Question

Will there be a difference between the following two ways of calling a function from an instance? Which is better?

    Motor M;
    M.moveToPosition(Speed, TargetPosition);

    Motor *M;
    M->moveToPosition(Speed, TargetPosition);

Thanks!

Answer 1

Your second version has Undefined Behavior, because the pointer is uninitialized!

You can dynamically allocate an object of type Motor(i.e. allocate it on the heap):

Motor *M = new Motor;
M->moveToPosition(Speed, TargetPosition);
...
delete M;

Smart Pointers will help you avoid to have to remember to delete objects allocated on the heap.

As for which is better, I am afraid it depends a lot on the context. Usually in C++ you should prefer automatic objects (on the stack) to dynamic objects (on the heap) unless you have a definite reason for the contrary.