can't find mistake. lost in references

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

Hi,
I used that code, which works fine for me:

$\ = $/;

sub add{
    my ($i, $j, $add) = @_;
    $_{value}[$i][$j] += $add;
    }

while(<DATA>){
    
    $tc ++;
    print "[$tc]";
    
    ($n, $m) = split;
    for $i (1 .. $n){
        $_ = <DATA>, chomp;
        for $j (1 .. $m){
            $_{value}[$i][$j] = substr $_, $j - 1, 1;
        }
    }

    &add(2, 3, 5);

    for $i (1 .. $n){
        print join " ", @{ $_{value}[$i] };
    }
}
__DATA__
3 3
011
111
111
6 7
1101011
0111111
1111101
1111111
1111110
0111111
[download]

OUTPUT:

[1]
 0 1 1
 1 1 6
 1 1 1
[2]
 1 1 0 1 0 1 1
 0 1 6 1 1 1 1
 1 1 1 1 1 0 1
 1 1 1 1 1 1 1
 1 1 1 1 1 1 0
 0 1 1 1 1 1 1
[download]

... but later I wanted to collect all my matrixes, so I tried to replace this "$_{value}[$i]" with that "$_[$tc]{value}[$i]" (I inserted [$tc] in all such places). And now seems that my subroutine fails? The OUTPUT is:

[1]
 0 1 1
 1 1 1
 1 1 1
[2]
 1 1 0 1 0 1 1
 0 1 1 1 1 1 1
 1 1 1 1 1 0 1
 1 1 1 1 1 1 1
 1 1 1 1 1 1 0
 0 1 1 1 1 1 1
[download]

Program:

$\ = $/;

sub add{
    my ($i, $j, $add) = @_;
    $_[$tc]{value}[$i][$j] += $add;
    }

while(<DATA>){
    
    $tc ++;
    print "[$tc]";
    
    ($n, $m) = split;
    for $i (1 .. $n){
        $_ = <DATA>, chomp;
        for $j (1 .. $m){
            $_[$tc]{value}[$i][$j] = substr $_, $j - 1, 1;
        }
    }

    &add(2, 3, 5);

    for $i (1 .. $n){
        print join " ", @{ $_[$tc]{value}[$i] };
    }
}
__DATA__
3 3
011
111
111
6 7
1101011
0111111
1111101
1111111
1111110
0111111
[download]

I can't understand why it fails.

Comment on can't find mistake. lost in references Select or Download Code

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Re: can't find mistake. lost in references by hdb (Monsignor) on Mar 14, 2015 at 17:24 UTC
In your first version you use `%_` to store data, which is a strange choice of variable. In the second version you use `@_` to store your data which is very strange and - as you found out - has funny side effects. I have not really looked at your code but using `$mat[$tc]` instead of `$_[$tc]` everywhere should solve your problem. UPDATE: In your subroutine `sub add{ my ($i, $j, $add) = @_; $_[$tc]{value}[$i][$j] += $add; }` [download] you are even referring to two different `@_` arrays explicitly. The one that passes the parameters into the subroutine and the global one that you use to store your data.	[reply] [d/l] [select]
Re^2: can't find mistake. lost in references (super global @_ is always in main @main::_ $main::_ ) by Anonymous Monk on Mar 14, 2015 at 18:16 UTC
you are even referring to two different @_ arrays explicitly. The one that passes the parameters into the subroutine and the global one that you use to store your data. :) There is only one @_ and it is "super global" that is anytime you write @_ its always @_ (its always @main::_ ) regardless of package Symbol isn't exactly authoritative but it does show this `$ perl -MSymbol=qualify -le " print qualify($_,q/Fooo/) for qw/ ARGV S +TDOUT STDERR _ AHOY / main::ARGV main::STDOUT main::STDERR main::_ Fooo::AHOY` [download] pervar says: Perl identifiers that begin with digits, control characters, or punctuation characters are exempt from the effects of the package declaration and are always forced to be in package main ; they are also exempt from strict 'vars' errors. A few other names are also exempt in these ways: ENV STDIN INC STDOUT ARGV STDERR ARGVOUT SIG	[reply] [d/l]
Re^3: can't find mistake. lost in references (super global @_ is always in main @main::_ $main::_ ) by hdb (Monsignor) on Mar 14, 2015 at 18:25 UTC
Thanks for the clarification! I should have said something like: referring to `@_` as if there were two of them...	[reply] [d/l]
Re^3: can't find mistake. lost in references (super global @_ is always in main @main::_ $main::_ ) by ikegami (Patriarch) on Mar 16, 2015 at 00:16 UTC
He'd have the same problem even if `@_` wasn't a "super global". The actual problem is that sub calls localize `@_` as part of placing the arguments in it. PS - There can be more than one `@_` in every package. It's just that unqualified `@_` always refers to `@::_`. You can access package `Foo`'s `@_` using `@Foo::_`.	[reply] [d/l] [select]
Re^2: can't find mistake. lost in references by rsFalse (Chaplain) on Mar 14, 2015 at 17:59 UTC
Ok, thank you! Now it is clear. I changed location of "`[$tc]`" to "`$_{value}[$tc][$i][$j]`", now it works.	[reply] [d/l] [select]
Re^3: can't find mistake. lost in references by GotToBTru (Prior) on Mar 14, 2015 at 18:14 UTC
Another alternative would be to use a regular variable instead of $_. Using a variable that depends on context sounds like a great way to ensure confusion. `replace $_[$tc]{value}[$i][$j] with $matrix[$tc]{value}[$i][$j]` [download] Updated to remove liability Dum Spiro Spero	[reply] [d/l]
Re^4: can't find mistake. lost in references by Anonymous Monk on Mar 14, 2015 at 18:19 UTC
Re^5: can't find mistake. lost in references by hdb (Monsignor) on Mar 14, 2015 at 18:26 UTC