C++ static member functions and variables

Question

I am learning C++ by making a small robot simulation and I\'m having trouble with static member functions inside classes.

I have my Environment class defined like this:<

Answer 1

The first error says that you cannot use non-static members in static member functions.

The second one says that you need to define static members in addition to declaring them You must define static member variables outside of a class, in a source file (not in the header) like this:

int Environment::numOfRobots = 0;

You don't need any static members. To have an absolutely correct and portable GLUT interface, have a file-level object of type Environment and a file-level (non-member) function declared with C linkage. For convenience, have also a member function named display.

class Environment 
{
 public:
   void display() { ... }
   ... 
};

static Environment env;
extern "C" void display () { env.display(); }