c++ - How to move elements in doubly linked list? -

i have custom list (doubly linked list , not std::list) implemented in code. requirement move element 1 left or right updating references. possible?

class elem {   elem *next;   elem *prev; } 

.......

void move_element_left(elem *e)    {     if(e->prev()==null)       return;           //left ... return      elem *left = e->prev();      left->next() = e->next();     e->prev() = left->prev();      if (left->next())         left->next()->prev() = left;      if (e->prev())         e->prev()->next() = e;      e->next() = left;     left->prev() = e;    } 

.......

int main() {   elemlist ls;   ...   ...   move_element_left(e);  //e of type elem *   ... } 

above code works except 2nd object in list want move left (or top most). (i.e. if list(obj5, obj9, obj11, obj12,..), moving obj9 first in list gives error)

works designed ?

following code in schema, shows works designed:

void move_element_left(elem *e)    {     if(e->prev()==null)       return;                  //ok ! left ... return     elem *left = e->prev();    // ok ! (1)     left->next() = e->next();  // ok ! (2)     e->prev() = left->prev();  // ok ! (3)      if (left->next())          // ok !         left->next()->prev() = left;   // ok ! (4)      if (e->prev())             // ok ! e prev left prev null         e->prev()->next() = e;       e->next() = left;          // ok ! (5)     left->prev() = e;          // ok ! (6)     } 

here schema (sorry childish aspect ;-) ):

so list in fact fine. problem elemlist contains pointer head of list . , pointer still points old first , second element. list no longer consitent.

how fix ?

one way out, make move_element_left() member function of elemlist. in case take care of special case e->left becomes null, in case need update elemlist's pointer first element.