Overload the Subscripting Operator [] - C++ Class

C++ examples for Class:Operator Overload

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Description

Overload the Subscripting Operator []

Demo Code

#include <iostream>
#include <new>
#include <cstdlib>
using namespace std;
template <class T, int len>
class MyArray {//w ww  .  ja v  a2  s  .c o  m
   T *aptr;
   int length;
   public:
   // The MyArray constructor.
   MyArray();
   // The MyArray copy constructor.
   MyArray(const MyArray &obj);
   // Release the allocated memory when a MyArray object
   // goes out of scope.
   ~MyArray() {
      delete [] aptr;
   }
   // Overload assignment.
   MyArray &operator=(const MyArray<T,len> &rh_op);
   T &operator[](int i);
   int getlen() { return length; }
};
template <class T, int len>
MyArray<T, len>::MyArray() {
   try {
      // Allocate the array.
      aptr = new T[len];
   } catch(bad_alloc ba) {
      cout << "Can't allocate array.\n";
      // Take appropriate action here. This is just
      // a placeholder response.
      exit(1);
   }
   // Initialize the array elements to their default value.
   for(int i=0; i < len; ++i) aptr[i] = T();
   length = len;
}
template <class T, int len>
MyArray<T, len>::MyArray(const MyArray &obj) {
   cout << "Using MyArray's copy constructor to make a copy.\n";
   try {
      aptr = new T[obj.length];
   } catch(bad_alloc ba) {
      cout << "Can't allocate array.\n";
      exit(1);
   }
   length = obj.length;
   // Copy contents of the array.
   for(int i=0; i < length; ++i)
      aptr[i] = obj.aptr[i];
}
template<class T, int len> MyArray<T, len> &
MyArray<T, len>::operator=(const MyArray<T, len> &rh_op) {
      cout << "Assigning one MyArray object to another.\n";
      if(aptr && (length != rh_op.length)) {
         delete aptr;
         try {
            aptr = new T[rh_op.length];
         } catch(bad_alloc ba) {
            cout << "Can't allocate array.\n";
            exit(1);
         }
      }
      length = rh_op.length;
      for(int i=0; i < length; ++i)
         aptr[i] = rh_op.aptr[i];
      return *this;
}
template <class T, int len> T &MyArray<T, len>::operator[](int i)
{
      if(i < 0 || i > length) {
         // Take appropriate action here. This is just
         // a placeholder response.
         cout << "\nIndex value of " << i << " is out-of-bounds.\n";
         exit(1);
      }
      return aptr[i];
}
template <class T, int len>
MyArray<T, len> f(MyArray<T, len> x) {
      cout << "f() is returning a copy of x.\n";
      return x;
}
class myclass {
      public:
      int x;
      myclass(int i) { x = i; };
      myclass() { x = -1; }
};
int main()
{
      // Use the integer array.
      MyArray<int, 5> i_ar;
      for(int i=0; i < i_ar.getlen(); ++i) i_ar[i] = i;
      cout << "Contents of i_ar: ";
      for(int i=0; i < i_ar.getlen(); ++i) cout << i_ar[i] << " ";
      cout << "\n\n";
      // To generate a boundary overrun, uncomment the following line:
      //  i_ar[19] = 10;
      // To generate a boundary underrun, uncomment the following line:
      //  i_ar[-2] = 10;
      // Create a copy of i_ar. This will invoke MyArray's copy constructor.
      cout << "Create i_ar2 and initialize it with i_ar. This results\n"
      << "in MyArray's copy constructor being called.\n\n";
      MyArray<int, 5> i_ar2 = i_ar;
      cout << "Contents of i_ar2: ";
      for(int i=0; i < i_ar2.getlen(); ++i)  cout << i_ar2[i] << " ";
      cout << "\n\n";
      cout << "Create i_ar3.\n";
      MyArray<int, 5> i_ar3;
      cout << "Original contents of i_ar3: ";
      for(int i=0; i < i_ar3.getlen(); ++i)
         cout << i_ar3[i] << " ";
      cout <<"\n\n";
      i_ar3 = f(i_ar);
      cout << "Contents of i_ar3 after receiving value from f(i_ar): ";
      for(int i=0; i < i_ar3.getlen(); ++i)
         cout << i_ar3[i] << " ";
      cout << "\n\n";
      MyArray<myclass, 3> mc_ar;
      cout << "Original contents of mc_ar: ";
      for(int i=0; i < mc_ar.getlen(); ++i)
         cout << mc_ar[i].x << " ";
      cout << endl;
      mc_ar[0].x = 9;
      mc_ar[1].x = 8;
      mc_ar[2].x = 7;
      cout << "Values in mc_ar after setting them: ";
      for(int i=0; i < mc_ar.getlen(); ++i)
         cout << mc_ar[i].x << " ";
      cout << "\n\n";
      MyArray<myclass, 3> mc_ar2;
      mc_ar2 = f(mc_ar);
      cout << "Contents of mc_ar2 after receiving f(mc_ar): ";
      for(int i=0; i < mc_ar2.getlen(); ++i)
         cout << mc_ar2[i].x << " ";
      cout << endl;
      return 0;
}

Result


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