read consecutive tabs as empty field fscanf

Question

I have a file that has certain fields separated by tabs. There will always be 12 tabs in a line, certain tabs are consecutive which indicates an empty field. I wanna use fscanf

Answer 1

I wanna use fscanf to read consecutive tabs as empty fields and store them in a structure.

Ideally, code should read a line, as with fgets() and then parse the string.

Yet staying with fscanf(), this can be done in a loop.

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The main idea is to use "%[^/t/n]" to read one token. If the next character is a '\t', then the return value will not be 1. Test for that. A width limit is wise.

Then read the separator and look for tab, end-of-line or if end-of-file/error occurred.

#define TABS_PER_LINE 12
#define TOKENS_PER_LINE (TABS_PER_LINE + 1)
#define TOKEN_SIZE 100
#define TOKEN_FMT_N "99"

int fread_tab_delimited_line(FILE *istream, int n, char token[n][TOKEN_SIZE]) {
  for (int i = 0; i < n; i++) {
    int token_count = fscanf(istream, "%" TOKEN_FMT_N "[^\t\n]", token[i]);
    if (token_count != 1) {
      token[i][0] = '\0';  // Empty token
    }
    char separator;
    int term_count = fscanf(istream, "%c", &separator);  // fgetc() makes more sense here
    // if end-of-file or end-of-line
    if (term_count != 1 || separator == '\n') {
      if (i == 0 && token_count != 1 && term_count != 1) {
        return 0;
      }
      return i + 1;
    }
    if (separator != '\t') {
      return -1;  // Token too long
    }
  }
  return -1;  // Token too many tokens found
}

Sample driving code

void test_tab_delimited_line(FILE *istream) {
  char token[TOKENS_PER_LINE][TOKEN_SIZE];
  long long line_count = 0;
  int token_count;
  while ((token_count = fread_tab_delimited_line(istream, TOKENS_PER_LINE, token)) > 0) {
    printf("Line %lld\n", ++line_count);
    for (int i = 0; i < token_count; i++) {
      printf("%d: <%s>\n", i, token[i]);
    }
  } while (token_count > 0);
  if (token_count < 0) {
    puts("Trouble reading any tokens.");
  }
}