Question

Can a function be assigned or alter its definition, just like overriding a function by derived classes.

But at this time, it is out of scope from the class.

I mean like this:

//class.h

class MClass
{
public:

  void function(); // this is the function I am referring to.
}
//class.cpp

void MClass::function() { }

//file1.cpp
MClass mclass;


void globalFunction() { }

mclass.function = globalFunction; //is this even possible?

Answer 1

Your function() is a real function, you want function Callback instead.

see sample program: on ideone

#include <functional>
class MClass
{
public:
  std::function<void(void)> func_ptr;

  void setFuncPtr(const std::function<void(void)>& ptr)
  {
    func_ptr = ptr;
  }

  void callFuncPtr()
  {
    func_ptr();
  }
};

You could set func_ptr to any callabe objet

MClass m;
m.setFuncPtr(globalFunction);   // set to standalone function
m.callFuncPtr();

// set lambda to it
m.setFuncPtr([](){ std::cout << " do something " << std::endl; });
m.callFuncPtr();

Or bind to other object

 struct Test
 {
   void print() { std::cout << "Test::print" << std::endl; }
 };
Test t;
m.setFuncPtr(std::bind(&Test::print, t));
m.callFuncPtr();

You could also pass parameter to function by using std::bind and placeholders.