As the FIX protocol evolves, new versions will be released to you to extend the current functionality. OnixS C++ FIX Engine currently supports the following FIX versions: 4.0, 4.1, 4.2, 4.3, 4.4, 5.0, 5.0 SP1, and 5.0 SP2.
OnixS::FIX::ProtocolVersion::Enum enum is used to identify a particular version of the FIX protocol in C++ FIX Engine.
To simplify development, as well as to increase code readability, C++ FIX Engine exposes separate namespaces for each version of the FIX protocol. Each such namespace contains objects and definitions that are unique for the particular version.