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[variant] apply_visitor/static access to which()
by Stefan Strasser 18 Nov '09

18 Nov '09

Hi, I have a problem regarding the static visitor of boost::variant. there is a variant and a mpl vector: variant<A1,A2,A3> var; typedef mpl::vector<B1,B2,B3> B_types; the variant and the vector have the same number of types, but not the same types. I need to "visit" the element of the variant, and access the B_types element at the same position as the element of the variant: struct visitor : static_visitor<void>{ template<class A> void operator()(A a) const{ typedef typename mpl::at_c<B_types,var.which()>::type B; //error } }; so if var.which() == 1, I need a typedef of type B2. obviously the code above doesn't work because which() is a runtime function. but the value of which() is known statically at this point (that's the point of visitation). is there a way to access it, with boost::variant visitors? I like neither of the solutions I can come up with: 1. write my own visitation pattern that not only instantiates the visitor with the variant type but also with the vector type. 2. convert the variant to template<class A,class B> struct A_holder{ typedef B B_type; A value; }; variant<A_holder<A1,B1>,A_holder<A2,B2>,A_holder<A3,B3> > var; 3. do a seperate "visition" of the mpl vector inside the variant visitor: struct visitor : static_visitor<void>{ template<class A> void operator()(A a) const{ switch(var.which()){ case... case... } } }; is there a better way to do this?

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Boost release 1.41.0 available
by Beman Dawes 18 Nov '09

18 Nov '09

Boost release 1.41.0 is now available. This release contains one new library and numerous bug fixes for existing libraries. For details, including download links, see http://www.boost.org/users/news/version_1_41_0 The release can also be downloaded directly from SourceForge. See http://sourceforge.net/projects/boost/files/ To install this release on your system, see http://www.boost.org/doc/libs/1_41_0/more/getting_started/index.html Thanks, --The Boost release team

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[asio] Error: should never be called
by Norbert Wenzel 18 Nov '09

18 Nov '09

Since a few days I do get strange exceptions (boost::system::system_error) from my asio network code, based on v1.39. The message logged with .what() and .code() gives the following line: winsock: error: should never be called (error: should never be called:16646560) (The .code() output is put in parentheses.) I found two functions that produce the message in error_code.hpp (line 479ff) but I have no idea why they shouldn't be called. There's a comment to explain the implementation that refers to VC++ 8, but I have VC++ 7.1, so it doesn't seem that this code is called for VC++ 8 only. Are there any known cases, that produce this error message? thanks, Norbert

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asio::async_write
by Lloyd 18 Nov '09

18 Nov '09

Hi, I have been trying very hard to "compile" this code. What is the reason for the compilation errors in the "async_write" call. #include <boost/bind.hpp> #include <boost/enable_shared_from_this.hpp> #include <boost/asio.hpp> using boost::asio::ip::tcp; class aa { public: void testme() { char a[20]="<test data>"; boost::asio::io_service io; tcp::socket s(io); boost::asio::async_write(s,boost::asio::buffer(a,sizeof(a)), boost::bind(&aa::handler,shared_from_this(),boost::asio::placeholders::error)); } void handler(const boost::system::error_code& error) { } private: }; int main() { aa x; x.testme(); return 0; } The erros I got are: ==================== 1>------ Build started: Project: del, Configuration: Release Win32 ------ 1>Compiling... 1>del.cpp 1>.\del.cpp(19) : error C2780: 'void boost::asio::async_write(AsyncWriteStream &,boost::asio::basic_streambuf<Allocator> &,CompletionCondition,WriteHandler)' : expects 4 arguments - 3 provided 1> C:\Program Files\boost140\boost/asio/write.hpp(510) : see declaration of 'boost::asio::async_write' 1>.\del.cpp(19) : error C2784: 'void boost::asio::async_write(AsyncWriteStream &,boost::asio::basic_streambuf<Allocator> &,WriteHandler)' : could not deduce template argument for 'boost::asio::basic_streambuf<Allocator> &' from 'boost::asio::mutable_buffers_1' 1> C:\Program Files\boost140\boost/asio/write.hpp(453) : see declaration of 'boost::asio::async_write' 1>.\del.cpp(19) : error C2784: 'void boost::asio::async_write(AsyncWriteStream &,boost::asio::basic_streambuf<Allocator> &,WriteHandler)' : could not deduce template argument for 'boost::asio::basic_streambuf<Allocator> &' from 'boost::asio::mutable_buffers_1' 1> C:\Program Files\boost140\boost/asio/write.hpp(453) : see declaration of 'boost::asio::async_write' 1>.\del.cpp(19) : error C2780: 'void boost::asio::async_write(AsyncWriteStream &,const ConstBufferSequence &,CompletionCondition,WriteHandler)' : expects 4 arguments - 3 provided 1> C:\Program Files\boost140\boost/asio/write.hpp(411) : see declaration of 'boost::asio::async_write' 1>.\del.cpp(19) : error C3861: 'shared_from_this': identifier not found 1>Build log was saved at "file://c:\Documents and Settings\Administrator\Desktop\del\del\Release\BuildLog.htm" 1>del - 5 error(s), 0 warning(s) ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== ______________________________________ Scanned and protected by Email scanner

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[Bimap] Many warnings
by Dylan Klomparens 18 Nov '09

18 Nov '09

I declared a bimap in my code and discovered that it generates 200+ warnings. I'm using MS Visual Studio 2008 with Boost 1.41. All the warnings are the same: C4503: '<long variable name>' : decorated name length exceeded, name was truncated Functionally, the program *should* still work despite all the warnings (from what I've found on Google), but I'd like to know why this many warnings are generated by declaring: "boost::bimap<int, int> RemoteIdentityMap;". Does anyone know? -- Dylan

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Shortest path problem: distance between two vertices
by Pedram Pedarsani 18 Nov '09

18 Nov '09

I am kind of new to C++ and also boost library, trying to use the bfs to find the distance between two vertices in a graph. As I read from previous posts, the easiest way would be to throw an exception once the target vertex has been discovered. Now the problem is that I can't figure out how to do this, and this is pretty urgent! Can you help me with a few lines of code which make the bfs_visitor and call the bfs function for this purpose? Thanks a lot!

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Re: [Boost-users] [Graph] changes in 1_40 (Meththa)
by Ralph Gauges 18 Nov '09

18 Nov '09

Hi, I think you can pass whatever you want for those parameters since they are actually not used in the algorithm. The only thing that is used it the topology. Actually the fruchterman algorithm in 1.40 was broken and did not work for me. Maybe you should give the newly released 1.41 a try because there the two parameters origin and extend have been removed and the bug that was in 1.40 has been fixed. Best Ralph

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How to upload a file with ASIO
by Ramon F Herrera 18 Nov '09

18 Nov '09

Hello, I have successfully implemented clients and servers, both in the Windows side and the Linux side. So far, the Windows client passes a set of parameters and the servers returns some text which is displayed on the client's screen. That part is working perfectly. My next challenge is to upload a whole file(s) from the client to the server and would like hear any tips, caveats from experienced ASIO users. Thanks to everyone for sharing their expertise. Regards, -Ramon

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Re: [Boost-users] [serialization] Problems with serializingashared_ptr
by Robert Ramey 17 Nov '09

17 Nov '09

dfs(a)savarese.org wrote: > In message <hdt8vh$66b$1(a)ger.gmane.org>, "Robert Ramey" writes: >> I'm pretty sure I addressed this in 1.41 Robert Ramey > the fix, report back, and possibly improve on the fix if required and > submit a patch via the issue tracking system. By the same token, when > users report a problem, it would be extremely helpful if they were to > post a concise self-contained compilable example that reproduces the > problem so that both the library maintainer and other users can > readily understand and isolate the issue as well as verify any > proposed fixes. > If this is already happening via the issue tracking system, then I > apologize for restating the obvious. I'm simply finding it very > difficult to determine which Boost.Serialization problems being > reported on the mailing list are real or imagined. Well, it's not always easy for me either. The tracking system has worked well for me and I make an effort address issues reported there. > Since I cannot reproduce either reported problem, I have to assume > the problems are either compiler-specific or caused by operator error > until shown otherwise. Looks like I may have been able to reproduce the problem here. I'll let you know. Robert Ramey

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[python] undefined symbol Py_InitModule4
by Jan Boehme 17 Nov '09

17 Nov '09

Hi, I'm new to boost python and built an extension on Centos 4 64bit using Boost 1.40 and python 2.3.4-14.7.el4_8.2 and it runs like a charm on the same machine. After that I tried to use my extension on a RHEL4 with python 2.3.4-14.3 installed and got the following error: ImportError: /tmp/install/lib/libboost_python.so.1.40.0: undefined symbol: Py_InitModule4 I get the same error when using python 2.6 on Fedora 11 64bit. Is this some kind of versioning issue? I'm quite helpless with this and your help is highly appreciated. Cheers, Jan.

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