On Mon, Nov 25, 2024 at 07:53:05PM -0500, Mouse wrote:
> There's also
>
> sizeof (int) - 1
>
> which is ambiguous even _with_ the parens; it means either
> (sizeof(int))-1
> or
> sizeof((int)-1)
>
> In this case, I think the ambiguity is resolved by operator precedence
C99 6.5.4 says
cast-expression ::=
unary-expression
| ( type-name ) cast-expression
and 6.5.3 says
unary-expression ::=
postfix-expression
| ++ unary-expression
| -- unary-expression
| unary-operator cast-expression
| sizeof unary-expression
| sizeof ( type-name )
The reason these are stratified is so that sizeof ( type-name ) is
unambiguous.
As written it also rules out ++(int)x, but that's a defect -- it is
not semantically valid but there's no reason to gratuitously make it
a syntax error. Especially since ++ +(int)x is accepted and that's
semantically equally invalid.
--
David A. Holland
dholl...@netbsd.org
