delete tail不会返回正确的列表

Question

I'm having some issues with the delete tail function, It does not work when I'm freeing the current node, but when I work with the next node everything works fine. Can someone explain to me what is happening and why it does not work?

this is the list

    typedef struct node {
    int codice;
    struct node *next;
} nodo;

typedef nodo * lista;

the delete tail function which does not work is

lista rimuovi_in_coda(lista l){
    if(l == NULL) return NULL;
    lista l_scorri = l;
    while(l_scorri->next != NULL)
        l_scorri = l_scorri->next;

    free(l_scorri);
    l_scorri = NULL;
    return l;
}

in this one the list l is not modified:

input: 0, 4
output: 0, 4

the working one is:

lista rimuovi_in_coda(lista l){
    if(l == NULL || l->next == NULL) {
        free(l);
        return NULL;
    }
    lista l_scorri = l;
    while(l_scorri->next->next != NULL)
        l_scorri = l_scorri->next;

    free(l_scorri->next);
    l_scorri->next = NULL;
    return l;
}

in this one the list returned is as expected

input: 0, 4
output: 0

Answer 1

You never reset any pointers or set any node's "next" to NULL. You just free an element but leave it in the list.

Answer 2

In the first function you are changing the local variable l_scorri

free(l_scorri);
l_scorri = NULL;

This does not change the value of the data member next of the preceding node.

In the second program you are indeed changing the data member next of the preceding node.

l_scorri->next = NULL;

The function can be written simpler. For example

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

typedef struct node 
{
    int codice;
    struct node *next;
} nodo;

typedef nodo * lista;

int rimuovi_in_coda( lista *l )
{
    int success = *l != NULL;

    if ( success )
    {
        while ( ( *l )->next != NULL ) l = &( *l )->next;

        free( *l );
        *l = NULL;
    }

    return success;
}

int main( void )
{
}