Singly Linked List of Strings With Sorted Insertion

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

#define MAXC 1024   /* if you need a constant, #define one (or more) */

typedef struct node_t {     /* list node */
    char *s;
    struct node_t *next;
} node_t;

/** helper function to allocate node, and storage for string.
 *  copies string to node and initializes node->next pointer NULL.
 *  returns pointer to allocated node on success, NULL otherwise.
 */
node_t *create_node (const char *s)
{
    size_t len = strlen (s);                        /* get string length */
    node_t *node = malloc (sizeof *node);           /* allocate node */

    if (!node) {    /* validate EVERY allocation */
        perror ("create_node: malloc node");
        return NULL;
    }

    if (!(node->s = malloc (len + 1))) {            /* allocate for string */
        perror ("create_node: malloc node->s");
        free (node);        /* on failure, free node before returning NULL */
        return NULL;
    }

    memcpy (node->s, s, len+1); /* copy string to node */
    node->next = NULL;          /* initialze next NULL */

    return node;    /* return allocated & initialized node */
}

/** add node in sort order to list.
 *  returns pointer to new node on success, NULL otherwise.
 */
node_t *add_node (node_t **head, const char *s)
{
    node_t *node = create_node (s);             /* allocate/initialze node */

    if (!node)                                  /* validate */
        return NULL;

    node_t **ppn = head,                        /* ptr2ptr to node - current */
            *pn = *head;                        /* pointer to iterate - next */

    /* iterate over each node checking sort order */
    while (pn && strcmp (node->s, pn->s) > 0) {
        ppn = &pn->next;                        /* ppn to address of next */
        pn = pn->next;                          /* advance pointer to next */
    }

    node->next = pn;                            /* set node->next to next */
    *ppn = node;                                /* set current to node */

    return node;                                /* return node */
}

/** print all nodes in list */
void prn_list (node_t *head)
{
    if (!head) {    /* check if list is empty */
        puts ("list-empty");
        return;
    }

    for (node_t *pn = head; pn; pn = pn->next)  /* iterate over each node */
        puts (pn->s);                           /* printing string */
}

/** delete all nodes in list */
void del_list (node_t *head)
{
    node_t *pn = head;              /* pointer to iterate */

    while (pn) {                    /* iterate over each node */
        node_t *victim = pn;        /* set victim to current */
        pn = pn->next;              /* advance pointer to next */
        free (victim->s);           /* free current string */
        free (victim);              /* free current node */
    }
}

int main (int argc, char **argv) {

    char buf[MAXC];         /* read buffer */
    node_t *list = NULL;    /* pointer to list (must initialize NULL */
    /* use filename provided as 1st argument (stdin by default) */
    FILE *fp = argc > 1 ? fopen (argv[1], "r") : stdin;

    if (!fp) {  /* validate file open for reading */
        perror ("file open failed");
        return 1;
    }

    while (fgets (buf, MAXC, fp)) {
        buf[strcspn(buf, "\r\n")] = 0;
        add_node (&list, buf);
    }

    if (fp != stdin)    /* close file if not stdin */
        fclose (fp);

    prn_list (list);    /* pring contents of list */
    del_list (list);    /* free all list memory */

    return 0;
}