Question

I’ve been looking into this issue for 2 days, but no luck.

I have the following struct predefined

struct Motor : Port {
Motor(port_t port) : Port(port) {}
void moveAtVelocity(int velocity) { move_at_velocity(m_port, velocity); }
....
};

I’ve then tried to call an instance of the struct

Motor M;

And I’m getting

Error: No matching function for call to Motor::Motor()
Note: Candidates are Motor::Motor(port_t)

How do I call an instance so for example I can use the following method

moveAtVelocity(..);

I know I messed up between classes and structures and constructors and destructors; The thing is that I can’t find a proper tutorial, extra kudos if you can link one for me.

Thanks in advance 🙂

Answer 1

That’s right; what you should have instead is:

Motor M(123);

(where 123 is a port).

When you just say Motor M;, the compiler attempts to construct this object by calling a parameterless constructor. You don’t have any defined. You can, however, just pass the required parameter like I’ve shown above.

An alternative solution is, of course, to just add a parameterless constructor, but this requires your base class, Port, to have one too, or for you to pass a fixed value:

Motor() : Port(123) {}  // fixed value
Motor() {} // assumes Port has a parameterless constructor