Thread: Deleting node from linked list, need explanation

Excellent, the code is following:

Code:

#include <stdio.h>
#include <stdlib.h>

typedef struct node *link;
struct node {
	char data;
	link next;
	link prev;
};

typedef struct Root *root;
struct Root {
	int size;
	link first;
	link last;
};

root InitList(void);
root AddFront(root list, char value);
link FindNode(root list, char value);
void FindNodeAndDelete(root list, char value);
void DeleteNode(root list, link node);
void PrintList(root list);


int main(void) {
	root list;
	link node;

	list = InitList();
	list = AddFront(list, 'M');
	list = AddFront(list, 'A');
	list = AddFront(list, 'B');
	
        /* This is where segmentation fault occurs */
 	FindNodeAndDelete(list, 'A');

	PrintList(list);
	node = FindNode(list, 'A');
 
        /* Ffunction below removes node without any issues*/
	/* DeleteNode(list, node); */
	PrintList(list);
	return 0;
}

root InitList(void) {
	root list;
	if ((list=(root)malloc(sizeof(root))) == NULL) {
		fprintf(stderr, "Not enough memory to allocate root\n");
		exit(1);
	}
	list->first=list->last = NULL;
	list->size = 0;
	return list;
}

root AddFront(root list, char value) {
	link newNode;
	if ((newNode=(link)malloc(sizeof(link))) == NULL) {
		fprintf(stderr, "Not enough memory to new node\n");
		exit(1);
	}
	if (list->first == NULL) {
			newNode->data = value;
			newNode->next = list->first;
			newNode->prev = NULL;
			list->last = newNode;
			list->first = newNode;
			++list->size;
			return list;
	}

	newNode->data = value;
	newNode->next = list->first;
	newNode->prev = NULL;
	list->first = newNode;
	++list->size;
	return list;
}

link FindNode(root list, char value) {
	link node = NULL;
	node = list->first;

	if (node == NULL) {
		printf("list is empty\n");
		return NULL;
	}
	else {
			while (node != NULL) {
			if (node->data == value)
				return node;
			node = node->next;
		}
	}
	printf("Node is not located returning NULL\n");
	return NULL;
	
}
void FindNodeAndDelete(root list, char value) {
	link node;
	node = FindNode(list, value);
	if (node == NULL)
		printf("Element is not located\n");
	else {
		printf("Node located, its value is &#37;c\n", node->data);
		node->next->prev = node->prev;
		node->prev->next = node->next;
		free(node);
	}
}

void PrintList(root list) {
	link element;
	element = list->first;
	
	if (element == NULL) 
		printf("List is empty\n");
	else 
		while (element != NULL) {
			printf("Node's value is %c\n", element->data);
			element = element->next;
		}
	printf("List size is %d\n", list->size);

}

Cheers

I think the main problem you are having is in your AddFront function.
You are inserting at the beginning of the list but dont update the previous
node value for the old first element. Something like:

Code:

newNode->prev = NULL;
list->first->prev = newNode;
list->first = newNode;

in AddFront should fix it.

Also, maybe consider something like:

Code:

void FindNodeAndDelete(root list, char value) {
    DeleteNode(list, FindNode(list, value));
}

dinjas