Re: Prototyping printf()

[bmorris@xxxxxxxxxx]

>Date: Sun, 24 Sep 2000 10:36:58 -0700
>From: "Eric N. Wilson" <doulos1@home.com>
>
>> printf() is a C function that expects a format string followed by zero
or more
>> substitution values....
>
>I had a long discussion about this and what you are asking for is the
>same thing I wanted. Support for the variable number of arguments that
>C supports (indicated in the function prototype as '...'). Basically I
>got the answer of not anytime soon if ever at all. Everyone was 'so'
>helpful by pointing out that I could prototype the different calls
>that I needed to printf.(Which I already knew and was not asking
>about)

C can support the ellipsis because it has only has 3 basic types: int,
double, pointer.  No matter what it sees as a parameter, it knows what
to actually put on the parameter stack (*usually* what the programmer
intended.  'a' gets passed as a 4-byte int, 1.3 gets passed as a double,
"abcde" gets passed as a pointer.  The problem is that RPG has many
more basic types than RPG does.

I'm sure you all know how to call printf generically with a single
prototype, but just in case ...  Rather than trying to code this:
          printf ('You have %d pending orders.' + newline
                : num)
you code this:
          printf ('%s' + newline
                : 'You have ' + %trim(%char(num)) + ' pending orders.')

As far as I know, other than %p, you can do any formatting in RPG that
you can with printf.  For %p formatting, you could write a procedure
like this:

  P fmtPointer      b
  D fmtPointer      pi          16a
  D    pointer                    *    value
  D buf             s           17a
  C         callp    sprintf (buf : '%p' : pointer)
  C         return   buf
  P                 e

Perhaps someday, ILE will have "externally-described" procedures, and RPG
will have good support for variable-typed parameters.  I don't think
printf and its dot-dot-dot friends are a good model for this, though.

Barbara Morris, IBM Toronto Lab, RPG Compiler Development


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