Percent sign as format delimiter in fscanf - c

Question

I am working on this piece of code that reads a file with records delimited by percent signs (%) and then saves the values in a node struct. The input is as follows:
2%c1%d3%33445.000000%2016%4%11
1%c2%d2%234.500000%2016%4%11
0%c1%d1%123.400000%2016%4%11
Each line will be a node containing the data separated by the percent signs. I am using fscanf to read the formatted input and save the values in the specific variables. It works well if the delimiter is any character but '%'.
I tried escaping the percent sign by doing '%%' but it won't work and fscanf returns -1. I have looked everywhere for a way of doing this, but can't find anything. Any help would be greatly appreciated. The following is a snippet from by code.
int recordID;
char category[255];
char detail[255];
float amount;
int year;
int month;
int day;
while(fscanf(pFile, "%d%%%s%%%s%%%f%%%d%%%d%%%d", &recordID, category, detail, &amount, &year, &month, &day) == 7) {
struct node* p = (struct node*) malloc(sizeof(struct node));
p->recordID = recordID;
copy_array(category, p->category, 255);
copy_array(detail, p->detail, 255);
p->amount = amount;
p->year = year;
p->month = month;
p->day = day;
add_node(p);
}
The pFile is the file containing the input specified above.
Thank you!

Answer 1

The problem is that %s reads a string, and you're not telling it to stop at the delimiter, so it gobbles up the % and everything past it. Use %[^%] instead of %s:
fscanf(pFile, "%d%%%[^%]%%%[^%]%%%f%%%d%%%d%%%d", ...
If you've never seen the scanf specifier %[, it works like this: %[abc] scans any combination of a's, b's, and c's. %[^abc] scans any string not containing an a, b, or c. You can also use ranges, like %[0-9]. Otherwise it's mostly like %s, writing to a char * destination buffer.
(As an aside, whoever chose % as a delimiter should be shot. I changed all the %'s to |'s, both in your code and your data file, so I could debug it without losing my mind, and then I changed them all back to % at the end, after I got it working.)
Addendum: John Bollinger is absolutely right, you need to worry about buffer overflow, also, as his solution shows.

Answer 2

[f]scanf() does not do pattern matching the way you hoped. In particular, the %s field descriptor matches a whitespace-delimited string, whereas you need to match a string delimited by '%' characters. You might have gotten a clue about this if you had examined the actual scanf() return value (but good on you for at least comparing it with the one you expected!).
You can match a string of characters from a given set via the %[ field descriptor, as #SteveSummit explained in his answer. Moreover, it is a good idea to specify maximum field widths in your format, so as to avoid overrunning the bounds of your arrays. That would be particularly effective with the format you are scanning, as an overlength input field for either of your strings will cause a matching failure to occur with the subsequent delimiter:
fscanf(pFile, "%d%%%254[^%]%%%254[^%]%%%f%%%d%%%d%%%d", &recordID, category,
detail, &amount, &year, &month, &day)