C Programming – Linked Lists. In this tutorial you will learn about C Programming – Linked Lists, Structure, Advantages of Linked List, and Types of linked list and Applications of linked lists. Linked lists are a type of data structure for storing information as a list. They are a memory efficient alternative to arrays because the size of the list is only ever as large as the data. Plus they do not have to shift data and recopy when resizing as dynamic arrays do. They do have the extra overhead of 1 or 2 pointers per data node, so they make sense only with larger records.
You would not want to store a list of integers in a linked list because it would actually double your memory overhead over the same list in an array. If you understand this linked list then you will be able to handle other two types of lists. A linked list does not require any extra space therefore it does not waste extra memory. It provides flexibility in rearranging the items efficiently.
A linked list node is comparable to an array element. A node contains a data portion and a pointer portion, and is declared as structs in C. An empty linked list will have this node and will be set to NULL.
This goes for all three types of linked lists. The last node in a linked list always points to NULL. There is more than one way to encounter segmentation faults when traversing a linked list, but if you are careful and follow 2 basic checks you will be able to handle segmentation faults.
Often called the current node as a reminder that it is keeping track of the current node. Always make sure to check that head is not NULL before trying to traverse the list or you will get a segmentation fault. You may also need to check that the next pointer of the current node is not NULL, if not, you will go past the end of the list and create a segmentation fault. We will need to cover the different cases of adding at the beginning, the middle or the end. When adding a first node to a linked list, you create a temporary node pointer and allocate memory for the new node. Then set head’s next pointer so that it points to the new node.
Here is a function that could accomplish just that. After we know the head is NULL, we set the head equal to the temporary node we created and set it’s next pointer to NULL to indicated it is the end of the list. In the second case (our else control block) we set the temporary node’s next pointer to head to insert it before head’s current position. Then by setting head equal to the new temporary node, we have squeezed it in at the front of the list and the new node is at the head of the list. Now let us add a node to the back of a linked list.
It takes two node pointers to add a node at the end of an nonempty linked list. You use one to allocate memory and copy the data into, and set it as next pointer to NULL since it will be at the end of the list. The other pointer is to traverse to the end of the list.
Once it reaches the end, set it as next pointer to the new node you created. Here is a function that would do just that in our high scores example: void addend(char name.
We create and copy our data, as we have in earlier examples, then we traverse the list according to our earlier formula for traversal. The last two lines are how we accomplish the actual adding of our new node to the end of the list as was explained above. We can also add new nodes to the middle of a list. To do this, it requires two spare pointers to keep from severing the list when the new node is inserted. It is also easier to do if the length of the list is known.
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You can add a simple variable to track that and just increment it whenever you add a node, if you desire this functionality from a linked list. Then as you traverse the list, make sure you have a counter that you increment to keep track of what position in the list your current pointer is currently at. To illustrate this imagine we know the position we want to insert a new node at. It is arbitrary how this is determined or whether you decide to base your counting at 0 or at 1. In our example we started our counting at 1.
Here is the snippet from our example program taken from the add. Node function: void addend(char name.
The while loop takes care of traversing the list as well as incrementing currentpos each time a new node is reached. Note in this case we use a previous pointer and a current pointer for moving through the list. Now, remember that previousnode pointer we brought along? We use it to keep from losing the end of the list past the node we are inserting. We set its next pointer to the new node and then set that new node’s next pointer to the current node which is acting as a placeholder for the rest of the list. This is quite contrived as an array would clearly be better for this but it works well for illustrating linked list implementation. We need to be able to create a list of players’ names, the associated score; we want the results sorted from greatest score to least score.
Not related toint findposition(int score). The scores are not entered in any particular order as would happen in real life so the findposition function takes care of sorting the new nodes according to the scores before they are put into the list. Feel free to ask any questions you might have.