Question Fortran like 2D array

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  1. #1
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    Lightbulb Question Fortran like 2D array

    Hi all,
    I try to write code that stores 2D array in a row, but I want to access to it by [][] operator. The code is

    Code:
    double** arr;
    int x=19,y=17;
    
    arr=(double**)malloc((x+1)*sizeof(double*))+1;
    arr[-1]=(double*)calloc(y*x,sizeof(double));
    for(int i=0;i!=x;i++)
      arr[i]=&arr[-1][i*y];
    May be there is an mistake causing errors in my numerical computation. Valgrind says there are no errors. Pleas hlep.
    P.S.: I hope you can understand my english

  2. #2
    Cat without Hat CornedBee's Avatar
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    Use Boost.Multi_Array. It does the memory management and index computation for you, and you can choose whether you want row-major (Fortran) or column-major (C) format.

    http://www.boost.org/libs/multi_array/doc/index.html
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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    I used Boost, but it was too slow

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    Super Moderator VirtualAce's Avatar
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    I used Boost, but it was too slow
    Boost is used in many high performance applications and games. It is not slow.

  5. #5
    Cat without Hat CornedBee's Avatar
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    On a proper inlining compiler, MultiArray should have just about zero overhead over a manual implementation of index computation - perhaps even be faster. It should definitely be faster than your nested allocation.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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    I was surpriced too. I used Boost.MultiArray library only and the performance was poor (may be because of bad ussage). Using standard C++ array shows better performance. Finally, fortran arrays are faster (as I heard), so I want to write function that stores a matrix in a vector.

  7. #7
    Cat without Hat CornedBee's Avatar
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    Quote Originally Posted by TauWich View Post
    Finally, fortran arrays are faster (as I heard)
    Technically impossible. Raw arrays are as fast as the hardware allows.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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    Ok, i shall read more about MultiArray library to know where the error was. Many thanks for replys

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