October 2007 - Boost-users - lists.preview.boost.org

Pattern-matching by metaprogramming - possible?
by Ovanes Markarian 18 Oct '07

18 Oct '07

I don't think that meta-programming will help check you the values. This can only be the case if the values are available (as const with external linkage) at compile time. If you need the checking pattern to be generated during the compilation than take a look at boost::xpressive. With Kind Regards, Ovanes On 10/18/07, Zeljko Vrba <zvrba(a)ifi.uio.no> wrote: > > On Thu, Oct 18, 2007 at 09:04:39AM +0200, Ovanes Markarian wrote: > > > > Hello Zeljko, > > > > may be another approach? Why not using a template method and static > concepts > > inside a function, which ensure that a parameter is of correct type? > > > Hmm, I didn't quite get you. But I want to match both on *type* and > *value* > as shown in this rule: > > > > > > | (Insn "addq", Reg "%rsp") -> (* do something *) > > > > The type here is (Insn, Reg) [particular types of larger variants]; > each component is also matched on the particular value ("addq" and > "%rsp" strings). > > > > > > | (_, Imm x) -> (* any 1st item; the 2nd must be Imm type, and > > > > the x variable is bound to the value carried by the > 2nd > > > > The type here is doesn't matter and (Imm x) - this is a match only > on type where the variable x gets bound to the value carried by > the variant type. > > _______________________________________________ > Boost-users mailing list > Boost-users(a)lists.boost.org > http://lists.boost.org/mailman/listinfo.cgi/boost-users >

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Pattern-matching by metaprogramming - possible?
by Zeljko Vrba 18 Oct '07

18 Oct '07

A short introduction: the ML language has a variant data type, tuples, and pattern matching construct. For example type operand = Imm of int | Reg of string type instruction = Insn of string | Pseudo of string Now, we can create tuples, e.g. (Insn "push", Reg "%rbp") is of type operand * instruction (a tuple of two typed elements). In function definitions, it is possible to do pattern matching as (it could be written slightly better in ML, but I want to show the match syntactic construct): let f x = match x with | (Insn "addq", Reg "%rsp") -> (* do something *) | (_, Imm x) -> (* any 1st item; the 2nd must be Imm type, and the x variable is bound to the value carried by the 2nd item *) | (_, Reg "%rsp") -> (* any value for 1st item _except_ Insn "addq" which has already been handled in the first alternative - alternatives are matched in order and first matching is taken *) | _ -> (* default case for anything else *) This is only a simplified example; but even this example would be much more ugly if rewritten with if/else statements, even if tuple tiers were used. Boost provides both the safe variant type and the tuple type. Would it be possible to construct pattern matching with syntax similar to the above in C++ ? [Yes, there are also other problems - incomplete matches: ML just throws an exception in that case; or redundant cases - nothing happens.]

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Quasi-random
by Joel C. Salomon 17 Oct '07

17 Oct '07

I've found some mention of this in the archives, but it seems it's never been done. How much work would it be to add the quasi-random sequence generators (faure, halton, hammersley, sobol, &c.) from the code at <http://people.scs.fsu.edu/~burkardt/cpp_src/cpp_src.html>? --Joel

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Problem lboost_filesystem-mgw-mt-s-l_33_l
by question boost 17 Oct '07

17 Oct '07

Hi , compiling a project under Code Blocks I get the following message: ld.exe:cannot find -lboost_filesystem-mgw-mt-s-l_33_l I go there http://www.boost.org/doc/html/jam/building.html I do:C:\Documents and Settings\src\boost\tools\jam\src>build mingw --debug (like explained) A new folder named bin.ntx86.debug is added after I go there http://www.boost.org/doc/html/bbv2/installation.html : 1:(done) 2:I do:C:\Documents and Settings\src\boost\tools\build\v2> bjam --version 3:I open the user-config.jam file (like explained) and I modify the file, the modification is the following: import toolset : using ; # GCC configuration # Configure gcc (default version) using gcc : : "C:\mingw\bin\g++" ; 4:I copy bjam.exe from C:\Documents and Settings\src\boost\tools\build\v2 to C:\Documents and Settings\src\boost\tools\build\v2\example\hello and I run bjam (like explained): C:\Documents and Settings\src\boost\tools\build\v2\example\hello>bjam I get the following message: "C:mingwbing++ n'est pas reconnu en tant que commande interne ou externe, un programme executable ou un fichier de commandes .." ..... "...failled gcc.compile.c++ bin\gcc\debug\hello.o... ...skipped <pbin\gcc\debug>hello.exe for lack of<pbin\gcc\debug>hello.o... ...failed updating one target.. ...skipped one target..." Where is my error (4)? Thanks, David _________________________________________________________________ Votez pour vos séries TV préférées et tentez de gagner un voyage à Hawaï ! http://messengerawards.divertissements.fr.msn.com/

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[ref] tying references between objects
by Robbie Morrison 17 Oct '07

17 Oct '07

Hi all The following kind of code is probably quite common. It involves: * using individual Register objects containing construction parameters to help factory-create new Entity objects * and, in the process, "tying" key object state variables so that each associated Registry object can watch these And yes, I know this breaks encapsulation! I chose C++ references and my code seems quite complicated for what should be a relatively straightforward task. Pointers were rejected because the dereferencing syntax can lead to really obscure numerical expressions (particularly for non-C/C++ programmers). However, boost::ref() seemed to offer a simpler solution and I experimented with this for quite some time to no avail. I also considered using a boost::ptr_vector and 1-tuples. In addition, adding cout statements to ctors and dtors led to more activity than I would have expected. Moreover, there were more dtor calls than ctor calls. Any comments or suggestions gratefully received! Also an explanation of the differences between a "type conversion" operator and an "address-of" operator. Is this simply related to role or is there a distinction? More information follows the program listing. many thanks in advance Robbie --- Robbie Morrison PhD student -- policy-oriented energy system simulation Institute for Energy Engineering (IET) Technical University of Berlin (TU-Berlin), Germany [from IMAP client] // --------------------------------------------------------- // Copyright: (c) 2007 Robbie Morrison. All rights reserved. // License: Unrestricted reuse in any form, for any purpose. // Version: $Id: frag-xeona-registers-9.cc,v 1.3 2007/10/17 15:23:43 robbie Exp $ // Tested using g++ 4.1.2 (-Wall -Weffc++ -pedantic), boost // 1.34.1 (source build), and valgrind (memory checker) on // Ubuntu 6.10 (7.04 is current) using Linux 2.6.17-12-generic. #include <iostream> // standard io #include <string> // C++ strings #include <vector> // STL sequence container #include <iomanip> // setw() and family #include <tr1/memory> // TR1 smart pointers using std::tr1::shared_ptr; // for convenience // --------------------------------------------------------- template <typename T> class Value // just for type conversion operator T&() { public: explicit Value(T v) : _value(new T(v)) { } operator T&() { return *_value; } // return aliasable value private: shared_ptr<T> _value; // pointer usage is essential }; // --------------------------------------------------------- class Register // initializes and watches selected { // .. Entity variables public: explicit Register() : _vec() { } // explicit for testing template <typename T> // would normally support int,double,bool Value<T> tieRef(const std::string& tag) // would normally search on tag! { T temp = 0.45; // would normally obtain value from user shared_ptr<Value<T> > val(new Value<T>(temp)); // actual object is shared _vec.push_back(val); // crude "last on" indexing for testing report(); return *_vec.back(); // given aforementioned "last on" indexing } void report() // just for doubles (could be templated) { double temp = *_vec.back(); // this line is interesting! std::cout << "Register : value : " << temp << std::endl; } private: std::vector<shared_ptr<Value<double> > > _vec; // data mirror }; // --------------------------------------------------------- class Entity // represents simulation 'things' { public: explicit // explicit for testing Entity(Register& r) : // pass-by-reference necessary _register(r), // for testing purposes _coeff(r.tieRef<double>("coeff")), // intuitive syntax _notInteresting() // rely on default construction { report(); } void modify(double d) { _coeff = d; // normal syntax (no pointer derefs) report(); // display this modification _register.report(); // confirm the modification propagated } void report() { std::cout << "Entity : value : " << _coeff << std::endl; } private: Register& _register; double& _coeff; // watched variable int _notInteresting; // ignored variable }; // --------------------------------------------------------- int main(int argc, char* argv[]) { std::cout << std::fixed << std::setprecision(2); std::cout << " creating a register" << std::endl; Register reg; std::cout << " creating an entity" << std::endl; Entity ent(reg); std::cout << " modifying the entity" << std::endl; ent.modify(0.01); ent.modify(2.0); } // ---- end-of-program ------------------------------------- // OUTPUT // creating a register // creating an entity // Register : value : 0.45 // Entity : value : 0.45 // modifying the entity // Entity : value : 0.01 // Register : value : 0.01 // Entity : value : 2.00 // Register : value : 2.00 // Development environment // // boost : 1.34.1 (via ./configure; make all; make install) // gcc : 4.1.2 20060928 (prerelease) (Ubuntu 4.1.1-13ubuntu5) // os : Ubuntu 6.10, Linux 2.6.17-12-generic (7.04 is current) // hardware : Toshiba Tecra A2 330 laptop (purchased 27-Aug-2004) // specs : 1.4GHz Intel Celeron M (32-bit) / 512MiB RAM / 40GB HDD // // Problem // // The problem involves sharing data between Entity objects, // used to represent various 'things' in my simulation -- // and Register objects ('register' in the sense of a book // recording important information), used to help construct // and then watch the state of Entity objects. A concrete // ObjectFactory object (not relevant to this discussion) // will be used to create the Entity objects (Alexandrescu // 2001 pp179-217). // // I would also like a relatively clear syntax for // programming the Entity's as there are lots of these and // they contain numerical expressions -- for instance, // dereferencing (smart) pointers would yield lines like: // // *_perf = 2.1 * local * *_coeff; // // Solution (provisional) // // The chosen strategy is to declare all to-be-observed // Entity object data members as references and then bind // these to the relevant Register object element upon // construction. // // An alternative approach could be to utilize the Memento // pattern (which relies on friendship) in conjunction with // the Iterator pattern (for traversing a population of // objects) (Gamma etal 1995 pp283-291 and pp257-271 // respectively). // // Design notes // // In relation to C++, a reference data member must be // initialized in the constructor's initializer list // (Lischner 2003 p36). And a reference may not be bound to // a class member (data member or member function) (p35). // // Class Value<T> is instead used to avoid an "invalid // initialization .. from a temporary" error when // initializing Entity::_coeff using the Register::tie<T> // member function. // // Class Value supplies a "type conversion operator" // (Lischner 2003 p112), in this case, Value::operator T&, // which binds to the non-const reference data member in // Entity. The code for Value derives from Lischner (2003 // p119 example 5-21). // // References // // Alexandrescu, Andrei. 2001. Modern C++ design : // generic programming and design patterns applied. // Addison-Wesley, Boston, USA. ISBN 0-201-70431-5. // // Gamma, Erich, Richard Helm, Ralph Johnson, and John // Vlissides. 1995. Design patterns : elements of // reusable object-oriented software. Addison-Wesley, // Boston, USA. ISBN 0-201-63361-2. // // Lischner, Ray. 2003. C++ in a nutshell : a language // and library reference, O'Reilly and Associates, // Sebastopol, California, USA. ISBN 0-596-00298-X.

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Re: [Boost-users] Boost Spirit and C++/CLI
by Hansi Hansi 17 Oct '07

17 Oct '07

When you use windows forms programs you can't use the standard main entry point with mixed unmanaged code. There is a bug in the initialization of the CRT in VS2005. It seems that the bug is not anymore in VS2008. Test it with the entry point '?mainCRTStartupStrArray@@$$FYMHP$01AP$AAVString@System@@@Z' Best regards Hansjörg _______________________________________________________________________ Jetzt neu! Schützen Sie Ihren PC mit McAfee und WEB.DE. 3 Monate kostenlos testen. http://www.pc-sicherheit.web.de/startseite/?mc=022220

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boost::serialization(1.34.1) Can not link 64-bit example.
by Oleg Udovenko 16 Oct '07

16 Oct '07

Hi, Now I'm trying to use the "serialization" library on 64-bit(x64, Visual C++ 8.0). And faced some troubles with that. First I've converted a Visual Studio 2003 solution (vc7ide) to Visual Studio 2005, and compiled 64-bit static library release/debug. It passed the compilation with lots of warnings. But when I tried build a 64-bit example demo_xml_load.cpp I've got a lots of linker errors. - Is somebody tried the "serialization" library on 64-bit? Thanks, Oleg.

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What would happen if boost::shared_ptr is reset to an address in the stack
by Peng Yu 16 Oct '07

16 Oct '07

Hi, The following program runs well in my system. However, if I change 1 to 0, it will terminate at the line with "delete". Does this mean that boost::shared_ptr can tell if the pointer is from the stack or the heap and does different things based on where the pointer is from? Thanks, Peng #include <iostream> #include <boost/shared_ptr.hpp> int main() { #if 1//try change this to 0 int a[100]; boost::shared_ptr<int> p(a); std::cout << std::endl; #else int a[100]; delete a; // would terminate here std::cout << std::endl; #endif }

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[shared_ptr] class ... has pointer data members but does not override ...
by Klaus Backert 16 Oct '07

16 Oct '07

Hello, a Boost newbie question: Arch: PPC, OS: Mac OS X 10.4.10, Compiler: GCC 4.0.1 In a C++ dynamic library, I'm just developing, I have: #include <boost/shared_ptr.hpp> namespace MyNameSpace { typedef boost::shared_ptr<std::string> StringPtr; } I get the following warning: /usr/local/include/boost/shared_ptr.hpp: In instantiation of 'boost::shared_ptr<std::string>': /Volumes/blablabla/MyClass.cpp:81: instantiated from here /usr/local/include/boost/shared_ptr.hpp:131: warning: 'class boost::shared_ptr<std::string>' has pointer data members /usr/local/include/boost/shared_ptr.hpp:131: warning: but does not override 'boost::shared_ptr<std::string>(const boost::shared_ptr<std::string>&)' The incriminated line in MyClass.cpp is the second line here: __attribute__((visibility("default"))) MyNameSpace::StringPtr MyClass::myFunction() const { /* .......... */ } I have experienced the same with classes of my own instead of std::string, i.e. with typedef boost::shared_ptr<MyOtherClass> MyOtherClassPtr; etc. May be it's just me, but the boost documentation and Google don't help. Can I ignore the warnings or should I do something? Thanks in advance Klaus

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How to add a type to is_arithmetic
by Peng Yu 16 Oct '07

16 Oct '07

Hi, Suppose I define a class fixed_point as class fixed_point{ ....some operations are defined here private: int _integer_part; unsigned _fractional_part } I want is_arithmetic<fixed_point>::type to be true_ Of cause, I can partially specialize the template class as template <> struct is_arithmetic<fixed_point> { ... blah blah }; If I use the above approach, shall I put it into the namespace boost or not? Also, I'm wondering if there is any generic way to do this? Thanks, Peng

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[optional] documentation errors
by Edward Diener 16 Oct '07

16 Oct '07

In the 1.34.1 documentation for optional<T>, in the Synopsis section, it is currently written: -------------------------------------------------------------------------- template<class InPlaceFactory> explicit optional ( InPlaceFactory const& f ) ; template<class TypedInPlaceFactory> explicit optional ( TypedInPlaceFactory const& f ) ; AND template<class InPlaceFactory> optional& operator = ( InPlaceFactory const& f ) ; template<class TypedInPlaceFactory> optional& operator = ( TypedInPlaceFactory const& f ) ; -------------------------------------------------------------------------- Since InPlacefactory and TypedInPlacePlactory are actual classes, these should be: template<InPlaceFactory> explicit optional ( InPlaceFactory const& f ) ; template<TypedInPlaceFactory> explicit optional ( TypedInPlaceFactory const& f ) ; AND template<InPlaceFactory> optional& operator = ( InPlaceFactory const& f ) ; template<TypedInPlaceFactory> optional& operator = ( TypedInPlaceFactory const& f ) ; ------------------------------------------------------------------------- In the Detailed Semantics these are shown correctly.

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[fusion] subset view
by Chris Weed 16 Oct '07

16 Oct '07

Hi, I would like to make a subset view of the element in a tuple. It would, for example, give me a view into the first, third, and fifth element of the tuple. It isn't clear how to do this with the available views. Thanks, Chris

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[serialization]-- serialize binary data to a memory buffer?
by Rich Peters 16 Oct '07

16 Oct '07

I saw an example where boost serialized a text archive to a strstream for sending via a socket. I would like to do something similar, but for binary data. Is there a way to do the binary serialization to a memory buffer, and then send it elsewhere? It doesnt seem like strstream and boost::archive::binary_oarchive would mix correctly. I have also seen some discussion regarding a binary_iostreams library, but its doesnt look like that exists yet. thanks Rich

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Re: [Boost-users] [continued][boost::fusion v2 and xpressive] versioning conflicts...
by Ovanes Markarian 16 Oct '07

16 Oct '07

Eric, I changed the files. Should I zip them and post via mailinglist? Or should I submit them somewhere else? List of files which were changed: detail/core/linker.hpp detail/core/matcher/alternate_matcher.hpp detail/static/productions/alt_compilers.hpp detail/utility/any.hpp detail/utility/cons.hpp proto/op_base.hpp proto/proto_fwd.hpp xpressive.hpp One problem is that xpressive.hpp has info about boost version, but this is the mostly used file for inclusion. Therefore I believe this check fill fail even in boost 1.35: #if BOOST_VERSION >= 103500 # ifndef BOOST_XPRESSIVE_FUSION_V2 # define BOOST_XPRESSIVE_FUSION_V2 # endif //BOOST_XPRESSIVE_FUSION_V2 #endif //BOOST_VERSION I also executed your examples from the boost/lib directory and they produced in both cases same results. Your answer today is highly appreciated, since I will be on vacation from tomorrow on. thanks, Ovanes > On 9/24/07, Ovanes Markarian < om_boost(a)keywallet.com> wrote: > > > > Eric, > > > > sorry for the delay. I only now found some time to work on that issue: > > http://lists.boost.org/boost-users/2007/08/30120.php > > > > > > After analysing your post and investigation what's going on, I would > > like to write my opinion: > > > > changing xpressive_fwd.hpp or proto_fwd.will not help. > > > > I grepped where fusion includes are used and need to enclose these in > > some conditional statements: > > > > #ifdef BOOST_XPRESSIVE_FUSION_V2 > > # include ... //fusion 2 headers > > #else > > # include ... // fusion 1 headers > > #endif > > > > Actually this can be done using some kind of a macro function like: > > > > #include BOOST_XPRESSIVE_FUSION_ROOT(sequence/cons.hpp) > > ... > > > > The macro function will deliver the root dependent on the predefined > > macros like: > > 1. if !defined XPRESSIVE_FUSION_ROOT and use V2 > > => choose the root for V2 > > else => choose the root for V1 > > > > As I found out the following files need to be changed: > > linker.hpp > > alternate_matcher.hpp > > alt_compilers.hpp > > any.hpp > > cons.hpp > > arg_traits.hpp > > op_base.hpp > > proto_fwd.hpp > > > > If you give me your green light I will do it and submit a patch. > > > > > > With Kind Regards, > > Ovanes > > > > > >

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Problem using Boost Graph Library - Python Bindings
by Camilo La Rota 16 Oct '07

16 Oct '07

Hello all, I have just installed the Boost Graph Library - Python Bindings. Everything seemed to be ok, I can read a graph from the example "mst.dot" file and from my own ".dot" files, I can write them back to a file. However, when I try the example script (at the end of the following page: http://www.osl.iu.edu/~dgregor/bgl-python/) -------------------------------------------------------------------- import boost.graph as bgl # Load a graph from the GraphViz file 'mst.dot' graph = bgl.Graph.read_graphviz('mst.dot') # Convert the weight into floating-point values weight = graph.convert_property_map(graph.edge_properties['weight'], 'float') ... etc ------------------------------------------------------------------- it stops at the third line with the following error: ---------------------------------------------------------------------------- Traceback (most recent call last): File "<pyshell#17>", line 1, in <module> weight = graph.convert_property_map(graph.edge_properties['weight'],'float') KeyError: 'weight' ------------------------------------------------------------------------ I receive the same error message if I write only: graph.edge_properties['weight'] The content of the example mst.dot file is: -------------------------------------------------- graph G { A -- C [weight="1.0"] B -- D [weight="1.0"] B -- E [weight="2.0"] C -- B [weight="7.0"] C -- D [weight="3.0"] D -- E [weight="1.0"] E -- A [weight="1.0"] E -- B [weight="1.0"] } -------------------------------------------------- Does any one have any idea about the source of this error. Thanks a lot in advance, Camilo

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Re: [Boost-users] How to add a type to is_arithmetic
by Chad Walters 16 Oct '07

16 Oct '07

It's not entirely clear from your description if you really need to have is_arithmetic be true for your fixed_point class or if you just want to have some predicate that is true for both the built-in arithmetic types and your fixed_point class. If the former, then you will likely run afoul of problems, for the reasons previously pointed out. Hopefully it is the latter - in which case you should just define your own predicate with the appropriate logic (true for fixed_point or is_arithmetic types). Chad

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Retrieve number os affected rows
by Hamilton Vera 16 Oct '07

16 Oct '07

How to retrieve the number of affected rows after an update? ( I am testing in a MySQL database) I only found this in the list; http://lists.boost.org/Archives/boost/2006/12/114037.php But I was unable to find the sql.rowsaffected() fuction. I am using soci version 2.2.0. -- Hamilton Vera int Administrator (char Network[],char ComputationalSystems[]); Seven Internet http://lib.seven.com.br "Google is my shepherd, no want shall I know"

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[xpressive] crash...
by Ovanes Markarian 16 Oct '07

16 Oct '07

Hello Eric, this code fragment will crash, since 'what' uses iterators into the invalid string x::smatch what; if(x::regex_match(std::string(" (some_type_ptr) xyz,"), what, regex)) //string goes out of scope after this sentance { std::cout << what[0] << endl; // boom! string iterators are no longer valid std::cout << what[1] << endl; } May be there is a way to probit this kind of behaviour during the compilation or at least this can be stated in the docs... With Kind Regards, Ovanes

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[system] in multi-threaded context
by Jeroen van der Wulp 16 Oct '07

16 Oct '07

Hello, I have some problems with the latest changes to asio, which turn out to be caused by problems with boost::system. The newer versions of boost::asio now use boost::error_code provided by boost::system for error handling. On OS X 10.4 with XCode 2.4.1 comparing two boost::error_code objects e1 & e2 always returns false. I believe this is caused by comparing objects accross threads. But this is just a guess. A problem I noticed on with Apple's version of gcc is that static instance variables behave strange, there seems to be a copy for each variable in each compilation unit that uses them? This may also somehow be the cause for my problems with boost::system. Another problem is that when I receive an error_code object, say e, from asio, trying to print e.message() fails with an access violation. This happens on Windows, Linux, OS X. What am I doing wrong? Thanks, Jeroen van der Wulp

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[boost-users] enable_if and checking if class derives from boost::operators does not work.
by chun ping wang 16 Oct '07

16 Oct '07

namespace boost { template <class T, class U> char (& is_op_test(boost::operators<T,U> const&) )[2]; template <class T> char is_op_test(T const&); template<class T> T const& make(); template <class T> struct is_operators : boost::mpl::bool_<(sizeof(is_op_test(make<T>())) == 2)> {}; } and this function declaration. template <typename T, template <typename ELEM, typename = std::allocator<ELEM> > class CONT > typename boost::enable_if<boost::mpl::or_<boost::is_integral<T>, boost:: is_operators<T> >, CONT<T> >::type primelist(const T& MAX_BOUND, const T& K, boost::function<bool(const T&, const T&)> f); BigInteger class declaration looks like this.. class BigInteger : public BigUnsigned, boost::operators<BigInteger>, boost::operators<BigInteger, int> { }; I compile with T = int and it works. When i compile with T = BigInteger I get the following errors. on visual c++. error C2770: invalid explicit template argument(s) for 'boost::enable_if<boost::mpl::or_<boost::is_integral<T>,boost::is_operators<T> >,CONT<T>>::type primelist(const T &,const T &,boost::function<bool(const T &,const T &)>)' ./cs512/c++/primeMain.cpp(24) : see declaration of 'primelist'" on mingw dev-cpp i get this error. unable to find function.... In both cases passing BigInteger does not work. thanks for the help. BigInteger does derive from boost::operators and theirs two overload.

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[filesystem] vacpp errors building 1_34_1 filesystem library on AIX
by Marty Fried 15 Oct '07

15 Oct '07

I've built all the boost libraries on Windows and Red Hat, but there are compiler errors building on AIX using Visual Age (xlC) for the filesystem library. It builds using gcc, but not vacpp, which is the AIX standard compiler. We are using the latest version, V. 8. There is more than one error, but I think they are all similar. I believe that the code envolved is not fully standard compliant. For example, in operations.hpp, there is an error on line 732, col 72; the full error is (I tried to wrap as best I could): The declaration of "end_itr" uses the undefined class "boost::filesystem:: basic_directory_iterator<boost::filesystem::basic_path <std::basic_string<char,std::char_traits<char>,std::allocator<char> >, boost::filesystem::path_traits> >" when the class must be complete. The code is called by line 730, called by 473, called by 689. The problem, I think, is that basic_directory_iterator is not defined until line 822, after all these calls. A coworker created a simple test that reproduced this error, fed it into an online ANSI/ISO C++ Standard test utility by Comeau computing, and it flagged it as an error. Has anyone compiled 1_34_1 using xlC/vacpp? If you need more information, or need the other errors, let me know. -- Marty Fried Left Coast, USA

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boost-build-2.0-m11 and gcc-4.2.2
by Michael Albert 15 Oct '07

15 Oct '07

Greetings. If in "jam_src" I attempt to compile with gcc-4.2.2, the "bjam" executable compiles (using ./build.sh), but "bjam --version" fails on a segmentation fault. I can compile with gcc 3.4.6. Any thoughts? Anyone else seen this behavior? Thanks! -Mike

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[ Boost-users] [preprocessor] - introduce mpl { ... } like asm { ... }
by Frank Bergemann 15 Oct '07

15 Oct '07

Hi, i posted this to comp.lang.c++.moderated: ------------------------------------------------------- Hi, i am just starting to work with "C++ Template Metaprogramming" - using the book of David Abrahams & Aleksey Gurtovoy. And you know, there are things like mpl::plus<> for some operator, mpl::if_<> for a control-struct, mpl:insert<>, mpl:erase<>, mpl:clear<> for STL container like operations, etc. Lots of things re-modeled the "unaccustomed template-syntax" - way for types, which are there in C/C++ language definition already for operating on variables and values. So i wonder if it would be a good option to introduce some mpl { ... } in remembrance of asm { ... } This time not for going down to the assembler level, but going up to the meta level. But with the goal to drop the template fashioned syntax for meta programming by a syntax already familiar in C/C++ language without templates (if this is possible - i don't now enough about that). Well, this is just a gut feeling, that there might be a chance this way to more align "standard" programming with "meta" programming, which then might enable to easier catch the the gray area of borderline between compilation and runtime execution and how to shift that back and forth. What do you think? rgds! Frank ------------------------------------------------------- Then i was thinking, that instead of extending the C++ language, it might be sufficient to use an own preprocessor before handing over to g++ (e.g.). For this maybe using boost::spirit? Finally i was remembering, that there is already some 'preprocessor' project in boost itself. But having a 1st look at it, it doesn't seem to do what i'd like to have. Just as an example - see this extract from boost::enable_if documentation: template <class T> typename enable_if_c<boost::is_arithmetic<T>::value, T>::type foo(T t) { return t; } I'd like to make it s.th. like: mpl { template <class T> if (is_arithmetic(T)) { T foo (T t) { return t;} } } This is just a simple example. But just imagine use of mpl metafunctions like mpl::and_ mpl::or_, mpl::plus, mpl::minus, mpl::equal_to, mpl::less, etc, that could come back to the "natural" &&, ||, +, -, ==, <, etc. [ hmm, i think, i mixed up mpl::enable_if with mpl::if_ - so my example is not correct - but i hope you get my point here ] Them maybe it would also be possible somehow: mpl { template <class T> if (is_arithmetic(T)) { T foo (T t) { return t;} } else { #error "instantiation of foo() not supported for given type T" } } ... to generate usefulcompiler warning/errors. The main point for me is to get find an equivalent to the "strange" template syntax that is more C/C++ alike way to deal with variables and values. Not because template syntax is "strange". But in order to re-align again. rgds! Frank

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[mpl][fusion] making a heterogeneous collection of classes from a list of types.
by Michael Marcin 15 Oct '07

15 Oct '07

Hello, I have the MPL book and I've used some metaprogramming before but I'm always at the edge of my understanding of the language when I do it. I have a problem right now which I suspect is trivial but I can't for the life of me figure out how to do it. I have a list of 25 resource types (class Sound, class Script, etc.) and since they are not mutable I want to share them so I have a resource cache template that looks something like: template< typename Resource > class Cache { public: typedef typename Tag<Resource>::type resource_tag; /// Retrieve a resource by id /// Throws cache_error if the resource couldn't be found in the Repository Resource& Retrieve( ResourceId id ) { // is the resource in the cache? typename ResourceMap::iterator it = m_resources.find( id ); if( it != m_resources.end() ) { return it->second; } else { return LoadResource( id ); } } /// Clears the cache and destructs all cached resources. void Clear() { m_resources.clear(); } private: Resource& LoadResource( ResourceId id ) { Stream stream( Repository::Instance().Retrieve( id, resource_tag::type::value ) ); if( !stream.fail() ) { Resource* res = new Resource(stream); m_resources.insert( id, res ); return *res; } else { throw cache_error( id, resource_tag::type::value ); } } typedef boost::ptr_map< ResourceId, Resource > ResourceMap; ResourceMap m_resources; }; I have a class which must contain a Cache for each of the 25 resource types and support calls to get a resource of a particular type given an id and be able to call Clear on all 25 caches. Something like class Manager { public: /// Returns Cache<Resource>::Retrieve( id ) template< typename Resource > const Resource& Get( ResourceId id ); /// Calls Cache::Clear for all resource types void Clear(); }; It would be pretty easy to just copy and paste it out 25 times but I would like to reduce code duplication and simplify maintenance through metaprogramming. I have a private boost::mpl::list25 named resource_list containing all the resource types. I think I need to transform that in to a boost::fusion::map of 25 Resource to Cache<Resource> pairs but I'm not sure that is what I really need to do or how to go about doing that. Thanks, Michael Marcin

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Header error in boost/python/object/make_holder?
by Michel Valstar 15 Oct '07

15 Oct '07

Hello, I am trying to build code of a recently graduated student, who is now unavailable to us (read: ignores us). When running scons in the appropriate directory, a lot gets build, until I get the following error: /usr/include/boost/python/object/make_holder.hpp:81: error: 'allocate' is not a member of 'boost::python::objects::value_holder<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, State> >' /usr/include/boost/python/object/make_holder.hpp:83: error: no matching function for call to 'boost::python::objects::value_holder<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, State> >::value_holder(int*&)' /usr/include/boost/python/object/value_holder.hpp:44: note: candidates are: boost::python::objects::value_holder<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, State> >::value_holder() /usr/include/boost/python/object/value_holder.hpp:44: note: boost::python::objects::value_holder<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, State> >::value_holder(const boost::python::objects::value_holder<std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, State> >&) scons: *** [trackerbase/trackerbasewrapper.os] Error 1 scons: building terminated because of errors. This does not seem to be an error in his own code, rather an error in the boost.python code? This is the first time I am using boost, and, as usual, I need to get this program working yesterday. My machine is a recently installed Ubuntu Feisty (hence the need for re-compilation). I am using the latest version of Boost (boost_1_34_1) and python 2.5.1 Any help would be appreciated. Thanks, MIchel -- Michel Valstar, PhD candidate http://www.doc.ic.ac.uk/~mvalstar Department of Computing Imperial College London 180 Queens' Gate London SW7 2AZ, U.K. tel.: +44 20 7594 8225 fax: +44 20 7581 8024

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