question regarding polymorphism

[agvogel]

Hi,

I'm having an issue trying to use the print() method of a subclass that is declared in the manner

Creature& cr = grid.get(i, j);

where grid.get(i, j) returns a Creature that has been initialized as a Dragon, a subclass of creature. The Creature is stored by value in the grid. When I call the print method, however, the Creature's print() method is called, and not the Dragon's. The print() function in both is defined as virtual.

Am I missing something obvious? Do I need to provide more code or explanation?

Thank you very much

[Disch]

Check the signature of Creature and Dragon's print function. They must match exactly for polymorphism to work.

If you have something like this:

void Creature::print() // Creature returns a void

int Dragon::print() // Dragon returns an int  BAD 

that will be a problem. The function need to have the same return type, the same parameters, etc, etc.

EDIT:
Since it would probably help, can you post your Creature::print and Dragon::print functions?

[agvogel]

They are identical. I've narrowed the problem down further. The grid stores data in a two-dimensional array. Each element is assigned as such:

Dragon d;
// default constructor

for (int i = 0; i < x; i++)		// nested for loop sets all values to dragon, just for testing
{
	for(int j = 0; j < y; j++)
	{
		type[i][j] = d;
	}
}

I see the problem. Since it's binding using value, it's not calling the right print(). So how can I bind by pointer or reference without causing all elements in the array to point to the same value?

Note: later I'm going to have all array cells set to a Creature representing an empty cell in this case.

Again, thank you for your help.