Accessing Structs within Structs in C

Question

Just a very brief question really which stemmed from another post, if I were to access my char *number within my ListNode, from my TreeNode, so that each TreeNode each has its own linked list of numbers, would I access it as follows ( where TreeNode *root):

root->name = strdup(name); root->numbers->number = strdup(number);

Cheers!

typedef struct ListNode {
  char            *number;
  struct ListNode *next;
}ListNode;

typedef struct TreeNode {
  char            *name;
  ListNode        *numbers;
  struct TreeNode *left;
  struct TreeNode *right;
}TreeNode;

EDIT: Here is my function to add a TreeNode and List to that Node:

int main(void) {
char my_string[50], name[25], number[25];
TreeNode *root = NULL;
ListNode *list = NULL;
while ((fgets(my_string, 50, stdin)) != NULL) {
    if (my_string[0] == '.')
        break;      
sscanf(my_string, "%s %s", name, number); 
root = AddNode(root, list, name, number);
}   
return 0;
}

TreeNode* AddNode(TreeNode *root, ListNode *list, char *name, char *number) {
int comparison;
if ( root == NULL) {
    root = (TreeNode *)malloc(sizeof(TreeNode));
    list = (ListNode *)malloc(sizeof(ListNode));
    root->name = strdup(name); root->numbers->number = strdup(number);
    root->left = root->right = NULL;

Brian Roach · Accepted Answer · 2011-11-19 18:48:38Z

1

The problem is you're passing in a pointer to a ListNode, but then are mallocing a ListNode, assigning to it, and not doing anything with it. I'm not sure what your intent is there:

list = (ListNode *)malloc(sizeof(ListNode));

The reason for the segfault is that you malloc a TreeNode but not the ListNode inside of it. You need to do:

root = (TreeNode *)malloc(sizeof(TreeNode));
root->numbers = (ListNode *)malloc(sizeof(ListNode));

Or if that's what you meant to do with the ListNode you malloc'd, you need to assign it:

root = (TreeNode *)malloc(sizeof(TreeNode));
list = (ListNode *)malloc(sizeof(ListNode));
root->numbers = list;

answered Nov 19, 2011 at 18:48

Brian Roach

77k12 gold badges140 silver badges164 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

PnP Over a year ago

Similarly then, to how I set root->left and root->right to NULL, at the end of my code, would I also do the same with root->numbers->next, so that the next pointer of my list, for that TreeNode, points to NULL?

Brian Roach Over a year ago

One thing you can do is use calloc() instead of malloc(). calloc() allocates the memory then zero-fills it, therefore any pointers you haven't assigned to will be NULL Edit: To clarify - Yes, you want root->numbers->next to be NULL

yati sagade · Accepted Answer · 2011-11-19 18:37:50Z

0

If you don't forget to malloc() that ListNode in there, that's the way to go!

answered Nov 19, 2011 at 18:37

yati sagade

1,38510 silver badges25 bronze badges

5 Comments

PnP Over a year ago

But I seem to seg fault when I access in that way, any ideas? I am mallocing it, since atm I am only testing with root == NULL to begin with.

AndersK Over a year ago

you should add that piece of info in the question.

yati sagade Over a year ago

Checking root as NULL? So when you start off building the tree, the call is AddNode(NULL, ....) - is that so?

yati sagade Over a year ago

In your AddNode, you should have a line like root->numbers = list

yati sagade Over a year ago

You're mallocating list, a local pointer and NOT the one inside root.

AndersK · Accepted Answer · 2011-11-19 18:46:28Z

0

i think root->numbers->number is causing the segment violation, you do not seem to set root->numbers to point to anything before you de-reference it.

answered Nov 19, 2011 at 18:46

AndersK

36.1k6 gold badges63 silver badges86 bronze badges

Collectives™ on Stack Overflow

Accessing Structs within Structs in C

3 Answers 3

2 Comments

5 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

2 Comments

5 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related