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[2001:8b0:bf73:93f7::51bb:e332]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-499dc9ad772sm853085e9.10.2026.08.25.10.15.17 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 25 Aug 2026 10:15:17 -0700 (PDT) Received: from jsm28 (helo=localhost) by digraph.polyomino.org.uk with local-esmtp (Exim 4.98.2) (envelope-from ) id 1wyuk0-00000006Xny-3FHR for sc22wg14@open-std.org; Tue, 25 Aug 2026 17:15:16 +0000 Date: Tue, 25 Aug 2026 17:15:16 +0000 (UTC) From: Joseph Myers To: sc22wg14@open-std.org Subject: Standard library typedef redeclaration response (issue 1024) Message-ID: <1a161a72-a8c1-e666-0ced-f1cb0507a37c@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: -Uh0x-rT88n_J6XRp2xWz_TEH2nX1wVe-fTzBASpEgA_1787678119 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Sender: owner-sc22wg14@open-std.org Precedence: bulk On further investigation of issue 1024 (where I took an action to propose wording to disallow redeclarations of standard library typedefs, since we didn't want to allow them), it turned out that all wording needed to make such redeclarations of standard library typedefs into undefined behavior was already present. Thus rather than proposing wording changes, I propose a response to the issue as follows that confirms the existing wording reflects the committee's intent. ### Suggested response C23 6.4.3.1 (Identifiers: General) specifies that: > If the program declares or defines an identifier in a context in > which it is reserved (other than as allowed by 7.1.4), the behavior > is undefined. C23 7.1.3 (Reserved identifiers) says: > * Each identifier with file scope listed in any of the following > subclauses (including the future library directions) is reserved > for use as a macro name and as an identifier with file scope in > the same name space if any of its associated headers is included. C23 7.1.4 (Use of library functions) does not provide any exceptions relevant to typedef names. Thus, it is undefined behavior for an application to declare a standard library typedef name with file scope in any translation unit that includes the associated header. The committee does not wish to allow such redeclarations. -- Joseph S. Myers josmyers@redhat.com