Re: attribute warn_unused_result

[Paul Eggert]

On 02/03/11 10:53, Stefan Monnier wrote:

> So, for each such case, we should think about it and if we indeed want
> to ignore the return value, we should put an explicit cast to that
> effect (which should hopefully be understood by gcc to silence the
> warning).

Gnulib's ignore-value module is designed for that.  I installed
the following: it suppresses the first warning in Eli's list that really
ought to be suppressed.  We can suppress the others as they
come up.  (I'm omitting auto-regenerated changes in this email.)


=== modified file 'ChangeLog'
--- ChangeLog   2011-01-31 23:54:50 +0000
+++ ChangeLog   2011-02-03 19:26:58 +0000
@@ -1,3 +1,9 @@
+2011-02-03  Paul Eggert  <address@hidden>
+
+       allow C code to suppress warnings about ignored return values
+       * Makefile.in (GNULIB_MODULES): Add ignore-value.
+       * configure, lib/Makefile.in, lib/gnulib.mk, m4/gl-comp.m4: Regenerate.
+
 2011-01-31  Chong Yidong  <address@hidden>
 
        * configure.in: Test existence of xaw3d library, not just the

=== modified file 'Makefile.in'
--- Makefile.in 2011-01-30 23:34:18 +0000
+++ Makefile.in 2011-02-03 19:14:20 +0000
@@ -330,7 +330,7 @@
 # Update modules from gnulib, for maintainers, who should have it in
 # $(gnulib_srcdir) (relative to $(srcdir) and should have build tools
 # as per $(gnulib_srcdir)/DEPENDENCIES.
-GNULIB_MODULES = dtoastr getopt-gnu mktime strftime
+GNULIB_MODULES = dtoastr getopt-gnu ignore-value mktime strftime
 GNULIB_TOOL_FLAGS = \
  --import --no-changelog --no-vc-files --makefile-name=gnulib.mk
 sync-from-gnulib: $(gnulib_srcdir)

=== modified file 'src/ChangeLog'
--- src/ChangeLog       2011-02-03 13:46:03 +0000
+++ src/ChangeLog       2011-02-03 19:25:14 +0000
@@ -1,3 +1,16 @@
+2011-02-03  Paul Eggert  <address@hidden>
+
+       allow C code to suppress warnings about ignored return values
+
+       We need to go through the code and for each such warning, either
+       fix the code to pay attention to the returned value, or tell GCC
+       that we really do want to ignore the returned value.  Here is one
+       example of how to do the latter.
+       * sysdep.c: Include <ignore-value.h>.
+       (sys_subshell): Suppress an undesirable warning about not checking
+       the returned value of 'write', as there's nothing useful one can
+       do with that returned value.
+
 2011-02-03  Jan Djärv  <address@hidden>
 
        * xterm.c (x_connection_closed): Remove all calls that calls

=== modified file 'src/sysdep.c'
--- src/sysdep.c        2011-01-25 04:08:28 +0000
+++ src/sysdep.c        2011-02-03 19:16:45 +0000
@@ -31,6 +31,8 @@
 #endif /* HAVE_LIMITS_H */
 #include <unistd.h>
 
+#include <ignore-value.h>
+
 #include "lisp.h"
 #include "sysselect.h"
 #include "blockinput.h"
@@ -263,7 +265,7 @@
 init_baud_rate (int fd)
 {
   int emacs_ospeed;
- 
+
   if (noninteractive)
     emacs_ospeed = 0;
   else
@@ -578,7 +580,7 @@
        write (1, "Can't execute subshell", 22);
 #else   /* not WINDOWSNT */
       execlp (sh, sh, (char *) 0);
-      write (1, "Can't execute subshell", 22);
+      ignore_value (write (1, "Can't execute subshell", 22));
       _exit (1);
 #endif  /* not WINDOWSNT */
 #endif /* not MSDOS */
@@ -3058,4 +3060,3 @@
 }
 
 #endif /* !defined (WINDOWSNT) */
-