function - C: Variable is uninitialized for linked list -

i'm relatively new c , creating program involves linked-list. here abbreviated version of code that's giving me trouble.

#include <string.h> #include <stdio.h> #include <stdlib.h>  #define strlen 100  struct gene {      int num[4];     struct gene *next;     }; typedef struct gene item;  void build_list(item *current, item *head, file *in);  int main() {      file *input;     file *output;     input = fopen("test.data", "r");     output = fopen("test.out", "w+");      item *curr;     item *head;      head = null;     int i;      build_list(curr, head, input);     curr = head;      while(curr) {         (i = 0; < 4; ++i)             fprintf(output, "%d\n", curr->num[i]);         curr = curr->next;         }      fclose(input);     fclose(output);     free(curr); }  void build_list(item *current, item *head, file *in) {      char gene[strlen];     char *tok;     char gene_name[strlen];     char *search = ",";     int j;      while (fgets(gene, sizeof(gene), in)) {          current = (item *)malloc(sizeof(item));         tok = strtok(gene, search);         strcpy(gene_name, tok);         (j = 0; j < 4; ++j) {             tok = strtok(null, search);             current->num[j] = atoi(tok);             }         current->next = head;         head = current;     } } 

when try compile this, says variable curr uninitialized, when initialize malloc throws segmentation fault, or prints out nothing @ all. why be?

@sourav ghosh have explained wrong code , suggested 1 way solve it. here way.

instead of passing current , head variables changed inside function (i.e. pointer-to-pointer), recommend use function return value. in way don't have use pointer-to-pointer.

something like:

item* add_item(item* head) {     // place 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))     {         // new item         head = add_item(head);          // fill data new item         tok = strtok(gene, search);         strcpy(gene_name, tok);         (j = 0; j < 4; ++j)         {             tok = strtok(null, search);             head->num[j] = atoi(tok);         }     }      return head; } 

and maincall like:

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

note: readability, skipped check failing malloc. in real code should check whether malloc returned null.