Segmentation Fault with linked list node assignment in C++

Question

I'm probably missing something pretty simple again but too many hours in the lab have left me unable to see what I did wrong here. I'm attempting to build a linked list of all the characters being read in from a file by creating a list and appending new nodes to it as new characters are read in until the end of file.

First some background, here's the code for the node structure:

typedef struct node
{
//each node holds a single character
char data;
//pointer to the next node in the list
struct node *next;
}node;

Through the use of a couple of printf statements I've managed to narrow the issue down to somewhere in this block of code.

FILE *infile = fopen("data.txt", "r");

int c;
int counter = 0;
node *head, *current = NULL;

//Get the count of our original rules and create the list
do{

   node *item = new node();

  c = fgetc(infile);      

  if(c == '\n'){
counter ++;
  }

  printf("From infile: %c \n", c);

item->data = c; 
item->next = NULL;

printf("Item data: %c", item->data);

if (head == NULL){
  head  = current =  item;
}
else {    
  current->next = item;
  current = item;
}

}while( c != EOF);

I'm not certain where it is but I know it's in there. If i could just get another pair of eyes to point out where this is going wrong I'd appreciate it.

Shafik Yaghmour · Accepted Answer · 2013-10-15 19:17:38Z

3

You do not intialize head here:

node *head, *current = NULL;

so it will have an indeterminate value, so most likely this check is failing:

if (head == NULL){

and therefore neither head nor current would be properly initialized.

If you are using C++11 then you should be using nullptr instead of NULL.

answered Oct 15, 2013 at 19:17

Shafik Yaghmour

160k44 gold badges466 silver badges778 bronze badges

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

3 Comments

Mgetz Over a year ago

this is c++ ideally we should be using nullptr

Avidan Borisov Over a year ago

@Mgetz Ideally, we shouldn't be using fgetc, printf, FILE*, naked pointers and redundant structs as well ;)

AtomDrake Over a year ago

That's got it! Thanks! Whew, if I missed that it might be time for a little break.

Collectives™ on Stack Overflow

Segmentation Fault with linked list node assignment in C++

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related