Thread: Multidementional arrays, need concept explanation??

  1. #1
    Registered User
    Join Date
    Apr 2008

    Multidementional arrays, need concept explanation??

    Hi everyone,
    today, My C prof covered multidimensional arrays...he says that, there exist, in addition to the two dimensional arrays, n-dimensional arrays.. he asks us not to pay attention to these concepts and focus only on the two dimensional model..
    The problem is that i want to go deeper in C, deeper than the school program, and i guess it's crucial to understand what means to have more than two dimensional array..
    PS: i can imagine what is gonna be like a three-dimensional array in reality...but how that works in memory??

  2. #2
    Kernel hacker
    Join Date
    Jul 2007
    Farncombe, Surrey, England
    You can have as many dimensions as you like [1]:

    int onedim[10];
    int twodim[10][10];
    int threedim[10][10][10];
    int fourdim[10][10][10][10];
    int fivedim[10][10][10][10][10];
    I'll leave it to you to figure out what sixdim and tendim would look like.

    And tendim might struggle to fit in a 32-bit machine - care to guess why?

    [1] I don't know if the C standard has a specific limit for what the compiler must cope with - if there is such a limit, it's still allowed for the compiler to allow more dimensions, if it likes to.

    Edit: I missed your last question. The compiler will translate ANY multidimensional array into a block of memory that is the right size to cope with the data. How that's organized is up to the compiler, but generally it's just like a one dimensional array with index calculation like this:
    n0 + n1 * n0_max + n2 * (n0_max * n1_max) ...

    Last edited by matsp; 04-29-2008 at 08:07 AM.
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  3. #3
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    Apr 2008
    Ok, so you wanna say that the compiler breaks everything down to only two dimensions..??

  4. #4
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    Oct 2001
    the compiler breaks all multidimensional arrays to one dimension, not two. So it's just a bunch of array elements in a row, and it calculates the position you want.
    Last edited by robwhit; 04-29-2008 at 11:07 AM.

  5. #5
    Registered User
    Join Date
    Feb 2008
    very interesting, I to was wondering this some time back. It's good to have an insight.

    n0 + n1 * n0_max + n2 * (n0_max * n1_max) ...

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