Thread: C programming Seg fault help

This is my program to read a file & print the lines out,
since im not familiar with link list, i got a seg fault from this.
Anyone can help me out,thx?

Code:

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

typedef struct Node {
     char   line[1000];
     struct Node *next;
} NodeT;

int main(int argc, char **argv) {
   

   char line [1000];
   FILE *fp;
   NodeT *s, *head;
   head = s;

   if(argv[1] != NULL){   
      if((fp = fopen(argv[1],"r")) != NULL) {
         while (fgets(s->line, 1000, fp) != NULL) {
         printf("%s" ,line);
         s = s->next;
         }
         s->next = NULL;
      }
   }
   free(s);
   free(head);

   head = NULL;
   s = NULL;

return 0;
}

You need to malloc() memory for `s' - at the moment, `s' and `head' both point to some unknown location.

i did put them but forgot to post them ;P i free them at the end....but after i malloc those two, im still getting seg fault.

NodeT *s = malloc(sizeof(NodeT* ));
NodeT *head = malloc(sizeof(NodeT* ));

This is what i got by now

Code:

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

typedef struct Node {
     char   line[1000];
     struct Node *next;
} NodeT;

int main(int argc, char **argv) {
   
	
   char line [1000];
   FILE *fp;
   NodeT *s = malloc(sizeof(NodeT* ));
   NodeT *head = malloc(sizeof(NodeT* ));

   if(argv[1] != NULL){   
      if((fp = fopen(argv[1],"r")) != NULL) {
         while (fgets(s->line, 1000, fp) != NULL) {
         printf("%s" ,line);
         s = s->next;
         }
         s->next = NULL;
      }
   }
   free(s);
   free(head);

   head = NULL;
   s = NULL;

return 0;
}

Code:

   if(argv[1] != NULL){   
      if((fp = fopen(argv[1],"r")) != NULL) {
         while (fgets(line, 1000, fp) != NULL) {
				s = malloc(sizeof(NodeT*));
				strcpy(s->line,line);
				s = s->next;
         }
         s->next = NULL;
      }
   }

i guess assume that's what you want me to do.
but still seg fault ;(
am i doing something wrong in other line?

I'm not quite getting it, say s is a pointer that will go through every nodes in the list, should I do "s = s -> next" to move pointer s to the next node?

oh wait..the problem occur after the loop, thx a lot for ur help!

Originally Posted by vince3214

I'm not quite getting it, say s is a pointer that will go through every nodes in the list, should I do "s = s -> next" to move pointer s to the next node?

Code:

				s = malloc(sizeof(NodeT*));
				strcpy(s->line,line);

But after those two lines, what is the value of s->next? Hint: You have not set it yet, so it is undefined or indeterminate.

should I initialize ever s->next = NULL then give them value in the loop?

*every