* io.c (rb_io_check_writable): restrict io_seek by

  READ_DATA_PENDING because io_seek(fptr, 0, SEEK_CUR) is
  meaningful only if read buffer is not empty.
  call io_seek regardless of NEED_IO_SEEK_BETWEEN_RW.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@7404 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 2 insertions, 3 deletions

diff --git a/io.c b/io.c
index a24faf964e..cc1b583955 100644
--- a/io.c
+++ b/io.c
@@ -251,11 +251,10 @@ rb_io_check_writable(fptr)
     if (!(fptr->mode & FMODE_WRITABLE)) {
 	rb_raise(rb_eIOError, "not opened for writing");
     }
-#if NEED_IO_SEEK_BETWEEN_RW
-    if ((fptr->mode & FMODE_RBUF) && !feof(fptr->f) && !fptr->f2) {
+    if ((fptr->mode & FMODE_RBUF) && !feof(fptr->f) && !fptr->f2 &&
+        READ_DATA_PENDING(fptr->f)) {
 	io_seek(fptr, 0, SEEK_CUR);
     }
-#endif
     if (!fptr->f2) {
 	fptr->mode &= ~FMODE_RBUF;
     }