Dynamic Data and a Dynamic Array

• Parts of this are from chapter 14.
• Parts of this are not.
• Data in most programs are stored in two places
  • Static data is stored on the stack.
  • Dynamic data is stored on the heap.
  • The compiler manages the stack.
  • The user manages (partially) the heap.
• Storage space on the heap
  • Is allocated with a call to new
  • Is released with a call to delete.
• new
  • ptrVar = new type
  • ptrVar = new type[int size]
  • For basic data types this function
    • Allocates memory on the heap
    • Returns a pointer to this memory.
  • For classes
    • It calls the constructor as well.
  • For the array version it will call the constructor many times.
  • If there is no memory available, it will throw an exception.
• delete
  • delete ptrVar
  • delete [] ptrVar
  • This will return the memory to the free store (heap)
  • If the memory contains a class, the destructor will be called.
  • THIS DOES NOT CHANGE THE VALUE OF ptrVar
  • You can only delete memory once.
  • You must match new [] and delete [] , new and delete
• A Memory Leak is the loss of memory space that occurs when dynamic data is allocated but not deallocated.
  • This is an attention to detail problem.
  • This is huge.
  • If you allocate memory, later you must deallocate it.
• A dangling pointer is a pointer to memory that has been deallocated.
• An inaccessible object is dynamic memory that has not been deleted but has not pointer pointing to it.
• All three of these are common errors.
  • There are structures to handle them in modern c++
  • But we need at least a basic understanding of raw pointers.