unable to use friend class' method - c++

Question

I have a problem with my code. I have two classes, Run and Robot, and I want an object of type Robot to change a private member of an object of type Run. To be specific, I want to increment the value of 'x' in the following code.
The following errors pop up:
error: 'getX' was not declared in this scope
error: 'getX' was not declared in this scope
I have pinpointed with an arrow (<---) the line where the error occurs. The following code is just a test, just to learn how to use the 'friend' keyword for a project.
#include <iostream>
#include <vector>
using namespace std;
class Robot;
class Run{
friend class Robot;
private:
int x;
vector<Robot*>robots;
public:
Run();
vector<Robot*>*getRobots();
void createRobot();
void movAll();
void setX(int);
int getX();
};
class Robot{
friend class Run;
public:
Robot();
void movingRobot();
};
Run::Run(){}
vector<Robot*>*Run::getRobots(){return &robots;}
void Run::createRobot(){getRobots()->push_back(new Robot);setX(1);}
void Run::movAll(){getRobots()->at(0)->movingRobot();}
int Run::getX(){return x;}
void Run::setX(int c){x=c;}
Robot::Robot(){}
void Robot::movingRobot(){setX(getX()+1);} <-------------------------
int main(){
Run Sim;
Sim.createRobot();
Sim.movAll();
}
Using the 'friend' keyword will definitely help on my project, so I am trying to understand how to use it.

Answer 1

You're just calling getX() and setX() as if they're methods of Robot. You need to call the function against an instance of Run, and in this case you don't need it to be a friend because getX() is public anyway.
That said, do you want each Robot to have an x value that you want to increment? In that case, you need it to be a member of Robot rather than Run.
If you want Run to have a single value of x that all instances of Robot can access and modify, then just make x static, then access it directly rather than calling the public methods, which don't require another class to be a friend anyway.

Answer 2

You called getX as if it were a function of the Robot-class. You need a run object to call it:
run.getX()

Answer 3

Ok you can remove the getX() function from The Robot class as it has no code body at present anyway, and for internal use the robot class can always utilise its X variable. Run doesn't need to have a friend class Robot, as Robot should not need to look into Run for anything, and as Run contains a vector of pointers to instances of Robot it can access any values of Robot instances by looking at the contents of its vector (for example myRunInstance.getRobots()[1]->getX() would return the x value of the 2nd robot in the vector of robots).
Now the getX function will have to vary a tad if it is to remain in the Run class: you will need to specify a way to make it gather the information of a specific instance of the Robot class, presumably from its vector of Robots. I have respecced your code above and added a small proof of concept set of code to the main, makes 10 robots moves them all using moveall, then sets Johnny5 to a special place (because he IS special:) Something along the lines of:
#include <iostream>
#include <vector>
using namespace std;
class Run;
class Robot{
friend class Run; // allows the Run class to access all the private data as if it were its own
private:
int x;
public:
Robot() {};
void setX(int newX) { x= newX; }
int getX() { return x; }
void movingRobot() { x+=1; }
};
class Run{
private:
vector<Robot*> robots;
public:
Run(){};
vector<Robot*> *getRobots() { return &robots; }
void createRobot() { robots.push_back(new Robot()); robots.back()->x =1; }
void movAll() { for (int i=0;i<robots.size();i++){ robots[i]->movingRobot();} }
int getX(int robotPosition){ return robots[robotPosition]->x; } //uses the friend status to read directly from Robot class instances x
void setX(int rpos, int xval){ robots[rpos]->setX(xval); }
};
int main()
{
Run *Sim = new Run();
for (int i =0; i< 10; i++)
{
Sim->createRobot();
Sim->setX(i,i); // uses the Run setX
std::cout << "Robot " << i << "(starting position): " << Sim->getRobots()->at(i)->getX() << std::endl;
}
Sim->movAll();
// lets move Johnny 5 to 55 as well...
(Sim->getRobots()->at(4))->setX(55); // uses the robot setx
for (int i=0; i< 10; i++)
{
std::cout << "Robot " << i << "(final position): " << Sim->getRobots()->at(i)->getX()<< std::endl;
}
return 0;
}
Source also viewable with sample output at Ideone