how does vec() return?

llancet has asked for the wisdom of the Perl Monks concerning the following question:

It just don't work as I thought.

use strict;

# generate a 64-bit all-1 mask
my $mask;
for (my $i=0; $i<64; $i++) {
    vec($mask,$i,1)=1;
}

# get a byte of value from 17
my $value = vec($mask,16,8);
print "$value\n";
[download]

In my opinion, $value should be string "255". Actually,

vec($mask,0,8)
[download]

give me that, but with start index other than 0, it always give me "0". So how does it work?

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Re: how does vec() return? by almut (Canon) on Sep 25, 2009 at 11:51 UTC
16 x 8 = 128 (i.e. > 64) With `... for (0..16) { my $value = vec($mask,$_,8); print "$value\n"; }` [download] I do get (as expected): `255 255 255 255 255 255 255 255 0 0 0 0 0 0 0 0 0` [download] In other words, the offset is in units as specified in width (8 bits here).	[reply] [d/l] [select]
Re^2: how does vec() return? by llancet (Friar) on Sep 26, 2009 at 03:05 UTC
Thanks a lot. I thought that the index was always in bits...	[reply]