Re: C Functions..

[bmorris@xxxxxxxxxx]

>Date: 18 Aug 1999 16:30:06 -0500
>From: "Scott Klement" <infosys@klements.com
>...
>In general, though:
>
>         int,long                         10I 0
>         unsigned int, unsigned long      10U 0
>...
>         in C, pointers point at a specific data type, in
>         RPG they don't.  so char * and int *, etc are all
>         just pointers in RPG.
>...

Even though int * is a pointer, it can be thought of as an int
passed by reference, so it's better to prototype it in RPG as
an int passed by reference.  My own rules for converting C
prototypes to RPG prototypes are as follows:

      C         |       RPG
----------------|-------------------------------------------
  int, long     |    10i 0 value
  unsigned int  |    10u 0 value
  double        |     8f   value
  int *         |    10i 0
  unsigned *    |    10u 0
  double *      |     8F
  char *        |      *   value options(*string)
  void *        |      *   value
                | OR       LIKE(someStructure)
  XXX           |          value LIKE(XXX)
  XXX *         |          LIKE(XXX)
  ... (ellipsis)| figure out what the ... stands for
                | and make one or more prototypes to
                | match the various combinations, possibly
                | with OPTIONS(*NOPASS) on some parms

Where XXX is some struct/union, defined in RPG as a data structure.

This part is for those advanced folks who know C and are creating
RPG prototypes for homegrown C functions (i.e. not part of the C
runtime):
  Also, watch out for C's widening rules.  Even though
  short = 5I 0, when it comes to passing parameters by value,
  short=10i 0 and char=10u 0.  These differences don't always
  cause a problem since the use of registers to pass parameters
  can cause these differences to be hidden.  Luckily, the C
  runtime rarely if ever has short or even char parameters
  passed by value.  Unfortunately, C doesn't ALWAYS widen - it
  depends on the absense of a #pragma nowiden.
  (We have some help for this widening problem coming in a
  future release of RPG)

Barbara Morris


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