Problem with pointers

kotoko · 06-12-2008, 04:10 AM

I'm having some problems doing the insert function for a linked list.

I have the basic struct

Code:

typedef struct Node
{
	Data* data;
	struct Node* next;
	
} No;

And the method to insert:

Code:

void insert (Node* node)
{
	Node* tmp, tmpProx;
	
	if (head == NULL)
	{
		head = node;
	}
	else
	{
		for(tmp = head; tmp->next != NULL  ||  calcDist(tmp->next->restaurante) > calcDist(no->restaurante)  ; tmp = tmp->next );
		
                // Problem Here!
		tmpProx = tmp->next;
		tmp->next = node;
		node->next = tmpProx;
                // End of Problem
		
	}
}

I'm having the error

Code:

error: incompatible types in assignment

Can someone explain me what the problem is please? I'm totally lost

Elysia · 06-12-2008, 04:45 AM

Code:

Node* tmp, tmpProx;

An evil pitfall in the language.
tmp is of type Node*, but tmpProx is of type Node.

To solve it, do either:

Code:

Node *tmp, *tmpProx;

...or my preferred way...

Code:

Node* tmp;
Node* tmpProx;

QuantumPete · 06-12-2008, 04:53 AM

That's because you've committed one of the cardinal sins of declaring pointers!
When you write:

Code:

int * a, b;

You're declaring a to be a pointer to an int, and b to be an int! It is equivalent to:

Code:

int * a;
int b;

You end up trying to assign tmp->next, which is a Node* to tmpProx, which is just a Node.
My recommendation is always to declare and initialise variables on their own line, i.e.

Code:

Node * tmp = NULL;
Node * tmpProx = NULL;

QuantumPete
Edit: Damn you Elysia

kotoko · 06-12-2008, 05:17 AM

Oh my God!

I would never remember to check that in a million years!

Thank you so much!

06-12-2008, 04:53 AM	#3
QuantumPete Technical Lead Join Date: Aug 2007 Location: London, UK Posts: 723	That's because you've committed one of the cardinal sins of declaring pointers! When you write: Code: int * a, b; You're declaring a to be a pointer to an int, and b to be an int! It is equivalent to: Code: int * a; int b; You end up trying to assign tmp->next, which is a Node* to tmpProx, which is just a Node. My recommendation is always to declare and initialise variables on their own line, i.e. Code: Node * tmp = NULL; Node * tmpProx = NULL; QuantumPete Edit: Damn you Elysia __________________ "No-one else has reported this problem, you're either crazy or a liar" - Dogbert Technical Support "Have you tried turning it off and on again?" - The IT Crowd Last edited by QuantumPete; 06-12-2008 at 04:54 AM. Reason: lack of proper touch typing skills
QuantumPete is offline

06-12-2008, 05:17 AM	#4
kotoko Registered User Join Date: Apr 2008 Posts: 75	Thank YOU! Oh my God! I would never remember to check that in a million years! Thank you so much!
kotoko is offline

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