[Solved] C: Variable is uninitialized for linked list

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@Sourav Ghosh have already explained what was wrong with your code and also suggested one way to solve it. Here is another way.

Instead of passing current and head as variables to be changed inside the function (i.e. as pointer-to-pointer), I would recommend that you use the function return value. In that way you don’t have to use pointer-to-pointer.

Something like:

item* add_item(item* head)
{
    // Place a new item in front
    item* current = malloc(sizeof(item));
    current->next = head;
    return current;
}

item* build_list(item* head, FILE *in) {

    char gene[STRLEN];
    char *tok;
    char gene_name[STRLEN];
    char *search = ",";
    int j;

    while (fgets(gene, sizeof(gene), in))
    {
        // Get a new item
        head = add_item(head);

        // Fill data into the new item
        tok = strtok(gene, search);
        strcpy(gene_name, tok);
        for (j = 0; j < 4; ++j)
        {
            tok = strtok(NULL, search);
            head->num[j] = atoi(tok);
        }
    }

    return head;
}

and from maincall it like:

head = NULL;
head = build_list(head, input);

Note: For readability, I skipped all check for failing malloc. In real code you should always check whether malloc returned NULL.

solved C: Variable is uninitialized for linked list