Re: return char from c++ module to rpg module -- RPG400-L

Steve,

This is probably a case of "C Widening."

Barbara Morris, IBM Toronto, wrote a great piece about "Converting from C prototypes to RPG prototypes." It includes a terrific discussion of the C Widening issue. You can find the article at

http://www.opensource400.org/callc.html.

If you are on V5R1 or later, the RPG compiler can handle the widening for you if you change the RPG prototype for ReturnChar as follows:

d ReturnChar pr 1a extproc(*CWIDEN:'ReturnChar__Fv')

If you are at V4R5 or earlier you will have to code the prototype as

d ReturnChar pr 10u 0 extproc('ReturnChar__Fv')

Upon return, you will have to pull the character out of the 4 byte unsigned integer. You can do this with a data structure, perhaps in a subprocedure similar to the one in Barbara's piece.

If you control the C code, there is a #pragma that can be specified for the function that tells it not to widen. Again, see Barbara's piece for more details.

Mel Rothman
Mel Rothman, Inc.

Steve Richter wrote:

I have a C++ proc that returns a "char" to an rpg proc.  It works on paper,
but in practice the rpg proc is always receiving x'00' as the return
variable.

When I return an "int", the return value is received ok.

Does anyone know how to return a "char" from C to RPG?

Here are the C functions:

int  ReturnInt( )
  {
  int  nVlu ;
  nVlu = 25 ;
  return nVlu ;
  }

char ReturnChar( )
  {
  char  ch ;
  ch = 'a' ;
  return ch ;
  }

and the rpg prototypes:
d ReturnInt       pr        10i 0 extproc('ReturnInt__Fv')
d ReturnChar      pr         1a   extproc('ReturnChar__Fv')

and the rpg code:
d ch1             s          1a
d int             s         10i 0
 /free
      ch1         = ReturnChar( ) ;
      int         = ReturnInt( ) ;
 /end-free

When I run this code ch1 contains x'00' when it should have 'a' and int
contains the correct value of 25.

thanks,
Steve Richter

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