[Gambas-user] gb3: writing variables to a string using a memory stream and pointer

[Benoît Minisini]

> On 09/12/2011 09:19 PM, Benoît Minisini wrote:
> >>> On Sun, Sep 11, 2011 at 07:40, Kevin Fishburne<
> >>> 
> >>> kevinfishburne at ...1887...>   wrote:
> >>>> My code looks like this:
> >>>> 
> >>>> ' For writing outgoing UDP data to memory.
> >>>> Public data As String
> >>>> Public mem As Stream
> >>>> 
> >>>> ' Create data string for outgoing transaction queue.
> >>>> data = Space(8)
> >>>> mem = Memory VarPtr(data) For Write
> >>>> mem.Begin
> >>>> 
> >>>>     Write #mem, (Server.DateCurrent + Server.DateUTC) As Float
> >>>> 
> >>>> mem.Send
> >>>> Print data
> >>>> 
> >>>> It throws signal 11 on the Print statement.
> >>>> 
> >>>> I have two questions. First is this the correct way to write one or
> >>>> more variables to a string in memory, and second what's up with the
> >>>> signal 11? I'm using revision 4094 and will update to the newest
> >>>> revision in a moment.
> >> 
> >> On 09/11/2011 08:13 AM, Jussi Lahtinen wrote:
> >>> Not sure what happen there, but try this:
> >>> 
> >>> Public pData As Pointer
> >>> Public mem As Stream
> >>> 
> >>> pData = Alloc(SizeOf(gb.Float))
> >>> mem = Memory pData For Write
> >>> mem.Begin
> >>> 
> >>>     Write #mem, (Server.DateCurrent + Server.DateUTC) As Float
> >>> 
> >>> mem.Send
> >>> 
> >>> Print Float@(pData)
> >> 
> >> Thanks everyone for your replies. I'm now using this code ('Data' is a
> >> string):
> >> 
> >> ' Create data string.
> >> DataPointer = Alloc(8)
> >> Mem = Memory DataPointer For Read Write
> >> Mem.Begin
> >> 
> >>     Write #Mem, (Server.DateCurrent + Server.DateUTC) As Float
> >> 
> >> Mem.Send
> >> 'Data = Read #Mem As Float
> >> Data = Read #Mem, 8
> >> 
> >> ' Send transaction.
> >> udp.Begin
> >> 
> >>     Write #udp, id As Byte
> >>     Write #udp, 56 As Byte
> >>     'Write #udp, (Server.DateCurrent + Server.DateUTC) As Float
> >>     Write #udp, Data, Len(Data)
> >> 
> >> udp.Send
> >> 
> >> The recipient gets the wrong value for 'Data' when it is converted back
> >> from a string to a float. It gets the correct value if I use the
> >> commented "Write #udp, (Server.DateCurrent + Server.DateUTC) As Float".
> >> Any ideas why I can't write the data stored at DataPointer to the string
> >> Data?
> >> 
> >> In case anyone forgot, I need the data to be saved as a string so it can
> >> be stored in an outgoing network transaction queue, which is an array of
> >> transaction structures. The Data property of the structure stores
> >> arbitrary groups of variables so grouping them as a string is the most
> >> convenient method since there will be up to 255 different transaction
> >> types.
> > 
> > 1) Using Begin/Send is useless if you have only one WRITE instruction.
> > 
> > 2) Every stream has a byte order. Did you check that the byte order of
> > your memory stream is the same as the byte order of your Udp socket
> > stream?
> 
> I corrected the Begin/Send issue, thanks.
> 
> I'd tried setting the byte order both ways before reading the stream and
> still had incorrect results. The client receiving the transaction
> reverses the byte order, which produces the correct results when sending
> the float directly. I tried altering the client code so that it did not
> reverse the byte order and still received incorrect results. I changed
> the code to look like this:
> 
> ' Create data string.
> DataPointer = Alloc(8)
> Mem = Memory DataPointer For Read Write
> Write #Mem, (Server.DateCurrent + Server.DateUTC) As Float
> Data = Read #Mem As Float
> Print "Original: " & (Server.DateCurrent + Server.DateUTC)
> Print "From Mem: " & Float@(Data)
> Print "Reversed: " & Float@(Convert.Reverse(Data))
> 

Your code cannot work : Data receives a Float ( Read #Mem As Float ), and 
later is used as a Pointer ( Float@(Data) ).

-- 
Benoît Minisini