segmentation fault w/ fgets using struct

Question

i'm still a beginner with coding; i'm writing a code to learn about structs and pointers but i get a segmentation fault when using fgets. here's the code

 #include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <malloc.h>
#include <string.h>
#include <stdbool.h>
#define a 100
#define MAX 200

int i;
typedef struct libreria{
    char titolo[a];
    char autore[a];
    int anno;
    char genere[a];
}libro;

libro *libroptr;
int inserisci_libro(libro *libroptr){
    printf("Titolo: \n");
    fgets((libroptr->titolo),a,stdin); // here is where i get the error
    printf("Autore: \n");
    fgets((libroptr->autore),a,stdin);
    printf("Anno: ");
    scanf("%i",&libroptr->anno);
    printf("Genere: ");
    fgets((libroptr->genere),a,stdin);

    return 0;
};

void main(){
    //printf("%d\n",sizeof(libroptr->titolo));
    typedef struct libreria libro[MAX];
    inserisci_libro(libroptr);
    return;
}

the idea is to create a library of book that the user have to insert. once i run the code i get the error on the fgets in the function inserisci_libro but i can't understand why. if someone can help thanks a lot.

You pass a `NULL` pointer to your function. You must allocate some memory for `libroptr` to point to — Gerhardh, Sep 07 '22 at 08:09
Having 2 typedefs with same name but different types is not a good idea. — Gerhardh, Sep 07 '22 at 08:10
Start by removing the `typedef` from the line in `main( )`... There should be compiler warnings. Work through those first... — Fe2O3, Sep 07 '22 at 08:11
It is unclear how you want to manage a library. Do you want to use an array? Then you need an array variable, that array typedef doesn't help. Or do you want to use a linked list? Then you are missing a pointer to link the book nodes. — Gerhardh, Sep 07 '22 at 08:20

Vlad from Moscow · Accepted Answer · 2022-09-07T08:55:47.153

You defined a null pointer

libro *libroptr;

and this null pointer is used to access memory as for example

fgets((libroptr->titolo),a,stdin);

So the program has undefined behavior.

You should define an object of the type libro in main as for example

libro libro_uno;

and pass a pointer to it to the function

inserisci_libro( &libro_uno );

And this declared typedef name as an alias for an array type

typedef struct libreria libro[MAX];

is not used in your program and will only confuse readers of the program because in the file scope there is already declared the alias libro for the structure type struct libreria.

Pay attention to that according to the C Standard the function main without parameters shall be declared like

int main( void )

So the OP would need to allocate memory for it. For reference- https://www.programiz.com/c-programming/c-dynamic-memory-allocation — L_R, Sep 07 '22 at 08:49

segmentation fault w/ fgets using struct

1 Answers1