matrix

This is a discussion on matrix within the C++ Programming forums, part of the General Programming Boards category; hi, I have written functions that add rows and columns (separately) to a matrix. Any existing data is retained. However, ...

  1. #1
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    matrix

    hi,

    I have written functions that add rows and columns (separately) to a matrix. Any existing data is retained. However, when I use both these functions in another function that grows the matrix to the size given by the parameters I am having a problem. The size of the new array is correct but I am not saving the existing data and don't know how to do this. Since I am using existing functions that already copy the old data I assumed that when I called the addrow or addcol function that the data would be copied at this time- but it isn't. Do I need to copy the existing data before I call either of the other functions (if, so how?) or is there another way of doing this? I am a real beginner, so answers in english (possibly with examples) would be very much appreciated.

    Thanks

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    Thanks

    have worked it out now - thanks all!

  3. #3
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    Still need help!!!

    I have not worked this problem out, I have worked out another problem but posted my thank-yous in the wrong place - please help with matrix problem!!!

  4. #4
    Super Moderator VirtualAce's Avatar
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    Well to save the current matrix you could simply do a memcpy to a temp matrix. The size of the matrix would be this:

    ((rows-1)*width)*(datawidth)


    memcpy(sourcematrix,targetmatrix,length)

    or you could do it the slow way in C with one for loop (second loop unwound) or with two fors which is slower. Memcpy is the best way to do it.

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    more info

    I have not used memcpy before so I don't know how to go about it.

    In my addrow function I did something like this...

    Array<BType, IType2>* *oldData = Data;
    // reference to the current data
    Data = new Array<BType, IType2>*[newRows];
    // allocate new Data memory of length newRows

    I thought that this would be performed when the addrow function was called and that the original data would be saved at this point - am I way off track!! Is there a similar way to write something that will save the previous matrix before the functions are called?

  6. #6
    Something Clever ginoitalo's Avatar
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    What about doing Bubba's solution before you call the function
    and the in the function ?

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