(C) parsing std in into a linked list, infinite loop - c

Question

For some reason the code keeps segfaulting after the first printf at the for loop near the end. It doesnt print the 2nd printf at all, can someone point me in the right direction? I think it has to do with a problem in memory
struct node{
char *fullString;
char fileName[1024];
int lineNumber;
char filler[1024];
struct node *next;
};
int main (int argc, char *argv[])
{
char tmpstring[1024];
/* This won't change, or we would lose the list in memory */
struct node *head = NULL;
//tail
struct node *tail = NULL;
/* This will point to each node as it traverses the list */
struct node *ptr, *newnode;
while (fgets(tmpstring, 1024, stdin) == tmpstring)
{
if ((newnode = (struct node *)malloc(sizeof(struct node))) == NULL) {
fprintf(stderr,"mklist: malloc failure for newnode\n");
exit(1);
}
if ((newnode->fullString = malloc(strlen(tmpstring)+1)) == NULL) {
fprintf(stderr,"mklist: malloc failure for newnode->str\n");
exit(1);
}
if (strncpy(newnode->fullString, tmpstring, strlen(tmpstring)+1) != newnode->fullString) {
fprintf(stderr,"mklist: string copy problem\n");
exit(1);
}
strcpy(newnode->fullString, tmpstring);
newnode->next = NULL;
// if (3 != scanf(tmpstring, "%255s:%d:%255s", newnode->fileName, &newnode->lineNumber, newnode->filler))
// abort();
if (tail == NULL)
head = tail = newnode;
else {
tail->next = newnode;
tail = newnode;
}
}
// Now print the list, element by element.
for (ptr = head; ptr != NULL; ptr = ptr->next)
printf("%s\n", ptr->fullString);
printf("%s:%d:%s\n", ptr->fileName, ptr->lineNumber, ptr->filler);
}

Answer 1

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#define MAX_LINE_SIZE 1024
struct node
{
char fullString[MAX_LINE_SIZE];
char fileName[MAX_LINE_SIZE];
int lineNumber;
char filler[MAX_LINE_SIZE];
struct node *next;
};
int main (int argc, char **argv)
{
char tmpstring[MAX_LINE_SIZE];
struct node *head = NULL;
struct node *tail = NULL;
struct node *ptr, *newnode;
while (fgets(tmpstring, MAX_LINE_SIZE, stdin))
{
size_t len = strlen(tmpstring);
char *cptr = tmpstring, *eptr;
if (0 == len || tmpstring[len - 1] != '\n')
assert(0), abort(); /* NOTE: will abort on too long lines and if EOF occurs mid-line */
if (NULL == (newnode = calloc(1, sizeof(struct node))))
assert(0), abort();
strcpy(newnode->fullString, tmpstring);
newnode->lineNumber = -1;
newnode->next = NULL;
if (NULL == (eptr = strchr(cptr, ':')))
assert(0), abort();
*eptr = '\0';
if (1 != sscanf(cptr, "%255s", newnode->fileName))
assert(0), abort();
cptr = eptr + 1;
if (NULL == (eptr = strchr(cptr, ':')))
assert(0), abort();
*eptr = '\0';
if (1 != sscanf(cptr, "%d", &newnode->lineNumber))
assert(0), abort();
cptr = eptr + 1;
strcpy(newnode->filler, cptr);
if (tail == NULL)
head = tail = newnode;
else {
tail->next = newnode;
tail = newnode;
}
}
for (ptr = head; ptr != NULL; ptr = ptr->next)
printf("%s:%d:%s", ptr->fileName, ptr->lineNumber, ptr->filler);
return 0;
}
Add some better error handling and that's probably what you were after -- so long as your input doesn't have lines longer than MAX_LINE_SIZE-1 characters.