Re^2: Is this a sane/safe way to pass an aref into a C function? (XS<Perl)

in reply to Re: Is this a sane/safe way to pass an aref into a C function? (XS<Perl)
in thread Is this a sane/safe way to pass an aref into a C function?

Thanks tye, that's great!

I was trying similar things, but did not realize pack was required. This is far easier and less error-prone as you said (as well it saves me from having to wrap one C function with another as this way, I can pass the data directly to the original function), but I am thankful that I was able to learn how to pass in perl variables into a C function, even though I'm going to revert to using this method instead:


use warnings;
use strict;
use feature 'say';

use Inline 'C';

my @b = (1..3, 253..255);
my $x = pack "V0C*", @b;

check($x, length($x));

__END__
__C__

#include <stdio.h>
#include <stdint.h>

void check(unsigned char* n, int len){

    int i;
    
    for(i=0; i<len; i++){
       printf("%d\n", n[i]);
    }
}
[download]

Output:

1
2
3
253
254
255
[download]

Of course, in the real code, I perform error checking.

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Re^3: Is this a sane/safe way to pass an aref into a C function? (XS<Perl) by Marshall (Canon) on Jan 23, 2017 at 03:44 UTC
Good thread. I tried to get this code working with Active State 5.20, but I don't have right "formula" to do that on my current little laptop. Is there a FAQ on this? What compiler is necessary, etc...? PS: I think your check() would be more "C like" coded something like this: `void check(unsigned char* n, int len) { while (len--) { printf ("%d\n", n++); } }` [download] The variable: int i is unnecessary. With the C calling convention on 32 bit machine, check() is passed a 32 bit pointer to n (pointer to an array of unsigned bytes) and a 32 bit signed integer, len on the stack. These are copies for the subroutine to modify and use as it wishes. This `n[i]` syntax is often coded by the compiler as (n isize_of_n) plus base address. Whereas n++ is coded as n plus the size_of_n.	[reply] [d/l] [select]

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Re^3: Is this a sane/safe way to pass an aref into a C function? (XS<Perl)
by Marshall (Canon) on Jan 23, 2017 at 03:44 UTC

PS: I think your check() would be more "C like" coded something like this:

void check(unsigned char* n, int len)
{
    while (len--)
    {
       printf ("%d\n", *n++); 
    }
}
[download]

This n[i] syntax is often coded by the compiler as (n i*size_of_n) plus base address. Whereas n++ is coded as n plus the size_of_n.

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