Passing a pointer to a function in C.

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

struct Person {
  char name[16];
  char text[24];
};

struct Node {
  void* data;
  struct Node* next;
};

struct List {
  struct Node* head;
};

struct Person* person_new(char* name, char* text)
{
  struct Person* p = (struct Person*) malloc(sizeof(struct Person));
  strncpy(p->name, name, 15);
  p->name[15] = '\0';
  strncpy(p->text, text, 23);
  p->name[23] = '\0';
  return p;
}

struct Node* node_new(void* data)
{
  struct Node* n = (struct Node*) malloc(sizeof(struct Node));
  n->data = data;
  n->next = NULL;
  return n;
}

struct List* list_append(struct List* lis, void* data)
{
  struct Node* new_node = node_new(data);
  struct Node* n = lis->head;
  if (! n) {
    lis->head = new_node;
  } else {
    while (n->next) {
      n = n->next;
    }
    n->next = new_node;
  }
  return lis;
}

void traverse(struct List* a, void (*f)(void*))
{
  struct Node* n = a->head;
  while (n) {
    f(n->data);
    n = n->next;
  }
}

static void print(void* data) {
  struct Person* p = (struct Person*) data;
  printf("%s\n", p->name);
}

int main(int argc, char** argv)
{
  /* create a sample two-item list and test it */
  struct List ps;
  struct Person* p;
  struct Person* p2;

  p = person_new("Jack", "");
  list_append(&ps, p);
  p2 = person_new("Jill", "");
  list_append(&ps, p2);

  traverse(&ps, &print);
}