Introduction to Templates

Two weeks ago we learned about templates and this week we are to implement a template for Fardad's dynamic array of integer array class. My understanding is that templates are used to abstract code in such a way that a generic datatype is used to account for the multiple instances of a known receiving datatype used within the class. This would allow the class to operate the same for different datatypes. From our previous lecture we used the Stack to point to nodes that store an integer and coded methods to work with that specific datatype. Using templates we could have created a stack to handle any type of data and still operate similarly.

/* 
   This Array of Int Array now works with Char and
   floating point numbers, but not with external 
   functions associated with strings such as strcpy. 
*/

#include <iostream>
using namespace std;

template <class T> 
class IntArray {
    T* _data;
    unsigned int _size;
  public:
    IntArray(unsigned int size) {
      _data = new T[_size = size];
    }
    T& operator[](unsigned int index) {
      if (index >= _size) {
        size(index < 1024 ? index + 1 : index + 1024);
      }
      return _data[index];
    }
    unsigned int size() {
      return _size;
    }
    void size(unsigned int newsize) {
      T* temp = new T[newsize];
      for (int i = 0; i < _size && i < newsize; i++) {
        temp[i] = _data[i];
      }
      delete[]_data;
      _data = temp;
      _size = newsize;
    }
    T* display(){
      return _data;
    }
    virtual ~IntArray() {
      delete[] _data;
    }
};

template <class T> 
class IntArrArr {
    IntArray<T>** _data;
    unsigned int _size;
    unsigned int _width;
  public:
    IntArrArr(unsigned int size, unsigned int width) {
      _data = new IntArray<T>*[_size = size];
      for (int i = 0; i < _size; i++) {
        _data[i] = (IntArray <T>*)0;
      }
      _width = width;
    }
    T Size() const {
      return _size;
    } 
    IntArray<T>& operator[] (unsigned int index) {
      if (_data[index % _size] == 0) {
        _data[index % _size] = new IntArray<T>(_width);
      }
      return *_data[index % _size];
    }
    virtual ~IntArrArr() {
      for (int i = 0; i < _size; i++) {
        if (_data[i]) {
          delete _data[i];
        }
      }
      delete[] _data;
    }
};

int main()
{
    IntArrArr<int> I(5, 4);   
    IntArrArr<double> D(5,4); 
    IntArrArr<char> C(5, 4);  
    int i;
    int j;
    int x = 0;
    
    for (i = 0; i < 5; i++) {
      for (j = 0; j < 4; j++) {
        I[i][j] = (i + 1) * (j + 1);
        D[i][j] = (i + 0.5) * (j + 0.5);
      }
    }

    cout << "Array of Int Array:" << endl;
    for (i = 0; i < 5; i++) {
      for (j = 0; j < 4; j++) {
        cout << I[i][j] << " ";
      }
      cout << endl;
    }

    cout << "Array of Double Array:" << endl;
    for (i = 0; i < 5; i++) {
      for (j = 0; j < 4; j++) {
        cout << D[i][j] << " ";
      }
      cout << endl;
    }

    cout << "Array of Char Array:" << endl;
    for (i = 0; i < 5; i++) {
      for (j = 0; j < 4; j++) {
        C[i][j] = 'a' + x++;
      }
    }

    for (i = 0; i < 5; i++) {
      for (j = 0; j < 4; j++) {
        cout << C[i][j] << " ";
      }
      cout << endl;
    }


    return 0;
}