Singleton in my C++ program

Question

I wrote 2 classes, Agent and Timing. The third class will contain the main() function and manage it all. The goal is to create n instances of Agent and a SINGLE instance of Timing. It's important to mention that Agent uses Timing fields and Timing uses Agent functions. How can I turn Timing to singleton?

//Agent.h
#ifndef Timing_h
#define Timing_h
#include <string>
#include "Timing.h"

class Agent{
    public:
        Agent(std::string agentName);
        void SetNextAgent(Agent* nextAgent);
        Agent* GetNextAgent();
        void SendMessage();
        void RecieveMessage(double val);
            //    static Timing runTime;

What I thought would solve my problem but I got:

'Timing' does not name a type

        ~Agent();

    private:
        std::string _agentName;
        double _pID;
        double _mID;
        Agent* _nextAgent;
};
#endif


//Timing.h
#ifndef Timing_h
#define Timing_h

class Timing{
    private:
        typedef struct Message{
            Agent* _agent;
            double _id;
        }Message;
        typedef Message* MessageP;

        Message** _messageArr;
        static int _messagesCount;

    public:
        Timing();
        void AddMessage(Agent* agent, double id);
        void LeaderElected(string name);
        void RunTillWinnerElected();
        ~Timing();
};
#endif

Is this really the way to create a singleton and if it is what is the problem? And if not, how can I turn it to a singleton?

Answer 1

This bit looks suspicious in Agent.h ...

#ifndef Timing_h
#define Timing_h

Seems like it's the same define-guard in Timing.h. Therefore Timing will not be included in Agent.

Change it to

#ifndef Agent_h
#define Agent_h

Answer 2

Nope, the wikipedia page on the singleton pattern has a good example as well as a nice write up of how a singleton is actually constructed.