CODEWITHSUNDEEP
c++pointerslinked-listqueuecopy-constructor
Nikhil Shinday
Nikhil Shinday

Reputation: 1256

(C++ Error: pointer being freed was not allocated) for linked lists

With this main:

void print_first(Queue q);

int main()
{
   Queue q1;
   Queue q2(4);
   q2.push(5);
   q2.push(3);
//   q2.print_list();
   for (int i = 0; i < 3; i++)
   {
      print_first(q2);
   }
   return 0;
}

void print_first(Queue q)
{
   if (!q.isEmpty())
   {
      cout << q.pop() << endl;
   }
   else
   {
       cout << "Nothing in queue" << endl;
   }
}

and these function definitions in a class Queue which has a linked lists with "head" and "tail" as pointers to the first and last Nodes in a linked list, each node which contains another struct "data" which stores an redefined type ElementType:

bool Queue::push(ElementType newElement)
{
   tail->next = new Node;
   if (tail->next == NULL)
   {
      return false;
   }
   tail->next->data.value = newElement;
   tail->next->next = NULL;
   tail = tail->next;
   return true;
}

ElementType Queue::pop()
{
   Node *newNode;
   ElementType returnData;
   returnData = head->data.value;
   newNode = head;
   head = head->next;
   delete newNode;
   return returnData;
}

bool Queue::isEmpty()
{
   if(head == NULL)
   {
       return true;
   }
   return false;
}

why am I getting this error? 4 Assembly Line Simulator(9701) malloc: * error for object 0x1001000e0: pointer being freed was not allocated * set a breakpoint in malloc_error_break to debug

Upvotes: 1

Views: 927

Answers (1)

Vlad from Moscow
Vlad from Moscow

Reputation: 310990

Having the code you showed I think that the problem is that you pass a copy of the queue q to function print_first.

void print_first(Queue q)

If you did not write correctly the copy constructor then you can have some problems with the function.

Upvotes: 1

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