I am currently using Eclipse Cyclone DDS C++ and I am wondering if it is possible to send data without any key specified with #pragma keylist in an IDL.
Is it possible to achive this through QoS-Settings? If so, how?
If you do #pragma keylist TYPE without listing any key fields, the IDL compiler will generate everything you need for creating a topic that doesn't have any key fields. So
struct S {
long something;
string orother;
};
#pragma keylist S
is perfectly valid, and then you can create a topic for S.
I am not entirely sure what you mean by
In this case writes to the same topic could not be distinguished by the readers.
The above will result in a single instance for this topic. You can still have a history and so, e.g., the reader can still ensure it sees every update by specifying a KEEP_ALL history setting. The reader can therefore still distinguish between the writes by looking at the content and/or the sample info, but for DDS these are all updates to this one instance.
Is it possible to achive this through the QoS-Settings?
No, you cannot (currently) override the key fields using the QoS settings.