Re^2: Arrays and Inline C (pack)

Thanks for the example - but somehow the trick doesn't seem to work:

use Inline 'C', <<'END_C'

void _munge( char *outlist, int size, char *inlist1, char *inlist2 )
{
    double *output = (double *) outlist;
    double *list1  = (double *) inlist1;
    double *list2  = (double *) inlist2;
    int i;
    for( i= 0; i < size; ++i ) {
        printf("%f %f\n", inlist1[i], inlist2[i]);
    }
}

END_C
    ;

my $size = 3;
my $out = "\0" x ( $size * length pack "d", 0.0 );
my $pack1 = pack "d$size", 1, 2, 3;
my $pack2 = pack "d$size", 4, 5, 6;
_munge( $out, $size, $pack1, $pack2 );
[download]

This prints

0.000000 0.000000
0.000000 0.000000
0.000000 0.000000
[download]

I expected it to print the numbers passed in. What happened?

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Re^3: Arrays and Inline C (pack) by tye (Sage) on Jun 23, 2010 at 15:40 UTC
You are passing 'char' values to your printf(), not 'double' values. Here is tested code that also includes the returning of values back to Perl: #!/usr/bin/perl -w use strict; use Inline 'C', <<'END_C'; void _munge( char outbuf, int size, char inbuf1, char inbuf2 ) { double output = (double ) outbuf; double list1 = (double ) inbuf1; double list2 = (double ) inbuf2; int i; for( i= 0; i < size; ++i ) { printf( "%f %f\n", list1[i], list2[i] ); output[i]= list1[i] list2[i]; } } END_C my $size = 3; my $out = "\0" x ( $size * length pack "d", 0.0 ); my $pack1= pack "d$size", 1, 2, 3; my $pack2= pack "d$size", 4, 5, 6; _munge( $out, $size, $pack1, $pack2 ); print $_, $/ for unpack "d$size", $out; [download] `$ perl double.pl 1.000000 4.000000 2.000000 5.000000 3.000000 6.000000 4 10 18` [download] - tye	[reply] [d/l] [select]

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Re^3: Arrays and Inline C (pack)
by tye (Sage) on Jun 23, 2010 at 15:40 UTC

You are passing 'char' values to your printf(), not 'double' values. Here is tested code that also includes the returning of values back to Perl:

#!/usr/bin/perl -w
use strict;

use Inline 'C', <<'END_C';

void _munge(
    char *outbuf,
    int   size,
    char *inbuf1,
    char *inbuf2 )
{
    double *output = (double *) outbuf;
    double *list1  = (double *) inbuf1;
    double *list2  = (double *) inbuf2;
    int i;
    for(  i= 0;  i < size;  ++i  ) {
        printf( "%f %f\n", list1[i], list2[i] );
        output[i]= list1[i] * list2[i];
    }
}

END_C


my $size = 3;
my $out  = "\0" x ( $size * length pack "d", 0.0 );
my $pack1= pack "d$size", 1, 2, 3;
my $pack2= pack "d$size", 4, 5, 6;
_munge( $out, $size, $pack1, $pack2 );
print $_, $/ for unpack "d$size", $out;
[download]

 $ perl double.pl
1.000000 4.000000
2.000000 5.000000
3.000000 6.000000
4
10
18
[download]

- tye

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