From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3F75E3A7186 for ; Tue, 16 Jun 2026 22:09:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781647783; cv=none; b=NtumDoviJpHeSBtSikqMNEZnn8S4/e0oyF2maFApCvYemt61E1yBHit2paIK6MjKlNX0qTRKqTlTGBfIoZO2ziMXCK9Lrg2FEXhDo8A6L+NLlrdVTJkX0IFOKeEFNSHNdRgqDGLpmPQ8XlVF4mvDHMbySq+7u8cHSUpkKSdKFEo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781647783; c=relaxed/simple; bh=HD93vC5GUSjBPvwkbLAfkCcpqogXKTDVtXeHijoQENw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=pwGsPJhUnIC9wGKHA04OiLvpE0bHDAzkCU3vRLZDTWUxrFvDrYA3rha/pV3/l5DM1g0xkWj/NTCohO41b//62PVibtv/sbWokWn6/6tO63KKwXwj9Mt5UeMAFAfGq5sTfD2IEjaT8iAajD8NVvswywAvZefg7ydoatoD+BRGHVA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=V97N9cjc; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="V97N9cjc" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D159B1F000E9; Tue, 16 Jun 2026 22:09:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781647781; bh=Ft2gXqosUq+mjpoBM632V0zqSraNHqN3W2FI0zraMas=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=V97N9cjcR9sQyA50CB3MEuHv1iWLC0k9vxTOnKuFcdDRVG9PEB795anDg1oJzAL+g UoV3DCOxr29fgrdS6YXjD7zO6jlShSAUySKsMKI5Alrw/C8VVRDenxOsUVKWqhVegb xDVZNv6Y/vN8gbRikccKV29LDGbIOCIL4u6FB85KRT2zC5qu//fkoiw0M1LOvtyt0l ufYP14majmM8nac+3AMhADR6tudiCG9BD5RgFINSjQrmylbC07n0wOInEnTSDY39rv VCcpYC8L0z+y4vB1nWVuw+PCEUjQ3DDL4vwdrl0XIKSx+v34sswOV4z58KXjTQP0bb I+I7DxDz2t18g== Date: Wed, 17 Jun 2026 00:09:37 +0200 From: Alejandro Colomar To: Joseph Myers Cc: libc-alpha@sourceware.org, gcc@gcc.gnu.org, linux-man@vger.kernel.org Subject: Re: _ISOCxx_SOURCE Message-ID: References: Precedence: bulk X-Mailing-List: linux-man@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="op66v3eztbmgsmcn" Content-Disposition: inline In-Reply-To: --op66v3eztbmgsmcn Content-Type: text/plain; protected-headers=v1; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable From: Alejandro Colomar To: Joseph Myers Cc: libc-alpha@sourceware.org, gcc@gcc.gnu.org, linux-man@vger.kernel.org Subject: Re: _ISOCxx_SOURCE Message-ID: References: MIME-Version: 1.0 In-Reply-To: Hi Joseph, On 2026-06-16T21:52:57+0000, Joseph Myers wrote: > On Tue, 16 Jun 2026, Alejandro Colomar via Gcc wrote: >=20 > > If one uses a modern GCC with an old glibc (which doesn't know C23), > > then, using -std=3Dc23 will be problematic: the compiler will enable C23 > > language mode, but the library will entirely and silently ignore > > _ISOC23_SOURCE, because it doesn't know about it, thus falling back to > > C89 mode (I guess), and thus will for example enable things like > > gets(3). >=20 > Since the relevant checks in features.h are based on __STDC_VERSION__ >= =20 > something or __STDC_VERSION__ >=3D something, Ahh, yup, it has || for either _ISOCxx_SOURCE or __STDC_VERSION__. That makes sense. > it will fall back to the most=20 > recent C standard version known by that glibc version, which is probably= =20 > what you want. Hmmm, it is. Then it's all fine. Thanks! Cheers, Alex --=20 --op66v3eztbmgsmcn Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEES7Jt9u9GbmlWADAi64mZXMKQwqkFAmoxyaAACgkQ64mZXMKQ wqkHrg/9Ep2vkbS1z27rXKvEIncJS8qAiLhYb1XZZjud6N5MR/hCfb7+9B+AOQxN vzw7vSzPDvHYJjb9K69OB8X6/bn+3dn97MopJYFnMx8vvkpo44S24gkqk2F93a+r CgHs5+8zExFPvxWsXKxKVevLdcui6pLj/JrbY1T9uxE84Z6U2EerfpiXgjoj5dRd 6EW4bIMBps4Rc+XnTJZYgq4qVNDZUOrFhiLj1GEFIe/fO8zG+XayWbbdvrUsCNiV bg4UQITNYud4LT7F3WldAm9cfktWhID4cllT2mUzBW8xTQVP3gkTTTlwVfCBoGS1 cJH7Hf7T2QUxuNownqtvx7HjL5VZXrW2r7PkQo4eHRgp2KlszIx1FAtaEDSImi2W CtXYEoKi3ynlKQXGpn0yMqoIP2GOFlnZFjgPzI9cQMwCfvdt2eisoXeKRgkwgEXJ y7vMTkqgiCHm55Ase2BKBvFyve7XZJ38zQadWfLVze0PGDv6nKkwRWofRTgToHmM KNe+YF3Juz8fG6RqKZV98R9zlT6p5Z8pmPxuYndJVUa4Xt3UUaSDPnowA+NlqrRW DfratKzfkapffcqSTHB1tFK9LkQELjLRzt4ElTFc4M/ZfRf0c5YM1NFmH3s0c1K3 PEeOoB1PL7bjTXJ8dKNJqNzTJLd5uaBJ4EEUQTw2ViFa3lWUAQg= =WQp5 -----END PGP SIGNATURE----- --op66v3eztbmgsmcn--