The gcc-4.0 manual says
* An expression-statement or the left-hand side of a comma
expression contains no side effects. To suppress the
warning, cast the unused expression to void. For example, an
expression such as `x[i,j]' will cause a warning, but
`x[(void)i,j]' will not.
This worked for earlier releases of gcc, but in gcc-4.0 the cast to void
doesn't avoid the warning.
$ gcc -v
Using built-in specs.
Target: powerpc-apple-darwin7.8.0
Configured with: /Users/bruno/data/work/gcc-4.0.0-20050410/configure
--prefix=/Volumes/UserData/experimental-macos --enable-shared
--enable-version-specific-runtime-libs --enable-languages=c,c++
Thread model: posix
gcc version 4.0.0 20050410 (prerelease)
$ gcc -W -c foo.c
foo.c: In function 'foo':
foo.c:4: warning: left-hand operand of comma expression has no effect
$ gcc -W -c bug.c
bug.c: In function 'copy_string':
bug.c:169: warning: left-hand operand of comma expression has no effect
--
Summary: "no effect" warning despite cast to void*
Product: gcc
Version: 4.0.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: bruno at clisp dot org
CC: gcc-bugs at gcc dot gnu dot org
GCC build triplet: powerpc-apple-darwin7.8.0
GCC host triplet: powerpc-apple-darwin7.8.0
GCC target triplet: powerpc-apple-darwin7.8.0
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21159
