 0)
> h = buf.ReadObject(ROOT.TH1F.Class()) # works!
>
> (Incidentally, it's odd that the TBuffer constructor takes the buffer as
> a null pointer... a char* seems a more sensible choice since it has to
> be a byte sequence.)
>
> Best,
> Andy
>
> On 11/14/2011 01:59 AM, wlavrijsen_at_lbl.gov wrote:
>> Andy,
>>
>>> msg = socket.recv(copy=False)
>>> buf = ROOT.TBufferFile(ROOT.TBuffer.kRead, len(msg.buffer),
>>> sip.voidptr(id(msg.buffer)).ascobject(), False)
>>> o = id(buf.ReadObjectAny(ROOT.TH1F.Class())) # error!
>>>
>>> I use SIP for casting, since I believe that's what PyROOT is written
>>> with
>>
>> it's not: PyROOT is based on CINT dictionaries. Are you sure btw. that
>> the
>> result of id() will yield a pointer to the underlying object for
>> msg.buffer?
>> It normally (and only in CPython) is a pointer to the python object; it
>> will
>> not work for PyROOT objects for sure (use ROOT.AsCObject() instead and
>> pass
>> that result around for those cases, but I don't know what socket
>> returns).
>>
>> Best regards,
>> Wim
>
Received on Mon Nov 14 2011 - 18:06:32 CET