linked list state unchanged when writing to it from a function

Question

i'm having trouble with a farelly simple function, i have to create a linked list with each node storing a character from a string, i made a function for that, however it doesn't seem to do anything at all

this is the function i'm talking about (variable names are in spanish, i'm sorry for that):

struct listaDoble crearMiADN()
{
    char miDni[] = "1234";
    struct listaDoble listado = crearLista(strlen(miDni));
    struct nodo *actual = listado.first;
    for(int i = 0; i<strlen(miDni); i++)
    {
        if(miDni[i] != '\0' && miDni[i] != EOF)
        {
            actual->tuNombre[0] = miDni[i];
            actual->tuNombre[1] = '\0';
            actual = actual->next;
        }
    }
    return listado;

}

and this is the function crearLista which works but you will probably need it to understand my code:

struct listaDoble crearLista(int num_nodos)
{
    struct listaDoble *result = (struct listaDoble *)malloc(sizeof(struct listaDoble));
    if(num_nodos > 0)
    {
        result->first = (struct nodo *)malloc(sizeof(struct nodo));
        result->first->prev = NULL;
        struct nodo *actual = result->first;
        struct nodo *prev = NULL;
        struct nodo *last;
        for(int i = 0; i < num_nodos; i++)
        {
            if(i + 1 != num_nodos)
            {
                actual->next = (struct nodo*)(malloc)(sizeof(struct nodo));
                actual->prev = prev;
                actual = actual->next;
                prev = actual;
            }
            else
            {
                actual->next = NULL;
                actual->prev = prev;
                last = actual;
            }
        }
        result->last = last;
        result->size = num_nodos;
    }
    else
    {
        result->first = NULL;
        result->last = NULL;
        result->size = 0;
    }
    return *result;

}

Requested in the comments

struct listaDoble
{
    struct nodo *first, *last;
    int size;
};

now this is how i call the crearMiADN thing

struct listaDoble dni = crearMiADN();

now the expected result would be something like this

NULL<-- [1] <-> [2] <-> [3] <-> [4] --> NULL

however this is what i'm getting

NULL<-- [] <-> [] <-> [] <-> [] --> NULL

i'm not very keen with pointer, my attempt to fixing it was literally trying to put a * somewhere and see if it works (spoiler alert, it doesn't)

so something like this

struct listaDoble dni = *crearMiADN(); //type mismatch

then i tried to fix the type mismatch my doing this

struct listaDoble crearMiADN()
    //...//
    return *listado;

}

which once again errors out, and now i'm pretty much stuck trying to put a * somewhere random and checking if it compiles and works

Answer 1

You are trying to return local variable. You should allocate that memory block and return pointers. Try again by correcting the code as follows.

struct listaDoble* crearMiADN()
{
    char miDni[] = "1234";
    struct listaDoble *listado = crearLista(strlen(miDni));
    ...
    return listado;

}
struct listaDoble* crearLista(int num_nodos)
{
    struct listaDoble *result = (struct listaDoble *)malloc(sizeof(struct listaDoble));
    ...
    return result;
}