Question

I have a header file:

using namespace std;

class IntList{
private:
    int *Intl;
    int Capacity;
    int Count;
public:
    IntList(int capacity){
        Capacity = capacity;
        Count = 0;
        Intl = new int[capacity];
    }

    ~IntList(){
        delete Intl;
    }

    //adds the integers of the specified collection to the end of the List; return false if the new Count will be greater than Capacity
    bool AddRange(const IntList &items){
        //int *Temp = items.;
        if(items.Count > Capacity - Count){
            return false;
        }else{
            for(int i = 0; i <items.Count; i++){
                Intl[Count] = items.Intl[i];
                Count++;
            }
            return true;
        }
    }
};

But I don’t know why I can’t return value to IntList object in there:

//creates a copy of a range of elements in the source List
        IntList GetRange(int index, int count){
            IntList A(count);
            for(int i = 0; i < count; i++){
                A.Intl[i] = Intl[index -1 +i];
            }   
            return A;
        }

I want to return value of A whose type is IntList but I meet an error on "_BLOCK_TYPE_IS_VALID(pHead->nBlockUse) in visual studio 2010. How can I repair it?

Answer 1

For an object which is returned by value makes a call to copy-constructor . You must make a copy-constructor and define it so that you get appropriate results. Returning by reference actually does not require call to copy constructor but should not be made for a temporary object. Also since you have a pointer type as member variable in class . It would be appropiate for you to overload the = operator. It should be define properly to avoid memory leak. Do something like this Intlist a=GetRange(index,count) . Also you should create a copy constructor for this . Your code also has a bug that it doesnot overload= operator for class Intlist .

you can write a copy constructor something like this :-

   Intlist::Intlist(const Intlist& cSource)
   {         
     capacity = cSource.capacity; 
     count=  cSource.count;
    // Intl is a pointer, so we need to deep copy it if it is non-null
    if (cSource.Intl)
     {
       // allocate memory for our copy
      Intl = new int[capacity];

    // Copy the Intl into our newly allocated memory in for loop
     for(i=0;i<capacity;i++)
     {
       // copy part
      }
    }
    else
    intl = NULL;
  }

Just an e.g how you should write it.