Re: [Discuss-gnuradio] Usage of Message Queues

[Martin Lülf]

Am 23.02.2013 17:09, schrieb Hanz:
> Thank you much for your answer. Indeed, its a shared pointer. I now figured
> out, the the only way to get the data is via .to_string().


> So my thought was, that all the messages then should contain one byte (with
> one bit information). At the end, my code looks like that:
>
> tb = top_block()
>         tb.start()
>
>         while 1:
>
>                         point=tb.sink_queue.delete_head()
>                         point=point.to_string()
>                         print len(point)
>
> The first curiosity is, that the length variates from 2 up to 2048. Can
> somebody explain why? The next question is, how to i convert the "bitvalue"
> of the string to an actual char?

Hi,

your code setup with the blocks and connects looks fine to me.

Although I have not checked the details of msg_sink I would expect it to 
process blocks of incomming bytes into messages. So a message can 
contain an abritrary amount of bytes in it (I think that is why your 
length varies). Once again speaking for the C++ interface with the 
method length() you will get the number of elements that this message 
contains. Then you can usually access the message's data through a call 
to the msg() function which returns a pointer to a byte array containing 
the bytes. This will be wrapped to some python code, so check the return 
type of msg() and try to process this returned data instead of 
to_string() if you are interested in the data itself. So I think your 
code should look something like this (not tested, please check agains 
the actual Python interface documented with Sphinx or Python docstrings):

message=tb.sink_queue.delete_head()
data=message.msg()
length=message.length()

for i in xrange(length) :
        byte=data[i]

Hope this gives you an idea on how to use the interface.

Martin