   Unresolved external symbol in C++/SDL.
  It's mentioning two files, player.obj and sprite.obj, both classes that "implement" my Locatable class.player.obj : error LNK2001: unresolved external symbol "public: virtual struct SDL_Rect * __thiscall Locatable::get_offset(void)" (?get_offset@Locatable@@UAEPAUSDL_Rect@@XZ)sprite.obj : error LNK2001: unresolved external symbol "public: virtual struct SDL_Rect * __thiscall Locatable::get_offset(void)" (?get_offset@Locatable@@UAEPAUSDL_Rect@@XZ) Here's the Locatable code:#ifndef LOCATABLE_H#define LOCATABLE_H#include "SDL.h"class Locatable{public: // Here, when I put this abstract function in, it creates the  // error in the other classes.virtual SDL_Rect* get_offset();virtual bool check_collision( Locatable*, Locatable* ) =0;virtual void draw() =0;};#endif // LOCATABLE_H When I remove that get_offset() function, it runs normally.  Is there any link I'm missing?   
  Fixed it, must be tired.   