Converting a 2d array to 2d vector of objects

Question

I have the following code and I'm trying to convert the two dimensional array to a two dimensional vector.

int main()
{
    const string ID_BASE = "56-123-";
    const int NUM_AISLES = 2;
    const int NUM_SHELVES = 3;

    // Declare 2-D array of objects.
    //Product products[NUM_AISLES][NUM_SHELVES];
    Product **products;

    int idNum = 0;
    int i, j;

    products = new Product *[NUM_AISLES];

   // Add a set of candy bars (all same price).
   for (i = 0; i < NUM_AISLES; i++)
   {
       products[i] = new Product[NUM_SHELVES];

        for (j = 0; j < NUM_SHELVES; j++)
        {
            // Build up id number using string stream.
            stringstream id;
            id << ID_BASE << setfill('0') << setw(2) << idNum;

            products[i][j].set(id.str(), 0.50, true);

            idNum++;
        }
    }

    // Increase prices and output each product.

    for (i = 0; i < NUM_AISLES; i++)
    {
        // Increase price for all products in aisle
        // (recall products is 2-d, but function
        // increasePrice() wants 1-d array).
       increasePrice(products[i], NUM_SHELVES, 1.0);

        for (j = 0; j < NUM_SHELVES; j++)
        {
            // Output individual product in 2-d array.
            products[i][j].output();
            cout << endl << endl;
        }
    }

Nearly all of my searches about multidimensional vectors are based on primitive data types, and the fact that I'm trying to create a two dimensional vector of objects is tripping me up. Can anyone explain this to me?

Answer 1

I just give you a simple example of initializing a 2D Vector of objects and hope this will help you getting started:

#include <vector>
class Foo {};
typedef std::vector<Foo> FooVector;
typedef std::vector<FooVector> FooMatrix;
main(){
    FooMatrix X;
    for (int i=0;i<imax;i++){
        FooVector Y;
        for (int j=0;j<jmax;j++){
            Y.push_back(Foo());
        }
        X.push_back(Y);
    }
    // ... this is equivalent to ...
    FooMatrix X2 = FooMatrix(imax,FooVector(jmax,Foo()));
}

and if have a function that takes a vector:

void bar(FooVector x,int y){ /*...*/ }

you can call it like this:

for (int i=0;i<X2.size();i++){
     bar(X2[i],i);
     // ... or ...
     bar(X2.at(i),i);
}

Hope this helps...

Answer 2

Use a two dimensional vector:

1) you could use vector<vector<Product *>> products;

vector<vector<Product *> > products;

products[i].push_back(new Product());

Remember to release the objects once done via pointers.

2) you could use vector<vector<Product>> products;

products[i].push_back(Product());

If you decide to store them by pointers, you must manage allocation/deallocation of these objects.

There are many other things to be taken care of: vector of pointers

On the other hand, storing object by copies in vectors will provide a better locality of reference.