Defined Terms

allocator Library class that allocates unconstructed memory.

dangling pointer A pointer that refers to memory that once had an object but no longer does. Program errors due to dangling pointers are notoriously difficult to debug.

delete Frees memory allocated by new. delete p frees the object and delete [] p frees the array to which p points. p may be null or point to memory allocated by new.

deleter Function passed to a smart pointer to use in place of delete when destroying the object to which the pointer is bound.

destructor Special member function that cleans up an object when the object goes out of scope or is deleted.

dynamically allocated Object that is allocated on the free store. Objects allocated on the free store exist until they are explicitly deleted or the program terminates.

free store Memory pool available to a program to hold dynamically allocated objects.

heap Synonym for free store.

new Allocates memory from the free store. new T allocates and constructs an object of type T and returns a pointer to that object; if T is an array type, new returns a pointer to the first element in the array. Similarly, new [n] T allocates n objects of type T and returns a pointer to the first element in the array. By default, the allocated object is default initialized. We may also provide optional initializers.

placement new Form of new that takes additional arguments passed in parentheses following the keyword new; for example, new (nothrow) int tells new that it should not throw an exception.

reference count Counter that tracks how many users share a common object. Used by smart pointers to know when it is safe to delete memory to which the pointers point.

shared_ptr Smart pointer that provides shared ownership: The object is deleted when the last shared_ptr pointing to that object is destroyed.

smart pointer Library type that acts like a pointer but can be checked to see whether it is safe to use. The type takes care of deleting memory when appropriate.

unique_ptr Smart pointer that provides single ownership: The object is deleted when the unique_ptr pointing to that object is destroyed. unique_ptrs cannot be directly copied or assigned.

weak_ptr Smart pointer that points to an object managed by a shared_ptr. The shared_ptr does not count weak_ptrs when deciding whether to delete its object.