LinuxQuestions.org - segmentation fault in program at run time

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segmentation fault in program at run time

I am making a program to do a breadth first search.
The code which I am posting here just makes a que of the nodes visited in a binary tree in inorder fashion,so this implementation is not yet complete.
While developing I got a segmentation fault which I was not able to understand why I am getting so I am posting since the tree of same program (without BFS) is working.

Code:





#include<stdio.h>

#include<stdlib.h>

struct node {

    struct node *left, *right;

    int data, color;

} *root;

//root is used to point to the root node of tree

int check = 0;

typedef struct node tree;

struct list {

    struct list *next;

    struct node *btree_node_ptr;    //btree_node_ptr stores the address of members of structure node

} *que_start;

typedef struct list que;

tree *create_node(int);

void add_tree(int value, tree *);

void travel_tree(tree *);

void enque(tree *);

void travel_que(void);

void deque(tree *);

que *que_add_node(tree *);

que *tree_que;

int main()

{

    int i, j,value;

    tree *nv;

    root = NULL;

    que_start = NULL;

    value = 0;

    while (0) {

        printf("enter value \n");

        scanf("%d", &value);

        if (value == 1)

            break;

        if (root == NULL)

            root = create_node(value);

        else if (root != NULL) {

            //      nv = create_node(value);

            add_tree(value, root);

        }

    }

    travel_tree(root);

    printf("\n travelling in que \n");

    travel_que();    

}



tree *create_node(int num)

{

    tree *temp;



    temp = (tree *) malloc(sizeof(tree));

    temp->data = num;

    temp->left = NULL;

    temp->right = NULL;

    temp->color=2;

    return temp;



}



void add_tree(int v1, tree * node)

{



    if (v1 <= node->data) {

        if (node->left != NULL) {

            add_tree(v1, node->left);

        } else {

            node->left = create_node(v1);

        }

        return;

    }

    if (v1 > node->data) {

        if (node->right != NULL) {

            add_tree(v1, node->right);

        } else {

            node->right = create_node(v1);

        }

        return;

    }



}



void travel_tree(tree *temp)

{

//      printf("\n inside travel_tree");



    if (temp->left != NULL)

        travel_tree(temp->left);

    printf(" \n %d ", temp->data);

    enque(temp);

    if (temp->right != NULL)

        travel_tree(temp->right);

    return;

}



que *que_add_node(tree * temp)

{

    que *b;

    b = (que *) malloc(sizeof(que));

    b->next = NULL;

    temp->color=1;

    b->btree_node_ptr = temp;

    return b;

}



void enque(tree *temp)

{

//to make a que of que

    tree_que=que_start;

    if (que_start == NULL) {

        que_start = que_add_node(temp);

        tree_que=que_start;

        return;

    }

    else

        {    while(tree_que->next!=NULL)

        {

        tree_que=tree_que->next;

        }

    tree_que->next=que_add_node(temp);

    }

    return;

}

void travel_que(void)

{

    tree_que=que_start;

    while (tree_que!=NULL)

        {

    printf("Data is %d color is %d\n",tree_que->btree_node_ptr->data,tree_que->btree_node_ptr->color);

    tree_que=tree_que->next;

    }

    return;

}

void deque (tree *temp)

{

 while (tree_que!=NULL)

    {

    tree_que=tree_que->next;



    }

    return;

}

"Use the source, Luke":

Assuming you're using GCC or G++:

1. (Re)build your code with "-g" (enable debugger)
2. Run your program in gdb
3. Type "where" to get a stack traceback when the problem occurs

PS:
Here's a good tutorial on using GDB:
http://www.unknownroad.com/rtfm/gdbtut/gdbtoc.html

The problem was that tree could not be travelled.
while(0)
any thing inside this statement was not executing.
I could not understand why.
I changed while(0) to while(1==1) and it worked,

Quote:

Originally Posted by tkmsr (Post 4129774)

Code:



int main()

{

    int i, j,value;

    tree *nv;

    root = NULL;

    que_start = NULL;

    value = 0;

    while (0) {

            ...

        }

    }

    travel_tree(root);

    printf("\n travelling in que \n");

    travel_que();    

}

Of course it segfaults...

Frankly, you've just given a very good reason why it would be a good idea to familiarize yourself with a debugger (if you haven't already).

ALSO:
1. As you know, this means "while (FALSE)":

Code:

while (0)

2. But, for the same reason, "while (1 == 1)" is duplicate redundant ;):

Code:

  while (1 == 1) // Comparing any number with itself is always TRUE



  // Equivalent:

  // In C/C++, any non-zero number BY ITSELF also evaluates "true"

  while (1)



  // Equivalent:

  // This is an idiom Kernighan and Ritchie use

  for ( ;; )

3. This is also redundant (at least in this case):

Code:

  // Poor

  if (root == NULL)

    root = create_node(value);

  else if (root != NULL)

    add_tree(value, root);



  // Better

  if (root == NULL)

    root = create_node(value);

  else

    add_tree(value, root);



  // Best

  if (!root)

    root = create_node(value);

  else add_tree(value, root);

Small stuff: the compiler will often optimize away this kind of stuff. But the cleaner you write, the easier it is to read and maintain.

IMHO ...