Re: perl XS - passing array to C and getting it back

An alternative approach is to pack and unpack the array from the Perl side:

# from perl

sub do_nothing {
  my $doubles = pack 'd*', @_;
  _do_nothing_c($doubles);
  return unpack 'd*', $doubles;
}


# from XS

void
_do_nothing_c(sv)
  SV *sv
PREINIT:
  STRLEN len;
  char *pv;
CODE:
  pv = SvPV_force(sv, len);
  do_nothing((double *)pv, len / sizeof(double));
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Re^2: perl XS - passing array to C and getting it back by syphilis (Archbishop) on Mar 30, 2016 at 11:26 UTC
An alternative approach is to pack and unpack the array from the Perl side Cool approach - it enables one to utilise the do_nothing() sub as it was presented in the original post. For my own benefit, I turned it into an Inline::C demo: use strict; use warnings; use Inline C => Config => BUILD_NOISY => 1, USING => 'ParseRegExp', ; use Inline C => <<'EOC'; double do_nothing(double x[], int sizeOfX) { int index; for(index=0; index<sizeOfX; index++) x[index] = 1; return x[0]; } void do_nothing_c(SV * sv) { STRLEN len; char * pv; pv = SvPV_force(sv, len); /* SvPV() also seems ok / do_nothing((double )pv, len / sizeof(double)); } EOC my @in = (2.3, 3.4, 4.5, 5.6, 6.7); my @ret = do_nothing(@in); print "@in\n@ret\n"; sub do_nothing { my $doubles = pack 'd', @_; do_nothing_c($doubles); return unpack 'd', $doubles; } __END__ Outputs: 2.3 3.4 4.5 5.6 6.7 1 1 1 1 1 [download] I was initially a little concerned about there being both a Csub and a Perlsub named "do_nothing" but, of course, the Csub does not bind to Inline::C and the only sub named "do_nothing" that is visible from perl space is the Perlsub. Conversely, the only sub named "do_nothing" that is visible from XS space is the Csub. The return value of the do_nothing() Csub is not being captured anywhere in this demo. For the purposes of this demo it might just as well have been coded as: `void do_nothing(double x[], int sizeOfX) { int index; for(index=0; index<sizeOfX; index++) x[index] = 1; }` [download] Cheers, Rob	[reply] [d/l] [select]

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Re^2: perl XS - passing array to C and getting it back
by syphilis (Archbishop) on Mar 30, 2016 at 11:26 UTC

An alternative approach is to pack and unpack the array from the Perl side

use strict;
use warnings;

use Inline C => Config =>
 BUILD_NOISY => 1,
 USING => 'ParseRegExp',
 ;

use Inline C => <<'EOC';

double do_nothing(double x[], int sizeOfX) {
  int index;
  for(index=0; index<sizeOfX; index++)  x[index] = 1;
  return x[0];
}

void do_nothing_c(SV * sv) {
 STRLEN len;
 char * pv;

 pv = SvPV_force(sv, len); /* SvPV() also seems ok */

 do_nothing((double *)pv, len / sizeof(double));

}

EOC

my @in = (2.3, 3.4, 4.5, 5.6, 6.7);
my @ret = do_nothing(@in);
print "@in\n@ret\n";


sub do_nothing {
  my $doubles = pack 'd*', @_;
  do_nothing_c($doubles);
  return unpack 'd*', $doubles;
}

__END__

Outputs:
2.3 3.4 4.5 5.6 6.7
1 1 1 1 1
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void do_nothing(double x[], int sizeOfX) {
  int index;
  for(index=0; index<sizeOfX; index++)  x[index] = 1;
}
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