How to correctly initialize an event

Question

I'm a student and currently experimenting with the QoS-settings in ROS 2. I'm trying to implement the (RMW_EVENT_REQUESTED_DEADLINE_MISSED) event.

First I declare the subscription and event:

static const rmw_subscription_t sub1
{
    "sub1", (void *) "gets deadline missed",  "topic1"
};
static const rmw_event_t deadline_missed =
{
    "event 1" , (void *) "deadline missed", RMW_EVENT_REQUESTED_DEADLINE_MISSED
};

After that I try to initialize the event:

rmw_subscription_event_init(deadline_missed, sub1, RMW_EVENT_REQUESTED_DEADLINE_MISSED);

But I get an error ( No matching function for call to 'rmw_subscription_event_init')

The program suggests me to change my subscription and event declaration to:

static const rmw_subscription_t *const sub1
{
    "sub1", (void *) "gets deadline missed",  "topic1"
};
static rmw_event_t *const deadline_missed =
{
       "event 1" , (void *) "deadline missed", RMW_EVENT_REQUESTED_DEADLINE_MISSED
};

But then I get the following error (Excess elements in scalar initializer).

How do I fix this problem and which of those 2 cases is the best? Or is there a completely other way of creating this event?

Thanks in advance!

Clonk · Answer 1 · 2019-10-02T11:18:42.120

rmw_subscription_event_init takes pointers as argument so you need to pass the memory adress of your objects rmw_subscription_tand rmw_event_t :

rmw_subscription_event_init(&deadline_missed, &sub1, RMW_EVENT_REQUESTED_DEADLINE_MISSED);

You can also change the definition of sub1 and deadline_missed to be pointers (as you suggested), but in that case you need to properly initialize the pointers to your structs. I recommand reading these excellent answers for more information.

How to correctly initialize an event

1 Answers1