CODEWITHSUNDEEP
cfilestructiolinked-list
surjit
surjit

Reputation: 348

Read linked list from a file and load the data

I wrote a C code to implement a dictionary using linked-list(nodes are in sorted order) I want to save the data to a file and be able to reload the data when I run the program next time. I'm having trouble loading the data from file. Here is my code for reading and writing data:

struct node{
    char word[20];
    char meaning[5][100]; //2D array for saving multiple meanings of a word
    struct node *next;
};

void ReadData(struct node *head)
{
    struct node *tail;
    FILE *fp = fopen("dictionary.data", "rb");
    if(fp == NULL)
    {
        printf("Error opening file..\n");
        return;
    }
    while(!feof(fp))
    {
        tail = (struct node*)calloc(1, sizeof(struct node));
        fread(tail->word, sizeof(head->word), 1, fp);
        fread(tail->meaning, sizeof(head->meaning), 1, fp);
        if(head == NULL) //for fresh run head is initialized with NULL
        {
            tail->next = head;
            head = tail;
        }
        else
        {
            head->next = tail;
            head = head->next;
        }
    }
    fclose(fp);
}

I can't load data from the file to the linked list. Code is not working. I can't figure out where the problem is..
Here's how I'm writing the data to the file :

/*I think this code is working because size of the file increases after running the code*/
void WriteData(struct node *head)
{
    FILE *fp = fopen("dictionary.data", "wb");
    if(fp == NULL)
    {
        printf("Error opening file..\n");
        return;
    }
    while(head != NULL)
    {
        fwrite(head->word, sizeof(head->word), 1, fp);
        fwrite(head->meaning, sizeof(head->meaning), 1, fp);
        head = head->next;
    }
    fclose(fp);
}

I've used sizeof, instead of strlen, it's a string. It'll have null character at the end - no problem with string. It'll consume more memory though.

Upvotes: 0

Views: 3072

Answers (1)

BLUEPIXY
BLUEPIXY

Reputation: 40145

try this (untested):

void ReadData(struct node **head){//or struct node *ReadData(void){ ... return head; }
    struct node temp = { .next = NULL };//{ {0}, {{0}}, NULL}
    struct node *hp, *curr;
    FILE *fp = fopen("dictionary.data", "rb");

    if(fp == NULL){
        printf("Error opening file..\n");
        return;
    }

    hp = *head;
    while(fread(temp.word, sizeof(temp.word), 1, fp) && fread(temp.meaning, sizeof(temp.meaning), 1, fp)){
        struct node *np = malloc(sizeof(*np));
        if(np == NULL){
            perror("couldn't make new node by malloc:");
            return ;//release list
        }
        *np = temp;

        if(hp == NULL){//for fresh run head is initialized with NULL
            curr = hp = np;
        } else {//If *head isn't NULL, you need to move to the last node first.
            curr = curr->next = np;
        }
    }
    fclose(fp);
    *head = hp;
}
//....................
int main(void){
    //...
    struct node *head = NULL;
    //...
    ReadData(&head);
    //...

Upvotes: 2

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