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I'm currently getting a run-time check failure #2 - stack around the variable city was corrupted. The input file that is read is formatted like so:

 Betty, 12 Main Street, North Elmo, NC 29801, 2000.20 Joe, 16 Maple Blvd., Stumptown, GA, 33125, 4000.40 Frank, 100 Avent Ferry, Raleigh, NC 27606, -3000.30

How can I fix this error?

int main(int argc, char *argv[]) { int c, i, zip; FILE *fp; char name[20], address[50], city[19], state[3]; float balance; for (i = 1; i < argc; i++) { fp = fopen(argv[i], "r"); if (fp == NULL) { fprintf(stderr, "cat: can't open %s\n", argv[i]); continue; } while ((c = getc(fp)) != EOF) { fscanf(fp, "%s%s%s%s%d%f", &name, &address, &city, &state, &zip, &balance); } printf("%s%s%s%s%d%f\n", name, address, city, state, zip, balance); fclose(fp); } return 0; }

Update:

Thanks for all of the help thus far. What I have done now is I have created a struct with each person in the struct containing a name, address, and balance. I just changed the previous statements to pass variables to a struct person p and then created an insert() method that inserts p into a struct person list.

while (fgets(line, sizeof(line), fp) != NULL) { p = malloc(sizeof(struct person)); sscanf(line, "%19[^,], %49[^,], %18[^,], %2[^ ] %d, %lf\n", p->name, p->address, p->city, p->state, &p->zip, &p->balance); printf("got [%s], [%s], [%s], [%s], [%d] and [%9.2f].\n", p->name, p->address, p->city, p->state, p->zip, p->balance); insert(p); }

I am trying to insert person into the list in alphabetical order and tried doing this by using strcmp. Upon running my program with this method, it hangs and stops execution at the first insert. Looking for help on where I went wrong on my insert() method.

void insert(struct person *p) { struct person *cur, *prev; int result = 0; for (cur = list, prev = NULL, result = strcmp(p->name, cur->name); cur != NULL && result > 0; prev = cur, cur = cur->next, result = strcmp(p->name, cur->name)); if (cur != NULL && result == 0) { printf("-------------------------\n" "DUPLICATE RECORD: %s\n" "-------------------------\n", p->name); free(p); return; } p->next = cur; if (prev == NULL) { list = p; } else { prev->next = p; } }

I tested this method out without the strcmp(). I just compared with p->name > cur->name and it was able to insert and print out the list just fine with my print() method. The only problem was the persons were not sorted alphabetically, so I went back and tried to implement strcmp().

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  • I don't know about the stack, but your fscanf conversion specification (after the corrections suggested by unapersson) applied to the input you provide results in name getting assigned with "Betty,"; address gets "12"; city gets "Main"; state gets "Street,"; zip and balance get indeterminate values and the return value is 4. Consider parsing the input with something other than scanf(). Commented Apr 27, 2011 at 22:12
  • Semi off topic: Zip codes are not integers, they're strings that just happen to contain integers (and sometimes a hyphen). Treating a zip code as an integer will cause problems when you lose the leading zeros or forget the a leading zero usually indicates octal. Commented Apr 27, 2011 at 22:19
  • @mu is too short thanks, but for this exercise we were told to treat it as an int Commented Apr 27, 2011 at 22:28

2 Answers 2

Reset to default
4

This:

fscanf(fp, "%s%s%s%s%d%f", &name, &address, &city, &state, &zip, &balance);

should be:

fscanf(fp, "%s%s%s%s%d%f", name, address, city, state, &zip, &balance);
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7 Comments

+1 ... or even better if (fscanf(fp, "%s%s%s%s%d%f", name, address, city, state, &zip, &balance) != 6) /* error */;
Hmm, that still didn't fix the run-time check failure #2 - stack around the variable city was corrupted. The text file that I am reading is formatted like so: Betty, 12 Main Street, North Elmo, NC 29801, 2000.20 Joe, 16 Maple Blvd., Stumptown, GA, 33125, 4000.40 Frank, 100 Avent Ferry, Raleigh, NC 27606, -3000.30
Thanks for the quick response. What should I use to read then?
@raphnguyen Frankly, to do it properly (handle commas embedded in data, for example) you need to write a parser, which is not totally trivial.
@unapersson Seems out of the realm of a beginning C Programming class. There's no other way to go about this with fscanf() or other commands?
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I guess your stack problem comes from trying to put more characters into state than it can hold.

You defined state as capable of holding 3 characters: 2 regular characters and 1 null terminator. Your fscanf statement when presented with the example input, tries to write 8 characters (7 regular and 1 null terminator) in that space for 3 characters.

This invokes what is called undefined behaviour. One way undefined behaviour can manifest itself is by corrupting variables.

Edit

To limit scanf to a fixed number of characters, use the maximum field width in the conversion specification:

char buf[42]; scanf("%41s", buf); /* reads at most 41 non whitespace characters to `buf` ** and appends a null terminator, ** for a maximum total of 42 characters */
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13 Comments

Thanks for explaining the stack error. I'm kind of confused about which way to go about this now since the text file is CSV and there doesn't seem to be an easy method. Would you suggest fgets() and tokenizing as well?
My suggestion is to write your own parser (it's not that difficult!). If you have well-behaved input with no embedded commas or optional quotes (your example isn't, as it has GA, 33125 in the 2nd line) you can try using the "%[" conversion specificer in scanf: if (scanf("%19[^,], %49[^,], %18[^,], %2[^ ]%d,%f", ...) != 6) /* error */;
@pmg Thanks, but I'm not entirely sure how parsers work. Is this syntax incorrect? fscanf(fp, "%s[^,]%s[^,]%s[^,]%s[^ ]%d%f", name, address, city, state, &zip, &balance); I'm not sure I understand your scanf if != 6 statement.
No, your syntax is incorrect. Use only one of %s or %[. %s reads non-whitespace characters, %[ reads a group of characters specified between the [ and a corresponding ]. Your format (%s[^,]) read non-whitespace characters followed by the constants '[', '^', ',', and ']'. Just replace the ... with the proper variables and hope the if will work :)
@pmg Thanks! I revised my code like so and added a print statement to test out printing the name: while ((c = getc(fp)) != EOF) { fscanf(fp, "%19[^,], %49[^,], %18[^,], %2[^ ], %d, %f", name, address, city, state, &zip, &balance); printf("%s\n", name); } The results are: etty 29801 mptown 0.40 Frank 27606 Press any key to continue . . . How do you go about entering a return in these comments? My comments are so much harder to read than yours.
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