How can I make these classes live in peace and cooperate with eachother?

[theperson]

When I have e forward declaration of PoliceOfficer the compiler complains invalid use of incomplete type 'struct PoliceOfficer'

But when I take away the forward declaration it complains that 'PoliceOfficer' has not been declared

#include <iostream>

using namespace std;


class PoliceOfficer;


class ParkingTicket
{
    public:

        string getOfficerName(PoliceOfficer &theOfficer)
        {
            return theOfficer.officerName;
        }

        int getOfficerBadgeNumber(PoliceOfficer &theOfficer)
        {
            return theOfficer.officerBadgeNumber;
        }

};


class PoliceOfficer
{
     friend class ParkingTicket;


    private:

        string officerName;
        int officerBadgeNumber;
        ParkingTicket* theTicket;


    public:
        void giveTicket()
        {
            theTicket = new ParkingTicket;
        }


};
         

int main()
{

    return 0;
}

[Peter87]

Use forward declaration of PoliceOfficer but do not define the functions that use this class until after the PoliceOfficer class has been defined.

[theperson]

Well, if I reverse the order of the classes like this and also forward declare parking ticket then I get

error: invalid use of incomplete type ‘struct ParkingTicket’|
error: forward declaration of ‘struct ParkingTicket’|
error: multiple types in one declaration|

#include <iostream>

using namespace std;


class PoliceOfficer;
class ParkingTicket

class PoliceOfficer
{
     friend class ParkingTicket;


    private:

        string officerName;
        int officerBadgeNumber;
        ParkingTicket* theTicket;


    public:
        void giveTicket()
        {
            theTicket = new ParkingTicket;
        }


};

class ParkingTicket
{
    public:

        string getOfficerName(PoliceOfficer &theOfficer)
        {
            return theOfficer.officerName;
        }

        int getOfficerBadgeNumber(PoliceOfficer &theOfficer)
        {
            return theOfficer.officerBadgeNumber;
        }

};


int main()
{

    return 0;
}

[Peter87]

You can define the functions outside the class definitions.