February 2022 - Boost - lists.preview.boost.org

Boost.Text is looking for a (mini-)review manager
by Zach Laine 07 Dec '22

07 Dec '22

I've made all the recommended changes to Boost.Text that came up in the review. Glen, the previous review manager, recommended a mini review of Boost.Text once I'd made those changes. If you'd like to manage the mini-review, please let me know. For everyone, including potential reviewers and review managers, here are the major changes: * All the specific review feedback issues have been addressed. * The string layer is now gone. * The text layer got a major re-work. It is now a set of template-based adaptors (basic_text<>, vs. a text typedef. etc.), which lets everyone get what they want. You can change the underlying storage type (including whatever allocator you prefer), select UTF-8 or UTF-16, and change the normalization form. Glen recommended I drop this layer, but the library is way less useful without this stuff, and these changes address all the concerns raised about the text layer in the review. The updated docs can be found here: https://tzlaine.github.io/text/doc/html/index.html Oh yeah, and I added concept constraints to the whole library when you build in C++20 mode. Zach

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[review][JSON] Review of JSON starts today: Sept 14 - Sept 23
by Pranam Lashkari 09 Aug '22

09 Aug '22

Boost formal review of Vinnie Falco and Krystian Stasiowski's library JSON starts today and will run for 10 days ending on 23 Sept 2020. Both of these authors have already developed a couple of libraries which are accepted in Boost(boost beast and Static String) This library focuses on a common and popular use-case for JSON. It provides a container to hold parsed and serialised JSON types. It provides more flexibility and better benchmark performance than its competitors. JSON highlights the following features in the documentation: - Fast compilation - Require only C++11 - Fast streaming parser and serializer - Easy and safe API with allocator support - Constant-time key lookup for objects - Options to allow non-standard JSON - Compile without Boost, define BOOST_JSON_STANDALONE - Optional header-only, without linking to a library (a point I would like to add in highlight: it has cool Jason logo 😝) To quickly understand and get the flavour of the library take a look at "Quick Look" <http://master.json.cpp.al/json/usage/quick_look.html> You can find the source code to be reviewed here: <https://github.com/CPPAlliance/json/tree/master> You can find the latest documentation here: <http://master.json.cpp.al/> Benchmarks are also given in the document which can be found here: <http://master.json.cpp.al/json/benchmarks.html> Some people have also given the early reviews, the thread can be found here: <https://lists.boost.org/Archives/boost/2020/09/249745.php> Please provide in your review information you think is valuable to understand your choice to ACCEPT or REJECT including JSON as a Boost library. Please be explicit about your decision (ACCEPT or REJECT). Some other questions you might want to consider answering: - What is your evaluation of the design? - What is your evaluation of the implementation? - What is your evaluation of the documentation? - What is your evaluation of the potential usefulness of the library? - Did you try to use the library? With which compiler(s)? Did you have any problems? - How much effort did you put into your evaluation? A glance? A quick reading? In-depth study? - Are you knowledgeable about the problem domain? More information about the Boost Formal Review Process can be found here: <http://www.boost.org/community/reviews.html> Thank you for your effort in the Boost community. -- Thank you, Pranam Lashkari, https://lpranam.github.io/

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[container] Contributing 'stationary_vector' to Boost
by Mehrdad Niknami 13 Jun '22

13 Jun '22

Hi all, Happy new year! New mailing list member here. I've developed an STL-style stationary_vector class that retains elements in-place when growing. Very briefly, it is effectively a piecewise-contiguous vector, with the following advantages over vector: - Appending has O(1) overhead in the *worst* case (e.g., push_back() does not move elements) - Insertion and random-access can be done in parallel, as prior iterators & references remain valid This has a variety of benefits, including better UX (no "hiccups" due to reallocations), and the ability to simplify parallel processing of streaming data. It occurred to me the larger C++ community might find this useful. I was wondering if there would be interest in incorporating it into Boost.Container, and if so, what steps I could take to make that happen? I'm of course happy to discuss the design etc. with anyone who might be interested. Summary: https://github.com/mehrdadn/libvital/blob/master/doc/vital/container/statio… Implementation: https://github.com/mehrdadn/libvital/blob/master/include/vital/container/st… Thank you, Mehrdad

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[release] Boost 1.7.0 beta 1 released
by Marshall Clow 13 Apr '22

13 Apr '22

Boost release 1.77.0 beta 1 is now available at: <https://boostorg.jfrog.io/artifactory/main/beta/1.78.0.beta1/source/> The SHA256 checksums are as follows: 7a3a025451dfa2923129214eef7d16b03c02310a353d02158a549f6caa4284b0 boost_1_78_0_b1.tar.bz2 c491b1dcb916195598aa6581d6708d57fcc750516641c22511c088d572de9c07 boost_1_78_0_b1.tar.gz 35e7a3b0eb412a3933e57c72ba96374eb7d88ff1f89dbec62a16d67ffea2105a boost_1_78_0_b1.7z e6b68feb2f63401c96ca9fe25e939b409189fbe526a6e784e4bd69832c8f09cb boost_1_78_0_b1.zip For details of what's in the release, see <https://www.boost.org/users/history/version_1_78_0.html>. Please download the beta, give it a try, and report any problems you encounter. Thanks, -- The Boost Release Team

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[Graph] Attempt to resolve open issue
by Anne van de Graaf 10 Mar '22

10 Mar '22

Hello all, I am trying to get an open issue in Boost.Graph resolved. Since I haven't received any response at the corresponding GitHub page nor from the Boost Users mailing list (where I posted the below message last Monday), I am reaching out to you. My aim is to get in touch with the maintainer(s) of Boost.Graph in order to discuss what is the preferred/most efficient way to fix the issue. Since this is my first post to this mailing list, please accept my apologies if you feel this is not the right way to get in touch with the maintainers. In that case, I would appreciate it very much if you could kindly explain what I should have done instead. Please find below a copy of my message that I sent last Monday to the Boost Users mailing list. Thank you very much for your attention and any replies. Original message: When I remove a vertex from a graph, I occasionally experience a crash (on a system running Red Hat Enterprise Linux 8.5). I have been able to replicate the behavior with the following test program: #include <vector> #include <boost/graph/adjacency_list.hpp> int main() { using MyGraph = boost::adjacency_list<boost::setS, boost::vecS, boost::undirectedS>; using MyVertexDescriptor = boost::graph_traits<MyGraph>::vertex_descriptor; using MyVertexDescriptorVec = std::vector<MyVertexDescriptor>; MyGraph g; MyVertexDescriptorVec vertices{ boost::add_vertex( g ), boost::add_vertex( g ), boost::add_vertex( g ) }; boost::add_edge( vertices[0], vertices[1], g ); boost::add_edge( vertices[1], vertices[2], g ); boost::clear_vertex( vertices[0], g ); boost::remove_vertex( vertices[0], g ); return 0; } Also on a Windows platform, I observe similar behavior. When I build the above code with Microsoft Visual Studio 2019 (MSVC 14.27.29110) and run it with a debugger, a debug assertion is triggered ("cannot increment value-initialized map/set iterator"). In both cases (on Linux and Windows platforms), the debugger reveals that the problem is at line 2071 of boost/graph/detail/adjacency_list.hpp. For clarity, I have copied the involved template function below: template < class EdgeList, class vertex_descriptor > inline void reindex_edge_list( EdgeList& el, vertex_descriptor u, boost::disallow_parallel_edge_tag) { for (typename EdgeList::iterator ei = el.begin(); ei != el.end(); ++ei) // line 2071: increment operator fails { if (ei->get_target() > u) { typename EdgeList::value_type ce = *ei; el.erase(ce); --ce.get_target(); el.insert(ce); } } } While I was searching for a proper place to post my question, I found the following issue at GitHub (which was opened on July 1 of this year): https://github.com/boostorg/graph/issues/268. This appears to be the exact same issue. So last week, I added a comment saying that I am facing the exact same problem. Unfortunately, so far no one has responded yet. To me, it seems that the problem is well-understood. Also, some have proposed a bug fix to resolve the issue (including a pull request). Nevertheless, no progress has been made over the past months. So I was just wondering what is the best way to proceed if we want to fix the issue in Boost itself? Is there anything that I can do (apart from starting this thread) to help in resolving the issue? Any feedback is greatly appreciated. Kind regards, Anne van de Graaf

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std::numeric_limits<__float128>::signaling_NaN + __float128-Type
by Gero Peterhoff 26 Feb '22

26 Feb '22

Hello, please see https://godbolt.org/z/Ksshxvhaj 1) std::numeric_limits<__float128>::signaling_NaN always returns 0 but gcc-__builtin_nansq doesn't. I think __builtin_nansq is correct as it is also distinct from std::numeric_limits<__float128>::quiet_NaN (__builtin_nanq). 2) The types __float128, __extension__ __float128 (gcc) and _Quad (intel) are identical, but there are different definitions in boost/config/detail/suffix.hpp and boost/math/cstdfloat/cstdfloat_types.hpp. I think it would make sense to have just one definition or is there a reason why it was done that way? If yes, which one is it? You could always use __float128 directly and/or adjust boost/config/detail/suffix.hpp so that it also works with clang/intel. Which way would be better? I would like to help consolidate this but without having to deal with different typedef's or long #define's. thx Gero

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Boost.URL Proposal
by Alan de Freitas 21 Feb '22

21 Feb '22

Hi! My name is Alan Freitas. Vinnie Falco and I are looking for a review manager for the library that we hope will become Boost.URL. I've taken over the project and in addition to introducing myself I would like to update you guys as to where we are on this in terms of progress: - Path segments can be represented as views of the underlying path - Query parameters can be represented as views of the underlying query - Percent-decoding methods return lazy constant strings with small buffer optimization and shared ownership - The library implements the specification as in RFC3986 <https://datatracker.ietf.org/doc/html/rfc3986> + its errata <https://www.rfc-editor.org/errata/rfc3986> - Non-ASCII characters are not considered valid URLs - Other specifications such as RFC3492 <https://datatracker.ietf.org/doc/html/rfc3492>, WhatWG <https://url.spec.whatwg.org/>, or any other form of relaxed parsing are out of the scope of the library Both Vinnie and I are available to answer questions about the library on the list, on the GitHub repository page <https://github.com/CPPAlliance/url>, via email <alandefreitas(a)gmail.com>, or on Slack (in #boost-url). -- Alan Freitas https://github.com/alandefreitas

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Understanding the code base.
by Rahul Sharma 21 Feb '22

21 Feb '22

So far I have been reading multiple documentations and reading the projects from past year GSoC and exploring some modules given on the GitHub and I came to understand now that in order to contribute to this organization the knowledge of only C++ and data structures is not enough. I have some questions which are halting my progress so far, it would be very generous of you if someone could address these issues I am facing…… 1. I am unable to understand the code base in the repositories on GitHub. 2. In order to contribute or to understand things in a better way do I need to learn how Boost libraries work. 3. What are some packages I need to install. It would be very kind of you if you could provide some useful resources for the same and also for the things you think could be of use to understand things clearly and for making some PRs. When I read the code base of some repositories and some documentations I got excited as I think there are many things and skills I need to learn, the skills, it takes to be a decent developer. Sent from [1]Mail for Windows References 1. https://go.microsoft.com/fwlink/?LinkId=550986

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[PATCH] futex: fix build on 32-bit architectures using 64-bit time_t
by Khem Raj 21 Feb '22

21 Feb '22

Fix the following build failure on 32-bit architectures using 64-bit time_t (e.g. riscv32): | ./boost/fiber/detail/futex.hpp:31:23: error: use of undeclared identifier 'SYS_futex' | return ::syscall( SYS_futex, addr, op, x, nullptr, nullptr, 0); | ^ | 1 error generated. Signed-off-by: Khem Raj <raj.khem(a)gmail.com> --- boost/fiber/detail/futex.hpp | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/boost/fiber/detail/futex.hpp b/boost/fiber/detail/futex.hpp index e64bd5990..d0353e9e5 100644 --- a/boost/fiber/detail/futex.hpp +++ b/boost/fiber/detail/futex.hpp @@ -12,6 +12,10 @@ #include <boost/fiber/detail/config.hpp> +#ifndef SYS_futex +#define SYS_futex SYS_futex_time64 +#endif + #if BOOST_OS_LINUX extern "C" { #include <linux/futex.h> -- 2.35.1

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unordered_map implementation
by Peter Dimov 19 Feb '22

19 Feb '22

I've been helping Christian Mazakas maintain Unordered, and we've been looking into trying to improve its performance on the synthetic benchmarks we have for it (https://github.com/boostorg/unordered/tree/develop/benchmark) One of the things that are hurting us is that we need to do a double indirection in order to find an element, because Unordered uses a singly-linked list for all its nodes, with the bucket array pointing at the element before the first one (in order to be able to support erasing.) There's also the option of using a doubly-linked list, which however increases the memory footprint. I'm looking at the iterator invalidation rules for std::unordered_map, and iterators are invalidated on every rehash. This makes me wonder why is it necessary to have all the elements in a single list, as every implementation seems to do. It seems to me that it's possible to just have singly- linked lists for each bucket, and then have a "fat" iterator that contains the bucket index and the pointer to the element. On increment, when the end of the bucket list is reached, the iterator can just go to the next non-empty bucket. Is there something I'm missing in the requirements that renders this implementation non-conforming?

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std::launder and its usage in Boost
by Mikhail Kremniov 18 Feb '22

18 Feb '22

Hi, Initially, I posted this question to the boost-users list, but then I was advised to repost it here. I wonder, what is the Boost community's opinion of std::launder? In particular, of its necessity when accessing an object that was created via placement-new in an aligned_storage. As I can see, it's used by Boost.Beast in its implementation of the variant type, but not in other parts of Boost. The reason I'm asking this is that I'm working on a C++14 code-base that uses Boost.Variant and Boost.Optional extensively (as well as other parts of Boost that use Variant and Optional internally). Now we're trying to switch to C++17 at least, and I worry whether it could potentially break things. To put things into context, C++ standard states in the [basic.life] section that if you had an object and then created a new one in the same location, you can use the pointer to the old object to refer to the new one only if (among other things) "the new object is of the same type as the original object (ignoring the top-level cv-qualifiers)". This means, as I understand it, that it's technically illegal to reinterpret_cast the pointer to aligned_storage to the pointer to the actual type of the object created via placement-new, because placement-new has already ended the lifetime of the aligned_storage object. So, implementations of Boost.Optional and Boost.Variant are illegal then (?). But it's been like that since C++03 and Boost worked fine all that time, so it looks like this UB existed only "on paper". But C++17 then added "Note: If these conditions are not met, a pointer to the new object can be obtained from a pointer that represents the address of its storage by calling std::launder". So now the language has the ability to deal with that UB, and a question arises, is it possible that compilers could start to use the UB to perform additional optimizations and make it a real UB? Also, I've seen a couple of times on stackoverflow.com people saying that it's actually fine to reinterpret_cast the storage in C++14, but in C++17 it's not (they didn't explain why though). So, can switching from -std=c++14 to -std=c++17 be a breaking change when using Boost? The fact that Boost.Variant and Boost.Optional don't use std::launder - is it an oversight or a conscious decision? Regards, Mikhail.

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Diagnostic improvements in 1.78/1.79
by Peter Dimov 15 Feb '22

15 Feb '22

This is a quick summary of some 1.78 and 1.79 changes in Assert, ThrowException, and System related to error reporting. In Boost 1.73, Assert acquired a new component, boost::source_location. This is a class encapsulating a source location (a collection of source file name, line number, column, and function name) that is modeled after C++20's std::source_location, except of course it doesn't require C++20. In 1.79, the macro that creates the current source location, BOOST_CURRENT_LOCATION, is now usable in a function default argument, similarly to std::source_location::current(). This enables functions to be declared like this: T& my_vector::at( size_t i, boost::source_location const& loc = BOOST_CURRENT_LOCATION ) { if( i >= size() ) { boost::throw_exception( std::out_of_range( "at" ), loc ); } return data_[ i ]; } Since functions such as `at` are called from many places in the program, it's more useful for the source location in the thrown exception to point at the call site, rather than inside of `at` (which doesn't provide much information.) See for example https://godbolt.org/z/6o9e187a1. Note that the location returned by diagnostic_information(x) points to line 35, which is the call to `v.at(5);` inside `main`. Recommendation one: add source_location default arguments to your throwing functions so that the information logged at the catch site points to the call that threw. In case you find boost::throw_exception too heavyweight, as it adds a boost::exception base class and support for boost::exception_ptr, and this would prevent you from applying the technique above, there is now an alternative function, boost::throw_with_location, in <boost/throw_exception.hpp>. It doesn't integrate with Boost.Exception or boost::exception_ptr, but does add a source location to the exception that can later be retrieved with boost::get_throw_location(x). The above example using boost::throw_with_location can be seen at https://godbolt.org/z/Pcj1xad3v. In 1.78, boost::system::error_code had also acquired support for source locations, although it's not as automatic as the above technique where the default argument automatically adds a location without the user needing to do anything. Since there's no space in error_code for the entire boost::source_location struct, it can only store a pointer to it. This requires the following incantation BOOST_STATIC_CONSTEXPR boost::source_location loc = BOOST_CURRENT_LOCATION; ec.assign( ENOENT, boost::system::generic_category(), &loc ); which can be wrapped in a macro. See the documentation of Boost.System: https://www.boost.org/doc/libs/1_78_0/libs/system/doc/html/system.html#usag… Unlike the case with exceptions, when working with error codes, the situation is reversed and we want to store the source location immediately after discovering the error, rather than the one of the user call that failed. That's both because this location gives the most information as to the source of the error (ENOENT on its own doesn't say much), and because error codes are generally checked close to the user call, so the call location isn't as useful. Recommendation two: add source locations to your error_codes if using Boost.System. Finally, when providing dual APIs, that is, APIs that can signal an error using both error_code or by throwing an exception, you can combine the above two approaches and store both the "deep" source location in the error_code and the "shallow" (user call) location in the system_error exception. I hope you find those useful. Further reading: https://www.boost.org/doc/libs/develop/libs/assert/doc/html/assert.html#sou… https://www.boost.org/doc/libs/develop/libs/throw_exception/doc/html/throw_… https://www.boost.org/doc/libs/develop/libs/system/doc/html/system.html

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Proposed BoostBook fix for invalid <h7> and <h8> elements
by Evan Lenz 14 Feb '22

14 Feb '22

Hello, The DocBook stylesheets used by BoostBook occasionally will output invalid heading elements (<h7> or <h8>). Some (but not all!) areas of the stylesheets properly cap the output to <h6>. In particular, the rule for <bridgehead> fails to do this. The consequences are described in this BoostBook issue: https://github.com/boostorg/boostbook/issues/12 And (originally) in this issue in the docca tool, which depends on BoostBook: https://github.com/boostorg/docca/issues/79 I have created a pull request that fixes the DocBook issue by overriding the bridgehead rule. Although the ideal fix would be in the DocBook stylesheets themselves, these stylesheets are no longer being regularly updated. Also, my proposed fix conforms to the pattern of other BoostBook-specific stylesheet overrides. Is there someone familiar with BoostBook who would be willing to review my pull request (and raise any questions or concerns as desired)? https://github.com/boostorg/boostbook/pull/13 Thanks very much for your time! Evan Lenz

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Building Boost, eventually
by Alain O' Miniussi 09 Feb '22

09 Feb '22

Hi, I finally got some time time to work on a Boost library and I am, as usual, fighting with bjam. === 14:58:08 [alainm@pollux boost]# ./bootstrap.sh --with-toolset=intel-linux Building B2 engine.. ... icpx (ICX) 2021.1 Beta 20200304 # why not icpc ? ... > icpx -x c++ -std=c++11 -O3 -s -static -DNDEBUG .... -o b2 ld: cannot find -lstdc++ ld: cannot find -lstdc++ === The problem here is the -static option, as libstdc++ is not available as an archive on linux (not on the ones I use). I submitted a fix, with no effect: https://github.com/bfgroup/b2/pull/133/files Also apparently some good soul (thank you!) started working on a CMake alternative that just work (checked twice). Its only issue is that the tests don't seems to have moved to CMake. So my question is: 1) Am I better off trying to port the testing of Boost.MPI to CMake and just forget about bjam or, 2) Try to invoke some demonic entity to get bjam working with intel-linux. What is the recommended build method recommended for libraries developers at this point ? Best regards ---- Alain Miniussi DSI, Pôles Calcul et Genie Log. Observatoire de la Côte d'Azur Tél. : +33492003009 (Mont-Gros) +33483618544 (Sophia Antipolis) +33609650665

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boost::throw_exception potential changes
by Peter Dimov 07 Feb '22

07 Feb '22

Currently, `boost::throw_exception(x)` automatically throws an exception derived from `x` that (1) injects a boost::exception base class if there's none, and (2) injects a base class that enables boost::exception_ptr support (boost::current_exception and boost::rethrow_exception.) This is convenient, but the downside is the amount of generated code, e.g. https://godbolt.org/z/5T8T8GEqP (422 lines) compared to https://godbolt.org/z/1zr1odf7n (36 lines.) This is not the end of the world as this code is only generated once per exception type, not on every call to throw_exception, but it's still unpleasant to see. It so happens that boost::exception_ptr has recently acquired the ability to work under C++11 without the need for the supporting base class, by using the standard std::exception_ptr infrastructure. So if we also remove the automatic injection of boost::exception as a base class, and ask users to derive their exceptions from it if they desire having it as a base, it's possible to simplify boost::throw_exception considerably. The normal call now can be almost the same as the naked throw, https://godbolt.org/z/WssWzfrfW (47 lines.) And if BOOST_THROW_EXCEPTION is used, which still adds the source location (file/line/function) to the exception, the result is 97 lines. (https://godbolt.org/z/nETnqrsx8) However, there is a downside. Due to the way std::exception_ptr works under GCC/Clang (and all compilers using the same ABI), the exception is never copied, not when it's captured with std::current_exception (and consequently boost::current_exception), nor when it's rethrown with boost/std::rethrow_exception. This causes problems if an exception is captured, rethrown, caught and modified, then rethrown again using the same exception_ptr. The second rethrow throws the modified exception. This problem can be seen in https://godbolt.org/z/K9eh71ovP. So... what do we do? Should I go ahead with these changes to throw_exception (having a macro to revert to the old behavior, of course)? Or is that too much of a break? We can of course offer the same functionality as part of Boost.Exception, like boost::exception::raise, or similar, but would that be enough to offset the inconvenience?

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[concept_check][ublas] Fixing deprecated copy warnings
by Antony Polukhin 07 Feb '22

07 Feb '22

Hi, There are two PR that fix deprecated copy warnings for GCC and Clang: * https://github.com/boostorg/concept_check/pull/35 * https://github.com/boostorg/ublas/pull/153 Please review those. They make the intent explicit and the code becomes more portable. Trivial sample that causes the warning https://godbolt.org/z/YaPvGfedv -- Best regards, Antony Polukhin

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Primary test compilers in Boost release notes
by Peter Dimov 01 Feb '22

01 Feb '22

We have an issue, https://github.com/boostorg/boost/issues/610, that points out that the "Primary test compilers" section in the Boost 1.78 release notes is misleading, because it doesn't actually reflect whether a Boost library works with a specific compiler or not. The specific example cited is Multiprecision. The release notes say that on Linux, the following C++11 GCC compilers are "primary": GCC, C++11: 4.7.3, 4.8.5, 11 However, Multiprecision doesn't work with GCC 4.7.3 or 4.8.5, and likely never will, because these compilers do not actually implement the C++11 standard. (They don't implement reference qualified member functions and don't have a conforming <type_traits> header.) It would be better for everyone involved if the primary test compilers are somewhat aligned with (a) what Boost libraries actually support or require, and (b) what Boost libraries actually test with. The section historically lists what's in our test matrix, but nowadays most libraries depend on CI for testing, specifically on Github Actions (after the untimely death of open source Travis) and Appveyor. There's a fair bit of discussion in the linked issue above, but what I think is reasonable to list as primary test compilers as far as GCC is concerned is something like C++03: 4.8, 4.9, 5 C++11: 4.8(*), 4.9(*), 5 I would start with 4.8, because this is what GHA has on its 18.04 image. C++03 needs to have GCC up to 5 because this is the default -std level for these versions (GCC 6 is -std=c++14 by default), and the system- provided Boost is compiled with the default. 4.8 has enough of C++11 so it's possible for C++11 libraries to support it without much heroics, but we could go either way on this one, hence the asterisk.

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