September 2024 - Boost-users

[boost] Boost.LEAF in Embedded Systems (CppCon)
by Vinnie Falco 23 Sep '24

23 Sep '24

At CppCon 2024 the C++ Alliance sponsored a program to interview conference goers about Boost-related topics. This is the first video in the series: Boost.LEAF in Embedded Systems: Insights from Ex-Google Engineer Khalil Estelle at CppCon https://www.youtube.com/shorts/BksBxnTLltY Enjoy! Thanks

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[PFR] names_as_array doesn't work for structs with array fields
by Chinmay Dalal 23 Sep '24

23 Sep '24

Hi, `boost::pfr::names_as_array<T>()` does not compile if `T` has an array member. Someone commented a fix on a similar issue: https://github.com/boostorg/pfr/issues/170 What would be the appropriate place to ask for including this fix? Background: I'm trying to print structs as CSV. I came up with this: https://paste.sr.ht/~p00f/667e013c23c991ddec91e9cdaa00bd3c11cb2ceb But as soon as I include an array member: https://paste.sr.ht/~p00f/aa08531cd100f8b94c49ead2c541ff96f55b362e it does not compile: https://paste.sr.ht/~p00f/636c1e3ab4f5ba86aa865f70f32337b3d2872047 Thanks, Chinmay

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Boost.Asio UDP sockets guarantee for ordering
by Kalesis, Ioannis 18 Sep '24

18 Sep '24

Hello, I am using boost.asio for udp sockets to broadcast multicast traffic. For that, I am using async_send methods. I am aware that there is no guarantee for the order of the completion handlers for the async_send calls, and for that reason I have implemented a queueing mechanism, where the coroutine waits for the current async_send to complete before moving forward to the next call. However, given the low latency requirement of the application, I believe that the following approach may be more optimal: * The async_send operation would happen immediately one after another (not concurrently) without waiting for the previous ones to complete. * The queueing mechanism would be used but only for the post processing work completion handlers. The above will provide both better latency (by sending the packets sooner instead of having to enqeue/spawn_co/dequeue) and still maintain the strict ordering requirement of the post processing work. However, one concern that I have with this approach is with the "multiple" async_send calls being made one after the other. After searching on this topic, I arrived at the conclusion that this is "safe" given that they are not composed operations so there is no risk that the data will be interleaved between packets. The point that I need help understanding is whether there is a guarantee on the order of the packets being enqueued to kernels network stack. For the following example: ``` udp_socket.async_send(packet1,...); upd_socket.async_send(packet2,...); ``` Is there any possible way for "packet2" to be enqueued 1st in the kernel network stack? Similarly, Is it possible for it to be sent by the OS 1st? I acknowledge that even if everything went perfect on the machine, packets could still be received out-of-order to the clients and that is acceptable, however I would like at least to not have the application contribute to this as part of a software issue. The application has multiple threads that run the same io_context with strands in place to have thread-safety. My machine is a redhat 9, gcc 11.4 Thank you in advance for your time and cooperation. Best regards

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Re: [Boost-users] Boost-users Digest, Vol 5734, Issue 1
by Oran Johnson 09 Sep '24

09 Sep '24

Any ideas as to how to correct the following? johnson@fedora:~/opensource$ svn co https://svn.boost.org/svn/boost/sandbox sandbox svn: E170013: Unable to connect to a repository at URL 'https://svn.boost.org/svn/boost/sandbox' svn: E000111: Error running context: Connection refused ________________________________ From: Boost-users <boost-users-bounces(a)lists.boost.org> on behalf of boost-users-request(a)lists.boost.org <boost-users-request(a)lists.boost.org> Sent: Tuesday, August 27, 2024 8:00 AM To: boost-users(a)lists.boost.org <boost-users(a)lists.boost.org> Subject: Boost-users Digest, Vol 5734, Issue 1 Send Boost-users mailing list submissions to boost-users(a)lists.boost.org To subscribe or unsubscribe via the World Wide Web, visit https://lists.boost.org/mailman/listinfo.cgi/boost-users or, via email, send a message with subject or body 'help' to boost-users-request(a)lists.boost.org You can reach the person managing the list at boost-users-owner(a)lists.boost.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Boost-users digest..." Today's Topics: 1. Accessing the Boost Sandbox (oranjsr(a)gmail.com) ---------------------------------------------------------------------- Message: 1 Date: Mon, 26 Aug 2024 10:00:58 -0400 From: <oranjsr(a)gmail.com> To: <boost-users(a)lists.boost.org> Subject: [Boost-users] Accessing the Boost Sandbox Message-ID: <010601daf7c0$60c585b0$22509110$(a)gmail.com> Content-Type: text/plain; charset="utf-8" Hi, I'm looking at a source forge project with the following required libraries: 1) Boost version 1.39 or later 2) TBB (Threading Building Blocks) version 2.1 or later 3) MSM (Meta State Machine) version 1.2 or later 4) Boost Logging Library v2 #3 appears to be in the boost sandbox Does boost sandbox still exists? Boost Sandbox When boost was developed using subversion, the Boost Sandbox contained unreviewed code that is intended to eventually become a part of the Boost libraries. New libraries should be developed separately as <https://svn.boost.org/trac/boost/wiki/ModularBoost> git modules, and existing projects should be <https://svn.boost.org/trac/boost/wiki/ExtractSandbox> moved to GitHub. The sandbox remains as a historical record. Accessing the Boost Sandbox The Boost Sandbox lives at <https://svn.boost.org/svn/boost/sandbox> https://svn.boost.org/svn/boost/sandbox within the old Boost Subversion repository. Regards Oran

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[filesystem] why is this file not found?
by Michael Burr 04 Sep '24

04 Sep '24

I'm having difficulty using boost/filesystem.hpp on a simple test example. If I understand things correctly, this code should see if it can find the files called "test_file" and "test_file2" in the current directory. ``` #include <boost/filesystem.hpp> #include <iostream> using namespace boost::filesystem; int main() { path file1 = "test_file", file2 = "test_file2"; if(status(file1).type() == file_not_found) std::cout << "First file not found\n"; if(status(file2).type() == file_not_found) std::cout << "Second file not found\n"; return 0; } ``` If I run the following, ``` touch test_file g++ filesystem_check.cpp -lboost_filesystem ./a.out ``` the result is > First file not found > Second file not found I expected only the second file to be not found. I arrived at this question because exists(file1) was returning false when I thought it should return true, and I traced the issue back to this check. I've also tried this example with an absolute path, and the results were the same. This is using Boost 1.81 installed via macports on a mac with OS 12.5.1 (so slightly out-of-date OS). Is this a mac issue or am I missing something in my code?

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