trie.c

#include "trie.h"

void trie_create (trie_t **trie, char edgeName, trie_t *previousSibling, trie_t *parent)
{
  *trie = calloc(1, sizeof(struct trie));

  (*trie)->edgeName = edgeName;

  if (previousSibling == NULL) {
    if (parent != NULL) parent->firstChild = *trie;
  } else {
    previousSibling->nextSibling = *trie;
  }
}

void trie_destroy (trie_t **trie)
{
  while ((*trie)->firstChild != NULL)
    trie_destroy(&(*trie)->firstChild);

  trie_t *next = (*trie)->nextSibling;

  free(*trie);

  *trie = next;
}

int trie_search (trie_t *trie, char *name, trie_t **dest)
{
  while (*name != '\0') {
    if (trie == NULL) {
      return 0;
    } else if (trie->edgeName == *name) {
      if (*++name != '\0')
        trie = trie->firstChild;
    } else {
      trie = trie->nextSibling;
    }
  }
  *dest = trie;
  return 1;
}

trie.h

#ifndef TRIE_H
#define TRIE_H

#include <stdlib.h>

typedef struct trie {
  char         edgeName;
  struct trie *nextSibling;
  struct trie *firstChild;

  void        *value;
} trie_t;

void trie_create  (trie_t **trie, char edgeName, trie_t *previousSibling, trie_t *parent);
void trie_destroy (trie_t **trie);
int  trie_search  (trie_t  *trie, char *name, trie_t **dest);
void trie_insert  (trie_t **trie, char *name, void *value);
void trie_delete  (trie_t **trie, char *name);

#endif

trie_test.c

#include <stdio.h>

#include "trie.h"

int main(int argc, char **argv)
{
  trie_t *first, *im1, *im2, *im3, *last1, *last2;

  printf ("Creating hello\n");

  trie_create (&first, 'h', NULL, NULL);
  trie_create (&im1,   'e', NULL, first);
  trie_create (&im2,   'l', NULL, im1);
  trie_create (&im3,   'l', NULL, im2);
  trie_create (&last1, 'o', NULL, im3);

  last1->value = "This is the result for 'hello'.";

  printf ("Creating hi\n");

  trie_create (&last2, 'i', im1, first);

  last2->value = "This is the result for 'hi'.";

  trie_t *dest;

  if (trie_search (first, "hello", &dest)) {
    printf ("hello => \"%s\"\n", dest->value);
  } else {
    fprintf (stderr, "hello: NOT FOUND\n");
  }

  if (trie_search (first, "hi", &dest)) {
    printf ("hi => \"%s\"\n", dest->value);
  } else {
    fprintf (stderr, "hi: NOT FOUND\n");
  }

  return 0;
}