c - Building a Huffman tree from a binary search tree -

i trying build huffman tree out of binary search tree. sadly code crashing (segmentation fault (core dumped)).

this how struct defined:

struct node {   unsigned char m_ch;   int m_freq;   struct node *m_ls,*m_rs;   struct node *m_hls,*m_hrs; }; 

delmin passed double pointer binary search tree, , deletes leftmost leaf unless reaches node m_ch==0 , return deleted node

i can't find mistake

struct node *delmin(struct node **root) {     struct node *current = *root;     struct node *b4current;      if (current == null)         return null;      while (current->m_ls != null)     {         if (current->m_ch == 0)             break;          b4current = current;         current = current->m_ls;     }      if (current->m_ch == 0)         b4current->m_ls = null;     else     {         if (b4current == null)             *root = current->m_rs;         else             b4current->m_ls = current->m_rs;     }      return current; }   struct node *huffman(struct node *root) {     struct node *left;     struct node *right;     struct node *temproot;     struct node *huffmantree;      while (root->m_ch != 0)     {         left = delmin(&root);         right = delmin(&root);         temproot = createnode((left->m_freq) + (right->m_freq), 0);         temproot->m_hls = left;         temproot->m_hrs = right;         inserttree(&root, temproot);     }      huffmantree = temproot;     return huffmantree; } 

edit: added code inserttree function called huffman

void inserttree(struct node **root,struct node *n) {   if (!*root)   {     *root=n;     return;   }   if(n->m_freq<(*root)->m_freq)   {     inserttree(&((*root)->m_ls),n);   }   else   {     inserttree(&((*root)->m_rs),n);   } } 

in delmin code section

if (current->m_ch == 0)     b4current->m_ls = null; else {     if (b4current == null)         *root = current->m_rs;     else         b4current->m_ls = current->m_rs; } 

there no guarantee b4current not null.

consider case root node has m_ch == 0 , m_ls == null. take if branch , dereference b4current.

you need initialize b4current null , check before dereference.

you need ensure root non-null before initializing current = *root in delmin or dereferencing in huffman

these should initialized null

struct node *left; struct node *right; struct node *temproot; struct node *huffmantree; 

and possible, again, never enter while loop, leaving temproot unset causing potential segfault in caller of huffman when return value.