One common mistake in C is to do sizeof(x) where x is a pointer and
what was really wanted was sizeof(*x). Similar to requiring
parentheses around assignments in conditionals, I'd like an optional
warning to be added when sizeof is done on a variable that is a
pointer. For example, in the code below, the first sizeof would
give a warning. To prevent this warning, sizeof(char *) can be
used instead.
void fu (void)
{
char *x;
printf(" x %d\n", sizeof(x));
printf("char * %d\n", sizeof(char *));
printf("char * %d\n", sizeof("hello world"));
}
I've done a proof of concept for gcc 3.3 as below. I haven't done
extensive testing and I didn't make the warning optional.
*** c-parse.y 2005/12/05 22:19:42 1.1
--- c-parse.y 2005/12/05 22:54:43
***************
*** 494,502 ****
--- 494,506 ----
if (TREE_CODE ($2) == COMPONENT_REF
&& DECL_C_BIT_FIELD (TREE_OPERAND ($2, 1)))
error ("`sizeof' applied to a bit-field");
+ warning("`sizeof' reference #1");
+ if (TREE_CODE (TREE_TYPE ($2)) == POINTER_TYPE)
+ warning("`sizeof' applied to a pointer variable");
$$ = c_sizeof (TREE_TYPE ($2)); }
| sizeof '(' typename ')' %prec HYPERUNARY
{ skip_evaluation--;
+ warning("`sizeof' reference #2");
$$ = c_sizeof (groktypename ($3)); }
| alignof unary_expr %prec UNARY
{ skip_evaluation--;
--
Summary: feature request: generate a warning for sizeof on a
pointer
Product: gcc
Version: 4.2.0
Status: UNCONFIRMED
Severity: enhancement
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: meklund at cisco dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25702
