Modern C++ API: Don’t Declare Entities As Pointers
Entities, such as the DomainParticipant or the DataReader should never be created as pointers (i.e. using new). They already implement reference semantics and behave like a shared_ptr. A DomainParticipant (or any other reference type in the API) is a wrapper of shared_ptr<DomainParticipantImpl>.
Whenever you declare an Entity, as a class member, a local variable, etc., declare it as a regular variable, for example:
1 2 3 4 5 6 7 8 9 10 11 | class MyClass { ... // Correct declaration: DomainParticipant my_participant; // Don’t do this: // DomainParticipant * my_participant; // nor this: // shared_ptr<DomainParticipant> my_participant; }; |
This may force you to call a DomainParticipant constructor in the constructors of MyClass, for example:
1 2 3 4 5 6 7 8 9 | class MyClass {public: MyClass(int domain_id) : my_participant(domain_id) { }private: DomainParticipant my_participant; }; |
But if for some reason you can’t create the object right there, you can use the constructor that receives dds::core::null (or nullptr in C++11) and create the actual DomainParticipant later:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | class MyClass {public: MyClass() : my_participant(nullptr) { } int create_participant(int domain_id) { // Creates the DomainParticipant and assigns the reference // to my_participant. After this assignment, this DomainParticipant's // reference count is 1. my_participant = DomainParticipant(domain_id); }private: DomainParticipant my_participant;}; |
Note that the DomainParticipant will be automatically deleted by MyClass's implicit destructor, since we are not holding any other references to it other than my_participant.