January 2025 - Boost - lists.boost.org

Adding optional<T&> find like method to associative containers in boost.
by Ivan Matek 18 Jul '25

18 Jul '25

Hi everybody, I presume somebody thought of this before but for some reason it never happened, but just in case it was never discussed I wonder if people here believe adding an nicer version of find(with different name obviously) to associative containers in boost would be beneficial? Since boost::optional allows references this would work. I presume naming is what most people will have strong feeling about. I personally prefer ofind/oat since I love short names, Barry suggested different names in his blog <https://brevzin.github.io/c++/2023/05/23/map-api/>, e.g. try_at. boost::optional did not get all the updates C++23 std::optional got, e.g. transform that make this usage compose nicely, but those could be added to boost::optional.

13 85

[review] [sqlite]
by Richard Hodges 29 Jun '25

29 Jun '25

Dear All, Surprise! The Boost formal review of the Boost SQLITE library starts *TODAY*, taking place from November 13th, 2024 to November 22nd, 2024 (inclusive). I apologise profusely for springing this on you without prior warning. The error is entirely mine. I am extending the period by one day to compensate. The library is authored by Klemens Morgenstern (@klemens-morgenstern in the CppLang slack). Documentation: https://klemens.dev/sqlite/ <https://anarthal.github.io/mysql/index.html> Source: https://github.com/klemens-morgenstern/sqlite <https://github.com/anarthal/mysql/> >From the documentation: boost.sqlite is a simple to use C++ sqlite library. It provides a modern interface using facilities like error_code, views (e.g. for blobs) and the ability to use boost.describe or boost.pfr for parameterised queries. Supported features include: - typed queries - prepared statements - json support - custom functions (scalar, aggregate, windows) - event hooks - virtual tables SQLite provides an excellent C-API, so this library does not attempt to hide, but to augment it. Please provide in your review information you think is valuable to explain your choice to ACCEPT or REJECT including SQLITE as a Boost library. Please be explicit about your decision (ACCEPT or REJECT). Some other questions you might want to consider answering: - Will the library bring additional out-of-the-box utility to Boost? - What is your evaluation of the implementation? - What is your evaluation of the documentation? - Will the choice of API abstraction model ease the development of software that must talk to a SQLITE database? - Are there any immediate improvements that could be made after acceptance, if acceptance should happen? - 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 at: http://www.boost.org/community/reviews.html The review is open to anyone who is prepared to put in the work of evaluating and reviewing the library. Prior experience in contributing to Boost reviews is not a requirement. Thank you for your efforts in the Boost community. They are very much appreciated. Richard Hodges - review manager of the proposed Boost.SQLITE library Klemens is often available on CppLang Slack and of course by email should you require any clarification not covered by the documentation, as am I.

19 67

Pretty printer module
by Дмитрий Архипов 14 Apr '25

14 Apr '25

Recently Niall Douglas posted about his idea to embed GDB pretty printers into binaries using a header. At the time I was thinking about a good way to deploy pretty printers for JSON that facilitates their autoloading. After Niall's post I experimented a little bit more, and I came to the conclusion that indeed nothing beats embedding via a C++ header in terms of convenience. At the same time I was also thinking about testing that pretty printers do in fact work. Given that pretty printers (usually) are implemented as a Python module, it initially looked like one could just run a Python program and import GDB Python modules. But actually you cannot. It turns out, though, you can run a Python script with GDB as the interpreter. After several iterations I arrived at this setup: https://github.com/boostorg/json/blob/develop/test/printers.cpp. A script converts this file into a Python script that uses GDB to break on certain lines and check if a particular expression produces a particular output when printed. While doing all this I thought that most of this work can be useful to other libraries. So, I moved the reusable parts into a separate directory (https://github.com/boostorg/json/tree/develop/pretty_printers) and added both a b2 module, and a CMake module. For B2. Importing: https://github.com/boostorg/json/blob/develop/build.jam#L8-L9 https://github.com/boostorg/json/blob/develop/build/Jamfile#L13 (Re)generating the header: https://github.com/boostorg/json/blob/develop/build/Jamfile#L88-L95 Testing: https://github.com/boostorg/json/blob/develop/test/Jamfile#L96-L101 For CMake: Importing: https://github.com/boostorg/json/blob/develop/CMakeLists.txt#L54-L55 (Re)generating the header: https://github.com/boostorg/json/blob/develop/CMakeLists.txt#L56-L63 Testing: https://github.com/boostorg/json/blob/develop/test/CMakeLists.txt#L80-L88 My questions to the community: do you find this useful? Would you use it in your Boost or non-Boost library? If you do, the module should be moved to tools rather than stay in libs/json.

12 26

asio::strand: Order of execution
by Georg Gast 11 Feb '25

11 Feb '25

Hi, If I use a asio::strand and post() there multiple function objects, are they executed in the same order or is the order of execution not specified? I think to use it as a work queue but I need them to be processed in sequence... Thx Georg

5 9

Decimal: Formal review begins.
by John Maddock 31 Jan '25

31 Jan '25

The review of the proposed Decimal Number library by Matt Borland and Chris Kormanyos begins today and runs until 22nd Jan. You will find documentation here: https://cppalliance.org/decimal/decimal.html And the code repository is here: https://github.com/cppalliance/decimal/ Boost.Decimal is an implementation of IEEE 754 <https://standards.ieee.org/ieee/754/6210/> and ISO/IEC DTR 24733 <https://www.open-std.org/JTC1/SC22/WG21/docs/papers/2009/n2849.pdf> Decimal Floating Point numbers. The library is header-only, has no dependencies, and requires C++14. Please provide feedback on the following general topics: - 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? Do you already use it in industry? - 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? Ensure to explicitly include with your review: ACCEPT, REJECT, or CONDITIONAL ACCEPT (with acceptance conditions).header-only, has no dependencies, and requires C++14. Best, John Maddock (review manager).

18 94

Author assistance for WG21 display content
by Robert Beeston 30 Jan '25

30 Jan '25

Hello everyone, My name is Rob Beeston, and I’m the Product and Creative Director for C++ Alliance. I’m currently making arrangements for the upcoming WG21 event, and could use some help from some of the authors. We will be making posters, similar to this mockup ( https://downloads.cppalliance.org/images/boost-poster.png) to highlight the following libraries at the event: Hash2 Math Parser Scope Unordered Each poster would need a brief description, a longer explanation (perhaps 1-2 short paragraphs of what it does and/or how it works) and a code snippet that would best represent how to use it. Thanks and I’m looking forward to working with you. Rob

4 6

Interest for C++20 modules support of boost officially
by Chuanqi Xu 29 Jan '25

29 Jan '25

Hi Boost Developers, I am Chuanqi Xu, the maintainer for modules & serialization in clang and also a fan of C++20 modules. The post itself was motivated by a discussion (https://cpplang.slack.com/archives/C27KZLB0X/p1734335425348809 <https://cpplang.slack.com/archives/C27KZLB0X/p1734335425348809 >). You don’t need to read it if you’re not interested. I’ll try to make the post itself self contained. The original story comes from a high quality experiment for C++20 modules in boost (https://anarthal.github.io/cppblog/modules2 <https://anarthal.github.io/cppblog/modules2 >). The blog reads pretty good to me. However, anarthal (the author) told me later that the process of supporting modules in boost got suspended since the authors (or the maintainers) don’t want it since no one is going to use them. And if I want it, I need to send a mail here. Then this is the beginning of the story. First of first, I want to emphasize that “no one is going to use them” is not true. We’ve already used C++20 modules at larger scale internally for roughly a year. For boost (and other third party libraries), we choose to wrap a module ourselves as a workaround (with some compiler extensions to ease the refacotoring, but we don’t like it. We still want standard behavior). We didn’t reach out since we feel boost will support C++20 modules later or sooner so we don’t need to do anything specially. (Maybe we were wrong. We didn’t understand the ecosystem enough). Until yesterday, I just knew that boost didn’t know such needs. Before I wrote this email, I wondered a lot of words to emphasize that our need are a good example and the users of closed source are important users too. But just now, I searched the use of boost in modules in GitHub. I just realized I can show it (the importance of C++20 modules support for boost) much easily with the open source world. I searched `boost path:*.cppm` in GitHub and got the following list: https://github.com/infiniflow/infinity/blob/fa922afd58c973a9a317d2c09ad8cea… <https://github.com/infiniflow/infinity/blob/fa922afd58c973a9a317d2c09ad8cea… > https://github.com/ossia/score/blob/0ce6f62a97651a1248a92b3e13ce6ede10341d1… <https://github.com/ossia/score/blob/0ce6f62a97651a1248a92b3e13ce6ede10341d1… > https://github.com/RichardLuo0/make-dot-cpp/blob/e2ef10fd43060a2b56fc8f87f1… <https://github.com/RichardLuo0/make-dot-cpp/blob/e2ef10fd43060a2b56fc8f87f1… > https://github.com/slaakko/cmajor-mod/blob/32e6eb8dc099b395fa751340de96f478… <https://github.com/slaakko/cmajor-mod/blob/32e6eb8dc099b395fa751340de96f478… > https://github.com/df-com/dragonfly/blob/9dfcbc1153f292eb8581f1df7459600cc3… <https://github.com/df-com/dragonfly/blob/9dfcbc1153f292eb8581f1df7459600cc3… > https://github.com/nofe1248/Helium/blob/92ec4452b8c05e6d86c972f843196a4392a… <https://github.com/nofe1248/Helium/blob/92ec4452b8c05e6d86c972f843196a4392a… > https://github.com/LagrangeDev/liblagrange/blob/10e3b48f8d47fd65de00b14cfed… <https://github.com/LagrangeDev/liblagrange/blob/10e3b48f8d47fd65de00b14cfed… > https://github.com/yudaichen/feature-db/blob/e94ade969af682ed5dd25d70bf282b… <https://github.com/yudaichen/feature-db/blob/e94ade969af682ed5dd25d70bf282b… > This is not a complete list even for my search only and I believe there are other patterns to use boost with modules now (e.g., at least `*.cppm` is not the defacto suffix). And I also believe, from my experience as a C++ user, if boost provide modules, I may try to use it. But if boost didn’t provide it, maybe I won’t ask for it if I don’t want modules super bad. Since modules doesn’t add any new functionality actually. So most users may not ask for it explicitly. But if boost provides it, people may give it a try. The above text are the body of the post. I hope it can show it is needed. — Following of are some technical discussion for the extra maintainance burden by introducing modules. The conclusion is, I think, the burden is pretty low. Since modules are not complex to users. Different from other big features in C++, modules are pretty easy to understand. The complexity of modules are majorly on tools and the ecosystem. For programmers who don’t get involved to much to the ecosystem (or infrastructure), modules should be pretty easy to understand. For authors of libraries, after boost introduce modules, you only need to do 2 extra things: - In headers, add a macro (assume its name as BOOST_MODULE_EXPORT, which will be ‘export’ conditionally) to the entities that need to be exported. - In headers, include standard headers and other dependent headers conditionally so that we don’t include anything if the headers are in a module unit. e.g., https://github.com/boostorg/pfr/blob/f09e6aeae9d050897fff72b93d5f5e866cc5e1… <https://github.com/boostorg/pfr/blob/f09e6aeae9d050897fff72b93d5f5e866cc5e1… > then that’s roughly all you need for maintaining it at source level. For building and distributing related things, anarthal told me that the boost will handle it globally so the individual arthors don’t need to care about it. — In slack, there are some other discussion about module names and linking problems (https://cpplang.slack.com/archives/C27KZLB0X/p1734345716728609 <https://cpplang.slack.com/archives/C27KZLB0X/p1734345716728609 >). But I feel they are implementation details. I may not talk too much for that as a user at least now. And also there are opinions for configuration flags. These are the jobs of build systems (cmake is working on it). I think boost don’t need to worry for that. Similarly, at least libc++ has similar problems but libc++ still released std module. — Boost has a special position in the C++’s ecosystem. The most simple and impressive answer I’ve heard for the question “when can we start to use modules” is, “when boost makes it”. Thanks, Chuanqi

15 85

observing process blocked on find_or_construct
by Murali Kishore 28 Jan '25

28 Jan '25

Hi , We are trying interprocess scenario, one process created shared memory objects and killed and second process open the object using find_or_construct seeing this process blocked at getting lock. bt as shown below, #0 __lll_lock_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:135 #1 0x00007fa6b6733eb6 in _L_lock_941 () from /lib64/libpthread.so.0 #2 0x00007fa6b6733daf in __GI___pthread_mutex_lock (mutex=mutex@entry=0x7fa6b198b070) at ../nptl/pthread_mutex_lock.c:113 #3 0x0000000001bc3822 in lock (this=0x7fa6b198b070) at /x86/include/boost/interprocess/sync/posix/recursive_mutex.hpp:90 #4 lock (this=0x7fa6b198b070) at /x86/include/boost/interprocess/sync/interprocess_recursive_mutex.hpp:163 #5 scoped_lock (m=..., this=<synthetic pointer>) at /x86/include/boost/interprocess/sync/scoped_lock.hpp:81 #6 boost::interprocess::segment_manager<char, boost::interprocess::rbtree_best_fit<boost::interprocess::mutex_family, boost::interprocess::offset_ptr<void, long, unsigned long, 0ul>, 0ul>, boost::interprocess::iset_index>::priv_generic_named_construct<char> (this=0x7fa6b198b010, type=<optimized out>, name=0x7ffde183ca20 "reported_slice_config_list", num=1, try2find=<optimized out>, dothrow=<optimized out>, table=..., index=..., is_intrusive=...) at /x86/include/boost/interprocess/segment_manager.hpp:1076 #7 0x0000000001bee007 in boost::interprocess::segment_manager<char, boost::interprocess::rbtree_best_fit<boost::interprocess::mutex_family, boost::interprocess::offset_ptr<void, long, unsigned long, 0ul>, 0ul>, boost::interprocess::iset_index>::priv_generic_construct (this=<optimized out>, name=name@entry=0x7ffde183ca20 "reported_slice_config_list", num=num@entry=1, try2find=try2find@entry=true, dothrow=dothrow@entry=true, table=...) at /x86/include/boost/interprocess/segment_manager.hpp:760 #8 0x0000000001bf112d in generic_construct<boost::container::map<unsigned int, gnb::broadcast_plmn_list, std::less<unsigned int>, boost::interprocess::allocator<std::pair<unsigned int const, gnb::broadcast_plmn_list>, boost::interprocess::segment_manager<char, boost::interprocess::rbtree_best_fit<boost::interprocess::mutex_family>, boost::interprocess::iset_index> > > > (table=..., dothrow=true, try2find=true, num=1, name=0x7ffde183ca20 "reported_slice_config_list", this=<optimized out>) at /x86/include/boost/interprocess/segment_manager.hpp:704 #9 operator()<std::less<unsigned int>, boost::interprocess::allocator<std::pair<unsigned int const, gnb::broadcast_plmn_list>, boost::interprocess::segment_manager<char, boost::interprocess::rbtree_best_fit<boost::interprocess::mutex_family, boost::interprocess::offset_ptr<void, long int, long unsigned int, 0ul>, 0ul>, boost::interprocess::iset_index> >&> (this=<optimized out>) at /x86/include/boost/interprocess/detail/named_proxy.hpp:132 please let me know in which cases this can be occured, we see first process also hangs in termination. -- Regards, Murali Kishore

3 3

End of Boost.Decimal Review
by John Maddock 25 Jan '25

25 Jan '25

The review of the proposed Decimal library has now ended - although given that there was a lot of lively discussion for me to sort through, there is still time to submit a late review if you wish. If I've counted correctly there were 5 reviews (4 on the list, one private): one firm reject and 4 conditional accept, plus many more people involved in the discussion than gave reviews. I have to be honest, I would have liked to have seen a couple more reviews in order to have reached a clearer consensus, so please bare with me while I sift through all the comments and try and reach a conclusion. My thanks to everyone who took part, and of course to Matt and Chris for submitting the library. Best, John.

1 0

GSoC 2025 Projects
by Matt Borland 24 Jan '25

24 Jan '25

All, In the modules thread and on Slack, I asked if Boost had a current plan for participation in GSoC 2025. I haven't received any responses yet, so I'll assume there isn't a plan. I'm wondering if anyone has: a) Projects they would like to propose for GSoC, and b) An interest in mentoring. Here are some ideas that I think could be beneficial and approachable: 1) A proof of concept for a Boost module, including distribution and installation processes, and potentially adding support to select libraries. This project could have easy access to the Clang and MSVC teams via their mentor it seems. 2) Bi-variate interpolation has been requested before in Math. ACM TOMS algorithms 751 and 761 could fit the bill, but their references are written in F77. A faithful translation and implementation of those papers would be a good start. 3) Chris Kormanyos and I are working on a cryptographic module that we intend to have certified under FIPS 140-3 and then propose to Boost. An extension of this could be a TLS project where a student provides a proof of concept with a generic file transfer server or similar that works securely with OpenSSL, and then also with our new module. I can mentor at least one of these projects. If anyone has past applications for the organization, please send a link or copies. We have until mid-Feb to apply as an organization, which I can do if no one else volunteers. Best, Matt

5 8