Unable to deallocate memory for a tree structure.

Hi, I'm trying to deallocate a kd tree which I created dynamically.
There were no problems
creating the structure and I can access it easily but there is a
problem while trying to free
it. Here's the structure for the a single node in the tree:


typedef struct kdnode_s
{
bbox box; /* Bounding box */
int splitplane; /* -1 for leaf node*/
union
{
struct
{
struct kdnode_s *child[2]; /* Children node */
double split;

}nonleaf;

struct
{
size_t nt;
node *thead; /* Link list */

}leaf;

}info;

}kdnode;


Some other supporting data structures :

/* vector */

typedef struct
{
double coord[3];

}vector;

/* bounding box */

typedef struct
{
vector maxB, minB;

}bbox;

/* link list node */

typedef struct node_s
{
struct node_s *next;
void *data;

}node;


Heres the function I wrote to free the kdtree. I pass the address of
the root node pointer
and traverse the tree until I reach a leaf node which is characterised
by splitplane member
being -1. If it is not -1, then it has values 0,1,2 and it is a
nonleaf node. The leaf node
is freed and then I try to free other nodes as I climb back. a
leaf node is freed its
pointer is made NULL. This makes it easier to free other nodes once
their children have
been freed.

void free_kd_tree(kdnode **kd)
{
if (*kd != NULL)
{
if ((*kd)->splitplane == -1)
{
free_list((*kd)->info.leaf.thead);
*kd = NULL;
return ;
}
else
{
free_kd_tree(&(*kd)->info.nonleaf.child[0]);
free_kd_tree(&(*kd)->info.nonleaf.child[1]);

if ((*kd)->info.nonleaf.child[0] == NULL &&
(*kd)->info.nonleaf.child[1] == NULL)
{
free(*kd);
*kd = NULL;
}
}
}
}

In this program the free_list is a routine to free the link list given
its head pointer and this
is how I wrote it:

void free_list(node *head)
{
node *p;

p = head;
while (p != NULL)
{
free(p);
p = p->next;
}
}

For some reason I observed, the free(p) is not able to execute and the
program terminates
at the point without any warning or message. What could be wrong ?

pereges wrote:
Hi, I'm trying to deallocate a kd tree which I created dynamically.
There were no problems
creating the structure and I can access it easily but there is a
problem while trying to free
it. Here's the structure for the a single node in the tree:
>
>
typedef struct kdnode_s
{
bbox box; /* Bounding box */
int splitplane; /* -1 for leaf node*/
union
{
struct
{
struct kdnode_s *child[2]; /* Children node */
double split;
>
}nonleaf;
>
struct
{
size_t nt;
node *thead; /* Link list */
>
}leaf;
>
}info;
>
}kdnode;
>
>
Some other supporting data structures :
>
/* vector */
>
typedef struct
{
double coord[3];
>
}vector;
>
/* bounding box */
>
typedef struct
{
vector maxB, minB;
>
}bbox;
>
/* link list node */
>
typedef struct node_s
{
struct node_s *next;
void *data;
>
}node;
>
>
Heres the function I wrote to free the kdtree. I pass the address of
the root node pointer
and traverse the tree until I reach a leaf node which is characterised
by splitplane member
being -1. If it is not -1, then it has values 0,1,2 and it is a
nonleaf node. The leaf node
is freed and then I try to free other nodes as I climb back. a
leaf node is freed its
pointer is made NULL. This makes it easier to free other nodes once
their children have
been freed.
>
void free_kd_tree(kdnode **kd)
{
if (*kd != NULL)
{
if ((*kd)->splitplane == -1)
{
free_list((*kd)->info.leaf.thead);
*kd = NULL;
return ;
}
else
{
free_kd_tree(&(*kd)->info.nonleaf.child[0]);
free_kd_tree(&(*kd)->info.nonleaf.child[1]);
>
if ((*kd)->info.nonleaf.child[0] == NULL &&
(*kd)->info.nonleaf.child[1] == NULL)
{
free(*kd);
*kd = NULL;
}
}
}
}
>
In this program the free_list is a routine to free the link list given
its head pointer and this
is how I wrote it:
>
void free_list(node *head)
{
node *p;
>
p = head;
while (p != NULL)
{
free(p);
p = p->next;
}
}
>
For some reason I observed, the free(p) is not able to execute and the
program terminates
at the point without any warning or message. What could be wrong ?

p is freed ('free(p);') what do you think 'p->next' means?

--
Joe Wright
"Everything should be made as simple as possible, but not simpler."
Albert Einstein

Unfotunately, my pelles C compiler never reports such dangerous
situations. Can some one please tell me of some easy to use debugger
in windows mode which will give warnings and stuff ? I know valegrind
is a good one but its for linux. Pelles C has a debugger but it
produces enormous amount of illegible assembly code and various stack
information. I feel extremely frustrated because of these bugs.

pereges wrote:

Unfotunately, my pelles C compiler never reports such dangerous
situations. Can some one please tell me of some easy to use debugger
in windows mode which will give warnings and stuff ? I know valegrind
is a good one but its for linux. Pelles C has a debugger but it
produces enormous amount of illegible assembly code and various stack
information. I feel extremely frustrated because of these bugs.

Have you tried static code checking tools like PC-Lint or splint? They
would've caught the mistake you made.