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[release] Boost 1.76.0 Beta 1 Release Candidate 1
by Marshall Clow 11 Mar '21

11 Mar '21

The first release candidates for the 1.76.0 beta release are now available at: <https://dl.bintray.com/boostorg/beta/1.76.0.beta1/source/> The SHA256 checksums are as follows: a222d325cd3c9f66951ec9026eca6ff6f48dd563c9a025911d598d2aca8770ce boost_1_76_0_b1_rc1.tar.bz2 6b90b510a3de38fc30a071ac798da37545fb60a1d6b21aed1130b47c9c598977 boost_1_76_0_b1_rc1.zip b01627bd9ce934b092037da81696bb4482a44e6a31c8791dbed82eafe04b69fa boost_1_76_0_b1_rc1.tar.gz dbef57adbab1d4395d14000f0a2420fc82f87476e10d48359ceff7125a74b77a boost_1_76_0_b1_rc1.7z As always, the release managers would appreciate it if you download the candidate of your choice and give building it a try. Please report both success and failure, and anything else that is noteworthy. -- The Release managers

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(no subject)
by Jinlong Shen 11 Mar '21

11 Mar '21

Dear Madam/Sir, I used the boost::statechart asynchronous_state_machine to create a simple state machine. The state machine, the events and states are regular classes and are not class templates. Everything builds and works well on linux and qnx platform. However, on windows I got message that the the initial state is undefined. I think I have dealt with forward declaration well since it is build on linux and qnx. On Windows microsoft this compiler is used: Microsoft (R) C/C++ Optimizing Compiler Version 19.00.24215.1 for x64 The error message is like this. (ClCompile target) -> C:\Program Files\boost_1_64_0\boost/statechart/state_machine.hpp(701): error C2027: use of undefined type 'xxxx::FirstState' C:\Program Files\boost_1_64_0\boost/statechart/state_machine.hpp(701): error C3861: 'initial_deep_construct': identifier not found Any hint how it could be wrong with Microsoft C++? Best regards,Jinlong Shen

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Boost accepted in Google Summer of Code 2021
by David Bellot 09 Mar '21

09 Mar '21

We're in again! https://github.com/boostorg/wiki/wiki/Google-Summer-of-Code%3A-2021 David

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MSM and multithreading. Not clear what pattern to follow.
by Andrea Fiorito 08 Mar '21

08 Mar '21

Hi, I'm trying to use MSM to implement a client server component for my app. The client is broadcasting a msg, that servers in a local network will detect and respond. The client at that point will connect to one of the servers and interact following the network protocol. For the network and threading I'm using boost ASIO. I have 2 submachines that manage one the discovering part, and the other the connection and dialogue with one server part. I found that would be beneficial to run the submachines in one thread managed by an io_context, with the idea of stopping that context to cancel all the asynchronous operations. Unfortunately there are some weird behaviours with submachines, and not getting if I missed the right way of doing things or else. the description of my last stopper is here: https://github.com/boostorg/msm/issues/37 Is anyone able to point me on the right direction? Regards, Andrea

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CMake's PCH support and boost.test linker error
by Olaf Peter 04 Mar '21

04 Mar '21

Hello Boost users I have here a strange problem which occurs only if I try to build with precompiled headers using CMake. I've configured the project for use with dynamically linking. The error is: /usr/bin/ld: /usr/lib/gcc/x86_64-redhat-linux/10/../../../../lib64/crt1.o: in function `_start': (.text+0x24): undefined reference to `main' Something obvious? Thanks in advance The project's reduce is: ---8<--- test_driver.cpp --- 8< ---- #defineBOOST_TEST_MODULE "My Test Suite" #include<boost/test/unit_test.hpp> --->8------>8------>8--- ---8<--- test_x.cpp --- 8< ---- #include<boost/test/unit_test.hpp> .... --->8------>8------>8--- ---8<--- src/CMakeLists.txt --- 8< ---- ... set_source_files_properties(src/test_xxx.cpp APPEND PROPERTIES COMPILE_DEFINITIONS "BOOST_TEST_DYN_LINK" ) .... --->8------>8------>8------>8------>8------>8--- ---8<--- pch.pp --- 8< ---- #pragma once #include<boost/test/unit_test.hpp> --->8------>8------>8---

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How should a "using zlib ..." jam statement look, for Boost to link to ZLib in the form of SO filename (libz.so) instead of by -lz?
by Bob 03 Mar '21

03 Mar '21

Hello Boost mailing list, I am building a code project in my user home directory on OpenBSD, and doing this involves both a local build of Boost and also a local build of ZLib. I do the whole build using GCC. This is a relatively ordinary build use case, however GCC on OpenBSD (at least in its current version) has a peculiarity to it, which is that it adds to LD the argument "-L/usr/lib" in the leading position, and this means that LD's search for libz.so will find and use the operating system's bundled ZLib binary which is /usr/lib/libz.so ALWAYS, and NEVER use my local libz.so . Can you help me understand if Boost can be customized to link to ZLib in the following way: I can force GCC/LD to use a particular libz.so file, by specifying it by filename, e.g. "gcc ... libz.so ...", "gcc ... /my/dir/libz.so ...", instead of by the conventional "-lz". Boost's build process is hardwired to "-lz" and I ask you to help me understand if there is a way to circumvent that. ZLIB_LIBRARY_PATH will not make "-lz" hit anything else than /usr/lib/libz.so , per the compiler's default -L/usr/lib in leading position, so it will not be of help to solve my problem. To my best awareness ZLIB_INCLUDE has nothing to do with linking, so it will not be of help to solve my problem. ZLIB_NAME would only be to customize the library name would it e.g. to "-lmycustomz", or what is it for? Please clarify so I could figure if it could be of help, though ideally i keep my local ZLib having its default name "libz.so". And this brings me to the path of solving the problem that I imagine could work, but that I don't understand fully from the Boost documentation: There is the possibility to customize ZLib build settings through the JAM configuration, that is user-config.jam . The syntax used is "using zlib ...". Can you please help me understand if this route works, if so how would that "using zlib ..." statement look, such that Boost's build process will NOT build ZLib itself, and then will NOT link to it via "-lz", but will instead link to it by "$MYCUSTOMBUILDDIR/libz.so"?

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Boost.Python + `RecursionError` during deallocation
by Andrew Jones 01 Mar '21

01 Mar '21

Hi, I just raised the following issue on the Python issue tracker: https://bugs.python.org/issue43351 But I'm sharing it here to widen the net ... Basically, when moving from Python 2.7.14 to Python 3.7.5, and when using Boost.Python (Boost version 1.6.9), I'm seeing a crash in finalisation due to: ``` Exception ignored in: <Boost.Python.life_support object at 0x2acf473c5d10> RecursionError: maximum recursion depth exceeded while calling a Python object Fatal Python error: Cannot recover from stack overflow. ``` Everything else with the Python that's running, and the Boost.Python interface, is consistent between 2.7.14 and 3.7.5 -- it is just the Python version that's changing. I should say, Python 3.7.5 does otherwise seem operable, it just falls over when running this certain code (which just walks a linked-list of ~1400 elements via Boost.Python). Has anyone seen anything like this before? Does this list feel this is more likely a Python-proper issue, or a Boost.Python issue? Cheers, Andrew

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[boost::units] Best practices for implementing custom units and quantities
by Alexandru Onea 01 Mar '21

01 Mar '21

Hello community, I am working on a project which works with units such as scale intervals (cents, moria, etc.) depending on the temperament system used (24-EDO, 72-EDO, etc.). My implementation defines a namespace for each tuning system. Within the namespaces I define base units, units and a system, as well as conversion factors between the systems. The base dimension is defined in only one of the namespaces (corresponding to the tuning system which I consider "standard" which is the 1200 cents per octave system). 1. Does such an approach qualify as a good approach in general (leaving aside the musical aspects)? 2. Is it a good practice to place all these namespaces in boost::units (extend boost::units)? Or should I keep them within my own namespaces? Learning the answer to #2 is more interesting to me, even in the absence of an answer to #1. Best regards, Alexandru Onea

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Question about Boost Integer
by Emilio Paolini 28 Feb '21

28 Feb '21

Hi everyone, i'm pretty new to Boost. I need to use as a default type for the CNL. The problem is that i would need an integer type that can assume only 2^4 values (so basically that stays on 4 bits). What i am asking is that if there is a way to define an integer like int128_t but instead of 128 i would need to have 4. Thank you very much for your answers. Emilio

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flyweights, nested flyweights and shared libraries
by Andreas Buykx 25 Feb '21

25 Feb '21

I want to use boost::flyweight to capture some structures containing const data. The documentation states that if flyweights are exported across shared library boundaries that the intermodule holder should be used. Since my flyweights are all created in the same shared library I would prefer to use the static holder but I keep getting crashes. I tried the intermodule holder but I'm having trouble compiling my sources with that. So my thinking was to wrap all flyweight types in accessor classes which are exposed instead, and the accessor classes create the flyweights within the same shared library to store the data. Would that be a valid approach? Also, is it possible to have nested flyweights (when they are wrapped by accessor classes)? And would that cause any additional problems in the above scenario? Below is an example of what I'm trying to achieve... Thanks for your advice! Andreas === Foo.h === struct FooDetails { FooDetails( std::string text_, std::vector<double> values ); std::string text; std::vector<double> values; }; class STUFF_EXPORT Foo { public: Foo( std::string text_, std::vector<double> values ); // rule-of-5 constructors declared, and default-implemented in cpp file const std::string& text() const; const std::vector<double>& values() const; private: boost::flyweight<FooDetails> m_data; }; === Foo.cpp === FooDetails( ( std::string text_, std::vector<double> values_ ) : text(text_), values( values_ ) { } Foo::Foo( std::string text_, std::vector<double> values_ ) m_data( FooDetails( text_, values_ ) ) { } std::string Foo::text() const { return m_data.get().text; } std::vector<double> Foo::values() const { return m_data.get().values; } === Bar.h === struct BarDetails { BarDetails( Foo foo_, std::vector<long> ids_ ); Foo foo; //< Foo holds a flyweight std::vector<long> ids; }; class STUFF_EXPORT Bar { public: Bar( std::string text_, std::vector<double> values_, std::vector<long> ids_ ); // rule-of-5 constructors declared, and default-implemented in cpp file const std::string& text() const; const std::vector<double>& values() const; const std::vector<long>& ids() const; private: boost::flyweight<BarDetails> m_bar; }; === Bar.cpp === BarDetails::BarDetails( Foo foo_, std::vector<long> ids_ ) : foo( foo_ ), ids( ids_ ) { } Bar::Bar( std::string text_, std::vector<double> values_, std::vector<long> ids_ ) : m_bar( Foo( text_, values), ids_ ) { } const std::string& Bar::text() const { return m_bar.get().m_foo.text(); } const std::vector<double>& Bar::values() const { return m_bar.get().foo.values(); } const std::vector<long>& Bar::ids() const { return m_bar.get().ids; }

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