c - Program received signal SIGSEGV, segmentation fault, Linked list program

Question

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

typedef struct node{
    int value;
    struct node* next;
}Node;

Node* createNode(int data);
Node* insertFront(Node* first, Node* newNode);
void printList(Node* first); 
void deleteList(Node* first);

int main(int argc, const char **argv)
{
    int numItems, ch;
    FILE *fp;

    fp = fopen(argv[1], "r");
    while ((ch = getc(fp)) != EOF)
    {
        if (ch = '
') numItems++;
    }
    fclose(fp);

    Node *first = NULL;
    Node *newNode;
    Node *Next;

    int i;

    for(i = 1; i <= numItems; i++)
    {
        newNode = createNode(i);
        first = insertFront(first, newNode);
    }

    printList(first);
    deleteList(first);

    return 1;
}

Node* createNode(int data)
{
    Node *newNode;

    newNode = malloc(sizeof(Node));

    newNode -> value = data;

    newNode -> next = NULL;

    return newNode;
}

Node* insertFront(Node* first, Node* newNode)
{
    if (newNode == NULL) {
        /* handle oom */
    }

    newNode->next=NULL;

    if (first == NULL) {
        first = newNode;
    }

    else {
        Node *temp=first;

        while(temp->next!=NULL)
        {
            temp = temp->next;
        }

        temp->next=newNode;

        first = newNode;
    }

    return first;
}

void printList(Node* first)
{
    Node *temp;
    temp=first;

    printf("elements in linked list are
");
    while(temp!=NULL)
    {
        printf("%d
",temp->value);
        temp=temp->next;
    }
}

void deleteList(Node* first)
{
    Node  *temp;
    temp=first;
    first=first->next;
    temp->next=NULL;
    free(temp);
}

Tried running with gdb and this is what I got, first real experience trying to make a linked list.

Program received signal SIGSEGV, Segmentation fault. _IO_getc (fp=0x0) at getc.c:40 40 _IO_acquire_lock (fp);

I'm not sure what I'm doing wrong here? Thanks for any tips in advance.

Answer 1

You did not initialize numItems to zero. As unitialized it can be any number, including e.g. negative ones. Because of this your list is not created, hence pointer first points to NULL. Then the code segfaults in the function deleteList, when it tries to free memory at location NULL.