doubly linked-list ins in-order, reverse, delete

/*
 *  for: https://stackoverflow.com/a/66997713/3422102
 *
 *  example inut file:
John 12345
Sam 54321
Daivd 1000
Mike 5391
Lion 43222
Phil 8332
Bill 2853
 *
 *  then:
 *
 *    add (&list, "Zylon", "12");
 *
 *  defines:
 *    DEBUG - output:  "previous current next" pointers for each node
 *
 */

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

#define NAMENUM 20

typedef struct person {
  char  *firstName,
        *age;
  struct person *previous,
                *next;
} Person;

void print (Person* list)
{
  while (list) {
    printf ("%s %s\n",list->firstName,list->age);
    list = list->next;
  }
}

void prnptrs (Person *list)
{
    while (list) {
        printf ("%p  %p  %p\n", (void*)list->previous, (void*)list, (void*)list->next);
        list = list->next;
    }
}

void reverseList (Person **list) {

  Person *current = *list;
  Person *last = current;

  if (!current || !current->next)
    return;

  do {
    Person *temp = current->previous;
    current->previous = current->next;
    current->next = temp;
    last = current;
  } while ((current = current->previous));
  *list = last;
}

Person *createnode (const char *firstName, const char *age)
{
  size_t len;
  Person *node = malloc (sizeof *node);   /* allocate node, use dereference ptr for size */

  if (!node) {                            /* validate EVERY allocation */
    perror ("malloc-node");
    return NULL;
  }
  node->next = node->previous = NULL;     /* initialize next and previous NULL */

  len = strlen (firstName);                         /* get length of firstName */
  if (!(node->firstName = malloc (len + 1))) {      /* allocate/validate */
    perror ("malloc-node->firstName");
    free (node);                                    /* free node before return */
    return NULL;
  }
  memcpy (node->firstName, firstName, len + 1);     /* copy firstName to node */

  len = strlen (age);                               /* get length of age */
  if (!(node->age = malloc (len + 1))) {            /* allocate/validate */
    perror ("malloc-node->age");
    free (node->firstName);                         /* free node->firstName, and */
    free (node);                                    /* free node before return */
    return NULL;
  }
  memcpy (node->age, age, len + 1);                 /* copy age to node */

  return node;
}

/* add node to list using address of list and pointer to list
 * returns pointer to new node on success, NULL otherwise.
 */
Person *add (Person **list, const char *firstName, const char *age)
{
  Person **ppn = list,                            /* address of list */
          *pn = *list,                            /* pointer to list */
          *node = createnode (firstName, age);    /* initialize & validate new node */

  if (!node)                /* node creation failed, return list */
    return NULL;

  while (pn) {  /* loop over each node */
    if (strcmp (firstName, pn->firstName) <= 0) { /* compare sorts before pn->firstName */
      node->previous = (*ppn)->previous;          /* if so, insert new before pn */
      node->next = pn;
      pn->previous = node;
      *ppn = node;          /* update node at address of current node to new node */
      return node;
    }
    if (!pn->next) {        /* if pn is last node, insert at end */
      pn->next = node;
      node->previous = pn;
      break;
    }
    ppn = &pn->next;        /* advamce address to address of next node */
    pn = pn->next;          /* advance pointer to next */
  }

  return pn ? node : (*list = node);  /* if not 1st node, return node, else *list=node */
}

/** delete node where firstName equals name
 *  returns 1 if node found/deleted, 0 otherwise
 */
int delete (Person **list, const char *name)
{
  if (!*list) {             /* list-empty */
    puts ("List Empty");
    return 0;               /* return 0 - no replacement */
  }

  Person **ppn = list,      /* address of node (pointer-to-pointer-to-node) */
          *pn  = *list;     /* pointer to node */

  for (; pn; ppn = &pn->next, pn = pn->next) {    /* loop over all nodes */
    if (strcmp (pn->firstName, name) == 0) {      /* if node with name found */
      *ppn = pn->next;                    /* replace node at current address with next */
      if (pn->next)                       /* if not last node (*ppn now NULL) */
        (*ppn)->previous = pn->previous;  /* update node at address w/exiting previous */

      free (pn->firstName); /* free all memory for existing node */
      free (pn->age);
      free (pn);

      return 1;             /* return 1 - replacement made */
    }
  }

  fprintf (stderr, "warning: name not found '%s'.\n", name);

  return 0;
}

/** delete all nodes in list */
void del_list (Person *list)
{
  while (list) {
    Person *victim = list;
    list = list->next;
    free (victim->firstName);
    free (victim->age);
    free (victim);
  }
}

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

  char name[NAMENUM], num[NAMENUM];
  Person *list = NULL;
  /* use filename provided as 1st argument (stdin by default) */
  FILE *in = argc > 1 ? fopen(argv[1], "r") : stdin;

  if (!in) {    /* validate file open for reading */
    perror ("fopen-in");
    return 1;
  }

  while (fscanf (in, "%s %s",name, num) == 2)
    add (&list, name, num);

  fclose (in);

  add (&list, "Zylon", "12");

  printf ("Original List\n***\n");
  print (list);
#ifdef DEBUG
  puts ("\nPointers\n***");
  prnptrs (list);
#endif

  printf ("\nReversed List\n***\n");
  reverseList(&list);
  print (list);

  puts ("\nRemoving Bill, Phil, Sam, bananas from reversed list\n***");
  delete (&list, "Bill");
  delete (&list, "Phil");
  delete (&list, "Sam");
  delete (&list, "bananas");
  print (list);

  del_list (list);  /* free all allocated memory */

  return 0;
}

/*

Example Input File:

$ cat dat/ypzgttvk.txt
John 12345
Sam 54321
Daivd 1000
Mike 5391
Lion 43222
Phil 8332
Bill 2853

Example Use/Output

$ ./bin/ll_reverse_ptp dat/ypzgttvk.txt
Original List
***
Bill 2853
Daivd 1000
John 12345
Lion 43222
Mike 5391
Phil 8332
Sam 54321
Zylon 12

Reversed List
***
Zylon 12
Sam 54321
Phil 8332
Mike 5391
Lion 43222
John 12345
Daivd 1000
Bill 2853

Removing Bill, Phil, Sam, bananas from reversed list
***
warning: name not found 'bananas'.
Zylon 12
Mike 5391
Lion 43222
John 12345
Daivd 1000

*/