Trouble with error: Segmentation fault: 11

[cabbdeng]

The problem probably caused by the function insertfix. I don't know why, is that because there is no enough space for the pointer I used in this function?

Please help me solve this problem. rly important to me.

#include<iostream>
using namespace std;
typedef struct node* tree;
struct node{
	int key; // jobID
	int total_time;
	int execute_time;
	tree parent;
	char color;
	tree left;
	tree right;
};
class RBtree {
	tree root;
	tree q;
public:
	RBtree() {
		q = NULL;
		root = NULL;
	}
	void insert(int,int);
	void insertfix(tree);
	void leftrotate(tree);
	void rightrotate(tree);
	void del(int key);
	void delnode(tree);
	tree successor(tree);
	void delfix(tree);
	tree search(int);
	tree upper_bound(int);
	tree lower_bound(int);
};

tree empty_node() {
	tree t = new node;
	t->key = 0;
	t->execute_time = 0;
	t->total_time = 0;
	return t;
}

void RBtree::insert(int key,int total_time){
	int i = 0;
	tree p, q;
	tree t = new node;
	t->key = key;
	t->total_time = total_time;
	t->execute_time = 0;
	t->left = NULL;
	t->right = NULL;
	t->color = 'r';
	p = root;
	q = NULL;
	if (root == NULL){
		root = t;
		t->parent = NULL;
	}
	else{
		while (p != NULL){
			q = p;
			if (p->key<t->key)
				p = p->right;
			else
				p = p->left;
		}
		t->parent = q;
		if (q->key<t->key)
			q->right = t;
		else
			q->left = t;
	}
	insertfix(t);
}

void RBtree::del(int key) {
	tree p;
	p = root;
	int found = 0;
	while (p != NULL && found == 0) {
		if (p->key == key)
			found = 1;
		if (found == 0) {
			if (p->key < key) p = p->right;
			else
				p = p->left;
		}
	}
	delnode(p);
}

void RBtree::delnode(tree p) {
	if (p == NULL)
		return;
	tree y = NULL;
	tree q = NULL;
	if (p->left == NULL || p->right == NULL)
		y = p;
	else
		y = successor(p);
	if (y->left != NULL)
		q = y->left;
	else {
		if (y->right != NULL)
			q = y->right;
		else
			q = NULL;
	}
	if (q != NULL)
		q->parent = y->parent;
	if (y->parent == NULL)
		root = q;
	else {
		if (y == y->parent->left)
			y->parent->left = q;
		else
			y->parent->right = q;
	}
	if (y != p) {
		p->color = y->color;
		p->key = y->key;
	}
	if (y->color == 'b' && q != NULL)
		delfix(q);
}


// void RBtree::insertfix(tree t){
// 	tree u;
// 	if (root == t){
// 		t->color = 'b';
// 		return;
// 	}
// 	while (t->parent != NULL && t->parent->color == 'r'){
// 		tree g = t->parent->parent;
// 		if (g->left == t->parent){
// 			if (g->right != NULL){
// 				u = g->right;
// 				if (u->color == 'r'){
// 					t->parent->color = 'b';
// 					u->color = 'b';
// 					g->color = 'r';
// 					t = g;
// 				}
// 			}
// 			else{
// 				if (t->parent->right == t){
// 					t = t->parent;
// 					leftrotate(t);
// 				}
// 				t->parent->color = 'b';
// 				g->color = 'r';
// 				rightrotate(g);
// 			}
// 		}
// 		else{
// 			if (g->left != NULL){
// 				u = g->left;
// 				if (u->color == 'r'){
// 					t->parent->color = 'b';
// 					u->color = 'b';
// 					g->color = 'r';
// 					t = g;
// 				}
// 			}
// 			else
// 			{
// 				if (t->parent->left == t)
// 				{
// 					t = t->parent;
// 					rightrotate(t);
// 				}
// 				t->parent->color = 'b';
// 				g->color = 'r';
// 				leftrotate(g);
// 			}
// 		}
// 		root->color = 'b';
// 		t = t->parent;
// 	}
// }

void RBtree::insertfix(tree t){
	tree *u = new tree;
	if (root == t){
		t->color = 'b';
		return;
	}
	while (t->parent != NULL && t->parent->color == 'r'){
		tree g = t->parent->parent;
		if (g->left == t->parent){
			if (g->right != NULL){
				u = &(g->right);
				if ((*u)->color == 'r'){
					t->parent->color = 'b';
					(*u)->color = 'b';
					g->color = 'r';
					t = g;
				}
			}
			else{
				if (t->parent->right == t){
					t = t->parent;
					leftrotate(t);
				}
				t->parent->color = 'b';
				g->color = 'r';
				rightrotate(g);
			}
		}
		else{
			if (g->left != NULL){
				u = &(g->left);
				if ((*u)->color == 'r'){
					t->parent->color = 'b';
					(*u)->color = 'b';
					g->color = 'r';
					t = g;
				}
			}
			else
			{
				if (t->parent->left == t)
				{
					t = t->parent;
					rightrotate(t);
				}
				t->parent->color = 'b';
				g->color = 'r';
				leftrotate(g);
			}
		}
		root->color = 'b';
		t = t->parent;
	}
}
void RBtree::delfix(tree p){
	tree s;
	while (p != root && p->color == 'b'){
		if (p->parent->left == p){
			s = p->parent->right;
			if (s->color == 'r'){
				s->color = 'b';
				p->parent->color = 'r';
				leftrotate(p->parent);
				s = p->parent->right;
			}
			if (s->right->color == 'b'&&s->left->color == 'b'){
				s->color = 'r';
				p = p->parent;
			}
			else{
				if (s->right->color == 'b'){
					s->left->color = 'b';
					s->color = 'r';
					rightrotate(s);
					s = p->parent->right;
				}
				s->color = p->parent->color;
				p->parent->color = 'b';
				s->right->color = 'b';
				leftrotate(p->parent);
				p = root;
			}
		}
		else{
			s = p->parent->left;
			if (s->color == 'r'){
				s->color = 'b';
				p->parent->color = 'r';
				rightrotate(p->parent);
				s = p->parent->left;
			}
			if (s->left->color == 'b'&&s->right->color == 'b'){
				s->color = 'r';
				p = p->parent;
			}
			else{
				if (s->left->color == 'b'){
					s->right->color = 'b';
					s->color = 'r';
					leftrotate(s);
					s = p->parent->left;
				}
				s->color = p->parent->color;
				p->parent->color = 'b';
				s->left->color = 'b';
				rightrotate(p->parent);
				p = root;
			}
		}
		p->color = 'b';
		root->color = 'b';
	}
}

void RBtree::leftrotate(tree p){
	if (p->right == NULL)
		return;
	else{
		tree y = p->right;
		if (y->left != NULL){
			p->right = y->left;
			y->left->parent = p;
		}
		else
			p->right = NULL;
		if (p->parent != NULL)
			y->parent = p->parent;
		if (p->parent == NULL)
			root = y;
		else{
			if (p == p->parent->left)
				p->parent->left = y;
			else
				p->parent->right = y;
		}
		y->left = p;
		p->parent = y;
	}
}

void RBtree::rightrotate(tree p){
	if (p->left == NULL)
		return;
	else{
		tree y = p->left;
		if (y->right != NULL){
			p->left = y->right;
			y->right->parent = p;
		}
		else
			p->left = NULL;
		if (p->parent != NULL)
			y->parent = p->parent;
		if (p->parent == NULL)
			root = y;
		else{
			if (p == p->parent->left)
				p->parent->left = y;
			else
				p->parent->right = y;
		}
		y->right = p;
		p->parent = y;
	}
}

tree RBtree::successor(tree p){
	tree y = NULL;
	if (p->left != NULL){
		y = p->left;
		while (y->right != NULL)
			y = y->right;
	}
	else
	{
		y = p->right;
		while (y->left != NULL)
			y = y->left;
	}
	return y;
}

tree RBtree::search(int key){
	tree p = root;
	int found = 0;
	while (p != NULL && found == 0){
		if (p->key ==key)
			found = 1;
		if (found == 0){
			if (p->key<key) p = p->right;
			else
				p = p->left;
		}
	}
	if (p == NULL)
		return empty_node();
	return p;
}
tree RBtree::upper_bound(int key) {
	tree p = root;
	tree res=empty_node();
	int distance = 999999;
	while (p != NULL) {
		if (p->key > key) {
			if (p->key - key < distance) {
				res = p;
				distance = p->key - key;
			}
			p = p->left;
		}
		else {
			p = p->right;
		}
	}
	return res;

}
tree RBtree::lower_bound(int key) {
	tree p = root;
	tree res = empty_node();
	int distance = 999999;
	while (p!=NULL) {
		if (p->key < key) {
			if (key - p->key< distance) {
				res = p;
				distance = key - p->key;
			}
			p = p->right;
		}
		else {
			p = p->left;
		}
	}
	return res;
}

[Handy Andy]

Hello cabbdeng,

I managed to fit up the code so it would compile and it did, but without what you did in main I can not test it.

No errors or warnings on compile, so I thinking is happens when it runs.

Andy

[dhayden]

Line 88: shouldn't you only call delnode if you found the key?

Beyond that, write a method to validate the tree and try calling it after you call each method. That should help you locate the problem.

[cabbdeng]

Hi, Andy, here is my Main and MinHeap code, glad to see that you are willing to help me try this code and find its problem for me.

#pragma once
#define ROOT 1
typedef struct Job *job,j;
struct Job {
	int jobID;
	int execute_time;
	int total_time;
};
class minHeap {
public:
	job jobs[100000];
	int len;
	minHeap() {
		len = 0;
		for (int i = 0; i < 100000; i++) {
			jobs[i] = new j;
			jobs[i]->jobID = jobs[i]->execute_time = jobs[i]->total_time = 0;
		}
	}
	void ShiftDown(int);
	void ShiftUp(int);
	void InsertHeap(int, int);
	int Parent(int);
	int LeftChild(int);
	int RightChild(int);
	bool Empty();
	job Pop();
	void swap(int,int);
	job top();
	job empty_job() {return jobs[0];}
private:
	int _v(int);
};
job minHeap::top() {
	return jobs[ROOT];
}
void minHeap::InsertHeap(int jobID, int total_time) {
	job jo = new j;
	jo->jobID = jobID;
	jo->total_time = total_time;
	jo->execute_time = 0;
	jobs[++len] = jo;
	ShiftUp(len);
}
job minHeap::Pop() {
	job j = jobs[ROOT];
	swap(ROOT, len);
	jobs[len]->jobID = jobs[len]->execute_time = jobs[len]->total_time = 0;
	len--;
	ShiftDown(ROOT);
	return j;
}
void minHeap::swap(int a, int b) {
	job t = jobs[a];
	jobs[a] = jobs[b];
	jobs[b] = t;
}
int minHeap::_v(int index) {
	return jobs[index]->execute_time;
}
void minHeap::ShiftUp(int index) {
	while (_v(index) < _v(Parent(index)) && index > 1) {
		swap(index, Parent(index));
		index = Parent(index);
	}
}
void minHeap::ShiftDown(int index) {
	while (index < len) {
		int v = _v(index);
		int location = index;
		if (LeftChild(index) <= len) {
			if (_v(LeftChild(index)) <= _v(location)) {
				if (_v(LeftChild(index)) == _v(location)) {
					if (jobs[LeftChild(index)]->jobID < jobs[location]->jobID) {
						v = _v(LeftChild(index));
						location = LeftChild(index);
					}
				}
				else {
					v = _v(LeftChild(index));
					location = LeftChild(index);
				}
			}
		}

		if (RightChild(index) <= len) {
			if (_v(RightChild(index)) < _v(location)) {
				if (_v(RightChild(index)) == _v(location)) {
					if (jobs[RightChild(index)]->jobID < jobs[location]->jobID) {
						v = _v(RightChild(index));
						location = RightChild(index);
					}
				}
				else {
					v = _v(RightChild(index));
					location = RightChild(index);
				}
			}
		}

		if (location == index)break;
		swap(index, location);
		index = location;
	}
}

int minHeap::Parent(int index) {
	return index / 2;
}
int minHeap::LeftChild(int index) {
	return index * 2;
}

int minHeap::RightChild(int index) {
	return index * 2 + 1;
}
bool minHeap::Empty() {
	return len == 0;
}

#include<iostream>
#include<vector>
#include<string>
#include<sstream>
#include<fstream>
#include"minheap.h"
#include"rbtree.h"
using namespace std;

RBtree rbt;
minHeap heap;
tree mark=NULL;
job running_job=NULL;
int cur_time = 0;
int running_time = 0;
fstream output("output.txt", fstream::out | ios_base::trunc);



void out(tree t) {
	//cout << "(" << t->key << "," << t->execute_time << "," << t->total_time << ")\n";
	output << "(" << t->key << "," << t->execute_time << "," << t->total_time << ")";
}
void out(job j) {
	//cout << "(" << j->jobID << "," << j->execute_time << "," << j->total_time << ")\n";
	output << "(" << j->jobID << "," << j->execute_time << "," << j->total_time << ")";
}

void Run() {
	if (heap.Empty())
		return;

	if (running_job == NULL) {
		running_job = heap.jobs[ROOT];
	}
	if (mark == NULL || mark->key != running_job->jobID)
		mark = rbt.search(running_job->jobID);
	running_job->execute_time++;
	mark->execute_time++;
	running_time++;

	if (running_job->execute_time == running_job->total_time) {
		running_time = 0;
		running_job = NULL;
		rbt.delnode(mark);
		heap.Pop();
	}
	else if(running_time==5){
		running_time = 0;
		heap.ShiftDown(ROOT);
		running_job = heap.jobs[ROOT];
	}
	//printf("At %d ms: Run!\n", cur_time);
}

void InsertJob(int jobID, int total_time) {
	heap.InsertHeap(jobID, total_time);
	rbt.insert(jobID, total_time);
	if (running_time == 0) {
		running_job = heap.jobs[ROOT];
	}
	//printf("At %d ms: Insert! jobID: %d  total_time: %d\n", cur_time, jobID, total_time);
}

void PrintJob(int jobID) {
	tree res = rbt.search(jobID);
	out(res);
	output << "\n";
	//printf("At %d ms: PrintJob! jobID: %d\n", cur_time, jobID);
}

void PrintJob(int low, int high) {
	vector<Job*> output_vec;
	int tot = 0;
	for (int i = ROOT; i <= heap.len; i++) {
		if (low <= heap.jobs[i]->jobID&&heap.jobs[i]->jobID <= high) {
			output_vec.push_back(heap.jobs[i]);
			tot++;
		}
	}
	for (int i = 0; i < output_vec.size(); i++){
		out(output_vec[i]);
		if (i == (output_vec.size()-1)) break;
		output << ",";
	}
	if (!tot)
		out(empty_node());
		output << "\n";
}

void NextJob(int jobID) {
	tree res = rbt.upper_bound(jobID);
	out(res);
	output << "\n";
	//printf("At %d ms: NextJob! jobID: %d\n", cur_time, jobID);
}

void PreviousJob(int jobID) {
	tree res = rbt.lower_bound(jobID);
	out(res);
	output << "\n";
	//printf("At %d ms: PreviousJob! jobID: %d\n", cur_time, jobID);
}

bool in(string s,string p) {
	return s.find(p) != -1;
}

void run2present(int run_time) {
	while (cur_time < run_time)
		Run(), cur_time++;
}

void LoadJobs(const string &path) {
	string s;
	ifstream input(path);
	int jobID, low, high, total_time, run_time;
	while (getline(input, s)) {
		if (in(s, "Insert")) {
			sscanf(s.c_str(), "%d: Insert(%d,%d)", &run_time, &jobID, &total_time);
			run2present(run_time);
			InsertJob(jobID, total_time);
		}
		else if (in(s, "PreviousJob")) {
			sscanf(s.c_str(), "%d: PreviousJob(%d)", &run_time, &jobID);
			run2present(run_time);
			PreviousJob(jobID);
		}
		else if (in(s, "NextJob")) {
			sscanf(s.c_str(), "%d: NextJob(%d)", &run_time, &jobID);
			run2present(run_time);
			NextJob(jobID);
		}
		else if (in(s, "PrintJob")) {
			if (in(s, ",")) { 
				sscanf(s.c_str(), "%d: PrintJob(%d,%d)", &run_time, &low, &high);
				run2present(run_time);
				PrintJob(low, high);
			}
			else {
				sscanf(s.c_str(), "%d: PrintJob(%d)", &run_time, &jobID);
				run2present(run_time);
				PrintJob(jobID);
			}
		}
	}
}

int main(int argc, char* argv[]){
	LoadJobs(argv[1]);
	output.close();
	//getchar();
	return 0;
}

[cabbdeng]

Hi dhayden,

It is a problem in line 88, thank you. But it's not serious to my code, because every time I delete a node, because a node has already finished its job, that means the node I will deleted must be a node in the current RBTree. But thank you anyway, correct this part can make my code be more generic.

[ne555]

int main(int argc, char* argv[]){
	LoadJobs(argv[1]);

¿how are we supposed to run your code?

[cabbdeng]

sorry guys, I forget to post the input file on,

Here is the sample input as a txt file. And the first number is the global time.

0: Insert(50,60000)
49950: Insert(19,55000)
99950: Insert(30,58000)
125900: PrintJob(19)
199500: Insert(1250,47000)
229500: Insert(1350,37000)
230000: PrintJob(30,5200)
235000: NextJob(1350)
236000: PreviousJob(1350)

[cabbdeng]

Is there anyone figure this problem out? I can't find where is my code wrong yet..

[Repeater]

You have really not made this easy for us. We have to basically recreate your program and input files to make it run.

You could have run this under a debugger which would have told you the exact line causing the crash. For the sake of ten minutes learning to use the debugger, you've wasted a day.


Here's what the debugger shows, as soon as its run: https://imgur.com/a/uiuEj

Bad pointer. The pointer 's' is NULL, but you're trying to use it anyway. You can see the call stack at the bottom right to follow the flow of code to this point.

[Handy Andy]

Hello cabbdeng,

I agree with what Repeater is saying. The program starts with "LoadJobs(argv[1])" in main, I think that "argv[1]" not having a value when I first started caused the "Segmentation fault", after I set it up right it worked.

The "LoadJobs" function works up to a point. After you get so far in this function you call other function(s) that eventually end up at the "RBtree::delfix" function and as Repeater showed you in his link "s" has a pointer value of "null" because "p->parent->left" has a value of "null".

I have not traced down every function call yet, but I do wonder based on the function name why is the program in the "delfix" function.

Also thinking that it may be a good idea to check "s" for being "null" and deal with that before entering the next if statement.

Still lookong.

Hope that helps,

Andy

[dhayden]

Your RBTree::delnode follows my very old copy of Introduction to Algorithms by Cormen, Leiserson and Rivest. But there are some problems:

Line 99: what if successor(p) is NULL?
Line 119: This isn't in my copy of the book.
Line 120. You should copy the total_time and execute_time fields too.

Yesterday I wrote:

write a method to validate the tree and try calling it after you call each method. That should help you locate the problem.

Did you do that? When I wrote a validate method I found that insertfix() is setting the parent field incorrectly in some case. Comparing your insertfix() to the one in the book, I see differences.

[cabbdeng]

Thx, guys, followed by your instruction, I finally figure this out. There are some problems in function Insertfix and delfix. Appreciate your helps.

[dhayden]

Further investigation shows that your rotate methods are wrong.

[cabbdeng]

Hi dhayden， thx for your comments, I noticed this problem also, and I have rewritten these two part already.

void RBtree::leftrotate(tree pt){
	if (pt->right == NULL)
		return;
	else{
		tree pt_right = pt->right;
 
	    pt->right = pt_right->left;
	 
	    if (pt->right != NULL)
	        pt->right->parent = pt;
	 
	    pt_right->parent = pt->parent;
	 
	    if (pt->parent == NULL)
	        root = pt_right;
	 
	    else if (pt == pt->parent->left)
	        pt->parent->left = pt_right;
	 
	    else
	        pt->parent->right = pt_right;
	 
	    pt_right->left = pt;
	    pt->parent = pt_right;
	}
}

void RBtree::rightrotate(tree pt){
	if (pt->left == NULL)
		return;
	else{
		tree pt_left = pt->left;
 
	    pt->left = pt_left->right;
	 
	    if (pt->left != NULL)
	        pt->left->parent = pt;
	 
	    pt_left->parent = pt->parent;
	 
	    if (pt->parent == NULL)
	        root = pt_left;
	 
	    else if (pt == pt->parent->left)
	        pt->parent->left = pt_left;
	 
	    else
	        pt->parent->right = pt_left;
	 
	    pt_left->right = pt;
	    pt->parent = pt_left;
	}
}

[dhayden]

Does your code work after the change? If not then what are the symptoms? Did you write a validator method?