Hello. I know of two modules which are capable of doing this. One is C::DynaLoad::Struct and the other is C::Include. You could probably do it using C::Inline as well. C::Include is perl based, but requires Storable.pm for caching (I find this kinda odd). It however, is your best bet. If you wish to do this without installing modules ( a silly requirement), you can probably rip off C::Include real easy (I would at least strip the Storable caching stuff). All of these have a lot of documentation. Knowledge of c is required. I tried out C::Include, and all the samples included work. Good luck (btw - I am looking into the future, and I see a tutorial on one of these, or at least a meditation on how you dealt with it - and code, always code ;D)

update:

#!/usr/bin/perl -w
use C::Include;
use strict;
use vars qw/$inc $send $buffer/;

$inc = new C::Include( \*DATA );

# Make struct instance
$send = $inc->make_struct('send');
use Data::Dumper;
print Dumper $send;

# Fill struct fields
$$send{prevpass} = '0123456789';
$$send{answer} = 1;

# Pack struct to buffer
$buffer = $send->pack();

# Struct size
printf "Size of struct send: %d bytes\n",   $send->size;
printf "Size of unsigned long: %d bytes\n", $inc->sizeof('unsigned lon
+g');

# Print buffer to STDOUT
&hview( \$buffer );

#require 'hview.pl';
## crazyinsomniac's note ~ hview.pl is distributed with the module, pr
+ops to the author
sub hview(\$){
    my $str = shift;
    my @lines = unpack 'a16'x(length($$str)/16+(length($$str)%16?1:0))
+, $$str;

    for( 0..$#lines ){
        printf "%08X:  %-17sł %-17s  %-16s\n", $_*16,
            (map{
                sprintf '%-2s ' x 8, map{
                    sprintf'%02X',$_
                }unpack 'C*', $_
            }unpack 'a8a8', $lines[$_]),
            $lines[$_];
    }
}
1;

__END__
#define PORT 2345
#define CHALLENGE 0
#define CORRECT 1
#define WRONG 2

struct recv {
    int flag;
    int b[4];
    char nextpass[10];
};

typedef struct recv t_recv;

struct send {
    int answer;
    char prevpass[10];
};
typedef struct send t_send;
[download]

I tried the above, and got

$>perl test4.pl
$VAR1 = bless( {
                 '' => {
                         'length' => 14,
                         'mask' => 'iZ10',
                         'tag' => 'send',
                         'buffers' => [
                                        \undef,
                                        \undef
                                      ]
                       },
                 'prevpass' => ${$VAR1->{''}{'buffers'}[1]},
                 'answer' => ${$VAR1->{''}{'buffers'}[0]}
               }, 'C::Include::Struct' );
Size of struct send: 14 bytes
Size of unsigned long: 4 bytes
00000000:  01 00 00 00 30 31 32 33 ¦ 34 35 36 37 38 00         
   012
+345678

$>
[download]

That seems pretty cool.
** Note: I am using C::Include $VERSION = 1.40;

I tried $VERSION = 1.20;, but It didn't like your macro (WARNING: Unashed code ...) so I upgraded ... and all this after plenty of rum and coke (and some Jose Quervo tequila to boot)

 

______crazyinsomniac_____________________________ Of all the things I've lost, I miss my mind the most. perl -e "$q=$_;map({chr unpack qq;H*;,$_}split(q;;,q*H*));print;$q/$q;"