My XS pointer problem...

doneill has asked for the wisdom of the Perl Monks concerning the following question:

I'm having an interesting problem with my perl xs dongle: What I want to do is fairly simple, this is my whack at making /any/ XS module that can do at least most of what I need.. Basic string passing, essentially... Anyways, here's what I have as my .xs content:

MODULE = boink  PACKAGE = boink
char hello_new( char *woteva )
        PREINIT:
                char *boink;
                                                                      
+                                                                   
        CODE:
                printf("Boink::Malloc\n");
                boink = malloc( strlen( woteva ) + 3 );
                sprintf( boink, "[%s]", woteva );
                printf("Boink: Returning '%s'\n", boink );
                RETVAL = (int)boink;
                                                                      
+                                                                   
void hello_free( char *boink )
        CODE:
                printf("Boink::Free\n");
                free( boink );
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Not the most intuitive I'm certain, but it should suffice: In my .pm file, I have the essential wrappers (and possibly the centre of my woes):

my $mres;
my $textin;
my $ptr;
                                                                      
+                                                                   
sub hello {
        $textin = shift;
        $$ptr = boink::hello_new( $textin );
                                                                      
+                                                                   
        bless $ptr;
        $mres = $$ptr;
                                                                      
+                                                                   
        print $mres;
                                                                      
+                                                                   
        boink::hello_free( $ptr );
                                                                      
+                                                                   
        return $mres;
}
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Then, I have my little test script:

use ExtUtils::testlib;
use boink;
                                                                      
+                                                                   
boink::hello( "testing\n" );
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Ultimately, my result should be:

Boink::Malloc
Boink: Returning '[testing
]'
[testing
]
Boink::Free
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BUT instead, I get:

Boink::Malloc
Boink: Returning '[testing
]'
testing
Boink::Free
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Which, is actually what I originally passed /in/ to my subroutine... Any pointers here?

Comment on My XS pointer problem... Select or Download Code

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Re: My XS pointer problem... by MarkM (Curate) on Apr 08, 2003 at 02:21 UTC
It looks like you have a few problems, the first of which being that "CODE:" XS sections, although defining RETVAL, do not use RETVAL as the default OUTPUT argument. An explicit "OUTPUT: RETVAL" is necessary. The next problem that you will hit is that you are returning a 'char', casting a malloc()'d pointer to an 'int', and assuming that you can dereference this from Perl. You should be returning a 'char ' or 'SV ' instead. I recommend a little more reading up on the XS interface. It is very complicated stuff. Cheers, and good luck.	[reply]
Re: Re: My XS pointer problem... by doneill (Initiate) on Apr 08, 2003 at 15:55 UTC
Well, the idea was to follow tye's advice I found in some other articles on using as much perl/c to wrap the function, and less XS for reasons of cleanliness, simplicity, and debugging which constitutes the former two ideals. Read more... (609 Bytes)	[reply]