November 2009 - Boost-users

Re: [Boost-users] Automating Serialization?
by Brian Wood 27 Nov '09

27 Nov '09

Stefan Strasser writes: >Am Thursday 26 November 2009 14:05:18 schrieb Bilokon, Paul: >> Hi, >> >> By design Boost Serialization requires the user to list each field that >> needs to be serialised. >> >> This is in contrast, for example, with Java and some other languages where >> serialisation is supported (kind of) at the language level. >> >> The current approach requires some code duplication. We have to declare a >> field. We have to manually (de)serialise it. If we need to make a change, >> we make it in at least two distinct places. >> >> Is there any way to automate the process of serialisation, perhaps >> harnessing the power of the preprocessor? E.g. we could label the fields >> that need to be serialised. Is there anything in Boost that could help? > >not that I'm aware of, but I even think that's a good thing. >the serialize() function represents a file format, and you want file formats >to be stable and not being changed because someone added a runtime field to a >class. "runtime field" ? >usually when you do want to add a serialized field you'd also want old >versions of the file still to be readable, so you end up writing custom >(versioned) deserialization code anyway, even if your language has built-in >serialization support. I recommend avoiding the versioning support in Boost Serialization. It runs counter to good development practices by averting the type system. Consider for example a class called Account that uses versioning to support multiple releases of a product. In the usual case, later releases will have more fields and added complexity than earlier releases. Support then for a client at an early release, say 1.1, becomes inefficient since Account is being used to handle both 1.2 and 1.1 users. If instead Account_11 and Account_12 are used -- with Account_12 probably derived from Account_11 -- this weakness is avoided. Additionally this approach is beneficial from a testing perspective. In a 1.2 server, 1.1 clients are supported using Account_11, which has already been tested and is not messed with to support 1.2 clients. > >you could use some compile time code generator to write default serialization >code for you, using e.g. OpenC++, GCC-XML, or Doxygen, but I doubt those >generated functions would stay there very long. I'm not exactly sure what you are saying here, but if a user is simply improving the names of some of his fields, the functions won't stay the same very long. Automating this helps with a common problem of forgetting to update the serialization functions and the compiler then barking. I don't claim though that every class should be handled this way. The C++ Middleware Writer allows users to turn off the automated generation of marshalling functions if that is desired. In my experience, it is unusual to turn that functionality off. Regards, Brian Wood http://www.webEbenezer.net <http://www.webebenezer.net/> "Then Samuel took a stone, and set it between Mizpeh and Shen, and called the name of it Ebenezer, saying, so far the the L-RD has helped us."

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BOOST_FOREACH and boost::bimap
by Conoscenza Silente 27 Nov '09

27 Nov '09

Hi All I tried to use BOOST_FOREACH with bimap but it doesn't compile. What is wrong in using it the way is displayed below? Reading the specs it should be able to work since bimap provide .begin() and .end() methods. Thanks CS typedef boost::bimap<int,std::string > BMap; typedef boost::bimap<int,std::string >::value_type BMapVal; typedef boost::bimap<int,std::string >::const_iterator BMapKIt; BMap myBimap; myBimap.insert( BMapVal( 10, "hi") ); myBimap.insert( BMapVal( 20, "hihihi") ); BOOST_FOREACH( BMapKIt it, myBimap) // this line doesnt' compile: { std::cout << "LEFT: " << it->left << " RIGHT: " << it->right << std::endl; } TestBoost_Nov26.h:68: error: conversion from ‘boost::bimaps::relation::mutant_relation<boost::bimaps::tags::tagged<const int, boost::bimaps::relation::member_at::left>, boost::bimaps::tags::tagged<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::bimaps::relation::member_at::right>, mpl_::na, false>’ to non-scalar type ‘boost::bimaps::detail::set_view_iterator<boost::multi_index::detail::bidir_node_iterator<boost::multi_index::detail::ordered_index_node<boost::multi_index::detail::index_node_base<boost::bimaps::relation::mutant_relation<boost::bimaps::tags::tagged<const int, boost::bimaps::relation::member_at::left>, boost::bimaps::tags::tagged<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::bimaps::relation::member_at::right>, mpl_::na, true>, std::allocator<boost::bimaps::relation::mutant_relation<boost::bimaps::tags::tagged<const int, boost::bimaps::relation::member_at::left>, boost::bimaps::tags::tagged<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, boost::bimaps::relation::member_at::right>, mpl_::na, true> > > > > >’ requested

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[interprocess] file_lock permission denied
by Trigve Siver 27 Nov '09

27 Nov '09

Hi, I'm trying to use file_lock from interprocess but without success. Here is code I'm using: m_Stream.exceptions(std::ios::badbit); m_Stream.open(m_FileName.c_str()); boost::interprocess::file_lock lock(m_FileName.c_str()); ... { // Lock file boost::interprocess::scoped_lock<boost::interprocess::file_lock> scoped_file_lock(lock); // Write to stream m_Stream << "Some text"; m_Stream.flush(); } where m_Stream is std::ofstream. When "m_Stream.flush()" is executed, I've got a "badbit" exception with "errno" 0x001b0800 and message (with strerror()) "Permission denied". I've tried also with win32 CreateFile()/WriteFile() but without success. I'm using boost 1.40, Visual Studio 2005 SP1, Vista 32 bit SP2 Thanks Trigve

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Re: [Boost-users] Automating Serialization?
by Brian Wood 27 Nov '09

27 Nov '09

Emil Dotchevski writes: >On Thu, Nov 26, 2009 at 5:05 AM, Bilokon, Paul <paul.bilokon(a)citi.com> wrote: > >> The current approach requires some code duplication. We have to declare a >> field. We have to manually (de)serialise it. If we need to make a change, we >> make it in at least two distinct places. > > You are thinking in terms of reflection. Think in terms of states and > invariants and it'll make more sense. For example, if you have an > array of items and a pointer, and your invariant is that the pointer > always points the last element in the array, the pointer should not be > serialized. > I don't know if that is a common situation, but there are two ways to handle that with the C++ Middleware Writer. One as I mentioned in another post is to turn off the automatic generation of marshalling functions. The other is to place those fields which shouldn't be included in the marshalling process within an #ifdef SERVER_SIDE -- http://webEbenezer.net/ifdefSERVER.html . The macro is turned on when servers are built and off when clients are built. This approach enables servers to have a complete view of a type and clients to have an accurate, but limited view of the same type. Regards, Brian Wood http://www.webEbenezer.net <http://www.webebenezer.net/> "Then Samuel took a stone, and set it between Mizpeh and Shen, and called the name of it Ebenezer, saying, so far the the L-RD has helped us."

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using uint8_t & the like on open solaris
by Maróy Ákos 27 Nov '09

27 Nov '09

Mikko, > You could try > using boost::uint8_t; This is what I wanted to avoid. looking at the issue further, it seems that solaris doesn't have the <stdint> C++ include, only the <stdint.h> C include, and thus these definitions are incolded from there, into the global namespace. as a solution, <boost/cstdint.hpp> could put the contents of the <stdint.h> C include into the std namespace explicitly, to increase C++ compliance - as the C includ would be unaware of namespaces anyway. another workaround is to specify using boost::uint8_t; before usage. Akos

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using uint8_t & the like on open solaris
by Maróy Ákos 27 Nov '09

27 Nov '09

Hi, I'm have a silly problem of trying to use the integer type definitions in boost/cstdint.hpp in the following way: #include <boost/cstdint.hpp> using namespace boost; uint8_t value; on other platforms I've tried, this seems to be OK, but on OpenSolaris, with gcc 3 I get an error that uint8_t does not name a type, with gcc 4, it will say that uint8_t is ambiguous, since there's a typedef also in /usr/include/sys/int_types.h of course the above works the following way: boost::uint8_t value; but I really wanted to avoid having to specify the boost namespace all the time. Akos

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BGL: counting connected components subgraph
by Arman Khalatyan 27 Nov '09

27 Nov '09

Hello, I wondered are there way to count connected components in the minimum spanning tree? Currently I just making copy of graph to be able to count and collect connected components are there more efficient way to do that? ______________________________ std::vector < Edge > spanning_tree; Graph graphMST; kruskal_minimum_spanning_tree(graphFOREST, std::back_inserter(spanning_tree)); for (std::vector < Edge >::iterator ei = spanning_tree.begin(); ei != spanning_tree.end(); ++ei) { if(get(edge_weight, graphFOREST, *ei)<1.0)//lets cut the MTS by given threshold add_edge(source(*ei, graphFOREST),target(*ei, graphFOREST),get(edge_weight, graphFOREST, *ei),graphMST); } num = connected_components(graphMST, &component[0]); // Use components... _______________________________ Thank you beforehand Arman.

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Phoenix question
by Surya Kiran Gullapalli 26 Nov '09

26 Nov '09

Hello all, first of all, apologies for cross posting. I've a question in phoenix and I do not know where will it fit in. the piece of code is located at http://pastebin.com/f16f5c6a2 What is wrong with line #9 . Thanks, Surya

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Automating Serialization?
by Bilokon, Paul 26 Nov '09

26 Nov '09

Hi, By design Boost Serialization requires the user to list each field that needs to be serialised. This is in contrast, for example, with Java and some other languages where serialisation is supported (kind of) at the language level. The current approach requires some code duplication. We have to declare a field. We have to manually (de)serialise it. If we need to make a change, we make it in at least two distinct places. Is there any way to automate the process of serialisation, perhaps harnessing the power of the preprocessor? E.g. we could label the fields that need to be serialised. Is there anything in Boost that could help? Many thanks, Paul Paul Bilokon, Vice President Citigroup | FX - Options Trading | Quants 33 Canada Square | Canary Wharf | Floor 3 London, E14 5LB Phone: +44 20 798-62191 paul.bilokon(a)citi.com<mailto:paul.bilokon@citi.com>

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[shared_ptr] hangs on iPhone
by Igor R 26 Nov '09

26 Nov '09

Hello, My application works on iphone simulator, but hangs when running on iphone itself. Pausing it and looking at the stack trace shows the picture very similar to the one desribed here: http://article.gmane.org/gmane.comp.lib.boost.user/47644 I.e., the call stack origins from different place each time, but ends up with an attempt to addref shared_ptr and spinning in the spinlock. I could try and use XCode "native" tr1::shared_ptr version, but boost::shared_ptr is used by many other boost libraries, so it wouldn't help. So my question is if there's any fix/workaround/compiler-switch that I can apply to overcome this issue and avoid re-writing the whole project without boost? Thanks!

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