On 2004-02-03, at 08:14:19 -0800, Chris Masters wrote:
> Hi All,
>
> I have a C library that I am using that has a function
> that returns an array of 12 bytes as a character
> array.
>
> I have wrapped this like:
>
> void*
> mywrap(stringin)
> char *stringin
> CODE:
> RETVAL = myFunction(stringin);
> OUTPUT:
> RETVAL
>
>
> Why do I get different answers if the return type is
> defined as char *?
Because with the return type 'void *' the result is expected
to be a pointer, which will actually be returned as an IV.
With a return type 'char *', the result is expected to be a
string, making the XSUB return a PV (which is actually close
to what you want).
When in doubt about what happens when the return type changes,
it helps to have a look at the C code generated by xsubpp.
> How do I use the pointer within perl? I need to loop
> through each byte and print it's value (in hex or
> binary).
No way. The pointer is useless inside a perl script. What you
need is a copy of the array in a perl string.
You most probably want something like this:
SV *
mywrap(stringin)
char *stringin
CODE:
RETVAL = newSVpvn(myFunction(stringin), 12);
OUTPUT:
RETVAL
This will tell xsubpp that you want to return an SV *. You are
now responsible for creating the scalar value yourself. This
isn't very complicated. newSVpvn() creates a perl string (SV)
from a pointer and a length. The length is necessary, because
otherwise you cannot know only from the pointer that it points
to 12 bytes of valid data.
> OT: I need to prove I'm getting back the 12 bytes
> correctly. Should I convert the value to binary (96
> bits) using pack and unpack? If so, what TEMPLATES
> should I use?
>From perl, you maybe want to use unpack to turn the string
into an array again:
use XS::Test;
use Data::Dumper;
$x = XS::Test::mywrap('foo');
my @bytes = unpack 'C*', $x;
print Dumper([EMAIL PROTECTED]);
Just replace XS::Test with the name of your XS module.
> I'm almost there, just need a push in the right
> direction. Thanks for any help,
Hope this helps,
Marcus
--
Gold's Law:
If the shoe fits, it's ugly.
