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[iostreams] Truncate file?
by Adam Nielsen 28 Mar '10

28 Mar '10

Hi all, I'm trying to work out how to chop some data off the end of a file once I have finished modifying it. I'm not sure how to adjust the file size in a portable fashion, and although I'm using boost::iostreams I can't see how to either set the size of the underlying stream or how to otherwise indicate where the stream should end. Is this possible with boost:iostreams? If not, is there another portable way to remove data from the end of a file, causing its size to shrink? All I can find around the place are calls to ftruncate() and the like, but I would like my program to work on Windows as well as Linux, and hopefully other platforms too. Many thanks, Adam.

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Boost::ASIO Winsock.h already included?
by Sean McAllister 28 Mar '10

28 Mar '10

I'm getting this error when building on windows. Looking online it seems it can happen if you include windows.h before boost/asio.hpp without setting WIN32_LEAN_AND_MEAN. I've only got three places in my code that import windows.h on their own, and I prefixed them all with that macro, but I'm still getting one error. The only other thing I can think of is that one of the boost libraries is including it and that's throwing a wrench into things. Unforunately it's proving particularly pernicious to determine all the files that include windows.h. Does anyone know which libraries include it or have experience getting rid of this error?

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Find which boost header
by Mathijs Romans 27 Mar '10

27 Mar '10

Hi, I have trouble finding which header I should use when I want to use a part of boost. For instance, I wish to use boost::optional but am not entirely sure which header to use. In the documentation online I can find everything about boost::optional except which header is recommended. I'm sure it is boost/optional.hpp or boost/optional/optional.hpp but that's not really my question. Am I supposed to just browse through my local boost include dir to find an appropriate header? Or is there somewhere an overview of which header files are recommended for boost users? Thanks, Mathijs

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troubles deriving from using boost variant
by Greg Kellum 27 Mar '10

27 Mar '10

Hi all, I have been using boost's variant library in a project, and I've noticed that when I import the class using the variant class into other classes I start having the strangest compilation problems. I've been dealing with these problems for the last few months by isolating that code as much as possible. I've put it behind a factory which returns an abstract class which hides the fact that a variant is being used by the implementing class at all. This keeps other classes from having to import the implementing class and by extension the boost variant header, but it also makes it difficult to make full use of visitors together with the variant because creating new visitors that include the implementing class leads to these same strange compilation problems. I was hoping that someone might be able to give me a better diagnosis for the underlying reason for these problems. I've included the error output below. If anyone can give me any greater insight into what's causing these errors, I would be extremely grateful. Best, Greg 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C2544: expected ')' for operator '()' 1> C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(81) : see reference to class template instantiation 'boost::mpl::integral_c<T,N>' being compiled 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C2146: syntax error : missing ';' before identifier 'L' 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C2059: syntax error : ')' 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C2143: syntax error : missing ';' before 'const' 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C2059: syntax error : '{' 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C2334: unexpected token(s) preceding '{'; skipping apparent function body 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C2544: expected ')' for operator '()' 1> C:\Program Files (x86)\boost\boost_1_42\boost/type_traits/integral_constant.hpp(21) : see reference to class template instantiation 'boost::mpl::integral_c<T,N>' being compiled 1> with 1> [ 1> T=size_t, 1> N=0 1> ] 1> C:\Program Files (x86)\boost\boost_1_42\boost/type_traits/alignment_of.hpp(109) : see reference to class template instantiation 'boost::integral_constant<T,val>' being compiled 1> with 1> [ 1> T=size_t, 1> val=0 1> ] 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C2146: syntax error : missing ';' before identifier 'L' 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C2059: syntax error : ')' 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C2143: syntax error : missing ';' before 'const' 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C2059: syntax error : '{' 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C2334: unexpected token(s) preceding '{'; skipping apparent function body 1>C:\Program Files (x86)\boost\boost_1_42\boost/mpl/aux_/integral_wrapper.hpp(80): error C2544: expected ')' for operator '()' 1> C:\Program Files (x86)\boost\boost_1_42\boost/type_traits/integral_constant.hpp(21) : see reference to class template instantiation 'boost::mpl::integral_c<T,N>' being compiled 1> with 1> [ 1> T=size_t, 1> N=8 1> ] 1> C:\Program Files (x86)\boost\boost_1_42\boost/type_traits/alignment_of.hpp(89) : see reference to class template instantiation 'boost::integral_constant<T,val>' being compiled 1> with 1> [ 1> T=size_t, 1> val=8 1> ] 1> C:\Program Files (x86)\boost\boost_1_42\boost/type_traits/type_with_alignment.hpp(289) : see reference to class template instantiation 'boost::alignment_of<T>' being compiled 1> with 1> [ 1> T=boost::detail::max_align 1> ]

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Boost serialisation: base ptr regression in 1.42
by Avi Bahra 27 Mar '10

27 Mar '10

I have a serious regression in boost 1.42 serialisation. Now getting a unregistered class, exception, on Suse linux using gcc 4.2.1. This test passes on boost 1.39/1.40. There are 3 files involved to recreate the crash: included below: Main.cpp BaseHolder.hpp BaseHolder.cpp The file BaseHolder.hpp/cpp defines 3 classes Base Derived BaseHolder Here is what I found: 1/ If all the functionality is put in one file. i.e Main.cpp then _no_ crash 2/ If all 3 files are compiled together then _no_ crash 3/ However if BaseHolder is added to static library and linked with Main.cpp then we get the _crash_ ( only in 1.42 ) Also getting a spurious warning message: Again this warning only appears in 1.42 /var/tmp/ma0/boost/boost_1_42_0/boost/mpl/print.hpp: In instantiation of ?boost::mpl::print<boost::serialization::BOOST_SERIALIZATION_STATIC_WARNING_LINE<98> >?: /var/tmp/ma0/boost/boost_1_42_0/boost/serialization/static_warning.hpp:92: instantiated from ?boost::serialization::static_warning_test<false, 98>? /var/tmp/ma0/boost/boost_1_42_0/boost/archive/detail/check.hpp:98: instantiated from ?void boost::archive::detail::check_object_tracking() [with T = Derived]? /var/tmp/ma0/boost/boost_1_42_0/boost/archive/detail/oserializer.hpp:313: instantiated from ?static void boost::archive::detail::save_non_pointer_type<Archive>::invoke(Archive&, T&) [with T = Derived, Archive = boost::archive::text_oarchive]? /var/tmp/ma0/boost/boost_1_42_0/boost/archive/detail/oserializer.hpp:525: instantiated from ?void boost::archive::save(Archive&, T&) [with Archive = boost::archive::text_oarchive, T = Derived]? /var/tmp/ma0/boost/boost_1_42_0/boost/archive/detail/common_oarchive.hpp:69: instantiated from ?void boost::archive::detail::common_oarchive<Archive>::save_override(T&, int) [with T = Derived, Archive = boost::archive::text_oarchive]? /var/tmp/ma0/boost/boost_1_42_0/boost/archive/basic_text_oarchive.hpp:80: instantiated from ?void boost::archive::basic_text_oarchive<Archive>::save_override(T&, int) [with T = Derived, Archive = boost::archive::text_oarchive]? /var/tmp/ma0/boost/boost_1_42_0/boost/archive/detail/interface_oarchive.hpp:64: instantiated from ?Archive& boost::archive::detail::interface_oarchive<Archive>::operator<<(T&) [with T = Derived, Archive = boost::archive::text_oarchive]? /var/tmp/ma0/clientRoot/workspace/MyProject/SCRATCH/src/Main.cpp:16: instantiated from here /var/tmp/ma0/boost/boost_1_42_0/boost/mpl/print.hpp:55: warning: comparison between signed and unsigned integer expressions gcc.archive bin/gcc-4.2.1/debug/link-static/libnodeattr.a gcc.link bin/gcc-4.2.1/debug/test Here are the 3 files: // =========== file Main.cpp ============================ #include <iostream> #include <fstream> #include "BaseHolder.hpp" using namespace std; int main() { std::string fileName = "test.txt"; { // If this scope is commented out, crash goes away ??? Derived saved("varname"); { std::ofstream ofs( fileName.c_str() ); boost::archive::text_oarchive oa( ofs ); oa << saved; } Derived restored; { std::ifstream ifs( fileName.c_str() ); boost::archive::text_iarchive ia( ifs ); ia >> restored; } assert(saved == restored ); std::remove(fileName.c_str()); } { BaseHolder saved(Derived("varname")); { std::ofstream ofs( fileName.c_str() ); boost::archive::text_oarchive oa( ofs ); oa << saved; } BaseHolder restored; { std::ifstream ifs( fileName.c_str() ); boost::archive::text_iarchive ia( ifs ); ia >> restored; } assert(saved == restored); std::remove(fileName.c_str()); } cout << "Test passed \n"; } //=================== file BaseHolder.hpp ============= #ifndef BASEHOLDER_HPP_ #define BASEHOLDER_HPP_ // defines classes: // Base // Derived // BaseHolder #include <boost/archive/text_iarchive.hpp> #include <boost/archive/text_oarchive.hpp> #include <boost/serialization/base_object.hpp> #include <boost/serialization/serialization.hpp> #include <boost/serialization/vector.hpp> #include <boost/serialization/string.hpp> #include <boost/serialization/assume_abstract.hpp> class Base { public: Base(); virtual ~Base(); virtual bool compare(Base*) const = 0; virtual std::string name() const = 0; private: friend class boost::serialization::access; template<class Archive> void serialize(Archive &, const unsigned int){} }; class Derived : public Base { public: Derived(const std::string& n) : name_(n) {} Derived() {} bool operator==(const Derived& rhs) const; virtual std::string name() const { return name_;} virtual bool compare(Base*) const; private: std::string name_; friend class boost::serialization::access; template<class Archive> void serialize(Archive & ar, const unsigned int) { ar & boost::serialization::base_object<Base>(*this); ar & name_; } }; class BaseHolder { public: BaseHolder( const Derived& ); BaseHolder(); ~BaseHolder(); std::string name() const { return basePtr_->name();} bool operator==(const BaseHolder& rhs) const { return basePtr_->compare(rhs.basePtr_); } private: Base* basePtr_; friend class boost::serialization::access; template<class Archive> void serialize(Archive & ar, const unsigned){ ar & basePtr_; } }; #endif //============= File BaseHolder.cpp ========= // implements class: // Base // Derived // BaseHolder #include <assert.h> #include <sstream> #include <boost/serialization/export.hpp> #include "BaseHolder.hpp" using namespace std; // class Base Base::Base() {} Base::~Base() {} // class derived bool Derived::compare(Base* rb) const { Derived* rhs = dynamic_cast<Derived*>(rb); if(!rhs) return false; return operator==(*rhs); } bool Derived::operator==(const Derived& rhs) const { if (name_ != rhs.name_) { return false; } return true; } BOOST_CLASS_EXPORT(Derived); // class BaseHolder BaseHolder::BaseHolder() : basePtr_(NULL) {} BaseHolder::BaseHolder( const Derived& r) : basePtr_(new Derived(r)) {} BaseHolder::~BaseHolder() { delete basePtr_;} Best regards, Ta, Avi

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[proto] Comma Strangeness
by David Greene 27 Mar '10

27 Mar '10

Well, my little lambda-like experimental language is getting rather large. I'm really having fun with it and am close to actually doing something almost useful with it. :) Unfortunately I've run into a problem I can't seem to isolate to a small testcase. I'm doing something like this: proto::display_expr( list [ obj["name1"].attr["a"], obj["name2"].attr["a"], obj["name3"].attr["b"] ] ); Presume I have all of the terminals, members, etc. declared/defined correctly (at least "correctly" as I understand it). display_expr dumps out an expression without any comma operators. It just shows a subscript off "list" with one "index," obj["name3"].attr["b"]. It's the behavior I would expect if the operands of the commas were not protoized expressions, but they _should_ be protoized. The funny thing is, if I write a small testcase just isolating the terminals, members, etc. needed to construct the expression, it works as expected. But in the context of the (much) larger language, it fails. However, the grammar specification shouldn't have any bearing on what display_expr dumps out. So any ideas as to why commas might be gobbled up prematurely? -Dave

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Re: [Boost-users] [MPI] Code example leaks memory
by Brian Wood 27 Mar '10

27 Mar '10

> Hi all, > > the code example given at: http://www.boost.org/doc/libs/1_41_0/doc/html/mpi/tutorial.html > leaks memory as reported by Valgrind 3.5.0 There are several examples/main()'s on that page. I'm not sure which one you're talking about. I think the following paragraph from that page under the "User-defined data types" heading could be improved. "The redundant copy elimination optimization can only be applied when the shape of the data type is completely fixed. Variable-length types (e.g., strings, linked lists) and types that store pointers cannot use the optimiation, but Boost.MPI will be unable to detect this error at compile time. Attempting to perform this optimization when it is not correct will likely result in segmentation faults and other strange program behavior." I suggest the following: The redundant copy elimination optimization should only be applied when the shape of the data type is completely fixed. When a type has variable-length members (e.g., strings, linked lists) or pointers this optimization shouldn't be used as Boost.MPI will be unable to detect this error at compile time. Attempting to perform this optimization when it is not correct will likely result in segmentation faults and other strange program behavior. I changed "can" to "should" in the first sentence and reworked the second sentence, including correcting the spelling of optimization. Brian Wood Ebenezer Enterprises http://webEbenezer.net (651) 251-9384 "Then Samuel took a stone, and set it between Mizpeh and Shen, and called the name of it Ebenezer, saying, Till now has the L-RD helped us."

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issues with cost_map is a_star algo
by Mangal 27 Mar '10

27 Mar '10

I have a working modified Dijkstras algo using boost. My graph has an edge_property called my_edge_property. The type of distance_map is time_duration. I provide a distance_combine class which has a function with signature time_duration my_distance_combine::operator()(const time_duration &timeAtVertex, const my_edge_property &weight) { //My Implementation } distance_infinity has a value pos_infin. This modified version of Disjkstra algorithm works fine and runs correctly. Now I want to use a_star algorithm instead of dijisktra. So I provided a hueristic class with a function time_duration myhuersticClass::operator() (vertex_descriptor u) { //My Implementation } and pass that as the hueristic function to a_star algorithm. I expected this should be enough for everything to work but I get compile errors. the error is in file astar_search.hpp (line 289) put(cost, *ui, inf);// compile error at this line error C2679: binary '=' : no operator found which takes a right-hand operand of type 'const boost::date_time::special_values' (or there is no acceptable conversion) Now in the same file one line above that statement put(distance, *ui, inf); compiles fine. The documentation says that the type of cost_map and distance_map are be the same. If that is the case then why does assiging pos_inifn to cost_map does not work?? Looking at it closely I see that CostInf=boost::date_time::special_values, (which is correct) CostZero=my_edge_property (???? do not understand) Also why is the type of CostZero= my_edge_property (if I try to pass distance_zero as minutes(0) compiler does not like it and complains that time_duration cannot be converted to my_edge_property) Looks like cost_map is vector<my_edge_property> and not vector<time_duration> which is what the distance_map is. I don't see any way to passthe cost_map to a_star function. Any ideas?? -- View this message in context: http://old.nabble.com/issues-with-cost_map-is-a_star-algo-tp28054643p280546… Sent from the Boost - Users mailing list archive at Nabble.com.

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boost filesystem::ifstream for files larger than 2GB on OS X
by lucasvickers 27 Mar '10

27 Mar '10

Hello, I have been using the std::ifstream w/o issue except my data files have grown > 2GB, and as is well documented it is failing. I am on OS X 10.6 and I have my executable compiling/running as a x86_64 (64bit) executable. I read that boost supports a 64bit streamposition in boost::filesystem::ifstream. I have compiled boost using darwin ports (I should state I never specifically said anything about x86_64 during this compilation). I have re-run my program and I have the same problem (I use tellg to confirm the issue is the streamposition). My questions are: 1 - Does the boost ifstream in fact support large files? 2 - If 1) is true, then what specifically needs to be done to get this support? 3 - Unrelated, but what do the "-mt" and "-d" added to the dylib file name mean? (libboost_filesystem-mt-d.dylib) thanks! Lucas -- View this message in context: http://old.nabble.com/boost-filesystem%3A%3Aifstream-for-files-larger-than-… Sent from the Boost - Users mailing list archive at Nabble.com.

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[Bind] How do you write it?
by Robert Jones 27 Mar '10

27 Mar '10

Hi All Ok, now I've found out what is really stopping my real code working. In this example my problem is that method has defaulted arguements, which I think mucks up bind's signature matching. Is there an easy way round this, or must I just add appropriate overloads of double_it to A? Thanks, Rob. #include <algorithm> #include <vector> #include "boost/bind.hpp" struct A { int double_it( int i, int j = 2 ) { return i * j; } } a; std::vector< int > v; int main( ) { for ( std::vector< int >::iterator i = v.begin( ); i != v.end( ); ++ i ) { a.double_it( * i ); } // Write it as a for_each/bind std::for_each( v.begin(), v.end(), boost::bind( & A::double_it, boost::ref( a ), _1 ) ); } -- ACCU - Professionalism in programming - http://www.accu.org

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