Read a line from file in C and extract the number of input

Question

I have a file input.dat. In this file, there are 3 lines:

1 2 3
5 7 10 12
8 9 14 13 15 17

I am going to read one of the three li

Answer 1

A bit cleaner version of chqrlie's answer. Started with a string as that is what the question is really about after fgets().

sscanf() won't step through the string, it always reads from the beginning.

strtol() looks for a long int in the beginning of the string, ignoring initial white-space. Gives back the address of where it stops scanning.

The manual of strtol() says that errno should be checked for any conversion error.

#include 
#include 
#include 

#define STRING_SIZE 2000

int main(void)
{
    char line[STRING_SIZE] = "5 7 10 12";

    char* start = line;
    char* end;

    int count = 0;

    while(1)
    {
        /**
         * strtol() look for long int in beginning of the string
         * Ignores beginning whitespace
         * 
         * start: where to strtol() start looking for long int
         * end: where strtol() stops scanning for long int
         */
        errno = 0; // As strol() manual says

        strtol(start, &end, 0);

        if (errno != 0)
        {
            printf("Error in strtol() conversion.\n");
            exit(0);
        }

        if (start == end) break; // Quit loop

        start = end;
        count++;
    }
    

    printf("count: %d\n", count);

    return 0;
}