program crashes while iterating through a linked list - c

Question

I am supposed to create a linked list with the following properties:
struct node{
char *word;
int times;
struct node *next;
}head;
I have to read each word from a file, check if it exists in the list, and if it doesn't, i should add it. If it already exists i need to increase times by one. I use the following code to accomplish that:
void append(char *wrd, struct node *start){
struct node *current = start;
while(current->next != NULL){
current = current->next;
}
current->next = malloc(sizeof(struct node));
strcpy(current->word, wrd);
current->times = 1;
current->next->next = NULL;
}
int iterate(char *wrd, struct node *start){
struct node *current = start;
while(current != NULL){
if(strcmp(current->word, wrd)==0){
current->times++;
return 1;
}
current = current->next;
}
return 0;
}
void read_file(struct node *start){
FILE *fp;
char wrd[20];
puts("give file name and format(max 19 characters)");
gets(wrd);
fp = fopen((const char*)wrd, "r");
fscanf(fp, "%s", wrd);
start->word = malloc(strlen(wrd)+1);
strcpy(start->word, wrd);
while(fscanf(fp, "%s", wrd) != EOF){
if(!iterate(wrd, start)){
append(wrd, start);
}
}
}
void print_data(struct node *start){
struct node *current = start;
while(current->next != NULL){
printf("word: %s , times: %d", current->word, current->times);
}
}
int main(int argc, char *argv[]) {
struct node *start = &head;
read_file(start);
return 0;
}
append takes a word, creates a new node containing it, and adds the node to the list.
iterate takes a word and searches the list for a match. If the word already exists within the list, then times is increased by one. 0 is returned if no match was found and 1 in the opposite case.
read_file initializes the head node, reads the file and calls the above functions for each word it reads.
Let's say i have a text file containing the following words:
hello hey world hello
world this is supposed to work
but it does not
The program successfuly runs for the first 3 words and creates the nodes. When the match hello is found the program crashes. I've determined that the error lies in iterate, but i can't figure out what's causing it. Any help is greatly appreciated.

Answer 1

First things first, I don't understand why you can confidently say that your program has an error in the iterate function.
You haven't allocated any memory to the word pointer before strcpy().
I would suggest doing this in your append() function:
void append(char *wrd, struct node *start){
struct node *current = start;
if(current == NULL){
start = (struct node*)malloc(sizeof(struct node));
start->word = (char *)malloc((strlen(wrd) + 1)*sizeof(char));
strcpy(start->word, wrd);
start->times = 1;
start->next = NULL;
return;
}
while(current->next != NULL){
current = current->next;
}
current->next = (struct node*)malloc(sizeof(struct node));
current->next->word = (char*)malloc((strlen(wrd) + 1)*sizeof(char)); //add this line
strcpy(current->next->word, wrd); //not current->word
current->next->times = 1; //not current->times
current->next->next = NULL;
}
Notice here that in the append function, you did not check if the list is already empty or not. The if block is to do the same. Also notice the mistake you made while using strcpy(). You wanted to copy the new word in the new pointer, but were doing it in the pointer which is the parent of the new node.
Now, you read_file() function will look a lot simpler!
void read_file(struct node *start){
FILE *fp;
char wrd[20];
puts("give file name and format(max 19 characters)");
gets(wrd);
fp = fopen((const char*)wrd, "r");
while(fscanf(fp, "%s", wrd) != EOF){
if(!iterate(wrd, start)){
append(wrd, start);
}
}
}
I don't think your iterate function needs an update, but print_data() surely does:
void print_data(struct node *start){
struct node *current = start;
while(current != NULL){
printf("word: %s , times: %d", current->word, current->times);
current = current->next;
}
}
Seems like the only function not having any error was iterate(). Happens when you play with pointers! :P