How can I create multiple items with one class in C++? - c++

Question

I have the class Furniture with:
Furniture.h:
#include <iostream>
#include <string>
using namespace std;
class Furniture {
public:
Furniture();
~Furniture();
void setname(string name);
void setprice(double price);
double getprice();
string getname();
virtual void printSpecs();
private:
string name;
double price;
protected:
static int NumberOfItems;
int Id;
};
furniture.cpp:
#include "furniture.h"
Furniture::Furniture() {
}
Furniture::~Furniture() {
}
void Furniture::setname(string name) {
this->name = name;
}
string Furniture::getname()
{
return this->name;
}
void Furniture::setprice(double price) {
this->price = price;
}
double Furniture::getprice() {
return this->price;
}
void Furniture::printSpecs() {
cout<<"Price: "<<this->price<<endl;
cout<<"Name: "<<this->name<<endl;
}
int main() {
Furniture *model = new Furniture();
model->setname("FinalDestiny");
model->setprice(149.99);
model->printSpecs();
delete model;
}
Everything works fine but I want to add multiple furniture items with the same class and just update the NumberOfItems. Is there any way to do that?
Also, is my code ok? I mean, how can I improve it? I'm quite new to OOP and I'd like to learn some good practices.
Thanks.

Answer 1

The idea is conceptually broken. You cannot do that; you really need different objects.
Alternatively, if you really want to have multiple identical items, you can create one item and create multiple pointers to it, and maintain a separate count for the number of active items. A shared_ptr does that for instance.
That said, your code shouldn’t use pointers at all, this is a common anti-pattern in C++ code. Furthermore, your code probably shouldn’t have setters, provide a proper constructor instead:
int main() {
Furniture model("FinalDestiny", 149.99);
model.printSpecs();
}
Much shorter, simpler, and no possiblity of leaking memory.

Answer 2

To keep track of the number of items, you can update the number of items in the constructor:
Furniture::Furniture() {
Id = NumberOfItems++;
}
and decrement in the destructor if you want:
Furniture::~Furniture() {
NumberOfItems--;
}
To access the item by Id, you need to have an extra manager class or use a map:
std::map<int,Furniture*> items;
which you can pass as parameter to the constructor and update it there:
Furniture::Furniture(std::map& items) {
Id = NumberOfItems++;
items[Id] = this;
}
And, outside, you can simply retrieve items with:
Furniture* f = items[3];

Answer 3

I would write in this way
#include <iostream>
#include <string>
using namespace std;
class Furniture {
public:
Furniture(string name = "", double price = 0)
: name(name), price(price), Id(NumberOfItems++)
{}
Furniture(const Furniture &f)
: name(f.getname()), price(f.getprice()), Id(NumberOfItems++)
{}
void setname(string name) { this->name = name; }
void setprice(double price) { this->price = price; }
double getprice() const { return price; }
string getname() const { return name; }
virtual void printSpecs() {}
private:
string name;
double price;
protected:
static int NumberOfItems;
int Id;
};
int Furniture::NumberOfItems;
int main_furniture(int, char **)
{
Furniture a("product 1", 100);
Furniture x(a), y(a), z(a);
}
I've inlined just to simplify. What's interesting to you should be the copy constructor implementation, and (OT) you forget the const on getter...

Answer 4

Just increment NumberOfItems in the constructor, and decrement it in the destructor.

Answer 5

Store the furniture instances in an array or better in a vector. You can access them with an index or iterator. The NumberOfItems field doesn't belong in the furniture class, an instance of furniture shouldn't know about how many furniture items there are in the system. Use the size () method from vector to get the furniture item count.