Using an undefined class?

[robione]

I'm probably going a bit overboard in writing some neural network code as far as OOP goes but I'd like to make it work if possible. The problem I am having is that I have defined classes: CNeuron, CGanglion (a layer in the network), CNetwork, and CLink (a graph edge.... a link from one neuron to another)

In CLink.h I have "class CNeuron;" before it's definition as one of the attributes is a pointer to a neuron. This works out okay. CNeuron.h includes Clink.h, but in CNeuron.h I have a method that uses CGanglion. So I placed "class CGanglion;" prior to my definition of CNeuron.... but now I get an error. If I place this in CLink.h instead I get an error.... it seems wherever I place it I get an error.

D:\Visual Studio Projects\ann\Neuron.cpp(41) : error C2027: use of undefined type 'CGanglion'

Stuff like this makes me still feel like a noob. There must be a solution. Thanks for any help.

/*************************************/
//CLINK.H

#include <stdlib.h>
#include <time.h>

class CNeuron;

class CLink  
{
public:
	CLink() {::memset(this,0,sizeof(*this));}
	~CLink() {}

	double dWeight;
	CNeuron *pNeuron;
};

/*************************************/
//CNEURON.H

#include <vector>
#include <cmath>
#include "Link.h"
using namespace std;

namespace afunc {
	double identity(double x);
	double step(double x);
	double bipolar(double x);
	double sigmoid(double x);
	double bisigmoid(double x);
}

class CGanglion;

class CNeuron  
{
public:
	void Attach(class CGanglion *pLayer);
	void Fire(void);
	CNeuron();
	virtual ~CNeuron();

	double dSummator;
	double (*pfActivation)(double);
	vector<CLink> vOutput;
private:
	void Repolarize(void) {dSummator = 0.;}
};

/*************************************/
//CGANGLION.H

#include "Neuron.h"

class CGanglion  
{
public:
	void Add(int n,bool b);
	CGanglion();
	virtual ~CGanglion();

	vector<CNeuron> vNeurons;

};

I don't understand why it works for one file but not the other.