From: Lyle Johnson <lyle.johnson@...>
Date: 2004-08-19T22:09:10+09:00
Subject: Re: calling a swig generated function

On Thu, 19 Aug 2004 09:58:32 +0900, Michael Hale
<michael@halefamilysite.com> wrote:

> I have a library that I wrapped with SWIG.  One of the SWIG generated
> functions looks like this:

<snip>

I'm guessing that the fifth argument is declared as a pointer to an
unsigned long, correct? The problem is that SWIG doesn't know which
one of the many interpretations of that to use. In this case, it
appears that the NSCalculateGap() function uses that unsigned long
pointer argument to return a value (i.e. for output), but as far as
SWIG knows you could be passing in a single unsigned long value, or
even an array of unsigned longs, as input.

> How should I call this function from ruby?

You're going to need to use a typemap of some kind to let SWIG know
that, in this case, that unsigned long pointer argument is actually an
output value. Depending on how you've written your SWIG interface
file, you'll want to do something like this:

    // Include declarations for output typemaps from the SWIG library
    %include typemaps.i

    // Apply SWIG's OUTPUT typemap for unsigned long values to the
"ulGap" argument
    %apply unsigned long *OUTPUT { unsigned long ulGap; }

    // Here's what I would guess the actual function declaration looks like...
    void NSCalculateGap(int iMode, int iSpeed, unsigned long
ulPacketLength, double dValue, unsigned long *ulGap, int iHub, int
iSlot, int iPort);

Now, when you call this function from Ruby you will only pass in the
seven input arguments, and catch the output value as the method
result, e.g.

    ulGap = Smartlib::NSCalculateGap(iMode, iSpeed, ulPacketLength,
dValue, hub, slot, port)

For more information, see the "Argument Handling" chapter of the SWIG manual:

    http://www.swig.org/Doc1.3/Arguments.html

Hope this helps,

Lyle