help! seg fault!

[98holb]

I have written a program that reads in words from a file "carol.txt" and stores them in a linked list, keeping a count of how many times each word occurs.

When i try to run the program i get a segmentation fault. After some investigation I think it may have something to do with fopen in main().
I don't have a debugger, so I'd be really grateful if someone could take a look at the code.

Here it is, sorry it's so long!

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

typedef struct L
{
        char *word;
	    int count;
        struct L *next;
} list;


list *makenode(char *a, list *t)
{
    list *h = calloc(1, sizeof(list));
    h->word = a;
    h -> count = 1;
    h -> next = t;
    return h;
}

/* strcmp didn't work so i had to create function comparestr*/
int comparestr (char *one, char *two)
{
	int i;
	
	for (i=0; i<50; i++)
	{
		if (one[i] == two[i])
		{
		return 0;
		}
	
	}
	return 1;
}


/* shows if word already exists in the list */
list *findword(char *a, list *b)
{
     while (1)
     {
	if (b->next==NULL)
	{
		return b;
	}
	else if (comparestr(a, b->next->word)==0)
	{
		(b->next->count)++;
		return NULL;
	}
	else
	{
		return (findword(a, b->next));
	}
    }
}


char *readword(FILE *file)
{
	int n;
	char *word;
	word = calloc(50, sizeof(char));

	word[0] = tolower(fgetc(file));
	while (islower(word[0])||word[0]==EOF)
	{
		word[0] = tolower(fgetc(file));
	}

	if (word[0]==EOF)
	{
		return NULL;
	}
	
	n=1;
	word[1] = tolower(fgetc(file));
	while ((islower(word[n])||word[n]==39||word[n]==44||word[n]==96) && n<49)
	{
		n++;
		word[n]=tolower(fgetc(file));
	}

	while (!(islower(word[n])))
	{
		word[n] = 0;
		n--;
	}

	n++;
	word[n]='\0';
	return word;
}

list *makelist(FILE *file)
{
	char *word;
	list *start= makenode(NULL, NULL);
	list *temp=NULL;

	while (1)
{

	word = readword(file);
	
	if (word == NULL)
	{
		return start;
	}

	temp=findword(word, start);

	if (temp !=NULL)
	{
		temp->next = makenode(word, NULL);
	}

	if (temp==NULL)
	{
		free(word);
	}
}
}
	
list *search (char *a, list *b)
{
     while (1)
     {
	if (b->next==NULL)
	{
		return NULL;
	}
	else if (comparestr(a, b->next->word)==0)
	{
		return b->next;
	}
	else
	{
		return (search(a, b->next));
	}
    }
}

void results(list *h, char *ve)
{
	   if (h == NULL)
         {
            printf("WORD NOT FOUND \n");
	    return;
         }
            printf(" %s occurs %d times\n", ve, h->count);
}

void query (list *li)
{
	char *nu;
	printf("type the word you would like to search for \n");
	nu = readword(stdin);
	results(search(nu, li), nu);
}
	



void close(list *ha)
{
	list *g;
	list *j;

	g = ha;
	while (g->next !=NULL)
	{
		j=g->next;
		free(g->word);
		free(g);
		g=j;
	}
	free(g->word);
	free(g);
}

int main()
{
	list *start;
	FILE *file;
	char array[15];

	file = fopen( "carol.txt" , "r" );

	start = makelist(file);
	
	while (1)
	{
		printf("do you want to make a query?\n");
		
	fgets(array, 15, stdin);
	
	if (tolower(array[0])=='y')
	{
		query(start);
	}

	if (tolower(array[0])=='n')
	{
		fclose(file);
		close(start);
		return 0;
	}

	if (tolower(array[0])!='y')
	{
		printf("you have entered an incorrect answer please try again\n");
	}
	}
}

thanks a lot.

[nkhambal]

Are you sure the file you are opening exists? Is it in the current working directory?

Always check the return value of fopen. If fopen fails, "file" will be NULL, and you are trying to dereference a NULL pointer. Its a sure crash. Add a check to see that (file != NULL) and exit there if it is.

[98holb]

yes, the file definatly exists in the working directory and fopen is still returning NULL. any idea why?

[nkhambal]

Does the file have read privilege? Do you own the file? Try giving the full path instead of just filename.

[Dave_Sinkula]

yes, the file definatly exists in the working directory and fopen is still returning NULL. any idea why?

I like to use this idiom so that the system can answer that question.

   static const char filename[] = "carol.txt";
   FILE *file = fopen(filename, "r");
   if ( file != NULL )
   {
      /* do stuff */
      fclose(file);
   }
   else
   {
      perror(filename);
   }

[dwks]

This page contains all the possible reasons fopen() might fail: http://www.opengroup.org/onlinepubs/...xsh/fopen.html

Usually it fails because the file doesn't exist or you don't have adequate permissions.