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Re: Vector - contiguous memory question.

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On 5/26/22 04:51, Muttley@dastardlyhq.com wrote:
> Is contiguous memory storage in a vector a recent thing or is it only
> in more recent versions of C++? Ie is the following always guaranteed to
> work no matter how old the compiler:
> 
> vector<u_char> mydata;
> :
> fill vector
> :
> write(fd,&mydata[0],mydata.size());
> 
> or 
> 
> write(fd,mydata.data(),mydata.size());

In the original, 1998 version of the C++ standard, there was no
requirement that std::vector<> be contiguous. I participated in several
discussions on comp.std.c++ about that issue. Some people argued that
contiguity could be inferred from other things that the standard said
about std::vector<>, but those inferrences were not correct. Notably,
all the reasons given for believing that std::vector<> had to be
contiguous applied equally well to std::valarray<>. This is a problem,
because std::valarray<> was explicitly required to be contiguous. If
those arguments were valid, then they should apply to std::valarray<>
too, with the result that there was no need for the standard to specify
that the it was contiguous.
You can find those discussions using groups.google.com and searching for
 	contig vector

My copy of C++98 is long gone, so I can't check this, but no one cited
any text from the standard mandating that it be contiguous. Since I'm an
inveterate standard-quoter, and was participating in that discussion, if
there had been any such text, I would have quoted it.

The consensus was that std::vector<> should have been required to be
contiguous, and that the standard was defective by reason of failing to
do so. Andrew Koenig filed DR69
<https://cplusplus.github.io/LWG/issue69>, and the proposed wording was
inserted in TC1.

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Thread

Vector - contiguous memory question. Muttley@dastardlyhq.com - 2022-05-26 08:51 +0000
  Re: Vector - contiguous memory question. Bo Persson <bo@bo-persson.se> - 2022-05-26 11:28 +0200
  Re: Vector - contiguous memory question. "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-26 12:36 +0200
    Re: Vector - contiguous memory question. Muttley@dastardlyhq.com - 2022-05-26 16:02 +0000
  Re: Vector - contiguous memory question. "Alf P. Steinbach" <alf.p.steinbach@gmail.com> - 2022-05-26 18:25 +0200
  Re: Vector - contiguous memory question. James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-05-26 13:53 -0400
  Re: Vector - contiguous memory question. Vir Campestris <vir.campestris@invalid.invalid> - 2022-05-27 17:12 +0100
    Re: Vector - contiguous memory question. James Kuyper <jameskuyper@alumni.caltech.edu> - 2022-05-27 12:32 -0400
      Re: Vector - contiguous memory question. Muttley@dastardlyhq.com - 2022-05-28 09:07 +0000
        Re: Vector - contiguous memory question. Ben <ben.usenet@bsb.me.uk> - 2022-05-28 16:36 +0100
          Re: Vector - contiguous memory question. "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-05-28 17:14 -0700
            Re: Vector - contiguous memory question. Ben <ben.usenet@bsb.me.uk> - 2022-05-29 01:47 +0100
            Re: Vector - contiguous memory question. "james...@alumni.caltech.edu" <jameskuyper@alumni.caltech.edu> - 2022-05-28 22:06 -0700
          Re: Vector - contiguous memory question. Muttley@dastardlyhq.com - 2022-05-29 07:32 +0000
            Re: Vector - contiguous memory question. Ben <ben.usenet@bsb.me.uk> - 2022-05-29 19:43 +0100

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