Perl

rose_bud4201 · 07-11-2007, 03:33 PM

This is ridiculous. I'm trying to get the elements of an array returned from a function in Perl, and somewhere in here I'm missing the boat:
The parts which are actually relevant to this are bolded. I'm not interested in actually passing an array to the function, but rather in how to get ahold of the array the function returns.

The Example's version:

Code:

@a = (1, 2);
@b = (5, 8);
@c = add_vecpair( \@a, \@b );
print "@c\n";
6 10 

sub add_vecpair {       # assumes both vectors the same length
    my ($x, $y) = @_;   # copy in the array references
    my @result;

    for (my $i=0; $i < @$x; $i++) {
      $result[$i] = $x->[$i] + $y->[$i];
    }

    return @result;
}

My code:

Code:

@temp = my_function($var);
print "Temp: @temp.\n";
...

sub my_function {
	my $entry = shift;
	my @ret = [$val1, $val2, $val3];
	return @ret;
}

Instead of the neat list of values which the example promises will be printed, I get:

Temp: ARRAY(0x397ab4).

For some reason, passing arrays has always been a foil of mine. Can anyone give me a pointer or two in the right direction? Thanks!

chrism01 · 07-12-2007, 12:42 AM

That's because you're creating an anonymous arrayref to be returned.
To initialise an array (which is what you seem to want) it's:

@array = ($var1, $var2);

bigearsbilly · 07-12-2007, 02:41 AM

yes,
you can do it like that but references are scalars

Code:

#!/usr/local/bin/perl -w

my $temp = my_function();
print "Temp: @$temp.\n";

sub my_function {
    my $entry = shift;
    my ($val1, $val2, $val3) = qw(one two trois);
    my $ret = [$val1, $val2, $val3];
    return $ret;
}

the hard bits of perl are really understanding that the context of
an operation are vital, i.e. list, scalar, etc. which is weird compared to other languages
and then getting references, that's about it really.
It's really simple once you "get" it but for some reason it takes a while.

Tinkster · 07-12-2007, 04:06 AM

Quote:

Originally Posted by bigearsbilly

yes,
you can do it like that but references are scalars

Code:

#!/usr/local/bin/perl -w

my $temp = my_function();
print "Temp: @$temp.\n";

sub my_function {
    my $entry = shift;
    my ($val1, $val2, $val3) = qw(one two trois);
    my $ret = [$val1, $val2, $val3];
    return $ret;
}

Shouldn't that say:

Code:

#!/usr/local/bin/perl -w

my $temp = my_function();
print "Temp: @$temp.\n";

sub my_function {
    my $entry = shift;
    my ($val1, $val2, $val3) = qw(one zwei trois);
    my $ret = [$val1, $val2, $val3];
    return $ret;
}

:}

Cheers,
Tink

bigearsbilly · 07-12-2007, 04:41 AM

hey, I'm the funny one

rose_bud4201 · 07-12-2007, 09:29 AM

() instead of [] - foiled again!

Thanks very much guys, I can't believe I didn't spot that.

Cheers!

chrism01 · 07-13-2007, 01:02 AM

Yeah, it's a Perl quirk;

Init empty array, hash
@array = ();
%hash = ();

but assign (or access) using [], {}
$array[1] = "true";
$hash{1} = "true";