c - How to split a linked-list into two lists -

i'm writing code split circular linked-list 2 linked lists equal number of codes, following code:

#include <stdio.h> #include <stdlib.h>  typedef struct node *ptr; struct node {     int element;     ptr prev;     ptr next; }; typedef ptr list; typedef ptr position;  int main() {     list l=malloc(sizeof(struct node));     list first=malloc(sizeof(struct node));     list second=malloc(sizeof(struct node));     splitlist(l,first,second);     return 0; }  void splitlist(list l, list first,list second) {     position p,temp;     p=malloc(sizeof(struct node));     temp=malloc(sizeof(struct node));     p=l;     int count=0;      while ((p)->next != l) {         count++;     }      int c=count;     while (c!=(count/2)-1) {         p=(p)->next;        temp=(p)->next;     }      first=l;     (p)->next=null;     second=temp;      c=count;     while (c!=(count/2)-1) {        temp=(temp)->next;     }     (temp)->next=null; } 

when compiling code gives no errors i'm not sure if it's working properly.

in order more readable , maintainable code, first step improve code create functions manipulating lists. candidate functions are:

• listinitialize()
• listpushfront()
• listpushback()
• listpopfront()
• listpopback()
• listgetfirstnode()
• listgetnextnode()
• listgetfront()
• listgetback()
• listempty()
• ...

with proper set of arguments , return values of course. can write splitlist function using basic list operation functions , code easier read , reason about.

also, in order handle empty list, should have list type not pointer node.

typedef struct node_tag { int value; struct node_tag *next; struct node_tag *prev } node, *nodeptr; typedef struct intlist_tag { nodeptr front; nodeptr back; } intlist;  // creates empty list. void listinitialize( intlist *plist ) { plist->front = null; plist->back = null; } void listpushfront( intlist *plist, int value )  { nodeptr newnode = malloc(sizeof(node));    if(null != newnode )    { newnode->next = plist->front;      newnode->prev = null; newnode->value = value;      plist->front = newnode;      if( plist->back == null ) plist->back = newnode; // first element...   } } // ... 

eventually, using functions, can write splitlist() function in concise , noise-free way:

void splitlist( intlist * source, intlist *target1, intlist *target2 ) {      intlist * currenttarget = target1;      for( nodeptr currentnode = listgetfirstnode(source); currentnode != null; currentnode = listgetnextnode(currentnode) )      {           listpushback(currenttarget, currentnode->value );           if(currenttarget == target1 ) currenttarget = target2;            else currenttarget = target1;      } } 

it might appear work create other list functions if want splitlist. in real world applications want other functions (or have them already). in homework situations, looks bit funny.