* consists of "msg" or (if "msg" is NULL pointer) a generic "Details unknown"
* and of errno's content (if it is non-zero).
*/
-extern void exit_err(int err, char * msg);
+extern void exit_err(int err, const char * msg);
/* Do exit_err() with "msg" as: "Trouble in ".parent." with ".child."." */
-extern void exit_trouble(int err, char * parent, char * child);
+extern void exit_trouble(int err, const char * parent, const char * child);