Order a book.txt alphabetically with Lists in C

book-ordering-list.c

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

typedef struct node* link;
struct node {
	char* item;
	link next;
	link prev;
};

void printerr(char* s) {
	printf("%s", s);
	exit(EXIT_FAILURE);
}

link new_node(char* word) {
	link node = malloc(sizeof(struct node));
	if (node==NULL) printerr("Malloc failed");
	node->item = malloc((strlen(word)+1)*sizeof(char));
	if (node->item==NULL) printerr("Malloc failed");
	node->next = NULL;
	node->prev = NULL;
	strcpy(node->item, word);
	return node;
}

link insert_node(link head, link node) {
	if (head==NULL) return node;
	link t = head;
	for(;t->next!=NULL;t=t->next);
	node->prev = t;
	t->next = node;
	return head;
}

void print_n(link node) {
	if (node->prev!=NULL && node->next!=NULL) 
		printf("%s <- %s -> %s", node->prev->item, node->item, node->next->item);
	else if (node->prev==NULL)
		printf("NULL <- %s -> %s", node->item, node->next->item);
	else if (node->next==NULL)
		printf("%s <- %s -> NULL", node->prev->item, node->item);
	printf("\n");
}

void node_swap(link a, link b) {
	char* t = malloc((strlen(a->item)+1)*sizeof(char));
	if (t==NULL) printerr("Malloc failed");
	strcpy(t, a->item);
	strcpy(a->item, b->item);
	strcpy(b->item, t);
	free(t);
}

void print_l(link head) {
	if (head==NULL) return;
	printf("%s\n", head->item);
	print_l(head->next);
}

void insertion_sort(link head) {
	link t = head;
	printf("Putting sentinel..\n");
	for (;t->next!=NULL;t=t->next);
	for (;t->prev!=NULL;t=t->prev)
		if (strcmp(t->item, t->prev->item)<0)
			node_swap(t, t->prev);
	int i=0;
	printf("Isort phases: ");
	for (t=head->next->next;t->next!=NULL;t=t->next) {
		printf("%d ", i++);
		link j = t;
		link v = new_node(t->item);
		while (j->prev!=NULL && strcmp(v->item, j->prev->item)<0) {
			strcpy(j->item, j->prev->item);
			j = j->prev;
		}
		strcpy(j->item, v->item);
		free(v);
	}
}

int main (int argc, const char * argv[]) {
	
	if (argc<2) printerr("Arg missing");
	
	FILE* fp = NULL;
	fp = fopen(argv[1], "r");
	if (fp==NULL) printerr("Fopen failed");
	link head = NULL;
	char* tword = malloc(sizeof(char)*20);
	if (tword==NULL) printerr("Malloc failed");
	printf("Reading words..\n");
	while (!feof(fp)) {
		if (fscanf(fp, "%s", tword)!=EOF)
			head = insert_node(head, new_node(tword));
	}
	fclose(fp);
	free(tword);
	
	printf("Calling Isort\n");
	insertion_sort(head);
	
	fp = NULL;
	char* outfile = malloc((strlen(argv[1])+1+6)*sizeof(char));
	strcpy(outfile, argv[1]);
	strcat(outfile, ".order");
	fp = fopen(outfile, "w");
	if (fp==NULL) printerr("Fopen failed");
	link t = head;
	for (;t->next!=NULL;t=t->next) fprintf(fp, "%s ", t->item);
	fclose(fp);
	
}