CS471/571 - Operating Systems

Displaying ./code/Pipes/seek.c

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

/**
 * Usage: seek <filename> <offset> [<length>]
 * length = 256 if omitted
 */

int main(int argc, char *argv[])
{
  if (argc < 3) {
    fprintf(stderr,"Usage: seek <filename> <offset> [<length>]\n");
    return 1;
  }
  char *filename = argv[1];
  int offset = atoi(argv[2]);
  int length = argc > 3? atoi(argv[3]) : 256;

  int fd = open(filename, O_RDONLY);
  if (fd < 0) {
    perror("open");
    return 1;
  }

  if (lseek(fd, offset, SEEK_SET) < 0) {
    perror("lseek");
    return 1;
  }

  char *buf = malloc(sizeof(char) * (length+1));

  int r = read(fd, buf, length);
  if (r < 0) {
    perror("read");
    return 1;
  }
  write(STDOUT_FILENO, buf, r);

  close(fd);
  return 0;
}