C to Perl conversion of *ptr++ - c

Question

I have a pointer to an array and either need to change the code considerably to make this work, or just figure out what the equivilent of the statement below is...
ptr = array;
*ptr++ = value;
So far I have most of it
$ptr = \#array;
$$ptr = $value;
but this doesn't increment the pointer. What do I do?

Answer 1

There are no pointers in Perl. What you have is:
my $ary_ref = \#array;
$ary_ref is now a reference to #array. You cannot dereference $ary_ref to get a scalar.
You can, however, iterate through the elements of #array in a variety of ways. For example, if you want, you can do:
#!/usr/bin/env perl
use strict; use warnings;
my #array;
my $ptr = sub {
my ($i, $ref, $val, $size) = (0, #_);
sub { $i < $size ? $ref->[$i ++ ] = $val : () }
}->(\#array, deadbeaf => 10);
1 while defined $ptr->();
use YAML;
print Dump \#array;
By the way, there is no reason you can't write
p[i] = value;
i++;
in C. In Perl, it might become:
$array[$_] = $value for 0 .. $#array;
or,
#array = ($value) x #array;
or,
$_ = value for #array;
etc. You should explain what the overall goal is rather than asking about a specific statement in C.

Answer 2

The C code modifies the first element of array and will likely change at least some part of the rest of the array.
#include <stdio.h>
int main(void)
{
int array[] = { 0, 0, 0, 0, 0 };
int value = 42;
int *ptr;
int i;
ptr = array;
*ptr++ = value;
for (i = 0; i < sizeof(array) / sizeof(array[0]); i++)
printf("%d ", array[i]);
puts("\n");
return 0;
}
Output:
42 0 0 0 0
Perl has references rather than pointers. References cannot be null, but there’s no reference arithmetic.
Modifying the first element of an array in Perl looks like
$ perl -wle '#a=(0)x5; $a[0] = 42; print "#a"'
42 0 0 0 0
or to be excessively literal
$ perl -wle '#a=(0)x5; $ptr = \$a[0]; $$ptr = 42; print "#a"'
42 0 0 0 0
Your question gives a single bookkeeping detail of the C code. What’s the broader context? What’s the C code doing?
In general, don’t write C in Perl. Considered broadly, C code tends to process arrays one item at a time, but Perl modifies the entire conceptual chunk, e.g., with a regex for strings or map or grep to transform entire arrays.