From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mailgate-1.zdv.net (mailgate-1.zdv.net [IPv6:2001:4c80:40:62d::25:1]) by sourceware.org (Postfix) with ESMTPS id A6E813856156 for ; Thu, 20 Oct 2022 11:46:54 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org A6E813856156 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=hs-kl.de Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=hs-kl.de X-IPAS-Result: =?us-ascii?q?A2B0FgDsM1Fj/2UNXY9agQmBUYUbhDeIIYhInU2Bew8BA?= =?us-ascii?q?QEOARQTHQQBAYl5JjwCDQECBAEBAQEDAgMBAQEBAQEDAQEBBQEBAQEBAQYDA?= =?us-ascii?q?YEchS9GhmwVdgImAl8NCAEBgnmDIaxagTKBAYRxgy2BZgkBgQctiFuIL4FVR?= =?us-ascii?q?IE8hz2BFYMKgmYElQYcJgQOAxkrHUACAQtuDVocMScOCSAcChsNBQYSAyBvB?= =?us-ascii?q?Qo4DygvaSscGweBDCooFQMEBAMCBhMDIgINKTEUBCkTDy0HI3EJAgMiagMDB?= =?us-ascii?q?CgsAwkhHwclJDwHWDoFAwIQIjwGAwkDAiJYdS8RFQUDDRclCAU3GgQIPAIFB?= =?us-ascii?q?lMSAgoRAxIPLUcOSj45FgYneQ8OFgOcEqM5nzY0B4IdgUiBRAYMnlcGQYNkA?= =?us-ascii?q?ZMRBpITlxqiO4UQAgQCBAUCFoIQgWczGiSDN1AXAg+ccoEuAgYLAQEDCYggg?= =?us-ascii?q?SUBgREBAQ?= IronPort-Data: A9a23:0RMAuKDmWSnKahVW/7Dhw5YqxClBgxIJ4kV8jS/XYbTApD0ghWFWm DBKCmrUO/+ONGf8Lt9zOYi38k4G7JXVztU3TANkpHpgZkwRpJueD7x1DKtR0wB+jCHnZBg6h ynLQoCYdKjYdleF+lH3dOCJQUBUjcmgXqD7BPPPJhd/TAplTDZJoR94kobVuKYx6TSCK17L6 I6aT/H3Ygf/gWcsaDpMsspvlTs21BjMkGJF1rABTagjUG/2zxE9EJ8ZLKetGHr0KqE88jmSH rurIBmRpws1zj91Yj+Xuu+Tnn4iG9Y+CTOzZk9+AMBOtPTgShsaic7XPNJEAateZq7gc9pZk L2hvrToIesl0zGldOk1C3Fl/y9C0aJuyqeeDV6AnpWo3WLUX1frzaRVXUgXBNhNkgp3KTkmG f0wOjwTKBaOm4pawpriFrIq159ldZKtZdtG0p1j5Wix4fIOfpHHQ6jO4Jl90TY9nOhOBrPdY 4wVZFKDaTyZPUQRYgxGU81WcOGA133CVWcJ8mqvuLso42ndyAgh3Zq0CY+AEjCNbYAP9qqCn UrJ9G+8AhweLPSQwjHD/XSxwOjVkkvGtJk6EbS58vF12ATVxndWCxlQWVbTTeSFt3NSkul3c yQ8khfCZ4BrnKB3ZrERhyGFnUM= IronPort-HdrOrdr: A9a23:bgwuDKjKTWjv4sRes4GOhiOB+HBQXu0ji2hC6mlwRA09TyXBrb HLoB1p726StN9xYgBapTnuAsm9qB/nmKKdpLNhWItKPzOWwldATrsSjrcKqgeIc0aVygce79 YDT0EUMrLN5C1B7PoSlzPXLz9P+rW6GeuT9IHjJj9WPHhXgo9bnn9ENjo= X-IronPort-Anti-Spam-Filtered: true X-IronPort-AV: E=Sophos;i="5.95,198,1661810400"; d="scan'208";a="161603937" Received: from mailgw01.hs-kl.de (HELO zdv.net) ([143.93.13.101]) by mailgate-1.zdv.net with ESMTP/TLS/AES256-GCM-SHA384; 20 Oct 2022 13:46:52 +0200 Received: from [192.168.0.107] (84.183.29.41) by klrz-mail01.ds.fh-kl.de (10.1.3.101) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.32; Thu, 20 Oct 2022 13:46:52 +0200 Message-ID: <8dc1aaa8-fe1b-e11b-b5e4-ae1acc30ff02@hs-kl.de> Date: Thu, 20 Oct 2022 13:46:52 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:106.0) Gecko/20100101 Thunderbird/106.0 To: Content-Language: de-DE From: Wilhelm Meier Subject: Unions, common-initial subsequence and UB Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [84.183.29.41] X-ClientProxiedBy: klrz-mail01.ds.fh-kl.de (10.1.3.101) To klrz-mail01.ds.fh-kl.de (10.1.3.101) X-Spam-Status: No, score=0.7 required=5.0 tests=BAYES_00,KAM_DMARC_STATUS,RCVD_IN_BARRACUDACENTRAL,SPF_HELO_PASS,SPF_PASS,TXREP autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Hi all, this is more a general question instead of a g++ specific one: the standard explicitly makes this exception: accessing an inactive union member is not UB if the members are structs with initial common sequence. Is this also true in a constexpr context? I ask this because the chapter for constexpr expression does not mention this exception accessing an inactive memeber. Thanks for hints, Wilhelm