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stdio: don't require ignore_value around fwrite

From: Paul Eggert
Subject: stdio: don't require ignore_value around fwrite
Date: Sun, 20 Mar 2011 12:18:27 -0700
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv: Gecko/20110223 Thunderbird/3.1.8

I've tried out the following proposed patch with Emacs.
However, I'm no expert with C++ and the C++ parts of it
need another pair of eyes to look at.

A similar fix is needed for fwrite_unlocked but I figured
one function at a time.


diff --git a/ChangeLog b/ChangeLog
index 1b42d3c..a1ff2b2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,32 @@
+2011-03-19  Paul Eggert  <address@hidden>
+       stdio: don't require ignore_value around fwrite
+       This patch works around libc bug 11959
+       <http://sources.redhat.com/bugzilla/show_bug.cgi?id=11959>.
+       Without this patch, applications must often write
+       ignore_value (fwrite (...)) even though the ignore_value is
+       not helpful here.  It's common to write many objects, using
+       fwrite/printf/etc., and then use ferror to detect output error.
+       I considered making this patch optional, but decided against it,
+       because libc is obviously being inconsistent here: there is no
+       reason libc should insist that user code must inspect fwrite
+       return's value without also insisting that it inspect printf's,
+       putchar's, etc.  If user code wants to have a strict style where
+       all these functions' values are checked (so that ferror need not
+       be checked), we could add support for that style in a new gnulib
+       module, but in the meantime it's better to be consistent and to
+       support common usage.
+       * lib/stdio.in.h (rpl_fwrite): Define this wrapper around fwrite,
+       to work around libc bug 11959, if __USE_FORTIFY_LEVEL indicates
+       that we are compiling in checking mode, and if not already
+       wrapping fwrite for some other reason.
+       (GNULIB_inline_rpl_fwrite): New macro, defined to 1 if this new
+       wrapper is in use.
+       (fwrite): Adjust to the possibility that this new wrapper is in use.
 2011-03-19  Jim Meyering  <address@hidden>
        maint.mk: fix po-file syntax-check rule
diff --git a/lib/stdio.in.h b/lib/stdio.in.h
index b5083d1..3ceb98a 100644
--- a/lib/stdio.in.h
+++ b/lib/stdio.in.h
@@ -481,22 +481,39 @@ _GL_WARN_ON_USE (ftell, "ftell cannot handle files larger 
than 4 GB "
                  "use ftello function for handling of large files");
+#if (0 < __USE_FORTIFY_LEVEL                                            \
+     && ! (@GNULIB_FWRITE@                                              \
+# define GNULIB_inline_rpl_fwrite 1
+static inline size_t _GL_ARG_NONNULL ((1, 4))
+rpl_fwrite (const void *ptr, size_t s, size_t n, FILE *stream)
+  size_t r = fwrite (ptr, s, n, stream);
+  (void) r;
+  return r;
+#if @GNULIB_FWRITE@ || GNULIB_inline_rpl_fwrite
+      || GNULIB_inline_rpl_fwrite)
 #  if !(defined __cplusplus && defined GNULIB_NAMESPACE)
 #   undef fwrite
 #   define fwrite rpl_fwrite
 #  endif
+#  if !GNULIB_inline_rpl_fwrite
 _GL_FUNCDECL_RPL (fwrite, size_t,
                   (const void *ptr, size_t s, size_t n, FILE *stream)
                   _GL_ARG_NONNULL ((1, 4)));
+#  endif
 _GL_CXXALIAS_RPL (fwrite, size_t,
                   (const void *ptr, size_t s, size_t n, FILE *stream));
 # else
 _GL_CXXALIAS_SYS (fwrite, size_t,
                   (const void *ptr, size_t s, size_t n, FILE *stream));
 # endif

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