lib/stdio/fseek.c

   1 /*
   2  * fseek.c - perform an fseek
   3  */
   4 /* $Header$ */
   5
   6 #include        <stdio.h>
   7
   8 #if     (SEEK_CUR != 1) || (SEEK_END != 2) || (SEEK_SET != 0)
   9 #error SEEK_* values are wrong
  10 #endif
  11
  12 #include        "loc_incl.h"
  13
  14 #include        <sys/types.h>
  15
  16 off_t _lseek(int fildes, off_t offset, int whence);
  17
  18 int
  19 fseek(FILE *stream, long int offset, int whence)
  20 {
  21         int adjust = 0;
  22         long pos;
  23
  24         stream->_flags &= ~(_IOEOF | _IOERR);
  25         /* Clear both the end of file and error flags */
  26
  27         if (io_testflag(stream, _IOREADING)) {
  28                 if (whence == SEEK_CUR
  29                     && stream->_buf
  30                     && !io_testflag(stream,_IONBF))
  31                         adjust = stream->_count;
  32                 stream->_count = 0;
  33         } else if (io_testflag(stream,_IOWRITING)) {
  34                 fflush(stream);
  35         } else  /* neither reading nor writing. The buffer must be empty */
  36                 /* EMPTY */ ;
  37
  38         pos = _lseek(fileno(stream), offset - adjust, whence);
  39         if (io_testflag(stream, _IOREAD) && io_testflag(stream, _IOWRITE))
  40                 stream->_flags &= ~(_IOREADING | _IOWRITING);
  41
  42         stream->_ptr = stream->_buf;
  43         return ((pos == -1) ? -1 : 0);
  44 }