Uninitialized memory blocks in VC++

// Call first to register hook
_CrtSetAllocHook(&zero_fill);



int zero_fill(int nAllocType,
              void* pvData,
              size_t nSize,
              int nBlockUse,
              long lRequest,
              const unsigned char *szFileName,
              int nLine )
  /// Very Importaint !!
  /// infinite recursion if this is removed !!
  /// _CRT_BLOCK must not do any thing but return TRUE
  /// even calling printf in the _CRT_BLOCK will cause
  /// infinite recursion
  if ( nBlockUse == _CRT_BLOCK )
    return( TRUE );
  switch(nAllocType)
  {
  case _HOOK_ALLOC:
  case _HOOK_REALLOC:
    // zero initialize the allocated space.
    memset(pvData,0,nSize);
    break;
  case _HOOK_FREE:
    break;
  }
  return TRUE;

char * p = new char[16];     // 16 bytes of random trash
strcpy(p, "StackOverflow");  // 13 characters, a '' terminator, and two bytes of trash
delete [] p;                 // return 16 bytes to the heap, but nothing else changes;

if (p != NULL)               // Why would p be NULL?  It was never set to NULL
    ASSERT(p[0] == 'S');     // In debug, this will crash, because p = 0xfeeefeee and
                             // dereferencing it will cause an error.
                             // Release mode may or may or may not work, depending on
                             // other memory operations

int *ptr=0;

#define SafeDelete(mem) { delete mem; mem = NULL; }
#define SafeDeleteArray(mem) { delete [] mem; mem = NULL; }