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Boost.Beast vs Boost.Asio
by Cristian Morales Vega 04 Dec '18

04 Dec '18

There are lots of things which I would expect to be in Boost.Asio which are actually in Boost.Beast. Why? Most of it is "helping" code/docs. For example: - Documentation about (and public interfaces to simplify) the creation of composed operations https://www.boost.org/doc/libs/develop/libs/beast/doc/html/beast/using_io/w… - beast::buffers_cat - beast::test::stream (to be fair, it's in experimental) But now we even have code to work around issues in Boost.Asio which ideally would simply be fixed in Boost.Asio. For example: beast::ssl_stream. I'm personally using all of the above, they are extremely useful. I just supposed it is because there is only one person working on Boost.Asio, and Christopher must be quite busy with life and getting Networking TS into the standard. I was hoping all this would go away by 2020 and I was ignoring the issue. But since now it seems Networking TS will have to wait for 2023... well, I am asking myself how to handle an increasing amount of references to Beast that in a future could change to Asio (potentially with slightly different names/semantics). So I am writing this hoping for some light on the situation.

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Re: [Boost-users] [asio] UDP recv error handling
by Bjorn Reese 03 Dec '18

03 Dec '18

On 11/22/18 3:44 PM, Klebsch, Mario via Boost-users wrote: > Are there any recommendations on how to decide, whether the receive > callback function should re-initiate a receive operation after a receive > error or not? Unlike TCP, UDP does not establish a connection. By default you will not receive any network errors on a UDP socket. You have to call connect() on the socket in order to receive (ICMP) error messages, but this has other implications. With UDP it is more common to rely on application layer error messages and/or timeouts.

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Monitor OSX kqueue descriptor for events with ASIO
by Blaine Walls 02 Dec '18

02 Dec '18

Hi all, I'm using boost::asio on OS X. I'd like to watch for changes to a particular regular file - per Apple's documentation, the preferred method for this is with the kevent API. So I do the following: 1) Wrap a kqueue file descriptor (obtained via a call to kqueue()) in a boost::asio::posix::stream_descriptor with boost::asio::posix::stream_descriptor::assign(). 2) Call boost::asio::posix::stream_descriptor::async_wait() to be notified of file events. The problem appears to be that boost::asio::posix::stream_descriptor::async_wait() uses ioctl() w/ FIONBIO to put the file into non-blocking mode, which fails with "Inappropriate ioctl for device". A normal blocking call to wait() works just fine. I realize that my problem is that the kqueue descriptor does not represent a stream of bytes, so it's probably invalid to use stream_descriptor to wrap it. Does anyone have any ideas on how to work around this? I looked for a type concept for a non-stream descriptor that I could implement, but I didn't see anything obvious. Thanks in advance for any advice, -Blaine

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boost/units - converting forces (lbf->N)
by Matt Vinson 01 Dec '18

01 Dec '18

To see if I understand the library, I want to create metric and imperial systems without using Boost Units predefined systems*. Conversions between lengths are going well. Conversion between forces are going well until pounds-force to newtons; line 182 in the link. What am I doing wrong when lbf will not convert to newtons? Here is my code: https://coliru.stacked-crooked.com/a/f5f80d39fbdf8013 Any help is appreciated. * //imperial namespace boost {namespace units { namespace us {}}}//sinamespace boost { namespace units { namespace si {}}}

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Boost on Android-ndk
by Philip_liu 30 Nov '18

30 Nov '18

Hi everyone, I want to build a boost on android-ndk in ubuntu18.04,I had tried boost 1.58 and 1.68 on android-ndk r10e r13b r15c,and all failed at the step "./b2 \"with error"version 'xx' of default 'g++' does not match".Hope to know how to solve the problem or tell me how to install successfully with the right version in ubuntu18.04. Best Regard, Philip Liu

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[Spirit] Qi Symbols mapping to AST enum
by Michael Powell 29 Nov '18

29 Nov '18

Hello, I've got a qi::symbols capturing some built-in types. At the moment, I gather, they are mapped to std::string. However, I would rather map them to an AST level enum. For instance, struct builtin_type_t : qi::symbols<char, std::string> { builtin_type_t() { this->add("double", "double") ("float", "float") // ... ; } } builtin_type; Instead, namespace ast { enum type_t { type_double, type_float /* , ... */ }; } struct builtin_type_t : qi::symbols<char, ast::type_t> { builtin_type_t() { this->add("double", ast::type_double) ("float", ast::type_float) // ... ; } } builtin_type; I assume this is possible? Am I missing something about that? Thanks! Michael Powell

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Boost intrusive list volatile hook
by nat ersoz 26 Nov '18

26 Nov '18

I intend to use the boost intrusive list to implement an observer pattern. - The list will cross interrupt boundaries; meaning one interrupt will produce the notifications and the other interrupt will observer the notifications. - The observer, in response to a notification, might detach itself from the list using the the hook's unlink() function. - I think that I will need the hook to be declared volatile in order to accommodate this. I have a minimal code sample here: https://github.com/natersoz/patterns/blob/master/observer/intrusive_list_me… My list hook member declaration: using list_hook_type = boost::intrusive::list_member_hook< boost::intrusive::link_mode<boost::intrusive::auto_unlink> >; list_hook_type hook; My list declaration: using list_type = boost::intrusive::list< Observer<NotificationType>, boost::intrusive::constant_time_size<false>, boost::intrusive::member_hook< Observer<NotificationType>, typename Observer<NotificationType>::list_hook_type, &Observer<NotificationType>::hook> >; If I a the volatile keyword to the list hood type, I cannot figure out how to get the list_type declaration to fit into the list template list. Is it possible? Thank you. -- Nat Ersoz 425-417-5182 (cell)

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Re: [Boost-users] Interprocess: limited boost::any in shared memory
by Ferguson, Neil D CTR (US) 26 Nov '18

26 Nov '18

Mr. de Vries, std::variant looks like it should work splendidly. boost::variant might be even better. Thank you. BTW: this is my first user group interaction; I hope I am responding correctly. Neil Ferguson -----Original Message----- From: Maarten de Vries [mailto:maarten@de-vri.es] Sent: Wednesday, November 21, 2018 1:06 PM To: boost-users(a)lists.boost.org Cc: Ferguson, Neil D CTR (US) <neil.d.ferguson.ctr(a)mail.mil> Subject: [Non-DoD Source] Re: [Boost-users] Interprocess: limited boost::any in shared memory All active links contained in this email were disabled. Please verify the identity of the sender, and confirm the authenticity of all links contained within the message prior to copying and pasting the address to a Web browser. ________________________________ On Wed, 21 Nov 2018 at 20:58, Ferguson, Neil D CTR (US) via Boost-users <boost-users(a)lists.boost.org < Caution-mailto:boost-users@lists.boost.org > > wrote: Sirs and madams, I hope to use boost interprocess shared memory to pass complex and dynamic data structures between processes on a host efficiently. The structures will be comprised only of simple primitives (int, float, etc.), interprocess basic_string, interprocess containers (vectors and maps), containers of containers, and (possible deal killer) boost::any. From the interprocess documentation, it _looks_ like the preceding is doable, aside from boost::any. The boost::any objects will themselves contain only primitives, basic_string, or interprocess vectors of unsigned char. So it _looks_ like the data held by the any should be okay. My question: does boost::any use pointers, references, or other constructs that preclude the class from working in shared memory? Thanks for your advice. Neil Ferguson Take a look at /usr/include/boost/any.hpp . You will see that the actual content of the any object is a pointer created with `new` and cleaned up with `delete`. So this will not work properly in shared memory. You could consider using std::variant instead, which does not put storage on the heap (unless contained objects do it themselves, of course). Kind regards, Maarten de Vries

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IOStream: Determine number of bytes written to array sink
by Peter Klotz 23 Nov '18

23 Nov '18

Hello The program below decompresses a std::string using Boost.IOStream. The target is an array sink of fixed size. The users know the decompressed size in advance but for security reasons I need to check the number of bytes written to the sink. If the array is too small, a "write area exhausted" exception is thrown, which is fine. If the array is too big, decompression succeeds. I would like to check the number of bytes written to the sink and throw an exception. How can I determine how many bytes have been written to the sink? Btw: I cannot use the "counter" filter because of the overhead involved in line counting and because the return value of its characters() method is "int". The buffers involved in my application require a 64 bit data type. Private base class basic_zlib_decompressor of class basic_gzip_decompressor has method total_out() which seems to return the value in question but its return type is also only an "int". Regards, Peter. #include <iostream> #include <stdexcept> #include <iomanip> #include <boost/iostreams/filtering_streambuf.hpp> #include <boost/iostreams/device/array.hpp> #include <boost/iostreams/filter/gzip.hpp> void decompress(const std::size_t p_bufferSize) { // decompressed string is "xy" const std::string s("\x1f\x8b\x08\x08\x58\xce\xf6\x5b\x02\x03\x78\x79\x00\xab\xa8\x04\x00\x99\x28\xe6\x8f\x02\x00\x00\x00",25); boost::iostreams::filtering_streambuf<boost::iostreams::output> filteringStreambuf; filteringStreambuf.push(boost::iostreams::gzip_decompressor()); const std::unique_ptr<char[]> buffer=std::make_unique<char[]>(p_bufferSize); filteringStreambuf.push(boost::iostreams::array_sink(buffer.get(),p_bufferSize)); boost::iostreams::write(filteringStreambuf,s.c_str(),s.size()); boost::iostreams::close(filteringStreambuf); } int main() { try { decompress(3); // works, although only 2 bytes are required, should be made to fail //decompress(2); // works, exactly fills the buffer //decompress(1); // throws exception "write area exhausted" as expected return 0; } catch (const std::exception& e) { std::cout << e.what() << std::endl; } return 1; }

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Overcoming AST forward declaration (includes online example)
by Michael Powell 23 Nov '18

23 Nov '18

Hello, Please find the example posted here: http://wandbox.org/permlink/NI2Luvrw1HF7lF1E The couple of concerns I have in question at the moment are: * How to best handle variants throughout the grammar. Can I use std::variant? Do I need to use boost::variant? Are there additional Spirit features that make this doable? * Embedded in that question is what to do with "nil" or "empty statements" which occurs throughout the grammar at times. I wondered if "empty statement" could synthesize "nothing", literally, not contribute to a variant alternative, for instance. Other AST examples seemed to inject a "struct nil {}" pattern, so I figured maybe this was the better approach? * The real kerfuffle for me at the moment is the AST forward declaration. From what I gather in the protocol, this is an absolute must have. It most occur before Group, and is also used by Message. Thoughts? Suggestions? And, please, before you suggest there are "proto compilers" already available: yes, I know, I've been down that road. I am not looking to parse the proto itself, per se, but rather do some code generation for target language artifacts other than the proto itself. Toward which end, I am also investigating a protoc compiler plugin approach. But I figured, I'd pursue this as a viable path to solving the problem as well, notwithstanding the above challenges. Thanks in advance! Cheers, Michael Powell

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