Dear Monks,

I have spent quite some time in trying to do a seemingly simple task with Inline::C, that of passing a reference to a function and the function modifying it so that caller gets results back. I don't want to use the return() mechanism, so my function looks like int func(SV *inp, SV *out); inp is a readonly ref and out is the ref I would like to write to.

I have 3 cases I would like to deal with:

  1. out is an arrayref, e.g. my @inp; my @out; func(\@inp, \@out); In this case I want to remove all elements of @out if any and then make it a 2D array of 5cols and 3rows, containing the number 42.

  2. out is a scalar, e.g. my @inp; my $out; func(\@inp, $out); In this case I want to make $out an arrayref and proceed to fill it as above, so that caller can dereference as my @out = @$out.

  3. out is a scalarref, e.g. my @inp; my $out; func(\@inp, \$out); In this case I want to find if its dereference, e.g. $out is a ref to any array or hash, or just a plain scalar. If it's a plain scalar I would like to make it an arrayref and proceed as above, so that caller can dereference as my @out = @$out.

Can anyone help me to fill any of the blanks in this advent calendar of perlguts?

Here is a test script testing each case.

use strict;
use warnings;

use Test::More;

use Inline C => Config =>
    BUILD_NOISY => 1,
    clean_after_build => 0,
    warnings => 10,
;
use Inline C => <<'EOC';
#include <stdio.h>

// checks if array is indeed an arrayref and sets array_sz to its size
+ and
// returns 1 else returns 0 (not an array)
int is_array_ref(
    SV *array,
    size_t *array_sz
){
    if( ! SvROK(array) ){ fprintf(stderr, "is_array_ref() : warning, i
+nput '%p' is not a reference.\n", array); return 0; }
    if( SvTYPE(SvRV(array)) != SVt_PVAV ){ fprintf(stderr, "is_array_r
+ef() : warning, input ref '%p' is not an ARRAY reference.\n", array);
+ return 0; }
    // it's an array, cast it to AV to get its len via av_len();
    // yes, av_len needs to be bumped up, it's $#array
    int asz = 1+av_len((AV *)SvRV(array));
    if( asz < 0 ){ fprintf(stderr, "is_array_ref() : error, input arra
+y ref '%p' has negative size!\n", array); return 0; }
    *array_sz = (size_t )asz;
    return 1; // success, it is an array and size returned by ref, abo
+ve
}

int func(
    SV *inp,
    SV *out
){
    AV *av, *av2;
    size_t i, j, asz;
    if( is_array_ref(out, &asz) ){
        printf("Case1: @out\n");
        // we have an \@R, e.g. func(\@R)
         av = (AV *)SvRV(out);
        // but first clear any contents
        if( asz > 0 ) av_clear(av);
    } else if( SvROK(out) ){
        printf("Case3: \\$out\n");
        // we have a scalar ref, e.g. func(\$x)
        av = newAV();
        sv_setsv(SvRV(out), (SV *)av);
    } else {
        printf("Case2: $out\n");
        // we have a scalar e.g func($x);
        av = newAV();
        sv_setsv(out, (SV *)av);
    }
        // and fill it in
    for(i=0;i<5;i++){
        av2 = newAV();
        av_extend(av2, 3);
        av_push(av, (SV *)av2);
        for(j=0;j<3;j++){
            av_store(av2, j, newSViv(42));
        }
    }
    return 0; // success
}
EOC

my @inp = (1..5);
my @out;
my $T = 'Case1';
is(func(\@inp, \@out),0, "$T: called success.");
is(scalar(@out), 5, "$T: rows are 5");
for(my $i=0;$i<5;$i++){
    ok(ref($out[$i])eq'ARRAY', "$T : item $i is ARRAYref.");
    is(scalar($out[$i]), 3, "$T : it has 3 elements.");
        for(my $j=0;$j<3;$j++){
          is($out[$i]->[$j], 42, "$T : it's value is 42.");
        }
}

$T = 'Case2';
my $out;
is(func(\@inp, $out),0, "$T: called success.");
is(ref($out)eq'ARRAY', "$T: it is now an ARRAYref.");
@out = @$out;
is(scalar(@out), 5, "$T: rows are 5");
for(my $i=0;$i<5;$i++){
    ok(ref($out[$i])eq'ARRAY', "$T : item $i is ARRAYref.");
    is(scalar($out[$i]), 3, "$T : it has 3 elements.");
        for(my $j=0;$j<3;$j++){
          is($out[$i]->[$j], 42, "$T : it's value is 42.");
        }
}

$T = 'Case3';
$out = undef;
is(func(\@inp, \$out),0, "$T: called success.");
is(ref($out)eq'ARRAY', "$T: it is now an ARRAYref.");
@out = @$out;
is(scalar(@out), 5, "$T: rows are 5");
for(my $i=0;$i<5;$i++){
    ok(ref($out[$i])eq'ARRAY', "$T : item $i is ARRAYref.");
    is(scalar($out[$i]), 3, "$T : it has 3 elements.");
        for(my $j=0;$j<3;$j++){
          is($out[$i]->[$j], 42, "$T : it's value is 42.");
        }
}
done_testing();

[download]

thanks in advance, bw, bliako

In reply to Inline::C : passing parameters to functions, modifying by reference by bliako

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