Problem with tree and enhanced queue.

[negative]

Dear all,

I want to create a tree, where every node has an undetermined number
of children (during the population of the tree, the exact number of
children of each node , will become clear). So i thought that i could
use in each node a queue in which we will add, every time a new child
is born, the address of this node. Here are the structures i have used:

// The queue node. Every node contains a pointer to a tree node and a
pointer to the next
// element of the queue
typedef struct queue_tag {
struct TreeNode_tag * child_ptr;
struct queue_tag * next;
} QueueNode;

// the queue
typedef struct {
QueueNode *head;
QueueNode *tail;
} queue;

// the tree. Every leaf contains an integer i and a queue which
contains the pointers to node's children
typedef struct TreeNode_tag {
int i;
queue *q;
} TreeNode;

// The tree
typedef TreeNode * tree;

The problem is that i get a segmentation fault every time i try to
access the queue of the tree node. Here is the code i use to start the
tree :

tree *t;
*t = (TreeNode *)malloc(sizeof (TreeNode));

(*t)->i = 0; // a random value
(*t)->q->head = NULL; // initially the node has no children.
(*t)->q->tail = NULL;

I use gcc.

Thank you for your time.

[Chris McDonald]

Re: Problem with tree and enhanced queue.

"negative" <panos84@gmail. com> writes:
[color=blue]
>The problem is that i get a segmentation fault every time i try to
>access the queue of the tree node. Here is the code i use to start the
>tree :[/color]
[color=blue]
>tree *t;
>*t = (TreeNode *)malloc(sizeof (TreeNode));[/color]

Where have you allocated space for the tree's queue? I think you require:

*t = malloc(sizeof(T reeNode));
(*t)->q = malloc(sizeof(Q ueue));

--
Chris.

[Ian Malone]

Re: Problem with tree and enhanced queue.

negative wrote:[color=blue]
> Dear all,
>[/color]

<snip>
[color=blue]
>
> // the tree. Every leaf contains an integer i and a queue which
> contains the pointers to node's children
> typedef struct TreeNode_tag {
> int i;
> queue *q;
> } TreeNode;
>
> // The tree
> typedef TreeNode * tree;
>
> The problem is that i get a segmentation fault every time i try to
> access the queue of the tree node. Here is the code i use to start the
> tree :
>
> tree *t;
> *t = (TreeNode *)malloc(sizeof (TreeNode));[/color]
No bearing on your problem, but the cast is unnecessary and
sizeof( *t ) (brackets optional) is often preferred to sizeof(TreeNode )
since it's harder to get wrong.
[color=blue]
>
> (*t)->i = 0; // a random value
> (*t)->q->head = NULL; // initially the node has no children.
> (*t)->q->tail = NULL;
>[/color]

(*t)->q is an uninitialised pointer.

--
imalone

[Roland Csaszar]

Re: Problem with tree and enhanced queue.

Hi,

At 5 Jan 2006 05:18:11 -0800,
negative wrote:
[color=blue]
> // The tree
> typedef TreeNode * tree;
>
> The problem is that i get a segmentation fault every time i try to
> access the queue of the tree node. Here is the code i use to start the
> tree :
>
> tree *t;[/color]
This is the same as
TreeNode **t;

Well, you got some errors here.
[color=blue]
> *t = (TreeNode *)malloc(sizeof (TreeNode));[/color]

Why did you do a typedef, when you are using this instead of
*t = (tree) malloc (sizeof (TreeNode));

Here you (try) initialize the value t points to with something, but
t points to some random place in memory. You should have done something
like
t = (tree *) malloc (sizeof (tree));
first.


Regards,
Roland
--
Roland Csaszar ----------- \\\ /// -------------- +43 316 495 2129
Software Development ------ \\\ /// ----------- http://www.knapp.com
KNAPP Logistics Automation - \\V// - mailto:roland.c saszar@knapp.co m

[negative]

Re: Problem with tree and enhanced queue.


Chris McDonald wrote:[color=blue]
> Where have you allocated space for the tree's queue? I think you require:
>
> *t = malloc(sizeof(T reeNode));
> (*t)->q = malloc(sizeof(Q ueue));
>
> --
> Chris.[/color]

thanks Chris

This was finally the problem. I had forgotten to allocate space for
the tree's queue.

Negative...