libc-top-half/musl/src/stdio/fseek.c

   1 #include "stdio_impl.h"
   2 #include <errno.h>
   3
   4 int __fseeko_unlocked(FILE *f, off_t off, int whence)
   5 {
   6         /* Fail immediately for invalid whence argument. */
   7         if (whence != SEEK_CUR && whence != SEEK_SET && whence != SEEK_END) {
   8                 errno = EINVAL;
   9                 return -1;
  10         }
  11
  12         /* Adjust relative offset for unread data in buffer, if any. */
  13         if (whence == SEEK_CUR && f->rend) off -= f->rend - f->rpos;
  14
  15         /* Flush write buffer, and report error on failure. */
  16         if (f->wpos != f->wbase) {
  17                 f->write(f, 0, 0);
  18                 if (!f->wpos) return -1;
  19         }
  20
  21         /* Leave writing mode */
  22         f->wpos = f->wbase = f->wend = 0;
  23
  24         /* Perform the underlying seek. */
  25         if (f->seek(f, off, whence) < 0) return -1;
  26
  27         /* If seek succeeded, file is seekable and we discard read buffer. */
  28         f->rpos = f->rend = 0;
  29         f->flags &= ~F_EOF;
  30
  31         return 0;
  32 }
  33
  34 int __fseeko(FILE *f, off_t off, int whence)
  35 {
  36         int result;
  37         FLOCK(f);
  38         result = __fseeko_unlocked(f, off, whence);
  39         FUNLOCK(f);
  40         return result;
  41 }
  42
  43 int fseek(FILE *f, long off, int whence)
  44 {
  45         return __fseeko(f, off, whence);
  46 }
  47
  48 weak_alias(__fseeko, fseeko);
  49
  50 weak_alias(fseeko, fseeko64);