VC++ debug assertion failed on program exit

Question

I'm trying to create a linked list class template (Yes, I know there's one in the c++ library but I wanted to create my own for fun). I've traced through the code and all seems well until the program exits.

Here's the used code:

list.h:

#ifndef LIST_H
#define LIST_H

#include "misc.h"

template <typename T> class CList {

private:

  class CNode {

  friend CList;

  private: T data; 
       CNode* next;

  public: CNode() : next(NULL) {}
      ~CNode() { delete [] next; }
  };

private: int length; 
         CNode* first;

public: 

  CList() : length(0), first(NULL) {}

  CList(int i_length) : first(NULL) {

    int i;

    CNode* cur = NULL;
    CNode* prev = NULL;

    if (i_length < 0) length = 0;
    else length = i_length;

    for (i=0;i<length;i++) {

      // allocate new CNode on heap
      cur = new2<CNode>();

      // attach preceding CNode pointer
      if (prev) prev->next = cur;
      else first = cur;

      prev = cur;
    }
  }

  ~CList() { delete first; }

};

misc.h

#ifndef MISC_H
#define MISC_H

#include <stdlib.h>
#include <stdio.h>
#include <string.h>

inline void terminate( const char* message, int code ) {
  printf("\n\n%s\n\n",message);
  system("pause");
  exit(code);
};

template <typename T> inline T* new2() {
  T* ret = new T;
  if (!ret) terminate("Insufficient Memory",-2);
  return ret;
}

template <typename T> inline T* new2(int num) {
  if (num <= 0) terminate("Invalid Argument",-1);
  T* ret = new T[num];
  if(!ret) terminate("Insufficient Memory",-2);
  return ret;
}


#endif

main.cpp

#include <stdio.h>
#include <stdlib.h>
#include "../Misc/misc.h"
#include "../Misc/list.h"

int main(int argc, char* argv[]) {

  //CList<int> m;
  CList<int> n(5);

  system("pause");

  return 0;
}

Here is what the variable "n" looks like at the breakpoint just before "return 0;".

http://s20.beta.photobucket.com/user/marshallbs/media/Untitled_zps52497d5d.png.html

Here's the context in which the error occurs. Unfortunately at this point I can no longer view the variable "n" on the watch list.

       _mlock(_HEAP_LOCK);  /* block other threads */
    __TRY

        /* get a pointer to memory block header */
        pHead = pHdr(pUserData);

         /* verify block type */
        _ASSERTE(_BLOCK_TYPE_IS_VALID(pHead->nBlockUse));

There is no error when I use the default constructor for my list. I don't understand what's going on as the memory release process should stop when it reaches the fifth CNode object which has a null "next" pointer. It acts as though it's trying to releasing an invalid non-null pointer but I don't see how this can happen.

Answer 1

One problem is that you allocate next using new and free it using delete[] . This is undefined behaviour.

Allocation:

   cur = new2<CNode>(); // new2 uses `new' and not `new[]'

Deallocation:

  ~CNode() { delete [] next; }

Replace the latter with delete next; .

Answer 2

I built and ran (from the debugger) the code as-is and got no assertion failures. In fact, there is no memory deallocation at all because CList doesn't have a destructor (didn't you post the complete code?).