Cでカプセル化するとこんな感じか?

// h
struct player_t;
extern void player_construct(struct player_t*);
extern void player_set_x(struct player_t*,int);
extern void player_set_y(struct player_t*,int);
extern int player_get_x(struct player_t*);
extern int player_get_y(struct player_t*);
extern void player_move(struct player_t*);