I have a .h file that contains my struct and I must NOT edit this file:
struct KnightTree
{
int key;
int level;
int balance; //will be used in AVL only, and be ignored in other cases.
KnightTree* pLeftChild;
KnightTree* pRightChild;
};
And a .cpp file that I write my code here, I've written a code to insert 2 values (key and level) into the BST:
void BSTinsert(KnightTree* tree, int k, int lvl)
{
KnightTree* newnode;
if (tree == NULL)
{
newnode->key=k;
newnode->level=lvl;
newnode->pLeftChild=NULL;
newnode->pRightChild=NULL;
tree = newnode;
}
else
{
if (tree->key > k)
BSTinsert(tree->pLeftChild,k,lvl);
else if (tree->key <= k)
BSTinsert(tree->pRightChild,k,lvl);
}
}
But when I run it, the console "thinks" itself for about 3 seconds and error pop-up said "exe has stop working" so I have to close the program. I think's simple but I'm kinda confused now... I'm using Visual C++ 6.0 (I have to use this old version...)
Thank you guys!
You have at least 2 major problems:
You do not allocate memory for your newnode, so by addressing it you just create memory corruption.
You do not attach your newly created node to the tree, assigning tree = newnode doesn't create the necessary link to the tree.
Proceed from fixing these 2 issues.
And one more thing: have you tried to actually debug it before posting the question here?
Related
I am building an AVL tree, using this structure:
typedef struct node* nodep;
typedef struct node {
int postal_number;
int h; /* height */
nodep left, right, parent;
} Node;
Everything is working great: rotating, searching and inserting. The problem is with deleting a node. It deletes most of the node, except for few leaves after deleting most of the tree. My delete code (the problematic part) is:
int delete_postal(nodep* t, int in_postal){
nodep to_delete;
nodep* the_parent;
to_delete = search_postal((*t), in_postal);
the_parent = &(to_delete->parent);
/** if the node we want to delete is a leave **/
if (to_delete->right == NULL && to_delete->left == NULL) {
if (to_delete == (*the_parent)->right){ /* the node we want to delete is right son */
(*the_parent)->right = to_delete->right;
else { /* the node we want to delete is left son */
(*the_parent)->left = to_delete->left;
}
I made it so (*the_parent) will be the node himself in the tree, and when debugging it stepping into the if, it acts as if it did the deletion (making the child of the node the child of the node's father - I'm not dealing with malloc right now), but it just does not do it. The father keeps on pointing to the node that I would like to delete and not to NULL.
All the rest of the first deletion (nodes and leaves) works fine with this syntax.
Does somebody know what I am missing?
I'm now implementing Barnes-Hut Algorithms for simulating N-body problem. I only want to ask about the building-tree part.
There are two functions I made to build the tree for it.
I recursively build the tree, and print the data of each node while building and everything seems correct, but when the program is back to the main function only the root of the tree and the child of the root stores the value. Other nodes' values are not stored, which is weird since I printed them during the recursion and they should have been stored.
Here's some part of the code with modification, which I thought where the problem might be in:
#include<...>
typedef struct node{
int data;
struct node *child1,*child2;
}Node;
Node root; // a global variable
int main(){
.
set_root_and_build(); // is called not only once cuz it's actually in a loop
traverse(&root);
.
}
Here's the function set_root_and_build():
I've set the child pointers to NULL, but didn't show it at first.
void set_root_and_build(){
root.data = ...;
..// set child1 and child2 =NULL;
build(&root,...); // ... part are values of data for it's child
}
And build:
void build(Node *n,...){
Node *new1, *new2 ;
new1 = (Node*)malloc(sizeof(Node));
new2 = (Node*)malloc(sizeof(Node));
... // (set data of new1 and new2 **,also their children are set NULL**)
if(some condition holds for child1){ // else no link, so n->child1 should be NULL
build(new1,...);
n->child1 = new1;
//for debugging, print data of n->child1 & and->child2
}
if(some condition holds for child2){ // else no link, so n->child2 should be NULL
build(new2,...);
n->child1 = new2;
//for debugging, print data of n->child1 & and->child2
}
}
Nodes in the tree may have 1~2 children, not all have 2 children here.
The program prints out the correct data when it's in build() function recursion, but when it is back to main function and calls traverse(), it fails due to a segmentation fault.
I tried to print everything in traverse() and found that only the root, and root.child1, root.child2 stores the value just as what I've mentioned.
Since I have to called build() several times, and even in parallel, new1 and new2 can't be defined as global variables. (but I don't think they cause the problem here).
Does anyone know where it goes wrong?
The traverse part with debugging info:
void traverse(Node n){
...//print out data of n
if(n.child1!=NULL)
traverse(*(n.child1))
...//same for child2
}
You may not be properly setting the children of n when the condition does not hold. You might want this instead:
void set_root_and_build()
{
root.data = ...;
build(&root,...); // ... part are values of data for it's child
}
void build(Node *n,...)
{
n->child1 = n->child2 = NULL;
Node *new1, *new2;
new1 = (Node*) malloc(sizeof(Node));
new2 = (Node*) malloc(sizeof(Node));
// set data of new1 and new2 somehow (read from stdin?)
if (some condition holds for new1)
{
n->child1 = new1;
build(n->child1,...);
//for debugging, print data of n->child1
}
else
free(new1); // or whatever else you need to do to reclaim new1
if (some condition holds for new2)
{
n->child2 = new2;
build(n->child2,...);
//for debugging, print data of n->child2
}
else
free(new2); // or whatever else you need to do to reclaim new2
}
Of course, you should be checking the return values of malloc() and handling errors too.
Also, your traversal is a bit strange as it recurses by copy rather than reference. Do you have a good reason for doing that? If not, then maybe you want:
void traverse(Node *n)
{
...//print out data of n
if (n->child1 != NULL)
traverse(n->child1)
...//same for child2
}
The problem in your tree traversal is that you certainly process the tree until you find a node pointer which is NULL.
Unfortunately when you create the nodes, these are not initialized neither with malloc() nor with new (it would be initialized with calloc() but this practice in cpp code is as bad as malloc()). So your traversal continues to loop/recurse in the neverland of random pointers.
I propose you to take benefit of cpp and change slightly your structure to:
struct Node { // that's C++: no need for typedef
int data;
struct node *child1,*child2;
Node() : data(0), child1(nullptr), child2(nullptr) {} // Makes sure that every created are first initalized
};
And later get rid of your old mallocs. And structure the code to avoid unnecessary allocations:
if(some condition holds for child1){ // else no link, so n->child1 should be NULL
new1=new Node; // if you init it here, no need to free in an else !!
build(new1,...);
n->child1 = new1;
...
}
if (... child2) { ... }
Be aware however that poitners allocated with new should be released with delete and note with free().
Edit: There is a mismatch in your code snippet:
traverse(&root); // you send here a Node*
void traverse(Node n){ // but your function defines an argument by value !
...
}
Check that you didn't overllok some warnings from the compiler, and that you have no abusive cast in your code.
I am fairly new to C and have been learning from K&R's book The C Programming Language.
After doing the exercises on Binary trees I wanted to make a header for binary trees for
char*, long and double.
There is a function in the following code that has been giving me grief - it should fill an array of character pointers with the values stored in the tree in lexicographical order however it has a bug somewhere. Here's the code for the String Tree Header btree.h:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/************** TYPES **************/
typedef struct ctree
{
char *name;
ctree *left;
ctree *right;
};
/************** Globals **************/
static int c_inc = 0;
/************** Function Prototypes **************/
ctree *add_to_c_tree (ctree *cnode, char *name);
void print_c_tree (ctree *cnode);
ctree *c_tree_alloc (void);
void c_tree_free (ctree *cnode);
void return_c_tree (ctree *cnode, char **array);
/************** Function Definitions **************/
/* add_to_c_tree() : Adds a new node to a *character binary tree */
ctree *add_to_c_tree (ctree *cnode, char *name){
/* If the node is null, allocate memory for it,
* copy the name and set the internal nodes to null*/
if(cnode == NULL){
cnode = c_tree_alloc();
cnode->name = strdup(name);
cnode->left = cnode->right = NULL;
}
/* If initialised then add to the left node if it is lexographically
* less that the node above it else add it to the right node */
else{
if(strcmp(name, cnode->name) < 0)
cnode->left = add_to_c_tree(cnode->left,name);
else if(strcmp(name, cnode->name) > 0)
cnode->right = add_to_c_tree(cnode->right,name);
}
return cnode;
}
/* print_c_tree() : Print out binary tree */
void print_c_tree(ctree *cnode){
if (cnode != NULL) {
print_c_tree(cnode->left);
printf("%s\n",cnode->name);
print_c_tree(cnode->right);
}
}
/* return_c_tree() : return array of strings containing all values in binary tree */
void return_c_tree (ctree *cnode, char **array){
if (cnode != NULL) {
return_c_tree (cnode->left,array+c_inc);
c_tree_free(cnode->left);
*(array+c_inc++) = strdup(cnode->name);
// printf("arr+%d:%s\n", c_inc-1,*(array+(c_inc-1)));
return_c_tree (cnode->right,array+c_inc);
c_tree_free(cnode->right);
}
}
/* c_tree_alloc() : Allocates space for a tree node */
ctree *c_tree_alloc(void){
return (ctree *) malloc(sizeof(ctree));
}
/* c_tree_free() : Free's Memory */
void c_tree_free (ctree *cnode){
free(cnode);
}
Which I have been testing with bt.c:
#include "btree.h"
int main(void){
ctree *node = NULL; char *arr[100];
node = add_to_c_tree(node, "foo");
node = add_to_c_tree(node, "yoo");
node = add_to_c_tree(node, "doo");
node = add_to_c_tree(node, "woo");
node = add_to_c_tree(node, "aoo");
node = add_to_c_tree(node, "boo");
node = add_to_c_tree(node, "coo");
print_c_tree(node);
return_c_tree(node,arr);
for (int i = 0; i < 7; ++i)
{
printf("%d:%s ..\n",i, arr[i]);
}
return 0;
}
The reason for this question is that I have been having issues with the return_c_tree() function, which is meant to mimic the behaviour of K&R's print_c_tree() function except instead of recursively calling itself until a NULL ptr and printing out the name of the nodes in lexicographical order it is meant to add their names to an array of character ptrs and free the nodes memory.
However the output I get when run as above is:
aoo
boo
coo
doo
foo
woo
yoo
0:aoo ..
1:(null) ..
2:boo ..
3:doo ..
4:foo ..
5:coo ..
6:(null) ..
Which shows that the print function works fine but the return function obviously isn't.
The confusing thing is that if the call to printf() in return_c_tree() is uncommented this is the result:
aoo
boo
coo
doo
foo
woo
yoo
arr+0:aoo
arr+1:boo
arr+2:coo
arr+3:doo
arr+4:foo
arr+5:woo
arr+6:yoo
0:aoo ..
1:(null) ..
2:boo ..
3:doo ..
4:foo ..
5:coo ..
6:(null) ..
Which implies that it actually does add the strings in the right order.
Also I have tried it without the c_inc variable -> ie just incrementing array
before passing it to the right node which the produces the same results from the printf
in return_c_tree() but different from main:
arr+-1:aoo
arr+-1:boo
arr+-1:coo
arr+-1:doo
arr+-1:foo
arr+-1:woo
arr+-1:yoo
0:foo ..
1:yoo ..
2:coo ..
3:(null) ..
4:(null) ..
5:(null) ..
6:(null) ..
I'm rather confused, so If anyone can help I would appreciate it greatly. I'm sure I'm just incrementing it in the wrong place but I can't work out where.
I thought I had finally understood pointers but apparently not.
Best
P
Your problem is how you handle your pointer to array when you recursively call. This will fix your return_c_tree function:
void return_c_tree (ctree *cnode, char **array)
{
if (cnode != NULL) {
return_c_tree (cnode->left,array); // <--- CHANGED 2ND PARAM
c_tree_free(cnode->left);
*(array+c_inc++) = strdup(cnode->name);
return_c_tree (cnode->right,array); // <--- AGAIN, CHANGED 2ND PARAM
c_tree_free(cnode->right);
}
}
You're using a global variable c_inc to keep track of the current index into the array. However, when you recursively called return_c_tree, you passed in array+c_inc, but you did not offset c_inc to account for this. Basically, you double-counted c_inc each time.
While this solves your particular problem, there are some other problems with your code.
In general, using global variables is asking for trouble. There's no need to do it here. Pass c_inc as a parameter to return_c_tree.
Also, mixing global variables with recursion is especially prone to problems. You really want recursive routines to keep their state on the stack.
As a commenter pointed out, all of your code in btree.h should really be in btree.c. The point of header files is to define an interface, not for code.
(This is more stylistic) Your return_c_tree function is really two distinct functions: copy the elements of the tree (in order) into the array, and free the memory used by the tree. These two operations are conceptually distinct: there are times that you'll want to do one and not both. There can be compelling performance (or other) reasons to mix the two, but wait until you have some hard evidence.
I'm coding a binary search tree and I'm having a little trouble finding a way to delete node effectively.
I have this code :
struct node* deleteNode(int i, struct node *N)
{
if (N==NULL)
{
return NULL;
}
else if (i<N->value)
{
N->size--;
N->lChild=deleteNode(i,N->lChild);
}
else if (i>N->value)
{
N->size--;
N->rChild=deleteNode(i,N->rChild);
}
else if (N->lChild==NULL)
{
return N->rChild;
}
else if (N->rChild==NULL)
{
return N->lChild;
}
else
{
N->size--;
N->value=findMin(N->rChild);
N->rChild=deleteNode(N->value,N->rChild);
}
return N;
}
And N is a node structure which have 5 fields : value, lChild, rChild, size, height.
In fact what I'm doing here is to make the tree not to point toward the node that I want to delete but when I'm trying to put something like :
else if (N->rChild==NULL)
{
free(N);
N=NULL;
return N->lChild;
}
Or every similar looking code, it doesn't work. Can someone point me in the right direction please?
Thank you.
First of all you're saying N=NULL and then calling N->lchild N is null and pointing to nothing so how do you expect to get the lchild value?
Since this is homework I won't give a direct answer but hints.
To delete the node, check if it has children, if it doesnt free it and remove references to it such as the parents child ptr.
If it has 1 child swap the ptr that points to the node you want to delete with the child and free the node. The same applies if you also have 2 children.
I have a list in C that is something like this:
typedef struct _node
{
int number;
DWORD threadID;
HANDLE threadH;
struct *_node next;
} *node;
And you have somthing like this:
node new_node = malloc(sizeof(node));
As you may have guessed out, this list will store information for threads, including their handlers and Id's. Still I am having trouble when I try to do this:
free(new_node);
Everytime I try to do this I encounter an unexpected error, VS saying that there was a data corruption. I've pinned down as much as possible and I found that the problem resides when I try to use free the handle.
I've searched on MSDN how to do this but the only thing I can find is the function that closes the thread (which is not intended here, since I want the thread to run, just deleting it's record from the list).
The question is: how I am supposed to free an handle from the memory? (Considering that this is only a copy of the value of the handle, the active handle is not being deleted).
EDIT: This is the function to insert nodes from the list:
int insereVisitanteLista(node* lista, DWORD threadID, HANDLE threadH, int num_visitante)
{
node visitanteAnterior;
node novoVisitante = (node)malloc(sizeof(node));
if(novoVisitante == NULL)
return 0;
novoVisitante->threadID = threadID;
novoVisitante->threadH = threadH;
novoVisitante->number = num_visitante;
novoVisitante->next = NULL;
if(*lista == NULL)
{
*lista = novoVisitante;
return 1;
}
visitanteAnterior = *lista;
while(visitanteAnterior->next != NULL)
visitanteAnterior = visitanteAnterior->next;
visitanteAnterior->next =novoVisitante;
return 1;
}
And this is the function to delete nodes:
int removeVisitanteLista(node * lista, DWORD threadID)
{
node visitanteAnterior = NULL, visitanteActual;
if(*lista == NULL)
return 0;
visitanteActual = *lista;
if((*lista)->threadID == threadID)
{
*lista = visitanteActual->next;
visitanteActual->next = NULL;
free(visitanteActual);
return 1;
}
while(visitanteActual != NULL && visitanteActual->threadID != threadID)
{
visitanteAnterior = visitanteActual;
visitanteActual = visitanteActual->next;
}
if (visitanteActual == NULL)
return 0;
visitanteAnterior->next = visitanteActual->next;
free(visitanteActual);
return 1;
}
What exactly is a node that you are trying to free? Is this a pointer to a struct _node? If yes, have you allocated it previously? If no, free is not needed, otherwise you have to check if node is not NULL and make sure you do not free it multiple times. It is hard to guess what you are doing and where is an error without a minimal working example reproducing the problem. The only thing I can suggest is to read about memory management in C. This resource might help.
UPDATE:
node in your code is a pointer to _node. So sizeof (node) is a size of a pointer, which is either 4 or 8 bytes (depending on architecture). So you allocate 8 bytes, for example, but assume you have a pointer to the structure which is much larger. As a result, you corrupt memory, and behavior of the program becomes undefined. So changing node novoVisitante = (node)malloc(sizeof(node)) to node novoVisitante = (node)malloc(sizeof(_node)) should fix the problem.
You haven't shown us the context of your call to free() so I need to speculate a little but my first concern is that you didn't mention removing the node from the list before deleting it.
Start by unlinking the node by modifying the next field of the previous (or head) node. If you still get the error, then you have corrupted memory somehow by writing past the end of one of your allocated memory structures or something similar.
Also, I assume node is a pointer. You really haven't provided much information about what you're doing.