implementing a TRIE data structure

Question

Hii , i Was implementing a trie in C ... but i am getting an error in the insert_trie function .

I could not figure out why the root node is not getting updated . Please help me with this.

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

typedef struct
 {
  char value;
  int level;
  struct node *next;
  struct node *list;
 }node;

 node *trie = NULL;

 node *init_trie()
  {
   node *new = (node *)malloc(sizeof(node));
   if(trie == NULL)
    {
     new->value = '$';
     new->next = NULL;
     new->list = NULL;
     new->level = 0;
     trie = new;
     printf("\n Finished initializing the trie with the value %c",trie->value);
     return trie;
    }
    printf("\n Trie is already initialized");
    return trie;
  }  

 node *insert_trie(char *s)
  {
   node *nodepointer = trie;
   node *new = (node *)malloc(sizeof(node));
   node *save = NULL;
   int i=0;
   while(s[i]!=NULL)
    {
       nodepointer = nodepointer->list;
     while(nodepointer!=NULL)
      {
        if(s[i] == nodepointer->value)
         {
          printf("\n Found %c",nodepointer->value);
          nodepointer = nodepointer->list;
          i++;
         }
         save = nodepointer;
         nodepointer = nodepointer->next;
      }
      new->value = s[i];
      new->next = NULL;
      new->list = NULL;
      printf("\n Inserting %c",new->value);
      save->next = new;     
      i++;
    }

   return trie;
  } 


 int main()
  {

   int num;
   char *s = (char *)malloc(sizeof(char)*10);
   trie = init_trie();
   printf("\n Enter the number of words to enter into the trie "); 
   scanf("%d",&num);
   while(num>0)
   {
   scanf("%s",s);
   //printf("%s",s);
   trie = insert_trie(s);
   printf("\n Finished inserting the word %s into the trie \n",s);
   num --;
   } 
   return 0;
  } 

I get a segmentation fault due to the line nodepointer = nodepointer->list in insert_trie function ... Why ????

P.S : This is not homework.But i am trying to implement it. I just could not find the mistake .

Answer 1

A trie holds one node per character and you're only performing one malloc per string. You should be calling malloc for every node. (Also, malloc.h is outdated. stdlib.h contains malloc since the ANSI C standard of 1989.)