C Programming - Insert value into singly linked list after specific node -

i have program have been sweating on , keep getting segmentation fault on function insertafter. given base code , asked create serveral functions. have gotten of them work, cannot insertafter insert value after specified node. haven't worked on insertbefore, assuming have same problem

so, here code: (i have included header node , function creates new node well)

struct lnode {     int data;     struct lnode *next; };   struct lheader {     struct lnode *start;     int len; };  struct lnode *makenode( int val ) {     struct lnode *box;     box = malloc( sizeof( struct lnode ) );     box->data = val;     box->next = null;     return box; } 

here function:

void insertafter( struct lheader *l, struct lnode *p ) {     int pos, value;     struct lnode *nn;     struct lnode *temp;     temp = p;     printf( "what number want insert? " );     scanf( "%d", &value );     printf( "insert after value: " );     scanf( "%d", &pos );     nn = makenode(value);     if ( l->start == null )     {          l->start = nn;     }     else     {          temp = l->start;          while( temp->next != null && temp->data != pos )          {              temp = temp->next;          }          if ( temp->data == pos )          {              nn->next = temp->next;              temp->next = nn;              printf("value %d: ", nn->data);          }          else          {              printf( "value %d not in list\n", pos );          }      } } 

i added in wrong spot, think!

thanks input. had pick kids , not program.

here the main function, print functions main calls. commented out of other functions.

void printlist( struct lnode *front ) {     struct lnode *mov;     mov = front;     while (mov != null)     {         printf("%d  ", mov->data);         mov = mov->next;     }     printf("\n"); }   void printer( struct lheader *alist ) {     struct lnode *mov;     printf("--------------------------\n");     printf("list print, len %d\n", alist->len);     printlist( alist->start );     printf("--------------------------\n"); }   int main() {     struct lheader *l;     struct lnode  *head, *tmp;     struct lnode  *mark;     int i, x;  l = makelist();  (i = 1; <= 5; ++i) {     x = rand() % 25 + 1;     printf("-- adding -- %d\n", x);     //insertfront( l, x );     insertback( l, x, );     printer( l ); }   printf(">>>>value search: "); scanf("%d", &x); = isinlist(l, x); printf("i %d\n", i); tmp = findnode(l, x); if (tmp == null) {          printf("nope\n"); { else {      printf("found node %d\n", tmp->data); {  insertafter( l, mark ); // printer( l ); // insertbefore( l, mark ); // printer( l ); return 0; } 

i tried debugger (first time) , said segmentation fault @ temp = temp->next in below snippet of code:

else {      temp = l->start;      while( temp->next != null && temp->data != pos )      {          temp = temp->next;      }      if ( temp->data == pos )      {          nn->next = temp->next;          temp->next = nn;          printf("value %d: ", nn->data);      }      else      {          printf( "value %d not in list\n", pos );      }  } 

}

you can check above conditions this:

• value: data inserted.
• loc: location after data inserted.

---

void insertafter(int value,int loc) {     struct node* newnode;     newnode=(struct node*)malloc(sizeof(struct node));     newnode->data=value;    if(head==null)     {       newnode->next=null;       head=newnode;     }     else     {         struct node* temp=head;         while(temp->next!=null)         {             if(temp->data==loc)             {                 newnode->next=temp->next;                 temp->next=newnode;                 break;             }             else             {                 temp=temp->next;             }         }         if(temp->next==null)             printf("location not found");     }     printf("new node inserted after %d",loc); }