Illegal call to non-static member function (C++)?

Question

I'm developing a game which is based around the user controlling a ball which moves between areas on the screen. The 'map' for the screen is defined in the file ThreeDCubeGame.cpp:

char m_acMapData[MAP_WIDTH][MAP_HEIGHT];

The ThreeDCubeGame.cpp handles most of the stuff to do with the map, but the player (and keyboard input) is controlled by ThreeDCubePlayer.cpp. When a player moves into a new map cell, the game will have to check the contents of that cell and act accordingly. This function in ThreeDCubeGame.cpp is what I am trying to use:

inline char GetMapEntry( int iMapX, int iMapY ) { return m_acMapData[iMapX][iMapY]; }

So, in order to check whether the player is allowed to move into a map cell I use this function call from ThreeDCubePlayer.cpp:

if (ThreeDCubeGame::GetMapEntry(m_iMapX+MAP_OFF_X, m_iMapY+MAP_OFF_Y) == ' ')
{
// do stuff
}

But, when I compile this, I get the warning "error C2352: 'ThreeDCubeGame::GetMapEntry' : illegal call of non-static member function". Is this something to do with the scope of the variables? Is it fixable without redesigning all the code?

Answer 1

class A {
  int i;
public:
  A(): i(0) {}
  int get() const { return i; }
};

int main() {
  A a;
  a.get();  // works
  A::get(); // error C2352
}

There's no object to call the function with.

Answer 2

GetMapEntry is not static so you can't call it without an object of the type ThreeDCubeGame.

Alternatives:
-Make GetMapEntry static: static inline char GetMapEntry
-Create an instance of ThreeDCubeGame and do instance.GetMapEntry(