in reply to XS routine returns an extra depth of array refs

Let's see your Perl code where you get the results of this function and do a Dumper on it. I expect to see: 
$ref = readdir_inode($dirname);
print Dumper($ref);

# or

@a = readdir_inode($dirname);
print Dumper($a[0]);          # not Dumper(\@a)

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I don't see anything obviously wrong with your code, but I want to eliminate some assumptions first before I go digging. :)

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Re: Re: XS routine returns an extra depth of array refs
by mugwumpjism (Hermit) on Nov 05, 2001 at 22:13 UTC

    You hit the nail right on the head... I had the second, but Dumper \@a instead of Dumper $a[0], and my test code was assuming I was returning a list. Hate it when that happens ;-)

    OK, so now at least I have it returning something sensible, which is always good. In which case, the question is why does this:

    AV *
readdir_inode(dirname)
     char*    dirname
INIT:
  struct dirent *ent;
  DIR* dir;
  SV* record[2];
  AV *entry, *ret_val;
CODE:
  RETVAL = newAV();
  dir = opendir(dirname);
  if (!dir)
    perror("Cannot open dir");
  while ((ent=readdir(dir))) {
    printf("%ld %x\n", ent->d_ino, ent->d_name);
    record[0] = newSVpv(ent->d_name, 0);
    record[1] = newSViv((IV)ent->d_ino);
    entry = av_make(2, record);
    av_push(RETVAL, newRV_inc((SV*) entry));
  }
  closedir(dir);
/*RETVAL=*ret_val;*/
/*RETVAL=newRV_inc((SV*) ret_val);*/
OUTPUT:
    RETVAL

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    Return an extra level of arrays?

    The calling code:

    my @ents = readdir_inode(".");
print Dumper @ents;

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    The output:

    $VAR1 = [
          [
            '.',
            67586
          ],
          [
            '..',
            255604

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    ...
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      When you use RETVAL, XS builds it in such a way that it's functionally the same as the first item on the return stack. Thus, you've effectively stuck an AV into $ents[0], which I'm guessing Perl DWIM's here and turns it into a reference to an array. Hence the additional level of references.

      The correct way (I believe) to return a list in this situation is to declare your function with a return type of void and simply push each element onto the return stack instead of trying to return an array, using PUSHs I think.

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