eboasson
commented
1 year ago With all the stuff going on it is hard for me to give you a date, at least a date by which we will finally complete the built-in topic support in the C++ binding — and I certainly can't say anything about when someone else might decide to sit down, do it and contribute it.
There are basically two parts to it:
- The "built-in subscriber" and looking up data readers in that subscriber for the built-in topic you care about. This part of the spec is, in my view, simply stupid, because it makes things vastly more complicated then necessary. In Cyclone you can simply create readers for the built-in topics without doing anything special, and this would translate directly to the C++ binding.
- The C code gives you the built-in topic samples in its own representation, in particular including the QoS setting. The C++ binding should convert these into things that fit the C++ API. With #434 merged, properly implementing readers for the built-in topics in the C++ binding should now be straightforward. If I am not mistaken, then making sure https://github.com/eclipse-cyclonedds/cyclonedds-cxx/blob/0e16805953134bb64113a08ae43afc96c1cd3b19/src/ddscxx/include/dds/sub/detail/LoanedSamples.hpp#L79 performs the C-to-C++ representation conversion first for the built-in topics should be enough, and, again, IINM, that just means specializing this template for 4 data types. So it means some work, but nothing too difficult. (But I don't know the C++ binding that well, and neither do I know C++ all that well, so I may be wrong here.)
You do have the option of using the C API directly for the built-in topics: you really don't need to deal with a lot of C for that, just a few lines really: thanks to get_ddsc_entity() you should be able to do something like:
#include "dds/dds.h"
auto dp = dds::domain::DomainParticipant(0);
auto reader = dds_create_reader(dp.get_ddsc_entity(), DDS_BUILTIN_TOPIC_DCPSPARTICIPANT, nullptr, nullptr);
void *sampleptr = nullptr;
dds_sample_info_t info;
int32_t n = dds_take(reader, &sampleptr, &info, 1, 1);
if (n > 0) { // really means n=1 because we limited dds_take to at most one sample
dds_builtintopic_participant_t const * const sample = static_cast< dds_builtintopic_participant_t const *>(sampleptr);
// do something with sample
dds_return_loan (reader, &sampleptr, n);
}(beware: I only copy-pasted some things together ...)
showmethejinw
The current builtin_subscriber function doesn't seem to support it. It seems that the implementation is underway. When will the implementation be completed?