Bruno Haible <bruno <at> clisp.org> writes:
>
> Eric Blake wrote:
> > I'm checking this in now, since I needed it to fix fflush on mingw (see
> > next email).
>
> Thanks. This was hard to understand, so I'm adding some comments.
I'm improving them somewhat, as well as the documentation for freading/fwriting.
2007-04-27 Eric Blake <[EMAIL PROTECTED]>
* lib/freading.h: Improve comments.
* lib/fwriting.h: Likewise.
* lib/fflush.c: Likewise.
Index: lib/fflush.c
===================================================================
RCS file: /sources/gnulib/gnulib/lib/fflush.c,v
retrieving revision 1.7
diff -u -r1.7 fflush.c
--- lib/fflush.c 27 Apr 2007 10:56:51 -0000 1.7
+++ lib/fflush.c 27 Apr 2007 18:02:32 -0000
@@ -46,11 +46,13 @@
recent operation was not input", POSIX and C99 requires that fflush
writes out any buffered data, and all implementations do this.
- When stream is, however, an input stream or an update stream in which
- the most recent operation was input, POSIX and C99 specify nothing.
- mingw, in particular, drops the input buffer, leaving the file descriptor
- positioned at the end of the input buffer. I.e. ftell (stream) is lost.
- We don't want to call the implementation's fflush in this case.
+ When stream is, however, an input stream or an update stream in
+ which the most recent operation was input, C99 specifies nothing,
+ and POSIX only specifies behavior if the stream is seekable.
+ mingw, in particular, drops the input buffer, leaving the file
+ descriptor positioned at the end of the input buffer. I.e. ftell
+ (stream) is lost. We don't want to call the implementation's
+ fflush in this case.
We test ! freading (stream) here, rather than fwriting (stream), because
what we need to know is whether the stream holds a "read buffer", and on
@@ -59,7 +61,8 @@
return fflush (stream);
/* POSIX does not specify fflush behavior for non-seekable input
- streams. */
+ streams. Some implementations purge unread data, some return
+ EBADF, some do nothing. */
pos = ftello (stream);
if (pos == -1)
{
@@ -79,7 +82,7 @@
return EOF;
/* After a successful lseek, update the file descriptor's position cache
in the stream. */
-#if defined __sferror /* FreeBSD, NetBSD, OpenBSD, MacOS X,
Cygwin */
+#if defined __sferror /* FreeBSD, NetBSD, OpenBSD, MacOS X, Cygwin */
stream->_offset = pos;
stream->_flags |= __SOFF;
#endif
Index: lib/freading.h
===================================================================
RCS file: /sources/gnulib/gnulib/lib/freading.h,v
retrieving revision 1.1
diff -u -r1.1 freading.h
--- lib/freading.h 26 Apr 2007 13:16:50 -0000 1.1
+++ lib/freading.h 27 Apr 2007 18:02:32 -0000
@@ -18,10 +18,17 @@
#include <stdbool.h>
#include <stdio.h>
-/* Return true if the stream STREAM is opened read-only, or if the last
- operation on the stream was a read operation. Return false if the stream
- supports writing and the last operation on it was a write operation or
- there was no such operation.
+/* Return true if the stream STREAM is opened read-only, or if the
+ last operation on the stream was a read operation. Return false if
+ the stream is opened write-only or append-only, or if it supports
+ writing and there is no current read operation (such as fputc).
+
+ freading and fwriting will never both be true. If STREAM supports
+ both reads and writes, then both freading and fwriting might be
+ false when the stream is first opened, after repositioning (such as
+ fseek, fsetpos, or rewind), after read encounters EOF, or after
+ fflush, depending on the underlying implementation.
+
STREAM must not be wide-character oriented. */
#if HAVE___FREADING && !defined __GLIBC__ /* Solaris >= 7, not glibc >= 2.2 */
Index: lib/fwriting.h
===================================================================
RCS file: /sources/gnulib/gnulib/lib/fwriting.h,v
retrieving revision 1.1
diff -u -r1.1 fwriting.h
--- lib/fwriting.h 26 Apr 2007 13:16:50 -0000 1.1
+++ lib/fwriting.h 27 Apr 2007 18:02:32 -0000
@@ -18,10 +18,18 @@
#include <stdbool.h>
#include <stdio.h>
-/* Return true if the stream STREAM is opened write-only or append-only, or
- if the last operation on the stream was a write operation. Return false
- if the stream supports reading and the last operation on it was a read
- operation or there was no such operation.
+/* Return true if the stream STREAM is opened write-only or
+ append-only, or if the last operation on the stream was a write
+ operation. Return false if the stream is opened read-only, or if
+ it supports reading and there is no current write operation (such
+ as fputc).
+
+ freading and fwriting will never both be true. If STREAM supports
+ both reads and writes, then both freading and fwriting might be
+ false when the stream is first opened, after repositioning (such as
+ fseek, fsetpos, or rewind), after read encounters EOF, or after
+ fflush, depending on the underlying implementation.
+
STREAM must not be wide-character oriented. */
#if HAVE___FWRITING /* glibc >= 2.2, Solaris >= 7 */
