Re: fflush after ungetc

[Eric Blake]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

According to Bruno Haible on 3/29/2008 5:59 AM:
| At this point, waiting for a resolution by the Austin Group (Geoff Clare's
| mail is an important opinion, but not yet a decision), I prefer to not
change
| the code, but just disable the test.

Thanks.  I'm committing this followup, which fixes a typo, and makes the
test-freadseek test pass on cygwin (at first I thought it was another
instance of ungetc undefined behavior, but on closer inspection, your
definition of freadseek is well-defined without any reliance on fflush -
the real bug was that freadseek was incrementing the in-memory pointer
beyond the bounds of the ungetc buffer).

Maybe we should add an even more fundamental test for ftell behavior after
both types of ungetc?

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.8 (Cygwin)
Comment: Public key at home.comcast.net/~ericblake/eblake.gpg
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iEYEARECAAYFAkfuQXMACgkQ84KuGfSFAYDTRgCeIFlnFVRnvHSBRY6Eb2st4gWz
ejUAn0+s97w0gInDkMfMbVF1s/Fazg9U
=/evQ
-----END PGP SIGNATURE-----

>From 16e403776065fa5173be83ccf84004b287b72dc7 Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Sat, 29 Mar 2008 07:15:50 -0600
Subject: [PATCH] Pass test-freadseek on cygwin.

* modules/freadseek (Depends-on): Use freadptr, not freadseek.
* lib/freadseek.c (freadseek): Don't increment beyond bounds of
ungetc buffer.
* tests/test-fflush2.c (main): Fix typo.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog            |    8 ++++++++
 lib/freadseek.c      |    4 ++--
 modules/freadseek    |    2 +-
 tests/test-fflush2.c |    2 +-
 4 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index bee33a2..5b5933c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2008-03-29  Eric Blake  <address@hidden>
+
+       Pass test-freadseek on cygwin.
+       * modules/freadseek (Depends-on): Use freadptr, not freadseek.
+       * lib/freadseek.c (freadseek): Don't increment beyond bounds of
+       ungetc buffer.
+       * tests/test-fflush2.c (main): Fix typo.
+
 2008-03-29  Bruno Haible  <address@hidden>
 
        * tests/test-fflush2.c (main): Temporarily disable the contents of
diff --git a/lib/freadseek.c b/lib/freadseek.c
index b3f2b18..37aeab7 100644
--- a/lib/freadseek.c
+++ b/lib/freadseek.c
@@ -22,7 +22,7 @@
 #include <stdlib.h>
 #include <unistd.h>
 
-#include "freadahead.h"
+#include "freadptr.h"
 
 int
 freadseek (FILE *fp, size_t offset)
@@ -34,7 +34,7 @@ freadseek (FILE *fp, size_t offset)
     return 0;
 
   /* Increment the in-memory pointer.  This is very cheap (no system calls).  
*/
-  buffered = freadahead (fp);
+  freadptr (fp, &buffered);
   if (buffered > 0)
     {
       size_t increment = (buffered < offset ? buffered : offset);
diff --git a/modules/freadseek b/modules/freadseek
index ce19eda..c9a8555 100644
--- a/modules/freadseek
+++ b/modules/freadseek
@@ -6,7 +6,7 @@ lib/freadseek.h
 lib/freadseek.c
 
 Depends-on:
-freadahead
+freadptr
 lseek
 
 configure.ac:
diff --git a/tests/test-fflush2.c b/tests/test-fflush2.c
index 884b555..0b6d6c9 100644
--- a/tests/test-fflush2.c
+++ b/tests/test-fflush2.c
@@ -54,7 +54,7 @@ main (int argc, char **argv)
      The Austin Group has not yet decided how this should behave.  */
 #endif
 #if 0
-  /* Check fflush after a non-backup ungetc() call.  This is case 1 in terms of
+  /* Check fflush after a non-backup ungetc() call.  This is case 2 in terms of
      <http://lists.gnu.org/archive/html/bug-gnulib/2008-03/msg00131.html>.
      The Austin Group has not yet decided how this should behave.  */
   /* Check that fflush after a non-backup ungetc() call discards the ungetc
-- 
1.5.4