Okay, sorry! Try this iterator then. It will handle upto 32 0s + 1s.

If you uncomment the second example it runs on a bit.

Update: Had to tweak the termination condition. It works now but I'm not happy with it.

Update2: D'oh! No need to count both 1s and 0s.

#! perl -slw
use strict;

sub combs {
    my( $ones, $zeros ) = @_;
    my $n = $ones+$zeros;
    my $max = 2**$n;
    my $p = 0;
    return sub {
        my $x = '';
        $x = unpack "b$n", pack 'V', $p++
            until $x =~ tr[1][] == $ones
            or $p > $max and return;
        return $x;
    }
}

my $iter = combs( 2, 3 );
print while $_ = $iter->();

#my $iter = combs( 14, 6 );
#print while $_ = $iter->();
__END__
C:\test>junk7
11000
10100
01100
10010
01010
00110
10001
01001
00101
00011
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