using a class constructor w/ class array

matt000r000 · 10-31-2009, 08:48 PM

I don't know how to describe this, so i'll give some example code:

Code:

class neural_node{
    public:
        nueral_node(int size){
            node_size=size;
        }
    private:
        int node_size;
}

class layer{
    public:
        layer(int node_size, int number_of_nodes){
            layer_nodes=new neural_node[node_size][number_of_nodes];
        }
    private:
        neural_node* layer_nodes;
}

in this, both nueral_node and layer are going to be treated as data types.

my question is this: how can I use the neural_node constructor for the array?

any help will be greatly appreciated!

p.s.
can i actually use a pointer on a class? it's been so long since i used classes.

Sebastiani · 10-31-2009, 09:34 PM

It isn't clear why you are trying to allocate a two-dimensional array, so I'm assuming that's just a typo. Anyway, you can't declare a variable-length array of objects that don't have a default constructor. Moreover, you shouldn't be using 'new' to allocate *any* array for that matter (quite error prone). The best solution would be to use an std::vector:

Code:

class neural_node 
{
    public:
        neural_node(int size){
            node_size=size;
        }
    private:
        int node_size;
};

class layer {
    public:
        layer(int node_size, int number_of_nodes)
	: layer_nodes( number_of_nodes, neural_node( node_size ) ) {
            // ...similar to...
	    layer_nodes.resize( number_of_nodes, neural_node( node_size ) );
        }
    private:
         std::vector< neural_node > layer_nodes;
};

Spidey · 10-31-2009, 09:36 PM

Quote:

can i actually use a pointer on a class? it's been so long since i used classes.

Yes, you can use a pointer on pretty much anything that has a memory address.

Your code has a lot of mistakes, layer_nodes is a pointer to neural node, and you are treating it as a 2D array, which is a pointer to a pointer. Also, when creating a dynamic array, the only constructor you can call is the default constructor(which must explicitly be present).

Also, when allocating dynamic memory, make sure you free it once your done.

Here is another way you can achieve what you were trying to do..

Code:

class neural_node{
    public:
		neural_node(){ }

		void set_size(int size) {
            node_size = size; 
        }
    private:
        int node_size;
};

class layer{
    public:
        layer(int node_size, int number_of_nodes){
            layer_nodes = new neural_node[number_of_nodes];
			for(int i = 0; i < number_of_nodes; ++i)
				layer_nodes[i].set_size(node_size);
        }
        ~layer()
	{
		delete[] layer_nodes;
	}
    private:
        neural_node* layer_nodes;
};

Elysia · 11-01-2009, 06:14 AM

Quote:

Originally Posted by Spidey

...and you are treating it as a 2D array, which is a pointer to a pointer...

A 2D array is not a pointer to pointer. It is a pointer to an array.

Spidey · 11-01-2009, 07:08 AM

Quote:

Originally Posted by Elysia

A 2D array is not a pointer to pointer. It is a pointer to an array.

oops! My Bad, Thats what I meant.

10-31-2009, 08:48 PM	#1
matt000r000 Registered User Join Date: Oct 2009 Posts: 1	using a class constructor w/ class array I don't know how to describe this, so i'll give some example code: Code: class neural_node{ public: nueral_node(int size){ node_size=size; } private: int node_size; } class layer{ public: layer(int node_size, int number_of_nodes){ layer_nodes=new neural_node[node_size][number_of_nodes]; } private: neural_node* layer_nodes; } in this, both nueral_node and layer are going to be treated as data types. my question is this: how can I use the neural_node constructor for the array? any help will be greatly appreciated! p.s. can i actually use a pointer on a class? it's been so long since i used classes.
matt000r000 is offline

10-31-2009, 09:34 PM	#2
Sebastiani Guest Join Date: Aug 2001 Posts: 4,923	It isn't clear why you are trying to allocate a two-dimensional array, so I'm assuming that's just a typo. Anyway, you can't declare a variable-length array of objects that don't have a default constructor. Moreover, you shouldn't be using 'new' to allocate any array for that matter (quite error prone). The best solution would be to use an std::vector: Code: class neural_node { public: neural_node(int size){ node_size=size; } private: int node_size; }; class layer { public: layer(int node_size, int number_of_nodes) : layer_nodes( number_of_nodes, neural_node( node_size ) ) { // ...similar to... layer_nodes.resize( number_of_nodes, neural_node( node_size ) ); } private: std::vector< neural_node > layer_nodes; };
Sebastiani is offline

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