Reading "unfixed" number of integers after a semicolon from a file in c

Question

What is the best way to use sscanf or any other command to read from a file after a semicolon, for example if my file has 5: 4 5 6 7. how can I store the values after the colon in an array. Also the number of integers may vary after the semicolon ie in the example I have given above they are 4 but they can be 5 3 or 10. What is the best way to handle this.

Answer 1

All the numbers being on one line makes it easy. Basically, you want to read a line using fgets() , and split it up into individual numbers by splitting at whitespace, and convert each of those words to an integer. There's a bunch of ways to do that, but I like taking advantage of how strtol() will record where the end of the number it converts is to combine the two steps in one. Something like:

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

int main(void) {
  char line[] = "5: 4 5 6 7";
  char *curr = line;

  while (*curr) {
    char *end;
    int n = strtol(curr, &end, 10);
    if (curr == end) {
       fputs("Found something not a number!\n", stderr);
       return EXIT_FAILURE;
    } else if (*end == ':') {
      printf("Line header: %d\n", n);
      end++;
    } else {
      printf("Number %d\n", n);
    }
    curr = end;
  }
  return 0;
}

Compiling and running this produces:

Line header: 5
Number 4
Number 5
Number 6
Number 7

You'd of course store the numbers in an array instead of just printing them out, but that should give you the general idea.