How can I print the values in my linked list?

Question

I have, for a large portion of the day, been trying to write a simple program with linked lists. My main issue seems to be not understanding why the memory I am accessing is not what I think it is. I am printf crazy and outputting every possible form of data I can and still am having trouble understanding why it will not work.

For example when I pass the &head to a function which takes node **location and I want to check whether the value inside location (and therefore head) is NULL or not, should I use if(!*location) return; or should I use if(!location) return;, It seems the later is correct, but why?

And when I want to create a node *current inside a function to keep track of things, should I start with node* current = *head or node* current = head, and most importantly, why? I have noticed that the later is better, but I cannot make sense of it still. Warnings go away when I typecast the statements, but it seems to fix nothing.

Here is some functions I have been writing, can you please give me hints on where I am not making sense in the code. Preferably, I hope to understand why the output seems to be a memory location and then accessing bad memory.

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

typedef struct node_struct
{
    int val;
    struct node *next;
} node;

node* return_create_neck(node **head, int value)
{
    node* ptr;
    *head = ptr = (node *)malloc(sizeof(node));
    (*head)->val = value;
    (*head)->next = NULL;
    return ptr;
}

node* return_append_tail(node **location, int value)
{
    node* ptr;
    *location = ptr = (node *)malloc(sizeof(node));
    (*location)->val = value;
    (*location)->next = NULL;
    return ptr;
}

void print_linked_list(node **head)
{
    if(!head)
        return;

    node *current = head;
    while(current)
    {
        printf("%d ", current->val);
        current = current->next;
    }
    printf("\n");
    return;
}

int main(void)
{
    node *head=NULL, *current=NULL;
    int i=0;
    for( current = return_create_neck(&head, 1);
        i < 4;
        current = return_append_tail(&current, i+1))
    { ++i; }

    printf("Pritning...\n");
    print_linked_list(&head);
    return 0;
}

Answer 1

Your return_append_tail function doesn't actually append anything, unless called with the correct location, which you do not.

You should call it with &current->next from the main function.