how to understand it

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how to understand "one of the reason to add head node to the link list is that the operations on the empty list and the non-empty list can be the same."
It will be much better if there is a sample showing the details. Thank you!

Posted 29-Jul-11 3:58am

johan1990

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Sergey Chepurin 29-Jul-11 14:09pm

If you simply search for, say, "dummy head node in linked list", you will get a lot of good and reliable answers on this including pages from universities.

3 solutions

Solution 3

The STL std::list is implemented as a dual linked-list with a dummy node working as both head and tail.

Just look the <list> header.

Posted 29-Jul-11 7:00am

Emilio Garavaglia

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YvesDaoust · Accepted Answer · 2011-07-29T04:25:00

Adding a dummy head node makes the list more homogeneous in that every node is pointed to by another node. Without it, the first node is different, it is pointed to by the head pointer, not by a node.

In the case of an insertion operation, you insert after a given node. When the list is empty, there is no such node and you have to handle this as a special case. When there is a dummy node, you can always insert after it.

Maximilien · Accepted Answer · 2011-07-29T04:18:00

Solution 1

Me think adding a non-functional (dummy) node to a linked-list is not a good thing.

Just check the initial pointer against NULL.

for example (simplified-ish code)

struct node
{
  int data;
  node* next;
};

node* myList = NULL; // empty list.

// traversal on an empty list; if the list is empty it will not traverse.
node* myIterator = myList;
while ( myIterator != NULL )
{
   myIterator = myIterator->next;
};

Posted 29-Jul-11 4:18am

Maximilien

Comments

Philippe Mori 29-Jul-11 19:38pm

There is a big problem with that solution... How to you pass an empty list to a function that could add items to the list?

Maximilien 30-Jul-11 10:39am

The same way you pass a pointer to a function that will modify it : by passing a pointer to the pointer or a reference to the pointer.

void f( node** list );
void f( node*& list );
// or is it ? (I don't remember).
void f(node &* list );

M.