Unprototyped Dynamic Call with Varying Parameter

The procedure below produces correct results.  For example, the following
code causes the DSPLIBL screen to be displayed.
/free
      Command('DSPLIBL');
/end-free

CmdStr is defined as a varying string (2 leading bytes containing the
string length followed by 4096 data bytes).

Question: Does the address of CmdStr point to the first byte of the two
byte string length?  If so, what rule tells the compiler that the
unprototyped call to QCMDEXC is to have the address of the CmdStr parameter
offset by the two bytes? Would it be more efficient to define CmdStr with
OPTIONS(*VARSIZE) instead of VARYING? Why?


*--------------------------------------------------------------------------
     P Command         B                   export
     D Command         PI
     D  CmdStr                     4096A   value varying

      *- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
- -

      * some error trapping should be implemented here at some point
      * like a return code, job log message, errorlog file msg, etc.
     C                   callp(e)  QCMDEXC( CmdStr  : %Len(CmdStr))
     C                   return

     P Command         E

*--------------------------------------------------------------------------


Thanks, Dave

David Keck
NBTY, Inc
Phone (631) 200-5809
DavidKeck@xxxxxxxx