Pointers - Segmentation fault (core dumped)

Question

I'm having difficulty understanding what I'm doing wrong here. I'm making a program to organize a database of Books. I'm using a linked list to save the book structs to memory. When it comes to inputting the books information, I get

Segmentation fault (core dumped)

after inputting the first value, book identifier. In my AddBook function, I create a temp book struct ( aBook ). I then ask the user to input an identifier for the new book then attempt to save it to aBook 's identifier attribute. This is where the error occurs.

Anyway, I included the top part of my program where I include libraries, declare functions etc, and I also included the menu function and addbook function so hopefully someone can spot what my mistake is. Thanks in advance.

Top Section of my code:

//Libraries
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>

//only 10 books maximum
#define MAX 10;

//function prototypes
void fileInput();
void menuSystem();
int writeAndCloseFile();

void addBook();
void takeOutBook();
void returnBook();
void deleteBook();
void viewAllBooks();
void viewBook();
void viewYearCollection();
int exitSystem();

bool isEmpty();

//The File
FILE *fp;

//LinkedList Initialization
struct bookData {

    //book variables
    char* identifier;
    char* title;
    char* author;
    int year;
    bool status;
    char* customer;
    int timesTakenOut;
    char* genre;

};

//struct for one node
struct node {

    struct bookData *element;
    struct node *next;

};

//first and last nodes
struct node *firstBook = NULL;
struct node *lastBook = NULL;

Menu function and AddBook function (where error is occurring):

//MENU SYSTEM FUNCTION
void menuSystem()
{
        int chosenOption = 0;

        printf("****************\n\n");
        printf("      MENU\n\n");
        printf("****************\n\n");

        printf("1 - Add book\n");
        printf("2 - Take out book\n");
        printf("3 - Return book\n");
        printf("4 - Delete book\n");
        printf("5 - View all books\n");
        printf("6 - View book\n");
        printf("7 - View Year Collection\n");
        printf("8 - Exit\n\n");

        printf("Chosen Option: ");
        scanf("%d", &chosenOption);

        //1. ADD BOOK
        if(chosenOption == 1)
        {
            addBook();
        }else if(chosenOption == 2){
        //2. TAKE OUT A BOOK
            takeOutBook();
        }else if(chosenOption == 3){
        //3. RETURN A BOOK
            returnBook();
        }else if(chosenOption == 4){
        //4. DELETE A BOOK
            deleteBook();
        }else if(chosenOption == 5){
        //5. VIEW ALL BOOKS
            viewAllBooks();
        }else if(chosenOption == 6){
        //6. VIEW A BOOK
            viewBook();
        }else if(chosenOption == 7){
        //7. VIEW YEAR COLLECTION
            viewYearCollection();
        }else if(chosenOption == 8){
        //8. EXIT SYSTEM
            printf("\n\nGoodbye!\n\n\n\n");
            exitSystem();
        }
    }


void addBook(){

    printf("\n*** ADDING BOOKS ***\n");

    struct node *aBookNode;
    struct bookData *aBook;

        aBook = (struct bookData *)malloc(sizeof(struct bookData));

        if (aBook == NULL)
            printf("Error - no space for new book data\n\n\n");
        else
        {
            //INPUT BOOK INFO

            //Identifier
            printf("\nIdentifier(####-####): ");
            scanf("%9s", aBook->identifier);
            fflush(stdin);

            //Title
            printf("Title: ");
            scanf("%s", aBook->title);

The console output (After I inputted a random number for the identifier):

Could not open the file book.dat

****************** The database is empty. Books will need to be manually entered ******************






*** ADDING BOOKS ***

Identifier(####-####): 1234-1234
Segmentation fault (core dumped)

Answer 1

You allocate the bookData structure, but you don't allocate memory for the strings inside the structure.

So when you ask scanf to write to aBook->identifier it will write to a seemingly random location and you end up with undefined behavior and the crash.

Either declare those members that are supposed to be strings as fixed-size arrays, or allocate memory for the strings.

Answer 2

scanf("%9s", aBook->identifier);

You need to reserve space for aBook->identifier and aBook->title , an easy way is using strdup (is not part of the standard but it is available in many implementations):

char temp[10];

scanf("%9s", temp);
aBook->identifier = strdup(temp);
if (aBook->identifier == NULL) { /* Always check the return of strdup */
    perror("strdup");
    exit(EXIT_FAILURE);
}

Don't forget to call free(aBook->identifier); at then end.