[Discuss-gnuradio] Message passing as input and output in block (C++ coding)

[Jose Torres Diaz]

Hi All, 

I have another question about the message passing technique. In this opportunity, I would like to create a block that takes message as input, but also that post message downstream as output. In my initial attempt, I'm using the original blob_to_stream example (see below), the incoming message is taken using:

_msg = this->pop_msg_queue();

and then, in order to output the incoming message, it is used:

std::memcpy(output_items[0].get(), blob_mem, noutput_bytes);

However, 

(1) Is it possible to use an alternative way like this:

post_msg(0,_msg.key, _msg.value,_id);   ?

The goal is to output the same message to downstream. 


**************Example blob to stream****************************

 int work(
        const InputItems &input_items,
        const OutputItems &output_items
    ){
        //loop until we get a blob or interrupted
        while (_offset == 0){
            _msg = this->pop_msg_queue();
            if (pmt::pmt_is_blob(_msg.value)) break;
        }
        if (pmt::pmt_blob_length(_msg.value) == 0) return -1; //empty blob, we are done here

        //calculate the number of bytes to copy
        const size_t nblob_items = (pmt::pmt_blob_length(_msg.value) - _offset)/_item_size;
        const size_t noutput_bytes = _item_size*std::min<size_t>(output_items[0].size(), nblob_items);

        //perform memcpy from blob to output items
        const char *blob_mem = reinterpret_cast<const char *>(pmt::pmt_blob_data(_msg.value)) + _offset;
        std::memcpy(output_items[0].get(), blob_mem, noutput_bytes);

        //adjust the offset into the blob memory
        _offset += noutput_bytes;
        if (pmt::pmt_blob_length(_msg.value) == _offset) _offset = 0;

        return noutput_bytes/_item_size;
    }

Thanks for your kind help, 

Regards, 

Jose.