Returning a null pointer from a C function, comparison seg faults -

i'm working on file system simulator using c. node struct looks this:

typedef struct node {   char name[64];   char type;   struct node* child;   struct node* sibling;   struct node* parent; }node; 

my recursive function, findnode(), returns null if can't find node in tree specific name.

node* findnode(char* name, node* start) {   printf("inside findnode, looking %s, starting @ %s\n", name, start->name);   node* current = start;   if(strcmp(name, current->name) == 0)   {     printf("inside findnoe, node found.\n");     return current;   }   if(current->sibling->name != 0)   {     return findnode(name, current->sibling);   }   if(current->child->name != 0)   {     return findnode(name, current->child);   }   printf("inside findnode, node not found.\n");   return 0; } 

upon calling findnode() , comparing 0, program seg faults.

if(findnode(bname,current) != 0) //seg fault here   {     printf("error: node basename exists under directory name.\n");      return;   } 

i know program reaching end of findnode() when hasn't found node, because prints "node not found" message.

i'm under impression it's possible return 0 when return type pointer. i've tried using null, , saving result node* variable before comparing it. neither worked.

can explain what's going on here? i'd appreciate it. in advance.

edit: code looks following. there's new check @ beginning see if current null, , i've stopped trying access child , sibling names.

node* findnode(char* name, node* start) {   node* current = start;   if(current == null)   {     printf("inside findnode, null passed in\n");     return null;   }   printf("inside findnode, looking %s, starting @ %s\n", name, current->name);   if(strcmp(name, current->name) == 0)   {     printf("inside findnode, node found.\n");     return current;   }   if(current->sibling != null && current->sibling != root)   {     return findnode(name, current->sibling);   }   if(current->child != null && current->sibling != root)   {     return findnode(name, current->child);   }   printf("inside findnode, node not found.\n");   return null; } 

first test: "/" , root node, name "/". second test: "hello" , root node, name "/". "hello" should not found.

inside findnode, looking /, starting @ / inside findnode, node found. inside findnode, looking hello, starting @ / inside findnode, node not found. segmentation fault 

i've wrote program test code. notice in main function initialized null pointer.

#include <iostream>  using namespace std;  typedef struct node {     char name[64];     char type;     struct node* child;     struct node* sibling;     struct node* parent; }node;  node* findnode(char* name, node* start) {     printf("inside findnode, looking %s, starting @ %s\n", name, start->name);     node* current = start;     if (strcmp(name, current->name) == 0)     {         printf("inside findnoe, node found.\n");         return current;     }     if (current->sibling->name != 0)     {         return findnode(name, current->sibling);     }     if (current->child->name != 0)     {         return findnode(name, current->child);     }     printf("inside findnode, node not found.\n");     return 0; }  int main() {     node *n = null;     char bname[] = "somename";     node *current = n;     if (findnode(bname, current) != 0) //seg fault here     {         printf("error: node basename exists under directory name.\n");     } } 

the output is(used visual studio 2015)

inside findnode, looking somename, starting @ (null)

so kaylum pointed out, line printf("inside findnode, looking %s, starting @ %s\n", name, start->name); causes segmentation fault. , reason because trying access pointer null.

at first need check, if pointer accessing null or not. must access attributes or values.

i hope makes sense.