input filestream to a doubly linked list

Coded

To append into a double linked list, you need to reset any links that change, that means the next link of the tail and the previous link of the new tail:

Code:

temp = new link;
temp->next = 0;
temp->prev = tail;
tail->next = temp;
tail = tail->next;

To prepend, you basically do the same thing reversed:

Code:

temp = new link;
temp->next = head;
temp->prev = 0;
head->prev = temp;
head = temp;

To insert, you have four links to fix:

Code:

temp = new link;
temp->next = after;
temp->prev = before;
before->next = temp;
after->prev = temp;

Naturally, you don't always need unique pointers to each node that changes. A lot of the time you can use next or prev chains to avoid temporary variables:

Code:

tail->next = new link;
tail->next->next = 0;
tail->next->prev = tail;
tail = tail->next;

Code:

head->prev = new link;
head->prev->next = head;
head->prev->prev = 0;
head = temp;

Code:

temp = new link;
temp->next = before->next;
temp->prev = before;
before->next->prev = temp;
before->next = temp;

// or

temp = new link;
temp->next = after;
temp->prev = after->prev;
after->prev->next = temp;
after->prev = temp;

p.s. Don't ever delete your post's content. Other people can learn from your question and any answers to it.