Thread: Segfault with Linked List Program

I am learning c and this program is for me to practice implementating single linked lists. I have run into a block.

In my program I am getting a segfault in the

Code:

printf("%s\n", temp_word->word);

line of my print_conc function. I think it might be error in my logic with the linked list implementation of my word_ins function but I am not sure. I have used gdb, which showed me where the segfault is, but I can't find the error in my logic that is causing it.

Anyone see where I am going wrong?

Thank you,
Kyle

Code:

#include <stdio.h>
#include <stdlib.h>

struct word {
	const char * word;
	struct word * next_word;
};

struct conc {
	char first_ltr;
	struct conc * next_ltr;
	struct word * next_word; 
};

int conc_ins_ltr( struct conc **next, char letter) {
	struct conc * temp;
	struct conc * new;
	struct word * new_word;
	while ( *next != NULL) {
		temp = *next;
		if ( temp->first_ltr < letter) {
			next = &temp->next_ltr;
		} else {
			break;
		}
	}
	temp = *next;
	new = (struct conc *)malloc( sizeof( struct conc) );
	new_word = ( struct word *)malloc( sizeof( struct word) );
	if (  (new == NULL) || (new_word == NULL) ) { return(0); }
	new_word->next_word = NULL;
	new->first_ltr = letter;
	new->next_ltr = temp;
	new->next_word = new_word;
	*next = new;
	return(1);
}

struct conc *find_first_ltr( struct conc *conc_root, char letter) {
	struct conc * temp = conc_root;
	while ( temp != NULL ) {
		if (temp->first_ltr == letter ) {
			return( temp);
		}
		temp = temp->next_ltr;
	}
	conc_ins_ltr(&conc_root->next_ltr, letter);
	return( find_first_ltr(conc_root, letter) );
}

int word_ins( struct word **next, char * n_word) {
	struct word *temp; 	
	struct word *new; 
	temp = *next;
	next = &temp->next_word;
	temp = *next;
	new = ( struct word *)malloc( sizeof( struct word));
	if ( new == NULL ) { return(0); }
	new->word = n_word;
	new->next_word = temp;
	*next = new;
	return(1);
}

void print_conc( struct conc * conc_root) {
	struct conc * temp_conc = conc_root;
	struct word * temp_word;
	while (temp_conc != NULL) {
		printf("%c\n", temp_conc->first_ltr);
		temp_word = temp_conc->next_word;
		while ( temp_word != NULL) {
			printf("%s\n", temp_word->word);
			temp_word = temp_word->next_word;
		}
		temp_conc = temp_conc->next_ltr;
	}
}

int main( int argc, char **argv) {
	struct conc conc_lvl1;
	conc_lvl1.next_ltr = NULL;
	conc_ins_ltr( &conc_lvl1.next_ltr, 'a' );
	conc_ins_ltr( &conc_lvl1.next_ltr, 'b' );
	word_ins( &(find_first_ltr(&conc_lvl1, 'a')->next_word), "apple");
	print_conc(conc_lvl1.next_ltr);
	return(0);
}

Found it:

Code:

temp_word = temp_conc->next_word;
//should be:
temp_word = temp_conc->next_word->next_word;

Since the first value is never actually initialized.