Linked list in C – search method - c

Question

As at the last time, suppose we have doubly linked list of nodes
#include <stdio.h>
#include <stdlib.h>
typedef struct Node {
int value;
struct Node* next;
struct Node* prev;
} Node;
typedef struct LinkedList {
Node *first;
Node *last;
} LinkedList;
void initList(LinkedList* l) {
l->first = NULL;
l->last = NULL;
}
and my task is to code search method, which should find a node with given value
Node* search(LinkedList *list, int value) { ... }
well, my attempt follows
Node* search(LinkedList *list, int value) {
Node *node = malloc(sizeof(Node));
if (node == NULL)
return NULL;
node->value = value;
node->prev = NULL;
node->next = list->first;
while((node->value != value) && (node->next != NULL)){
node->prev = node->next;
node->next = (node->next)->next;
}
return node;
}
according to the implemenatation tests (this is not my job :-)
void test_search_exist() {
printf("Test 3: ");
LinkedList l;
initList(&l);
Node n1, n2;
n1.value = 1;
n1.next = &n2;
n1.prev = NULL;
n2.value = 2;
n2.next = NULL;
n2.prev = &n1;
l.first = &n1;
l.last = &n2;
Node *i = search(&l, 2);
if (i == &n2) {
printf("OK\n");
}else{
printf("FAIL\n");
}
}
void test_search_not_exist(){
printf("Test 4: ");
LinkedList l;
initList(&l);
Node n1, n2;
n1.value = 1;
n1.next = &n2;
n1.prev = NULL;
n2.value = 2;
n2.next = NULL;
n2.prev = &n1;
l.first = &n1;
l.last = &n2;
Node *i = search(&l, 3);
if (i == NULL) {
printf("OK\n");
}else{
printf("FAIL\n");
}
}
my code breaks either for existing or non-existing nodes. So is there any logic mistake or whatever?

Answer 1

Firstly: Dont allocate within search. The data members already exist, since you created them ahead.
Secondly: Iterate through the list and check every node for it's value.
Node* search(LinkedList *list, int value)
{
Node *node = list->first;
Node *found = NULL;
while(node != NULL)
{
if(node->value == value)
{
found = node;
break;
}
node = node->next;
}
return found;
}
To be more specific with the error(s) you made:
You allocated a node then filled it with the pointers of the first node, but with the value you were searching for. Then you started to loop over the list with the condition to stop when node->value equals the value you were searching for. Since node->value was initialized with the value your were searching for, this comparison will always be false (since its the same), the loop will be terminated and you get a bad result.
Besides this, your original code would result in a memory leak, since you malloc a new node, but you dont free it.