I wouldn't put the declarations into <err.h> but use
a separate header. <err.h> is quite popular and used
by 3rdparty and local software, and your e* functions
have a high potential for namespace collisions.

Whether error messages are printed or not... not
sure what is right. But if error messages are printed,
they should not contain the strings passed by the user
as they could contain escape sequences or sensitive
information.

best regards
Matthias