Path: csiph.com!eternal-september.org!feeder.eternal-september.org!reader01.eternal-september.org!.POSTED!not-for-mail From: Tim Rentsch Newsgroups: comp.lang.c++ Subject: Re: [QT creator on "nix"] - getting a strict 8 bit (1 byte) array with no padding Date: Thu, 28 Nov 2019 12:51:23 -0800 Organization: A noiseless patient Spider Lines: 34 Message-ID: <86pnhbafn8.fsf@linuxsc.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Injection-Info: reader02.eternal-september.org; posting-host="dce185ee50ea005ee4a34884a21fb89a"; logging-data="26629"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+k61l5XqObBxDwUF8neX+T2d0PeE+HU0E=" User-Agent: Gnus/5.11 (Gnus v5.11) Emacs/22.4 (gnu/linux) Cancel-Lock: sha1:3BjS0CbKPfCfr/KLzHxm6lRwXh8= sha1:gwK1Ir3vCYevxXCmxV1+kdpFfW8= Xref: csiph.com comp.lang.c++:70092 James Kuyper writes: > On 11/22/19 10:49 AM, James Kuyper wrote: > >> On 11/22/19 4:10 AM, David Brown wrote: >> >>> On 22/11/2019 09:37, Keith Thompson wrote: >> >> ... >> >>>> Or an array wrapped in a struct to allow assignment. (An array of 4 >>>> uint8_t elements is guaranteed to be 32 bits, but a struct containing >>>> such an array is not -- but it's a nearly safe assumption that there >>>> will be no padding between the elements or at the end.) >>> >>> While it is true in theory that a struct can have extra padding at the >>> end (beyond what is needed for an array of the struct to have proper >>> alignment for all members), are there any compilers that have done so in >>> practice? >> >> I can't name names, but my understanding is that there have been (and >> might still be) implementations where all struct types have the same >> alignment requirement as the most strictly aligned type supported by >> that implementation. If that alignment requirement is greater than the >> requirements of any of the member types, that will sometimes require >> padding at the end of the struct. > > I said that wrong. Unless all members of the struct have the maximum > alignment requirement, it's possible that such an implementation would > have to put padding at the end. Don't you mean, unless the last member of a struct has the maximum alignment requirement, it's possible such an implementation would have to put padding at the end.