nil selection and enter (return)

how can I get cad to tell the difference between a nil selection and the
user just hitting enter (return)?

they both have the same result "nil"..

an example of this already in action is the offset command..
Command: offset
Specify offset distance or [Through] <Through>: Specify second point:
Select object to offset or <exit>: ;nil selection, so it loops
Select object to offset or <exit>: ;nil selection, so it loops
Select object to offset or <exit>: ;nil selection, so it loops
Select object to offset or <exit>: ;nil selection, so it loops
Select object to offset or <exit>: ;hit enter (return) so exit


cad can tell the difference, but I don't see how.

please help me out here..

 

ERRNO
Enter new value for ERRNO <0>:

Command: (entsel)

Select object: nil

Command: errno

Enter new value for ERRNO <7>: 0 <--- returned when nothing selected (value 7)

Command: (entsel)

Select object:
nil

Command: errno

Enter new value for ERRNO <52>: <---- returned when hit enter (value 52)

Tim
ps if you use this make sure you set errno to 0 when you start the routine each time.

 

sweet. thank you.