Thread: grow function to change size of array class

  1. #1
    Registered User
    Join Date
    May 2002

    Question grow function to change size of array class

    hi there y'all. I am study c++ and am trying to write a method to increase
    the size of an array when passed an int value determing the array size. This
    is my go at it which does not work. Can anybody give me some idea how to do
    this?? Thanks for your time

    template <class BType, class IType>
    void Array<BType, IType>::grow(int newS)
    arrayData = new BType[newS];
    assert (arrayData != 0);
    for (int i = 0; i <= hibnd - lobnd; ++i)
    arrayData[i] = BType[i];


  2. #2
    Registered User
    Join Date
    Mar 2002
    in Array have variables to keep track of largest possible size, and current size. If current size is or will be greater than possible size, then resize Array by growing. To grow, declare a new array of the largest possible size of Array. Copy all elements from the array in Array into temp. Then delete the old array. assign a new block of memory to hold the new desired largest possible size of array. check to make that much memory is available. Recopy temp back into array.

  3. #3
    Registered User
    Join Date
    May 2002
    thanks for your reply it helped

  4. #4
    Registered User
    Join Date
    May 2002

    Question inheriting the array class to matrix class

    Thanks for the help. I still am finding it hard to understand a couple of
    things about this code.
    This was the code I wrote and it worked.

    BType * newValues = new BType[newS];

    for (int i = 0; i < newS; ++i)
    newValues[i] = arrayData[i]; // copy old array

    delete [ ] arrayData; // delete the old array
    arrayData = newValues;

    ...all good. The next thing in the exercise we are instructed to do is
    create a matrix using two arrays from our array class. :

    template <class BType, class IType1 = int, class IType2 = int>
    class Matrix{
    IType1 lobnd1, hibnd1;
    IType2 lobnd2, hibnd2;
    Array<BType, IType2>* *MData; // this is clearer than Array<...> **MData
    bool outOfRange(IType1) const;
    Matrix(int, int, IType1 = 0, IType2 = 0); // constructor
    Matrix(const Matrix<BType, IType1, IType2> &); // copy constructor
    ~Matrix(); // destructor
    Array<BType, IType2>& operator[](IType1); // 1st [] operator
    Array<BType, IType2>& operator[](IType1) const; // ... and again
    Matrix& operator= (const Matrix<BType, IType1, IType2> &); // = operator
    void addCol(int = 1); // increase row length
    void addRow(int = 1); // increase column length
    void grow(int = 0, int = 0); // change size
    IType1 lo1() const; // inline functions
    IType1 hi1() const;
    IType2 lo2() const;
    IType2 hi2() const;

    template <class BType, class IType1, class IType2>
    Matrix<BType, IType1, IType2>::Matrix(int SZ1, int SZ2, IType1 l1, IType2
    : lobnd1(l1), hibnd1(l1 + SZ1 - 1), lobnd2(l2), hibnd2(l2 + SZ2 - 1)
    MData = new Array<BType, IType2>*[SZ1];
    assert(MData != 0);
    for (IType1 i = 0; i < hibnd1 + 1 - lobnd1; ++i)
    MData[i] = new Array<BType, IType2>(SZ2, l2);
    assert(MData[i] != 0);

    the thing then is we have to write the functions, addCol, addRow, and grow.
    I thought armed with my knowledge from the first exercise that it would be
    something like this:::

    template <class BType, class IType1, class IType2>
    void Matrix<BType, IType1, IType2>::addCol(int newC)
    BType * newCols = new BType[hibnd1+newC];

    for (int i = 0; i < newC; ++i)
    newCols[i] = MData[i];
    delete [] MData;
    MData = newCols;


    -- but I am somewhat confused. Thinking it through what I want to do is
    change the size of the arrays created from array.h,

    Thanks for your help


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