Please go through the code, is it pass by value?

Question

Can any one explain me the diff between call by value and call by reference in Subroutines.
ex :
PERFORM ADD_Z1CLASS1 USING LW_MARA-MATNR
                         CHANGING IDOC_DATA[].
FORM ADD_Z1CLASS1 USING    PV_MATNR TYPE MATNR
                 CHANGING PT_EDIDD TYPE EDIDD_TT.
Please let me know, if the above code is call by value or call by reference...?
Any suggestions will be appreciated!
Regards,
Kittu

Answer 1

hi,
using             --  Pass by reference
changing        --  Pass by reference
using value()   --  Pass by value
changing value( )--  Pass by value and result
The main difference between the pass by value and pass by reference is that " In pass by value the actual parameters are not changed while in pass by reference those are changed".
By reference Passes a pointer to the original memory location.  Very efficient
By value Allocates a new memory location for use within the subroutine. The memory is freed when the subroutine ends.  Prevents changes to passed variable
By value and result Similar to pass by value, but the contents of the new memory is copied back into the original memory before returning.  Allows changes and allows a rollback .
Go through the following eg:
pass by ref:
data f1 value 'A'.
perform s1 using f1.
write / f1.
form s1 using p1.
     p1 = 'X'.
     endform.
o/p is X
using and changing Are Identical in Function
  report ztx1805.
  data: f1 value 'A',
        f2 value 'B'.
  write: / f1, f2.
  perform s1 using f1
             changing f2.
  write: / f1, f2.
form s1 using p1
         changing p2.
     p1 = p2 = 'X'.
     endform.
o/p : A B
       X X
Pass by value:
data: f1 value 'A'.
  perform s1 using f1.
  write / f1.
  form s1 using value(p1).
      p1 = 'X'.
      write / p1.
     endform.
o/p is X
        A
Hope this is clear.
so the code which you have pasted comes under pass by reference.
Reward points if helpful.
Thanks and regards.