dynamic allocation and polymorphism - c++ [closed] - c++

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Need some insight on how to complete this last part of my Marina class. Any help would be greatly appreciated.
This is a big project I'm working on. I created a group of classes that are derived from a base class Boat using public inheritance. The Marina class represents the care of the boats in a Marina. The Marina class contains a fixed size array of pointers to Boat.
The function should place a new Boat into the Marina if there is room and each new boat must be dynamically allocated. The function should also ask the user what kind of boat they want and then add that kind to the next empty place in the array.

Answer 1

The error suggests that you forgot to include Boat.h (or anything defining class Boat) in your cpp file.
But anyway, code shown in question has some problems :
line _m[i] = NULL; is outside of the loop where i is declared and will raise an error - and I cannot imagine a reason to have it there ...
you create an uninitialized boat, and do not keep a pointer to it : how will you find and initialize it ?
You said that boats should be dynamically initialized, and that method _add_boat must be void. IMHO there are only two acceptable ways :
create the boat outside of the method and only use add_boat to put it in marina (throwing exception if marina if full) :
void Marina::_add_boat(Boat *boat)
{
for (unsigned i = 0; i < _num_boats; i++)
{
if (_m[i] == NULL)
_m[i] = boat;
return;
}
throw std::runtime_error("Marina full");
}
usage :
Boat b = new Boat();
marina._add_boat(b);
pass arguments to initialize boat
void Marina::_add_boat(int type, Owner& owner, ...) // arguments for Boat ctor
{
for (unsigned i = 0; i < _num_boats; i++)
{
if (_m[i] == NULL)
_m[i] = new Boat(type, owner, ...);
return;
}
throw std::runtime_error("Marina full");
}
Below is original answer left only because some interesting comments refere to it
Why not something like :
I assume you have an array of boats (Boat *) in the Marina of size _num_boats. An empty place is conventionnaly a NULL. It gives :
static const unsigned int _num_boats = 100; // the value you need or a constexpr
class Marina {
Boat * boats[_num_boats];
...
Boat * Marina::_add_boat() {
for (unsigned i=0; i<_num_boats; i++) {
if (boats[i] == NULL) {
boats[i] = new Boat();
return boats[i]; // returns dynamically created Boat if room in Marina
}
}
return NULL; // return NULL if Marina full
}
}
With this logic you set attributes of Boat after placing it in Marina ...