如何创建链表使用从 C 文件中读取的数据

Question

I'm new to C, I want to read a data file that contains integers one at a line and add them into a linked list (I'm being lazy here so did not put the typedef into a .h file, but just put it at the top of my .c file). The structure of linked list is like:

typedef struct Node{
    int num;
    struct Node *next;
    
}Node;

Now I wrote some code like following, the .c file compiled but cannot display linked list properly. I don't know why this is happending but I'm guessing it's related to the while loop condition and fscanf()?

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

typedef struct Node{
    int num;
    struct Node *next;
    
}Node;

Node* createLinkedlist(FILE* input_file, char* filename1);
void displayList(Node *head);

int main() {
    char *filename1 = "data";
    int number;
    FILE *input_file;

    Node *head = NULL;
    head = createLinkedlist(input_file, filename1);
    displayList(head);
    return(0);
    

}


Node* createLinkedlist(FILE* input_file, char* filename1) {
    Node* head = NULL;
    Node* newNodePtr = NULL;
    Node* p = NULL;


    input_file = fopen(filename1, "r"); /*open input file, read data*/
    if(input_file == NULL) {
        printf("Cannot open %s", filename1);
        exit(EXIT_FAILURE);
    } 
    while(fscanf(input_file, "r") != EOF) { 
        /*Create individual Node*/
        newNodePtr = (Node*)malloc(sizeof(Node));
        if(newNodePtr == NULL){
            printf("The storage was NOT allocated.");
            exit(EXIT_FAILURE);
        } else {
            /*Create signle Node data*/
            fscanf(input_file, "%d\n", &(newNodePtr->num));
        }

        if(head == NULL){
            head = newNodePtr;
        }else {
            p = head;
            while(p->next != NULL) {
                p = p->next;
            }
            p->next = newNodePtr;
        }
        
    }
    return head;
    
}

void displayList(Node* head) {
    Node *p = head;

    while(p != NULL){
        printf("\t%d->", p->num);
        p = p->next;
    }
}

Can someone help me to figure out my problem? Thank you so much, I'm really struggled...

Answer 1

The main problem, you didn't assign NULL value to the proper value. After get the entry,you must write it:

newNodePtr->next = NULL;

if you don't do that, this doesn't work:

else {
        p = head;
        while(p->next != NULL) {
            p = p->next;
        }
        p->next = newNodePtr;
    }

Because if you don't assign NULL, you won't be able to find NULL value.