Ignoring comment lines marked with "%" using open() in C on linux

Question

I am trying to read a file which has the first two lines marked with a "%" as the first character. I need to ignore these two lines, and then read 4 separate integer variables, separated by an unknown amount of white space. This then repeats for each line until EOF. I am attempting to use open() from fcntl.h.

Is there a way to begin reading after 2 full lines, and then separate the 4 values with white space between them into 4 integer variables?

This is a sample file:

% Input file
% number    time           time2         priority
0           10              4             2
1            8              2             1
2           12              0             5
3            2              4             4

Answer 1

When doing I/O using open() (not library buffered like fopen()), you want to read all the data into RAM, and then process it.

  int fd = open("file", O_RDONLY);
  if (fd < 0) {
    error();
  }
  long size = lseek(fd, 0, 2);
  lseek(fd, 0, 0);
  char *data = malloc(size + 2);
  read(fd, data, size);
  data[size] = 0;
  data[size+1] = 0;
  close(fd);

Now, parse the file:

  char *ptr = data;
  while (*ptr) {
    char *end = strchr(ptr, '\n');
    if (!end) {
      end = ptr + strlen(ptr);
    }
    *end = 0;
    if (*ptr != '%') { /* a valid line */
      int a, b, c, d;
      if (4 != sscanf(ptr, " %d %d %d %d", &a, &b, &c, &d)) {
        error();
      }
      /* do something with the values */
    }
    ptr = end + 1;
  }