I'm trying to acquire the reverse of a given exit, say, if supplied with west, it'll return east, where west is 3 and east is 1. Between rev_dir[] and get_exit_to(), I believe there is a simple way to do it, but without proper comments on the functions I have been unable to figure it out.

Something like:

int exit_num = ;
EXIT_DATA* exit = get_exit(current_room, exit_num);
ROOM_INDEX_DATA* to_room = exit->to_room;
ROOM_INDEX_DATA* from_room = get_exit(to_room, rev_dir[exit_num]);
printf(to_room == from_room);

See also find_door for how to resolve exit names to exit numbers. (That should really be in its own function, but whatever.)

Marvelous. I appreciate it.