In most cases, it is a better idea to invoke sd_bus_default_user(3), sd_bus_default_system(3) or related calls instead of the more low-level sd_bus_new() and sd_bus_start(). The higher-level calls not only allocate a bus object but also start the connection to a well-known bus in a single function invocation.

sd_bus_ref() increases the reference counter of bus by one.

sd_bus_unref() decreases the reference counter of bus by one. Once the reference count has dropped to zero, bus is destroyed and cannot be used anymore, so further calls to sd_bus_ref() or sd_bus_unref() are illegal.

sd_bus_unrefp() is similar to sd_bus_unref() but takes a pointer to a pointer to an sd_bus object. This call is useful in conjunction with GCC's and LLVM's m[blue]Clean-up Variable Attributem[][1]. Note that this function is defined as inline function. Use a declaration like the following, in order to allocate a bus object that is freed automatically as the code block is left:

{
        __attribute__((cleanup(sd_bus_unrefp)) sd_bus *bus = NULL;
        int r;
        ...
        r = sd_bus_default(&bus);
        if (r < 0)
                fprintf(stderr, "Failed to allocate bus: %s\n", strerror(-r));
        ...
}

sd_bus_ref(), sd_bus_unref() and sd_bus_unrefp() execute no operation if the passed in bus object is NULL.