The heart of XS is really dealing with type conversion. XS can deal with some type conversions itself via its inbuilt typemap. You really have two issues. One is how you plan to pass around your C structs. You will almost certainly need to have a custom typemap (see perlxs tutorial) The second appears to be how to return strings or multiple values from your C function. You can quite happily do this in several ways:

use Inline 'C';

my $str = string1();
print $str;
my $retval = string2($str);
print $str, "And the answer is $retval\n";

__END__
__C__

/* Reset the stack and push SV* onto it */
void string1() {
    char * set = "Hello \0";
    dXSARGS;
    sp = mark;
    XPUSHs(sv_2mortal(newSVpv(set,strlen(set))));
    PUTBACK;
}

/* Modify passed SV* C style, also return an int */
int string2( SV * str ) {
   char * set = "World!\n\0";
   sv_setpvn( str, set, strlen(set) ); 
  return 42;
}
[download]

Update: Here is an example using Inline::C. You can examine the XS code it generates (a bit of ugly stuff, but it works).

use strict;
use Inline (C => Config =>
             CLEAN_AFTER_BUILD => 0);
 
use Inline C => <<'END_OF_C_CODE';
 
void twoout() {
   int first = 42;
   char *second = "abc";
   Inline_Stack_Vars;
   Inline_Stack_Reset;
   Inline_Stack_Push(sv_2mortal(newSViv(first)));
   Inline_Stack_Push(sv_2mortal(newSVpvn(second,3)));
   Inline_Stack_Done;
}
END_OF_C_CODE
 
my ($num, $str) = twoout();
print "num = $num, str = $str\n";
[download]

I don't know of any sites, but get yourself a copy of Extending and Embedding Perl and join perlxs mailing lists. The mailing list is slow sometimes, but you will get some good help, as well as asking here.

Update:

I should have mentioned reading the man pages, perlxs & perlxstut. Here is nice site see how perl guts look :-), http://gisle.aas.no/perl/illguts/.

Have a look at these articles by Steven McDougall. They did help me most of all:

http://world.std.com/~swmcd/steven/perl/pm/xs/intro/

Quote:

This article is about XS. It explains what it is, why it is, how it works, and how to use it. It includes a complete, working example of an XS module, and a stub module that you can use as a starting point for your own code. It is an express goal of this article to provide the background and information necessary for you to write your own XS modules.

This article is in five parts

November - Introduction motivation, definitions, examples
December - Architecture the Perl interpreter, calling conventions, data representation
January - Tools h2xs, xsubpp, DynaLoader
February - Modules Math::Ackermann, Set::Bit
March - Align::NW Needleman-Wunsch global optimal sequence alignment

And it came to pass that in time the Great God Om spake unto Brutha, the Chosen One: "Psst!"
(Terry Pratchett, Small Gods)

Thanks to both of you. Those are some really good resources.

Much appreciated!

Lyle