can i jump into a gosub, then out early, using labels?

[stevmjon]

hi

just wondering about possible stack overflow. i jumped into a part of a gosub using 'goto label:' , read a small portion of it, then used 'goto label:' to jump back out to where i started from.

will this cause the same problem as not using return in a gosub?

i figured if i didn't use 'gosub label' it would be o.k. but i want to make sure.

thanks stevmjon

[kevin]

Without seeing the code,  all i can say is that this is potentially problematic design.

[kevin]

 Examples...

PlayBASIC Code: [Select]

  // Single Call point, Multiple Exit points..

   Do
      cls 0

         for lp=0 to 10000
            inc x
            Gosub SubRoutine
         next

         print X

      Sync
   loop


SubRoutine:

      if X>1 then return
      print "X not greater than 1"

   return

  Using a goto inside the subroutine to jump to the exit point..  This is legal, but ugly as hell..

PlayBASIC Code: [Select]

  // Single Call point, Single Exit..  
  
   Do
      cls 0

         for lp=0 to 10000
            inc x
            Gosub SubRoutine
         next

         print X

      Sync
   loop


SubRoutine:

      if X>1 then goto SubRoutineEnd
      print "X not greater than 1"

SubRoutineEnd:
   return

PlayBASIC Code: [Select]

  // Single Call point, Single Exit..  
  
   Do
      cls 0

         for lp=0 to 10000
            inc x
            Gosub SubRoutine
         next

         print X

      Sync
   loop



   // one entry point
SubRoutine:

      if X<=1
         print "X not greater than 1"
      endif

   // one exit point
   return

 
  This one has two entry points, and one exit point.  Regardless of entry point the code will flow through to the single exit point.  So it's legal.. ugly, but legal...

PlayBASIC Code: [Select]

   Do
      cls 0

         for lp=0 to 10000
            inc x
            Gosub SubRoutine_EntryPoint1
         next

         for lp=0 to 10000
            Gosub SubRoutine_EntryPoint2
         next

         print X

      Sync
   loop



   // first entry point
SubRoutine_EntryPOint1:

      if X<=1
         print "X not greater than 1"
      endif

   // second entry point
SubRoutine_EntryPOint2:


   // one exit point...
   return

   However if you goto into a subroutine, and expect to exit via Return, then this won't work.

PlayBASIC Code: [Select]

   Do
      cls 0

         for lp=0 to 10000
            inc x
            Gosub SubRoutine_EntryPoint1
         next

         for lp=0 to 10000
            Goto SubRoutine_EntryPoint2
         next

         print X

      Sync
   loop



   // first entry point
SubRoutine_EntryPOint1:

      if X<=1
         print "X not greater than 1"
      endif

   // second entry point
SubRoutine_EntryPOint2:


   // one exit point...
   return

[stevmjon]

thanks kev

the way i was thinking was slightly different to your examples. to enter via label, then exit via label, upon condition only.


do

   gosub subroutine_normal

   if condition=1 then goto enter_part_gosub
   exit_part_gosub:

   sync

loop


subroutine_normal:

   do stuff 1

enter_part_gosub:

   do stuff 2

   if condition=1 then goto exit_part_gosub

return

[kevin]

   I had a feeling that's what you we're asking.  To be blunt, that's a pretty awful  programming practice as your example is emulating a Gosub for no worthwhile  reason.

[stevmjon]

i figured as much, that's why i asked.  i was merely experimenting.

i just wanted to occasionly jump into part of a gosub, read one small portion, then jump out.

as you say, emulating a gosub is not good practice, so i won't be lazy, i will stick to normal practice.

thanks for your advice,  stevmjon