+
+
+
+/* If "err" != 0, exit with an error message "msg" and clean up. If "msg" is a
+ * NULL pointer, return generic "Details unknown". In any case, also print "err"
+ * as the "internal error code". Also print errno if it is non-zero.
+ */
+extern void exit_err(uint8_t err, struct World * world, char * msg);