c从txt文件读取的链表

Question

I'm pretty new in c and want to make a program that can read linked list from a txt file. For example, my file is something like

0 1 6 4 8 6 8 15 56 4 864 68

and I want to read the info and then try display it to user. This is what I have made. This gives me error that expected expression before head it writes it in main part where I declared.

A = readList(head); 
printList(head);

My code:

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

typedef struct linkedList{
    int value;
    struct linkedList *next;
} linkedList, head;

linkedList *readList(linkedList *head)
{
    FILE *dataFile;
    dataFile = fopen("duom.txt", "r");
    if(dataFile == NULL) {
        printf("Nepasisekė atidaryti failo\n");
    } else {
        printf("Duomenų failą pavyko atidaryti\n");
    }
    while (!feof (dataFile))
        if (head == NULL) {
            head = malloc(sizeof(linkedList));
            fscanf(dataFile, "%d", &head -> value);
            head -> next = NULL;
        } else {
            struct linkedList *current = head;
            struct linkedList *temp = malloc(sizeof(linkedList));
            while(current -> next != NULL) {
                current = current -> next;
            }
            fscanf(dataFile, "%d", &temp -> value);
            current -> next = temp;
            temp -> next = NULL;
        }
    return head;
}
void printList(linkedList *head)
{
    linkedList *current = head;
    while (current != NULL) {
        printf("%d->", current -> value);
        current = current -> next;
    }
    printf("NULL\n");
    return;
}
int main()
{
    linkedList A;
    A=readList(head);
    printList(head);
    return 0;
}

Answer 1

You are allocating space for head in readList, yet you're passing some un-existing parameter there (readList(head) and printList(head)). What you could do to fix your issue is: Change your main to:

int main()
{
    linkedList *A = NULL; /* creating pointer to your linked list. */
    A=readList(A);  /* Read linked list from file (And allocate it if it's not allocated */
    printList(A); /* print list */
    return 0;
}

If you want A to be globally acessible just move declaration of pointer A outside of main.

Answer 2

To answer your problem that is

this writes me error that expected expression before head it writes it in main part where I declare A = readList(head); printList(head);

You should change from

linkedList A;
A=readList(head);

to

linkedList* A;
A=readList(head);

It should solve the issue you are describing.

Answer 3

I think there is a problem about your typedef

typedef are a part of operations which are made at the pre-proccessing

It will replace all the #define and typedefs inyour code by their oponent.

So your double typedef typedef struct Linkedlist { .... } linkedList, head;

create 2 new type wich are linkedList and head.

When u write the word head in your code it will be replaced by struct Linkedlist so there is an error in your prototype after de pre-processing operation because the end statment will be Linkedlist *struct linkedlist

(the prototype of your read list function)