example_n_useful/utils/seekfd.c

   1 #define _FILE_OFFSET_BITS 64
   2 #include <string.h>
   3 #include <errno.h>
   4 #include <stdio.h>
   5 #include <stdlib.h>
   6 #include <sys/types.h>
   7 #include <unistd.h>
   8
   9 int main(int argc, char* argv[])
  10 {
  11     /* Arguments: fd [offset [whence]]
  12      * where
  13      * fd: file descriptor to seek
  14      * offset: number of bytes from position specified in whence
  15      * whence: one of
  16      *  SEEK_SET (==0): from start of file
  17      *  SEEK_CUR (==1): from current position
  18      *  SEEK_END (==2): from end of file
  19      */
  20     int fd;
  21     long long scan_offset = 0;
  22     off_t offset = 0;
  23     int whence = SEEK_SET;
  24     int errsv; int rv;
  25     if (argc == 1) {
  26         fprintf(stderr, "usage: seekfd fd [offset [whence]]\n");
  27         exit(1);
  28     }
  29     if (argc >= 2) {
  30         if (sscanf(argv[1], "%d", &fd) == EOF) {
  31             errsv = errno;
  32             fprintf(stderr, "%s: %s\n", argv[0], strerror(errsv));
  33             exit(1);
  34         }
  35     }
  36     if (argc >= 3) {
  37         rv = sscanf(argv[2], "%lld", &scan_offset);
  38         if (rv == EOF) {
  39             errsv = errno;
  40             fprintf(stderr, "%s: %s\n", argv[0], strerror(errsv));
  41             exit(1);
  42         }
  43         offset = (off_t) scan_offset;
  44     }
  45     if (argc >= 4) {
  46         if (sscanf(argv[3], "%d", &whence) == EOF) {
  47             errsv = errno;
  48             fprintf(stderr, "%s: %s\n", argv[0], strerror(errsv));
  49             exit(1);
  50         }
  51     }
  52
  53     if (lseek(fd, offset, whence) == (off_t) -1) {
  54         errsv = errno;
  55         fprintf(stderr, "%s: %s\n", argv[0], strerror(errsv));
  56         exit(2);
  57     }
  58
  59     return 0;
  60 }