Problem mit Zeigern

[Smaug]

Hallo!

Habe mir eine doppelt verkette Liste gebastelt:

#include <iostream>

using namespace std;

struct Node
{
	int value;
	Node *pred, *succ;
};

Node *head=NULL;

void insert(int info)
{
	Node *tmp;

	tmp=new Node;
	tmp->value=info;

	tmp->pred=NULL;
	tmp->succ=head;
	head=tmp;
}

void print(Node *first)
{
	Node *pos;
	pos=first;
	int i=1;

	cout << "HEAD" << endl;
	cout << "-------------------------------" << endl;

	while(pos)
	{
		cout << i << ". Wert: " << pos->value << endl;
		if(pos->succ)
			cout << "Wert Nachfolger: " << (pos->succ)->value << endl;
		//if(pos->pred)
		//	cout << "Wert Vorgaenger: " << (pos->pred)->value << endl;
		cout << "-------------------------------" << endl;
		pos=pos->succ;
		i++;
	}
}

int main(void)
{
	Node *n = new Node;

	insert(5);
	insert(4);
	insert(3);

	print(head);

	return 0;
}

Klappt alles so weit auch. Doch wie kann ich mir den Wert des Vorgängers ausgeben lassen?
Irgendwelche Tipps?

THX

Tobias

[Bashar]

pos->pred->value

[operator void]

Dazu sollte er aber pred erstmal irgendwo auf etwas anderes als NULL setzen.

[Smaug]

Das weiß ich auch. Nur, mein problem liegt in der insert-Funktion:

tmp->pred=NULL;

Wie Weise ich den Vorgänger zu?

[operator void]

if (head)
    head->pred = tmp;

?

[Bashar]

in insert fehlt das:

if (tmp->succ)
  tmp->succ->pred = tmp;

Wenn du einfügen in der Mitte implementierst wird es noch ekliger mit den Spezialfällen.

[Smaug]

Danke! Dann mach ich mich mal an die anderen Fälle!

[Smaug]

Hier mal die komplette Implementierung, für die die's interessiert:

#include <iostream>

using namespace std;

struct Node
{
	int value;
	Node *pred, *succ;
};

Node *head=NULL;

void add_front(int info)
{
	Node *tmp, *n;

	tmp=new Node;
	tmp->value=info;

	tmp->pred=NULL;
	tmp->succ=head;
	if (head) head->pred = tmp;
	head=tmp;
	//if (tmp->succ) tmp->succ->pred = tmp;

}

void delete_front(void)
{
	Node *tmp;

	if(head==NULL)
		return;
	else
	{
		tmp = head;
		head = head->succ;
		head->pred=NULL;
    	delete tmp;
	}
}

void add_rear(int info)
{
	Node *tmp, *pos;
	tmp = new Node;
	tmp->value=info;
	pos=head;

	if(head==NULL)
		add_front(info);
	else
	{
		while(pos->succ)
		{
			pos=pos->succ;
		}

		pos->succ=tmp;
		tmp->pred=pos;
		tmp->succ=NULL;
	}
}

void delete_rear()
{
	Node *tmp, *pos;
	pos=head;

	if(head==NULL)
		return;
	else
	{
		while(pos->succ)
		{
			pos=pos->succ;
		}

		tmp=pos;
		pos->pred->succ=NULL;
		delete tmp;
	}
}

void add_after(Node *p, int info)
{
	Node *neu;
	neu = new Node;
	neu->value=info;

	if(!p->succ)
		add_rear(info);
	else
	{
		neu->succ=p->succ;
		p->succ->pred=neu;
		p->succ=neu;
		neu->pred=p;
	}
}

void delete_after(Node *p)
{
	Node *tmp;

	tmp=p->succ;
	p->succ=tmp->succ;
	tmp->succ->pred=p;
	delete tmp;
}

void print(Node *first)
{
	Node *pos;
	pos=first;
	int i=1;

	cout << "HEAD" << endl;
	cout << "-------------------------------" << endl;

	while(pos)
	{
		cout << i << ". Wert: " << pos->value << endl;
		if(pos->succ)
			cout << "Wert Nachfolger: " << (pos->succ)->value << endl;
		if(pos->pred)
			cout << "Wert Vorgaenger: " << (pos->pred)->value << endl;
		cout << "-------------------------------" << endl;
		pos=pos->succ;
		i++;
	}
}

int main(void)
{
	Node *n, *p;
	n = new Node;

	add_front(5);
	add_front(4);
	add_front(3);
	add_front(2);
	add_front(1);

	print(head);

	cout << "*********************************************" << endl;

	delete_front();
	print(head);

	cout << "*********************************************" << endl;

	add_rear(10);
	print(head);

	cout << "*********************************************" << endl;

	delete_rear();
	print(head);

	cout << "*********************************************" << endl;

	p=head->succ;

	add_after(p, 22);
	print(head);

	cout << "*********************************************" << endl;

	delete_after(p);
	print(head);

	return 0;
}