Question

So I have one main file, and two classes: A display Class, and a job class.

What I want to achieve, is for the main class to be able to call the display class, as well as interface with the job class, BUT I also want the Job Class to be able to call methods from the Display class and send parameters to the display class as well.

I have tried multiple ways of fixing my current problem, but I have not been able to accomplish what I am wanting, I have heard about namespaces, but I am unfamiliar with them and am not sure if this is what I need.

I have also tried to pass the Job/Display objects from main, but that has not worked with what I want to do since in my header I already end up defining a new object.

Here is some example code of what I want to achieve (Please ignore simple compiler errors/This is just example code, and I am not going to post my entire project because that would be way to long/Ignore headers):

Main.cpp

 int main(){
    Display display;
    Job job;
    job.init();
    display.test();
    return 0;
}

Display.cpp

 void Display::test(){
     std::cout << "testing.." << std::endl;
 }

 void Display::test2(std::string ttt){
     Job job; //Do not want to create a whole new object here
     std::cout << "testing3333...." << job.getThree() << std::endl;
     std::cout << "testing2222...." <<  ttt << std::endl;
 }

Job.cpp

 void Job::init(){
      Display disp2; //I do not want to create a whole new object here, but I can't fix this
      disp2.test2("from Job");
 }

 std::string Job::getThree(){
       return "test3";
 }

Job.h

class Job{
private:
    Display disp; // Do not want a new object here as well
public:
    void init();
    std::string getThree();
};

Answer 1

You need to pass a Job pointer to the Display, and vice versa, so they know about each other, eg:

Main:

#include "Display.h"
#include "Job.h"

int main()
{ 
    Display display; 
    Job job; 
    display.init(&job);
    job.init(&display); 
    display.test(); 
    return 0; 
} 

Display.h:

class Job;

class Display
{
private:
    Job *_job;
public:
    Display();
    void init(Job *job);
    void test();
    void test2(const std::string &ttt);
};

Display.cpp:

#include "Display.h"

Display::Display()
    : _job(NULL)
{
}

void Display::init(Job *job)
{
    _job = job;
}

void Display::test()
{ 
    std::cout << "testing.." << std::endl; 
} 

void Display::test2(const std::string &ttt)
{ 
    std::cout << "testing3333...." << _job->getThree() << std::endl; 
    std::cout << "testing2222...." << ttt << std::endl; 
} 

Job.h:

class Display;

class Job
{
private:
    Display *_display;
public:
    Job();
    void init(Display *display);
    std::string getThree();
};

Job.cpp:

#include "Job.h"

Job::Job()
    : _display(NULL)
{
}

void Job::init(Display *display)
{ 
    _display = display;
    _display->test2("from Job"); 
} 

std::string Job::getThree()
{ 
    return "test3"; 
} 

Given the requirements you mentioned, the Display does not really need to remember the Job, only the Job needs to remember the Display, so you could do something like this as an alternative:

Main:

#include "Display.h"
#include "Job.h"

int main()
{ 
    Display display; 
    Job job;
    job.init(&display); 
    display.test(); 
    return 0; 
} 

Display.h:

class Job;

class Display
{
public:
    void test();
    void test2(Job *job);
};

Display.cpp:

#include "Display.h"

void Display::test()
{ 
    std::cout << "testing.." << std::endl; 
} 

void Display::test2(Job *job)
{ 
    std::cout << "testing3333...." << job->getThree() << std::endl; 
} 

Job.h:

class Display;

class Job
{
private:
    Display *_display;
public:
    Job();
    void init(Display *display);
    std::string getThree();
};

Job.cpp:

#include "Job.h"

Job::Job()
    : _display(NULL)
{
}

void Job::init(Display *display)
{ 
    _display = display;
    _display->test2(this); 
} 

std::string Job::getThree()
{ 
    return "test3"; 
}