resize array of pointers c++

Question

Let's say that I have this

#define T 10

StackOverflow *_stObject[H];

How can I "resize" this array to 20? I cannot use vectors. I have to copy that 11 positions to another array of pointers with 20 positions, but that way I will cannot use this object in my other functions.

This object stores data, and when it gets full I need to find a way to continue to add data.

How can I do this?

Ok here it is some more information because it's not working. I made the method extendArray() but it have an error when I make r = temp

This is a calculator and the class Reg stores the information the operation that I make in the calculator. The object "r" stores 10 operations and I have to expand this array of pointers if I make more than 10 operations.

The error message that I get is in r = temp and it says: incompatible types in assignment of 'Reg* [20]' to 'Reg* [10]'|

#define T 10

   class Calculator
    {
        public:
            Calculator();
            Calculator(NumComp&,NumComp&);
            ~Calculator();

            void printVisor();
            void setCalculator(const NumComp&,const NumComp&);
            void menu();
            void help();
            void clean();
            void run();
            void extendArray();

        private:
            NumComp n1, n2;
            Reg *r[T];
            int _tMax;
    };

        void Calculator::extendArray()
    {
        Reg *temp[T*2];

        for(int i = 0; i < 5; i++){
            temp[i] = new Reg;
            temp[i] = r[i];
          delete r[i];
         }

        r = temp;
        _tMax *= 2;
    }

Answer 1

You have to create a new array and do a deep copy.

 StackOverflow * array = new StackOverFlow[(H * 2)];

 for (int i = 0; i < H; i++)
       arrary[i] = _stObject[i];

Now you have an array twice the size of the original with all the data from the original.

Answer 2

If your assignment/homework states you cannot use any STL containers you can do something like this

#define T 10

class NumComp {
// ---
};

class Reg {
// ---
};


class Calculator
{
     public:
         Calculator();
         Calculator(NumComp&,NumComp&);
         ~Calculator();

         void printVisor();
         void setCalculator(const NumComp&,const NumComp&);
         void menu();
         void help();
         void clean();
         void run();
         void extendArray();

     private:
         NumComp n1, n2;
         Reg** r;
         int _tMax;

         void createArray();
         void cleanupArray(); 
};


Calculator::Calculator() {
    createArray();
}

Calculator::Calculator(NumComp&,NumComp&) {
    createArray();
}

Calculator::~Calculator() {
    cleanupArray();
}

void Calculator::createArray() {

    // create a pointer array
    r = new Reg*[T];

    // initialize to nulls
    for (int i = 0; i < T; i++) {
        r[i] = 0;
    }

    _tMax = T;
}

void Calculator::cleanupArray() {

    // make sure the contents of r[] are deleted by whoever allocates them
    delete [] r;
    r = 0;
}


void Calculator::extendArray()
{
    Reg** temp = new Reg*[_tMax*2];

    // copy contents of r to temp
    for(int i = 0; i < _tMax; i++) {
        temp[i] = r[i];
    }

    // initialize rest of temp
    for (int i = _tMax - 1; i < _tMax*2; i++) {
        temp[i] = 0;
    }

    // delete what was originally in r
    delete [] r;
    r = temp;

    _tMax *= 2;
}

The only way to extend an array is to copy its content to a larger array. You cannot simply assign a larger array to a smaller array (That's why you got the error incompatible types in assignment of 'Reg* [20]' to 'Reg* [10]' ). But you can assign a pointer-to-an-array of any size to another pointer-to-an-array (of same type). So to extend an array, you first create a larger array, copy contents of smaller array to it, clean up the smaller array, assign the pointer to the larger array to the smaller array.

Answer 3

If you can't use the std::vector (which would be the most reasonable thing to use), then you could write your own "vector" with simplified functionality:

class MyVector
{
    int size;
    int capacity;
    StackOverFlow ** data;

    public:

    MyVector() : size(0), capacity(10), data(new StackOverFlow * [10]) {}
    ~MyVector() {delete data;}

    void duplicateCapacity()
    {
        capacity *= 2;
        StackOverFlow ** tmp = new StackOverFlow * [capacity];
        for(int i=0; i<size; i++)
             tmp[i] = data[i];
        delete data; //<-- here was an error...
        data = tmp;
    }

    void add(StackOverFlow * item)
    {
        if(size == capacity)
            duplicateCapacity();
        data[size++] = item; 
    }

    StackOverFlow * get(int index) {return data[index];}
};

With this basic functionality you could get the job done.