[Bug c/39808] New: warn_unused_result fails to produce warning

[Bug c/39808] New: warn_unused_result fails to produce warning

[sandmann at daimi dot au dot dk]

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The program to be attached produces the warning

[ssp@dhcp-100-2-40 ~]$ gcc gb.c
gb.c: In function ‘main’:
gb.c:11: warning: ignoring return value of ‘foo’, declared with attribute
warn_unused_result

which is expected. However, it should also produce a warning for line 12, which
is exactly the same except a dummy variable is declared.



Using built-in specs.
Target: i386-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla
--enable-bootstrap --enable-shared --enable-threads=posix
--enable-checking=release --with-system-zlib --enable-__cxa_atexit
--disable-libunwind-exceptions
--enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk
--disable-dssi --enable-plugin
--with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre
--enable-libgcj-multifile --enable-java-maintainer-mode
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib
--with-cpu=generic --build=i386-redhat-linux
Thread model: posix
gcc version 4.3.2 20081105 (Red Hat 4.3.2-7) (GCC)


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           Summary: warn_unused_result fails to produce warning
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sandmann at daimi dot au dot dk
 GCC build triplet: i386-redhat-linux
  GCC host triplet: i386-redhat-linux
GCC target triplet: i386-redhat-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39808

[Bug c/39808] warn_unused_result fails to produce warning

[sandmann at daimi dot au dot dk]

------- Comment #1 from sandmann at daimi dot au dot dk  2009-04-18 17:32 -------
Created an attachment (id=17654)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=17654&action=view)
program


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39808

[Bug c/39808] warn_unused_result fails to produce warning

[pinskia at gcc dot gnu dot org]

------- Comment #2 from pinskia at gcc dot gnu dot org  2009-04-21 17:59 -------
I think neither of these cases should be warned about since you are using it
with a statement expression.


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pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |diagnostic


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39808

[Bug c/39808] warn_unused_result fails to produce warning

[sandmann at daimi dot au dot dk]

------- Comment #3 from sandmann at daimi dot au dot dk  2009-04-22 17:03 -------
Why not? If not using the return value is a bug, then it's also a bug if it
isn't used after being passed through a statement expression.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39808