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Passing 2D array to a sub()

Posted on 2008-06-20
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Last Modified: 2010-03-05
Hi,

I read a 2d array from file, so I have something like:

    @my2dArray[5][5];

I can iterate over it, ok. I want to pass it to a sub routine, like:

    pass2dArray(my2dArray);

    sub pass2dArray()
    {
        my (@array) = @_;
    }

Am I passing a copy of the 2d array to the function, or is it just referencing the original array?

Then, if I want to pass a single row of the array to another sub, how would I do that? I was hoping something like:

    sub pass2dArray()
    {
        my (@array) = @_;
   
        # pass row 2:
        passOneRowOf2dArray(2);
       
        # etc
        passOneRowOf2dArray(4);
    }

    sub passOneRowOf2dArray()
    {
        my (@row) = @_;
        for (my $i = 0; $i < @row; $i++) {
           ...
        }
    }
   

Thanks
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Question by:DJ_AM_Juicebox
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Expert Comment

by:Adam314
ID: 21831510
With this:
    pass2dArray(@my2dArray);
You are passing a copy of the original array, which contains references to the 2nd dimension.  You are not passing copies of the 2nd dimension.  Meaning, if your pass2dArray function, if you add or remove elements from @array, this will not be affected in @my2dArray.  But if you change, add or remove elements from any of the rows, this will be affected in @my2dArray.

To pass one row as a reference, you would use:
    passOneRowOf2dArray($array[2]);    #passes reference to second row
To pass one row as an array (not a reference), you would use:
    passOneRowOf2dArray(@{$array[2]});

If you want to pass a copy of a structure like this, you can use the Storable module's dclone function:
http://search.cpan.org/~ams/Storable-2.18/Storable.pm
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Author Comment

by:DJ_AM_Juicebox
ID: 21831577
>>To pass one row as a reference, you would use:
    passOneRowOf2dArray($array[2]);    #passes reference to second row


Ok, that's just what I put, but how do you recover the reference to the single row in the function? Like:

    sub passOneRowOf2dArray()
    {
        my @row = shift;
    }

???

That doesn't work though...

Thanks

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Accepted Solution

by:
Adam314 earned 500 total points
ID: 21831919

sub passOneRowOf2dArray {
    my $ref_to_row = shift;    #get reference
    
    #changes to $ref_to_row will show up in the original array
    print "first value=$ref_to_row->[0]\n";
    print "all values=" . join(", ", @{$ref_to_row}) . "\n";
    
    #Get as a regular array, makes a copy
    my @array_copy = @{$ref_to_row};
    
    #changes to @array_copy will not show up in the original array
    print "first value=$array_copy[0]\n";
    print "all values=" . join(", ", @array_copy) . "\n";
}

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Expert Comment

by:Adam314
ID: 21831928
This website might be helpful:
http://perldoc.perl.org/perlreftut.html
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Author Comment

by:DJ_AM_Juicebox
ID: 21834512
Perfect, thanks.
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