Segmentation Fault - in fgets () from /lib/lib.so.6

[stemby]

Hey,
i've just started studying software engineering and i am having a lot of trouble with a program i wrote for an assignment. the program is just meant to read a file line by line tokenise the line, check it against certain parameters and then print before going onto the next line.

after writing the program i got a segmentation fault, and then used gdb to see what was the problem. It compiles fine.

Gdb returned this:
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7ac22ad in fgets () from /lib/libc.so.6

the code is as follows:

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

int AR = 100;
char *item;
char line[201]="asdf";
int	a;
int isbn[11];
int first[100];
char checked[20];

int main()
{
	int i,sum,check,j,k,p;
	printf("%-13s %-15s %-10s %-20s\n\n","ISBN Code","Check Digit","Sum","Validation Message");
		
	FILE *fileisbn;
	fileisbn = fopen("isbn.txt","r");
	int e =0, d=0;

	/*while(fscanf(fileisbn,"%s",item))*/
 	while (fgets(line, 20, fileisbn))
	{item=strtok(line,"-");
	a = atoi(item);
	a=isbn[0];
	item=strtok(NULL,"");
	a = atoi(item);
	a=isbn[1];
	item=strtok(NULL,"");
	a = atoi(item);
	a=isbn[2];
	item=strtok(NULL,"");
	a = atoi(item);
	a=isbn[4];
	item=strtok(NULL,"-");
	a = atoi(item);
	a=isbn[5];
	item=strtok(NULL,"");
	a = atoi(item);
	a=isbn[6];
	item=strtok(NULL,"");
	a = atoi(item);
	a=isbn[7];
	item=strtok(NULL,"-");
	a = atoi(item);
	a=isbn[8];
	item=strtok(NULL,"\n");
	p=strcmp(item,"x");
	
	if (p=0)
		{isbn[9]=10;}
	else
		a=atoi(item);	
		a=isbn[9];
	
	
		for(i=0;i<9;i++)
			{sum+=isbn[i]*i;}
		check=sum%isbn[9];
	
	if (check=isbn[9])
		{strcpy(checked,"Validated");
		d++;}
	else
		strcpy(checked,"Error in ISBN code");


	printf("%d-",isbn[0]);
	for(j=1;j<=3;j++)	
		{printf("%d",isbn[j]);}
	printf("-");
	for(k=4;k<=8;k++)
		{printf("%d",isbn[k]);}
	if (p=0)
		{printf("-x");}
	else
	printf("-%d",isbn[9]);
	
	printf("%-15d",isbn[9]);
	printf("%-10d",sum);
	printf("%-20s\n",checked);
	e++;
	


}
	printf("Total number of ISBN codes processed = %d",e );
	printf("Total number of ISBN codes validated = %d",d);
return;
}

As i only used fgets once it is safe to assume the line in which the error is occuring.

[quzah]

You don't actually check to see that fopen was successful. For all you know you are trying to fgets from a failed fopen.


Quzah.

[itsme86]

Are you sure fileisbn is valid at the point fgets() is called? You should really check fopen()'s return value against NULL to see if the file opened successfully.