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Re^2: Initializing multidimensional arrays

by cyocum (Curate)
on Jun 01, 2005 at 12:37 UTC ( #462406=note: print w/ replies, xml ) Need Help??


in reply to Re: Initializing multidimensional arrays
in thread Initializing multidimensional arrays

Cody is right on this. Just declare the array and the treat it as if it were a 5x5 matrix because as long as you treat it like one, it will be one.

I guess you could do this:

use strict; use warnings; my @matrix; $matrix[4][4];
Perl will fill in the array with undef's for you.

update: monarch is correct. It should be 4 because Perl defaults to an index of 0 for arrays unless you set the special variable $[ = 1.


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Re^3: Initializing multidimensional arrays
by monarch (Priest) on Jun 01, 2005 at 13:25 UTC
    Just a question.. given that Perl arrays are 0 indexed would it be more correct to state:
    $matrix[4][4];
    . Also can't you do something like:
    $#matrix = 4;
    (not sure how you'd do the second dimension).
Re^3: Initializing multidimensional arrays
by ihb (Deacon) on Jun 03, 2005 at 19:57 UTC

    Note that ; $matrix[4][4]; only fills out the first level with five elements and populates the last with an array reference. This is because the last subscript doesn't do anything. Just like

    if ($foo[100000] == 1) { ... }
    doesn't extend @foo to be 100001 elements. This is also why it gives a "useless use of array element in void context" warning.

    The first level is extended though, but only filled with undefs except for the fifth element which becomes an array reference, which will be empty because of the reason above, looking like

    [ undef, undef, undef, undef, [ undef, undef, undef, undef , undef ], ]
    Using the element in some way, not just using the value, like
    $matrix[4][4] = undef
    would fill out the array reference at index four in the first level, but the other levels would still be untouched, so you'd have a "half-expanded" 2D array, looking like
    [ undef, undef, undef, undef, [ undef, undef, undef, undef , undef ], ]
    This is why Cody Pendant uses the for loop.

    ihb

    See perltoc if you don't know which perldoc to read!

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