The following program, compiled with gcc -Wunused, issues no warnings
int foo (void);
void
bar (int *p)
{
*p++; /* perhaps (*p)++ was intended? */
foo () + foo ();
foo () + foo (), foo ();
}
(gcc 2.9.6 issues warnings for all three lines)
I have found *p++; to be a fairly common error.
When sizeof(*p) == 1 or (*p)++ is illegal this is usually a superfluous `*',
but otherwise it is quite often a real bug and so there should be a warning.
I don't care much about things like 3+foo(), but mention them
because of this inoperative comment in c-typeck.c
/* With -Wunused, we should also warn if the left-hand operand does have
side-effects, but computes a value which is not used. For example, in
`foo() + bar(), baz()' the result of the `+' operator is not used,
so we should issue a warning. */
It looks like this code in stmt.c needs yet more tweaking:
maybe_warn:
/* If this is an expression with side effects, don't warn. */
if (TREE_SIDE_EFFECTS (exp))
return 0;
--
Summary: The -Wunused (value computed is not used) option missed
an important case
Product: gcc
Version: 4.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: trt at acm dot org
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23113
