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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: Taming The Switch-Statement
Date: Fri, 16 Oct 2026 04:46:03 -0700
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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

> [.. some syntanx changes were made as part of C23 ..]
>
> C23 made some changes with the goal of allowing a label to be
> immediately followed by a declaration or `}`.  It did so by changing
> the grammar for a compound-statement:
>
>     compound-statement:
>         { block-item-list[opt] }
>
>     block-item-list:
>         block-item
>         block-item-list block-item
>
>     block-item:
>         declaration
>         unlabeled-statement
>         label
>
> This means that in
>
>     switch (x) {
>         case 'A':
>         case 'B':
>         case 'C':
>             puts("blah");
>     }
>
> *there is no labeled-statement*.  Instead, each of `case 'A':`,
> `case 'B':`, `case 'C':`, and `puts("blah");` is a block-item, and all
> the block-items are at the same syntactic level within the
> compound-statement.  (The indentation is still appropriate IMHO.)
>
> Since control jumps to "the statement or declaration following the
> matched case label", there is no fallthrough.  If x == 'A', control
> jumps directly to the puts() call.
>
> In C17 and earlier, the same wording implies that when x=='A', control
> jumps to the statement
>     case 'B': case 'C': puts("blah");
> so one might arguably refer to that as "fallthrough".  In C23,
>     case 'B': case 'C': puts("blah");
> is not a statement.
>
> A weird but mostly harmless consequence of this is that C23 keeps
> the syntactic construct of a *labeled-statement*, but it's used
> extremely rarely.  Any C17-or-earlier labeled-statement at the
> top level of an enclosing compound-statement is no longer a C23
> labeled-statement, even though it looks like one.  In C23, a
> labeled-statement can only occur in an odd construct like this:
>
>     if (condition)
>         LABEL: statement;
>
> The proposal that led to this suggested an optional additional change,
> making labels outside of compound statements an obsolescent feature.
> That part of the proposal was not adopted.

Glad to hear it.  Good choice.