I'm fairly new to coding in c and have stumbled upon a problem. The code below is what I have so far and the problem at hand is how to looping through the node job_list.
We have two nodes, the first one creates a basic job post with a reference number (an integer) and job name (a string - an array of characters) as parameters, and the second is a list that holds job posts with the job_node being one parameter and then the second one being a standard struct job_list * next parameter.
I think you mixed few things up..
singly link list (that's what i understand you are up to) is not a fixed size data structure. it even not an increasing space data structure. link list use exactly the amount of memory you want to hold in it.
link list is a list of nodes. you can create list - and it will be an empty list.
then, you can add nodes with your desired data and every node you insert - create a new node (on the heap = dynamically allocated) which will contain your data and will be linked to the list.
every data node in the list will have a node_next it will point to, and node_prev which will point at this particular node(head and tail will not have this 2 nodes. head will point at node_next but will not have node_prev which point to it, and tail only have node_prev which will point to it).
so, if you want to create list you will have to dynamically allocate the space of the list which contain 2 nodes: head and tail(or end).
this is an example of create function:
slist_t *SlistCreate(void)
{
slist_t *list = malloc(sizeof(slist_t));
slist_iter_t dummy = NULL;
if(NULL == list)
{
return (NULL);
}
dummy = malloc(sizeof(node_t));
if(NULL == dummy)
{
free(list);
return (NULL);
}
dummy->next = NULL;
dummy->data = (void *)list;
list->head = dummy;
list->tail = dummy;
return (list);
}
then you will be able to insert nodes before particular node or after - that's depend on how you will implement this:
if you want to implement insert before:
you will have to encapsulate the list struct and prevent the user from sending your head to insert before.
or you can check every time if your insert function get the head of the list and update the head of the list (you can insert after and copy the head data to the head->next node and then use the head for the data the user wanted to be at the head of the list.
if you want to implement insert after:
you will have to check if the user sent you the tail (also called dummy_node cause it point to dummy_node->next = NULL), and use the same method i mentioned before, only the opposite way..
this is an example of insert before - in this example i used slist_iter_t which is pointer to node_t - the user isn't exposed to any of this structs (not to the list struct or the nodes struct):
slist_iter_t SlistInsert(slist_iter_t iterator, const void *data)
{
slist_t *ptr = NULL;
slist_iter_t dup = (slist_iter_t)malloc(sizeof(node_t));
if(NULL == dup)
{
return(NULL);
}
assert(NULL != iterator);
dup->data = iterator->data;
dup->next = iterator->next;
iterator->data = (void *)data;
iterator->next = dup;
if(NULL == dup->next)
{
ptr = (slist_t *)dup->data;
ptr->tail = dup;
}
return (iterator);
}
so, for using this DS you will have to write create function, insert function and destroy function (you will have to free all your dynamically allocated memory).
you may add more function such as remove, search data, clear list, is empty and so on. if you choose to encapsulate this implementation and hide from the user the struct of the list and the struct of the node, you will have to add more function such as get data function, get next node, and more..
you mentioned you need to insert if this data doesn't exist in the list so you can send from insert function to find function.
your function needs to look something like this:
struct job_list {
struct job_node * front;
struct job_list * next;
};
struct job_node {
int reference_number;
char * job_name;
struct job_node *next;
};
for your first function:
struct job_node *JobListCreate(void)
{
struct job_node *list = malloc(sizeof(struct job_node));
struct node_job dummy = NULL;
if(NULL == list)
{
return (NULL);
}
dummy = malloc(sizeof(node_t));
if(NULL == dummy)
{
free(list);
return (NULL);
}
dummy->next = NULL;
dummy->data = (void *)list;
list->head = dummy;
list->tail = dummy;
return (list);
}
for your second function:
void JobListInsertInFront(struct job_node *list, int reference_number, char * job_name)
{
slist_t *ptr = NULL;
struct node_job dup = NULL;
assert(NULL != list);
dup = (struct node_job)malloc(sizeof(node_t));
if(NULL == dup)
{
printf("Allocation failed\n");
return;
}
dup->reference_number = list->head->reference_number;
dup->job_name = list->head->job_name;
dup->next = list->head->next;
list->head->reference_number = reference_number;
list->head->job_name = job_name;
list->head->next = dup;
return;
}
and for the last function:
bool JobListInsertIfNotExist(struct job_node *list, int reference_number, char * job_name)
{
slist_t *ptr = NULL;
struct node_job dup = NULL;
assert(NULL != list);
while (NULL != dup)
{
if (dup->reference_number == reference_number && dup->job_name == job_name)
{
return false;
}
dup = dup->next;
}
dup = (struct node_job)malloc(sizeof(node_t));
if(NULL == dup)
{
printf("Allocation failed\n");
return;
}
dup->reference_number = list->head->reference_number;
dup->job_name = list->head->job_name;
dup->next = list->head->next;
list->head->reference_number = reference_number;
list->head->job_name = job_name;
list->head->next = dup;
return true;
}
As Jack Lilhammers pointed out in the comments, your code is very complex and there are a lot of mistakes in it, so I wrote down some general functions that you can then modify accordingly.
This is the basic struct, that we are going to work with:
struct node {
int data;
struct node *next;
};
Create a new node
Then this is how you'd create a new node:
#include <stdio.h>
#include <stdlib.h>
struct node *new_node(int data, struct node *next)
{
struct node *new = malloc(sizeof *new);
if (!new) {
printf("Error: memory allocation failed");
exit(EXIT_FAILURE);
}
new->data = data;
new->next = next;
return new;
}
You would initially call the function like this:
struct node *head = new_node(5, NULL);
Check if a node exists
Normally you would do something like this to check if a node with specific data exists in the linked list:
#include <stdbool.h>
/* Return whether or not the node exists */
bool node_exists(struct node *head, int data)
{
struct node *cursor = head;
while (cursor != NULL) {
if (cursor->data == data)
return true;
cursor = cursor->next;
}
return false;
}
Insert new node at the end
If you want to insert a new node at the end of the linked list, this is how it works:
void insert_last(struct node *head, struct node *new)
{
struct node **cursor = &head;
while ((*cursor) != NULL)
cursor = &(*cursor)->next;
*cursor = new;
}
Insert new node if nonexistent
You can combine the last two functions to only insert a new node at the end of the linked list, if the data doesn't already exist:
#include <stdbool.h>
/*
* Return whether or not the node exists. If it exists,
* insert the new node at the end of the linked list.
*/
bool new_insert_last(struct node *head, struct node *new)
{
struct node **cursor = &head;
while ((*cursor) != NULL) {
if ((*cursor)->data == new->data)
return true;
cursor = &(*cursor)->next;
}
*cursor = new;
return false;
}
This function could be called like this:
new_insert_last(head, new_node(3, NULL));
I have created a GitLab Snippet, so you can see the functions in action.
Let "List" be a struct that represents a singly-linked list, i have the following function:
int List_contains(List node, const char* key) {
List *search;
search=node.next;
assert(search->key!=NULL);
return 1;
}
and List is the following struct:
typedef struct List { /*A new node*/
char* key;
void* value;
struct List *next;
} List;
The function "List_contains" should tell me if "key" is contained in the list or not. Problem is, i can't iterate through the list, and the line
assert(search->key != NULL);
throws a Segfault. How can i iterate through the list with what i have?
(Note: The function is, obviously, not "completed".)
Here is an example of a search I wrote a while back.
struct node
{
int data;
struct node *next;
};
int
search_list(struct node *head, int search)
{
if (!head)
{
fprintf(stderr, "Invalid head\n");
return 1;
}
struct node *temp = head;
while (temp)
{
if (temp->data == search)
{
printf("Found %d\n", search);
break;
}
temp = temp->next;
}
return 0;
}
int List_contains(List node, const char* key) {
List *search;
search=node.next;
assert(search->key!=NULL);
return 1;
}
so a lot to parse here...
Generally you would pass in a pointer to the node so that it isn't copied, but it is actually safe to do what you have done, in this instance, assuming no multithreaded shenanigans go on...
but in the future I would look for:
int List_contains(List* node, const char* key) {
next line you make a pointer without a value... which is fine, because you assign it the next line, but that could be condensed...
// List *search;
// search=node.next; # could easily become:
List *search = node.next;
now at this point you actually know if you are at the end of the list...
if(search == null)
{
return 0;
}
after that you need to do some sort of compare...
if (strcmp(key,search->key) == 0)
{
//found it;
return 1;
}
now you have code that will match the key against the first element of the list, so you would need to put the whole thing in a loop, each iteration swapping search with search->next and checking for null
I'm having an issue: in a function, program needs to compare two nodes and delete one of them if the node values are the same (example: A -> B -> B -> C >>> A -> B -> C). In a few words: it have to leave only unique nodes.
Steps that I've done: created list from data given in data file and it prints out perfectly. Now I'm struggling comparing two nodes.
Steps that I'm thinking of doing: Put two nodes values in two different variables, then comparing those two and if latest node is equal to previous, delete the latest and somehow link previous node to next node. Then the cycle goes all over again.
Question: How do I compare node with further one?
Here's the code that I have right now:
#include <stdio.h>
#include <stdlib.h>
#define LENGTH 255
struct node {
int info;
struct node *next;
} *head = NULL;
int create(FILE **data){
char read[LENGTH];
printf("Write data file name: ");
scanf("%s", read);
*data = fopen (read, "r");
if (data == NULL) {
printf("Error reading given file.");
}
return 0;
}
int put_Symbols_into_list(FILE *data) {
struct node *new_node, *current;
char c;
printf("Data given: ");
while (!feof(data)){
new_node = (struct node*)malloc(sizeof (struct node));
c = fscanf(data, "%s", &new_node -> info);
printf("%s ", &new_node -> info);
if (head == NULL){
head = new_node;
current = new_node;
} else {
current -> next = new_node;
current = new_node;
}
}
}
int delete_Same_Symbols() {
}
int main() {
FILE *data;
struct node *n;
create(&data);
put_Symbols_into_list(data);
delete_Same_Symbols();
//display_List(n);
return 0;
}
An efficient way of remove duplicates is the following:
1. Sort the list
2. Run through the list once deleting any adjacent duplicates.
Whether this solution works for you depends on whether your data can be ordered.
Traverse the list from head to end and maintain a Hash table.
For every element,check whether value is in the hash table: if yes, remove the node; else put value in the hash table.
Time Complexity: O(n) on average (assuming that hash table access time is O(1) on average).
I'll give you the function that will remove the duplicates.
Assuming that your code is working fine and that the info is an int value
Note that if info is a string you will need strcmp function instead of head->info == info.
int exist(NODE *head, int info) {
while (head && head->info != info) // strcmp(info,head->info) != 0
head = head->next;
return head->info == info; // strcmp(info,head->info)
}
void removeDuplicates(NODE **phead, int info) {
NODE *tmp = *phead;
while (tmp->info != info) // strcmp(info,head->info) != 0
tmp = tmp->next;
NODE *tmp1 = tmp->next;
tmp->info = tmp1->info; // strcpy(tmp->info,tmp1->info)
tmp->next = tmp1->next;
free(tmp1);
}
I need to implement a LinkedList from a file .csv file. My node is defined like this:
struct NODE {
char username[50];
char password[50];
char usertype[50];
struct NODE *next;
} *head=NULL;
I have put my whole .csv file inside an 1D array called database. I then want to sscanf this array and put each corresponding word inside a particular field inside my node. I have the following code written down:
void createList() {
// I need a while-loop here //
struct NODE* toAdd = (struct NODE*)malloc(sizeof(struct NODE));
sscanf(database, "%[^','],%[^','],%[^'\n']", toAdd->username, toAdd->password, toAdd->usertype);
if (add(toAdd) == false) {
printf("Error: was unable to initialize password validation!");
exit(EXIT_FAILURE);
}
}
My add function looks like this:
BOOLEAN add(struct NODE *p) {
if (p == NULL) return false;
if (head == NULL) {
p->next = NULL;
head = p;
} else {
p->next = head;
head = p;
}
return true;
}
Is there something wrong with the functions above? To sum up, I want to read from an array. I "break" this array into three-word-block, then assign the first one to the username field of the node, the second one to the password field, etc. I want to do this on my whole array, therefore creating one big LinkedList of nodes.
Thank you for your help.
I am creating a linked list as in the previous question I asked. I have found that the best way to develop the linked list is to have the head and tail in another structure. My products struct will be nested inside this structure. And I should be passing the list to the function for adding and deleting. I find this concept confusing.
I have implemented the initialize, add, and clean_up. However, I am not sure that I have done that correctly.
When I add a product to the list I declare some memory using calloc. But I am thinking shouldn't I be declaring the memory for the product instead. I am really confused about this adding.
Many thanks for any suggestions,
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define PRODUCT_NAME_LEN 128
typedef struct product_data
{
int product_code;
char product_name[PRODUCT_NAME_LEN];
int product_cost;
struct product_data_t *next;
}product_data_t;
typedef struct list
{
product_data_t *head;
product_data_t *tail;
}list_t;
void add(list_t *list, int code, char name[], int cost);
void initialize(list_t *list);
void clean_up(list_t *list);
int main(void)
{
list_t *list = NULL;
initialize(list);
add(list, 10, "Dell Inspiron", 1500);
clean_up(list);
getchar();
return 0;
}
void add(list_t *list, int code, char name[], int cost)
{
// Allocate memory for the new product
list = calloc(1, sizeof(list_t));
if(!list)
{
fprintf(stderr, "Cannot allocated memory");
exit(1);
}
if(list)
{
// First item to add to the list
list->head->product_code = code;
list->head->product_cost = cost;
strncpy(list->head->product_name, name, sizeof(list->head->product_name));
// Terminate the string
list->head->product_name[127] = '/0';
}
}
// Initialize linked list
void initialize(list_t *list)
{
// Set list node to null
list = NULL;
list = NULL;
}
// Release all resources
void clean_up(list_t *list)
{
list_t *temp = NULL;
while(list)
{
temp = list->head;
list->head = list->head->next;
free(temp);
}
list = NULL;
list = NULL;
temp = NULL;
}
============================== Edited ============================
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define PRODUCT_NAME_LEN 64
// typedef struct product_data product_data_t;
typedef struct product_data
{
int product_code;
char product_name[PRODUCT_NAME_LEN];
int product_cost;
}product_data_t;
typedef struct list
{
struct list *head;
struct list *tail;
struct list *next;
struct list *current_node;
product_data_t *data;
}list_t;
void add(list_t *list, int code, char name[], int cost);
int main(void)
{
list_t *list = NULL;
list = initialize(list);
add(list, 1001, "Dell Inspiron 2.66", 1299);
add(list, 1002, "Macbook Pro 2.66", 1499);
clean_up(list);
getchar();
return 0;
}
void add(list_t *list, int code, char name[], int cost)
{
/* Allocate memory for the new product */
product_data_t *product = (product_data_t*) calloc(1, sizeof(*product));
if(!product)
{
fprintf(stderr, "Cannot allocate memory.");
exit(1);
}
/* This is the first item in the list */
product->product_code = code;
product->product_cost = cost;
strncpy(product->product_name, name, sizeof(product->product_name));
product->product_name[PRODUCT_NAME_LEN - 1] = '\0';
if(!list->head)
{
/* Assign the address of the product. */
list = (list_t*) product;
/* Set the head and tail to this product */
list->head = (list_t*) product;
list->tail = (list_t*) product;
}
else
{
/* Append to the tail of the list. */
list->tail->next = (list_t*) product;
list->tail = (list_t*) product;
}
/* Assign the address of the product to the data on the list. */
list->data = (list_t*) product;
}
If you are looking to better understand the basics of linked lists, take a look at the following document:
http://cslibrary.stanford.edu/103/LinkedListBasics.pdf
Arguably you want your list data structure to be external to the data that it stores.
Say you have:
struct Whatever
{
int x_;
}
Then your list structure would look like this:
struct Whatever_Node
{
Whatever_Node* next_
Whatever* data_
}
Ryan Oberoi commented similarly, but w/o example.
In your case the head and tail could simply point to the beginning and end of a linked-list. With a singly linked-list, only the head is really needed. At it's most basic, a linked-list can be made by using just a struct like:
typedef struct listnode
{
//some data
struct listnode *next;
}listnodeT;
listnodeT *list;
listnodeT *current_node;
list = (listnodeT*)malloc(sizeof(listnodeT));
current_node = list;
and as long as list is always pointing to the beginning of the list and the last item has next set to NULL, you're fine and can use current_node to traverse the list. But sometimes to make traversing the list easier and to store any other data about the list, a head and tail token are used, and wrapped into their own structure, like you have done. So then your add and initialize functions would be something like (minus error detection)
// Initialize linked list
void initialize(list_t *list)
{
list->head = NULL;
list->tail = NULL;
}
void add(list_t *list, int code, char name[], int cost)
{
// set up the new node
product_data_t *node = (product_data_t*)malloc(sizeof(product_data_t));
node->code = code;
node->cost = cost;
strncpy(node->product_name, name, sizeof(node->product_name));
node->next = NULL;
if(list->head == NULL){ // if this is the first node, gotta point head to it
list->head = node;
list->tail = node; // for the first node, head and tail point to the same node
}else{
tail->next = node; // append the node
tail = node; // point the tail at the end
}
}
In this case, since it's a singly linked-list, the tail is only really useful for appending items to the list. To insert an item, you'll have to traverse the list starting at the head. Where the tail really comes in handy is with a doubly-linked list, it allows you to traverse the list starting at either end. You can traverse this list like
// return a pointer to element with product code
product_data_t* seek(list_t *list, int code){
product_data_t* iter = list->head;
while(iter != NULL)
if(iter->code == code)
return iter;
iter = iter->next;
}
return NULL; // element with code doesn't exist
}
Often times, the head and tail are fully constructed nodes themselves used as a sentinel to denote the beginning and end of a list. They don't store data themselves (well rather, their data represent a sentinel token), they are just place holders for the front and back. This can make it easier to code some algorithms dealing with linked lists at the expense of having to have two extra elements. Overall, linked lists are flexible data structures with several ways to implement them.
oh yeah, and nik is right, playing with linked-lists are a great way to get good with pointers and indirection. And they are also a great way to practice recursion too! After you have gotten good with linked-list, try building a tree next and use recursion to walk the tree.
I am not writing the code here but you need to do the following:
Create and object of list, this will remain global for the length of program.
Malloc the size of product _ data _ t.
For first element (head is NULL), point head to the malloced' address.
To add next element, move to the end of list and then add the pointer of malloced address to next of last element. (The next of the last element will always be NULL, so thats how you traverse to end.)
Forget tail for a while.
If you are learning C pointer theory this is a good exercise.
Otherwise, it feels like too much indirection for code that is not generic (as in a library).
Instead of allocating a static 128 byte character string, you might want to do some more pointer practice and use an allocated exact length string that you clean up at exit.
Academically, kungfucraigs' structure looks more generic then the one you have defined.
You're calloc'ing space for your list_t struct, just pointers to list head and tail, which isn't what you want to do.
When you add to a linked list, allocate space for an actual node in the list, which is your product_data_t struct.
You're allocating the wrong chunk of memory. Instead of allocating memory for each list element, you're allocating for the list head and tail.
For simplicity, get rid of the separate structure for the head and tail. Make them global variables (the same scope they're in now) and change them to be listhead and listtail. This will make the code much more readable (you won't be needlessly going through a separate structure) and you won't make the mistake of allocating for the wrong struct.
You don't need a tail pointer unless you're going to make a doubly linked list. Its not a major element to add once you create a linked list, but not necessary either.
In memory your items are linked by pointers in the list structure
item1 -> item2
Why not make the list structure part of your item?
Then you allocate a product item, and the list structure is within it.
typedef struct product_data
{
int product_code;
char product_name[PRODUCT_NAME_LEN];
int product_cost;
struct list_t list; // contains the pointers to other product data in the list
}product_data_t;
I think u first need to Imagin back-end. Code are nothing to important. Go here and visualize back-end basic c code of all insertion.
1) Insertion at beginning Visit and scroll to get every instruction execution on back- end
And u need front and imagin Go here
Back end imagin
And All other possible insertion here.
And important thing u can use this way.
struct Node{
int data;//data field
struct Node*next;//pointer field
};
struct Node*head,*tail; // try this way
or short cut
struct Node{
int data;//data field
struct Node*next;//pointer field
}*head,*tail; //global root pointer
And << Click >> To visualize other linked list problem.
Thanks.
A demo for Singly Linked List. If you prefer, try to check Circular Linked List and Doubly Linked List.
#include <stdio.h>
#include <stdlib.h>
typedef struct node {
int val;
struct node * next;
} node_t;
// Iterating over a list
void
print_list(node_t *head)
{
node_t *current = head;
while(current != NULL)
{
printf("%d\n", current->val);
current = current->next;
}
}
// Adding an item to the end of the list
void
push_end(node_t *head, int val)
{
node_t *current = head;
while (current->next != NULL)
{
current = current->next;
}
current->next = malloc(sizeof(node_t));
current->next->val = val;
current->next->next = NULL;
}
// Adding an item to the head of the list
void
push_head(node_t **head, int val)
{
node_t *new_node = NULL;
new_node = malloc(sizeof(node_t));
new_node->val = val;
new_node->next = *head;
*head = new_node;
}
// Removing the head item of the list
int
pop_head(node_t **head)
{
int retval = -1;
node_t *next_node = NULL;
if (*head == NULL) {
return -1;
}
next_node = (*head)->next;
retval = (*head)->val;
free(*head);
*head = next_node;
return retval;
}
// Removing the last item of the list
int
pop_last(node_t *head)
{
int retval = 0;
node_t *current = NULL;
if (head->next == NULL) {
retval = head->val;
free(head);
return retval;
}
/* get to the second to last node in the list */
current = head;
while (current->next->next != NULL) {
current = current->next;
}
/* now current points to the second to last item of the list.
so let's remove current->next */
retval = current->next->val;
free(current->next);
current->next = NULL;
return retval;
}
// Removing a specific item
int
remove_by_index(node_t **head, int n)
{
int i = 0;
int retval = -1;
node_t *current = *head;
node_t *temp_node = NULL;
if (n == 0) {
return pop_head(head);
}
for (i = 0; i < n - 1; i++) {
if (current->next == NULL) {
return -1;
}
current = current->next;
}
temp_node = current->next;
retval = temp_node->val;
current->next = temp_node->next;
free(temp_node);
return retval;
}
int
main(int argc, const char *argv[])
{
int i;
node_t * testnode;
for (i = 0; i < argc; i++)
{
push_head(&testnode, atoi(argv[i]));
}
print_list(testnode);
return 0;
}
// http://www.learn-c.org/en/Linked_lists
// https://www.geeksforgeeks.org/data-structures/linked-list/
The linked list implementation inspired by the implementation used in the Linux kernel:
// for 'offsetof', see: https://stackoverflow.com/q/6433339/5447906.
#include <stddef.h>
// See: https://stackoverflow.com/q/10269685/5447906.
#define CONTAINER_OF(ptr, type, member) \
( (type *) ((char *)(ptr) - offsetof(type, member)) )
// The macro can't be used for list head.
#define LIST_DATA(ptr, type, member) \
CONTAINER_OF(ptr, type, member);
// The struct is used for both: list head and list nodes.
typedef struct list_node
{
struct list_node *prev, *next;
}
list_node;
// List heads must be initialized by this function.
// Using the function for list nodes is not required.
static inline void list_head_init(list_node *node)
{
node->prev = node->next = node;
}
// The helper function, mustn't be used directly.
static inline void list_add_helper(list_node *prev, list_node *next, list_node *nnew)
{
next->prev = nnew;
nnew->next = next;
nnew->prev = prev;
prev->next = nnew;
}
// 'node' must be a list head or a part of a list.
// 'nnew' must not be a list head or a part of a list. It may
// be uninitialized or contain any data (even garbage).
static inline void list_add_after(list_node *node, list_node *nnew)
{
list_add_helper(node, node->next, nnew);
}
// 'node' must be a list head or a part of a list.
// 'nnew' must not be a list head or a part of a list. It may
// be uninitialized or contain any data (even garbage).
static inline void list_add_before(list_node *node, list_node *nnew)
{
list_add_helper(node->prev, node, nnew);
}
// 'node' must be part of a list.
static inline list_node *list_del(list_node *node)
{
node->prev->next = node->next;
node->next->prev = node->prev;
return node->prev;
}
Example of usage:
#include <stdio.h>
// The struct must contain 'list_node' to be able to be inserted to a list
typedef struct
{
int data;
list_node node;
}
my_struct;
// Convert 'list_node *' to 'my_struct*' that contains this 'list_node'
static inline my_struct* get_my_struct(list_node *node_ptr)
{
return LIST_DATA(node_ptr, my_struct, node);
}
void print_my_list(list_node *head)
{
printf("list: {");
for (list_node *cur = head->next; cur != head; cur = cur->next)
{
my_struct *my = get_my_struct(cur);
printf(" %d", my->data);
}
printf(" }\n");
}
// Print 'cmd' and run it. Note: newline is not printed.
#define TRACE(cmd) \
(printf("%s -> ", #cmd), (cmd))
int main()
{
// The head of the list and the list itself. It doesn't contain any data.
list_node head;
list_head_init(&head);
// The list's nodes, contain 'int' data in 'data' member of 'my_struct'
my_struct el1 = {1};
my_struct el2 = {2};
my_struct el3 = {3};
print_my_list(&head); // print initial state of the list (that is an empty list)
// Run commands and print their result.
TRACE( list_add_after (&head , &el1.node) ); print_my_list(&head);
TRACE( list_add_after (&head , &el2.node) ); print_my_list(&head);
TRACE( list_add_before(&el1.node, &el3.node) ); print_my_list(&head);
TRACE( list_del (head.prev) ); print_my_list(&head);
TRACE( list_add_before(&head , &el1.node) ); print_my_list(&head);
TRACE( list_del (&el3.node) ); print_my_list(&head);
return 0;
}
The result of execution of the code above:
list: { }
list_add_after (&head , &el1.node) -> list: { 1 }
list_add_after (&head , &el2.node) -> list: { 2 1 }
list_add_before(&el1.node, &el3.node) -> list: { 2 3 1 }
list_del (head.prev) -> list: { 2 3 }
list_add_before(&head , &el1.node) -> list: { 2 3 1 }
list_del (&el3.node) -> list: { 2 1 }
http://coliru.stacked-crooked.com/a/6e852a996fb42dc2
Of course in real life you will most probably use malloc for list elements.
In C language, we need to define a Node to store an integer data and a pointer to the next value.
struct Node{
int data;
struct Node *next;
};
To add a new node, we have a function add which has data as an int parameter. At first we create a new Node n. If the program does not create n then we print an error message and return with value -1. If we create the n then we set the data of n to have the data of the parameter and the next will contain the root as it has the top of the stack. After that, we set the root to reference the new node n.
#include <stdio.h>
struct node
{
int data;
struct node* next;
};
int main()
{
//create pointer node for every new element
struct node* head = NULL;
struct node* second = NULL;
struct node* third = NULL;
//initialize every new pointer with same structure memory
head = malloc(sizeof(struct node));
second = malloc(sizeof(struct node));
third = malloc(sizeof(struct node));
head->data = 18;
head->next = second;
second->data = 20;
second->next = third;
third->data = 31;
third->next = NULL;
//print the linked list just increment by address
for (int i = 0; i < 3; ++i)
{
printf("%d\n",head->data++);
return 0;
}
}
This is a simple way to understand how does pointer work with the pointer. Here you need to just create pointer increment with new node so we can make it as an automatic.
Go STL route. Declaring linked lists should be agnostic of the data. If you really have to write it yourself, take a look at how it is implemented in STL or Boost.
You shouldn't even keep the *next pointer with your data structure. This allows you to use your product data structure in a various number of data structures - trees, arrays and queues.
Hope this info helps in your design decision.
Edit:
Since the post is tagged C, you have equivalent implementations using void* pointers that follow the basic design principle. For an example, check out:
Documentation | list.c | list.h