---

Linked List in C++

---

• Insert and delete list element at head in Java
  • Recall the insert at head and delete at head method in Java:

    public class ListElem { public int value; public ListElem next; public ListElem() { value = 0; } public ListElem(int x) { value = x; } } public class List { public ListElem head; public List() { head = null; // Start with empty list } // ************************************************* // delete(): delete at head // ************************************************* public void delete() { ListElem p2; if ( head != null ) { p2 = head; head = p2.next; // The second is the new "first element" } } // ------------------------------- // insert(v): insert at head // ------------------------------- public void insert(ListElem elem) { elem.next = head; // Link new element head = elem; } }

  ---

  ---

• The ListElem in C++
  • The main difference that we must be aware of is the difference in meaning of the following definition:

    Java: public class ListElem { public int value; public ListElem next; ... }

    ---

  • The definition of the variable next in "ListElem next" means:

    in Java: next is a reference (pointer) variable that contains an address of a ListElem object in C++: next is a ListElem object !!!           To define a reference (pointer) variable to a ListElem object, we must use: ListElem *next;

    ---

    ---

  • Example:

    public class ListElem { public: int value; ListElem * next; // Pointer !!!! ListElem() { value = 0; } ListElem(int x) { value = x; } }

  ---

  ---

• Inserting and deleting at head in C++
  • I will write the declaration and definition separately

    Again, the most important thing to remember is:

    You need to define reference (pointer) variables to point to the head of the List

    ---

  • The List class definition (only the variable definitions and signatures (declaration) of functions

    class List { public: ListElem * head; // Pointer variable !!! List(); // Constructor void delete(); // Member functions void insert(ListElem * elem); } ; // Don't forget the ; !!!

    ---

  • The List class definition (only the variable definitions and signatures (declaration) of functions

    #include "List.h" // Always include declarations first ! // ************************************************* // Constructor // ************************************************ List::List() { head = NULL; // Start with empty list } // ************************************************* // delete(): delete at head // ************************************************* void List::delete() { ListElem * p2; if ( head != null ) { p2 = head; head = p2->next; // The second is the new "first element" } } // ------------------------------- // insert(v): insert at head // ------------------------------- void List::insert(ListElem * elem) { elem->next = head; // Link new element head = elem; }

    ---

  • Example Program: (Demo above code)                                                
    • The ListElem declaration (and implementation) file: click here
    • The List declaration file: click here
    • The List implementation Prog file: click here
    • The test program file: click here

    How to run:

    CC -c List.C CC -c main.C CC main.o List.o or: CC main.C List.C Run: a.out