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boost::object_pool
by wugui 22 Aug '02

22 Aug '02

class A; class B; class AB : virtual public A, virtual public B; all destruct is virtual boost::object_pool<AB> pool_ab; B * pb = pool_ab.constuct(); pool_ab.destroy(pb); // is this right?

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boost lambda library compile error
by khuroth 21 Aug '02

21 Aug '02

I have searched already in this list and the dev list for these MSVC compiler errors, but none of the solutions have worked so far. I have turned off precompiled headers, built clean, tried defining BOOST_NO_MEMBER_TEMPLATES before including "boost/lambda/lambda.hpp" (or "boost/lambda/bind.hpp"), and I still always get this error under Visual C++ 6 SP5 (Win2k Pro SP3), in both the Debug and Release configurations: Deleting intermediate files and output files for project 'dWin - Win32 Release'. --------------------Configuration: dWin - Win32 Release--------------- ----- Compiling... dwin-button.cpp dwin-common-control.cpp dwin-dialog.cpp C:\TMP\BOOST\BOOST_1_28_0\boost/lambda/detail/lambda_fwd.hpp(31) : fatal error C1001: INTERNAL COMPILER ERROR (compiler file 'msc1.cpp', line 1794) Please choose the Technical Support command on the Visual C++ Help menu, or open the Technical Support help file for more information Not sure what I'm doing wrong..

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Boost Concept Check Library
by igor_bashkirov 21 Aug '02

21 Aug '02

Hello, I work on big software project that is ported to several platforms/compilers, including Linux,Solaris/GCC 2.95.2,3.0.4); Windows/MSVC 6.0; AIX/VisualAge; MacOS X / GCC 2.95.2 (Apple). Recently, I decided to make use of Boost library (v 1.28) and the first thing I tried was Boost Concept Check Library (BCCL). Unfortunately, the use of the library wasn't as smooth as I expected, namely, with respect to BOOST_CLASS_REQUIRES macro. Thus, I'd like to submit a couple of observations and one proposal regarding usage of this macro. Let's start with observations: following is the snippet from <boost/concept_check.hpp> header: [code // The BOOST_CLASS_REQUIRES macros use function pointers as // template parameters, which VC++ does not support. #if defined(BOOST_NO_FUNCTION_PTR_TEMPLATE_PARAMETERS) #define BOOST_CLASS_REQUIRES(type_var, concept) .... #else #define BOOST_CLASS_REQUIRES(type_var, concept) \ typedef void (concept <type_var>::* func##type_var##concept)(); \ .... end code] As you could see, BOOST_CLASS_REQUIRES macros evaluate to nothing if BOOST_NO_FUNCTION_PTR_TEMPLATE_PARAMETERS symbol is defined. But, to my great surprise, I didn't find any more references to BOOST_NO_FUNCTION_PTR_TEMPLATE_PARAMETERS symbol throughout the Boost library. Moreover, the above comment about VC++ not supporting function pointers as template parameters is wrong (at least for MSVC 6.0 with SP5). Not to be unfounded, I will provide following sample program successfully compiled and run under MSVC 6.0 with SP5: [code #include <iostream> using namespace std; typedef void(*FP)(); template <FP T> class X { FP fp_; public: X() : fp_(T) {} void print() const { cout << fp_ << endl; } }; void f() {} int main(int, char**) { X<&f> x1; x1.print(); return 0; } end code] The same is true for pointers to member functions of both ordinary and template classes. OK, this observation could be treated as "cosmetic" one, but the following won't. Let's look at the definition of BOOST_CLASS_REQUIRES macro: [code #define BOOST_CLASS_REQUIRES(type_var, concept) \ typedef void (concept <type_var>::* func##type_var##concept)(); \ template <func##type_var##concept _Tp1> \ struct concept_checking_##type_var##concept { }; \ typedef concept_checking_##type_var##concept< \ BOOST_FPTR concept <type_var>::constraints> \ concept_checking_typedef_##type_var##concept end code] and at a typical usage of this macro (taken from Boost documentation): [code template <class T> struct generic_library_class { BOOST_CLASS_REQUIRES(T, EqualityComparableConcept); // ... }; end code] Here, the "EqualityComparableConcept" is a concept checking class defined in the "boost" namespace. OK, that's great and works fine until "generic_library_class" is also declared in the "boost" namespace. Let's now suppose "generic_library_class" is declared in namespace "ns1". Then, BOOST_CLASS_REQUIRES macro evaluates to following: [code namespace ns1 { template <class T> struct generic_library_class { typedef void (EqualityComparableConcept <T>::* funcTEqualityComparableConcept)(); ... }; } end code] Did you see the problem places? Yes, it's where "concept" parameter of the macro is substituted for "EqualityComparableConcept". This name is not declared in the namespace "ns1"! The first itch could be to specify "boost::EqualityComparableConcept" as a value of the second parameter of the macro, but, "not so fast, Skywalker!" - in this case we will end up with "funcTboost::EqualityComparableConcept" name for the pointer to member function that is not a legal name of C/C++ identifier. Someone could say "What a big deal?! Just write 'using namespace boost;' or 'using boost::EqualityComparableConcept;' just before declaring 'generic_library_class'.". Well, the declaration of "generic_library_class" seems to be in the header, right? And what do you think about writing "using-directives" in header files? Yes, right, - it's evil! Especially for large production code. Just check your favorite C++ book. Though, the use of "using-declarations" in headers is a moot point, I also consider it as evil for the same reasons as for "using- directives". Anyway, "using-declarations" won't help us, - they just don't work under MSVC 6.0 in our case. So, what do we have, - "exclusive circle"? I hope not. Finally, I got to the proposal that should help us to eliminate defects of the macro and to obviate above-stated difficulties. What if to add one more parameter, say, "ns", to the BOOST_CLASS_REQUIRES macro to pass the name of the namespace the concept checking class belongs to? Let's look at the new definition of the macro: [code #define BOOST_CLASS_REQUIRES(type_var, ns, concept) \ typedef void (ns::concept <type_var>::* func##type_var##ns##concept) (); \ template <func##type_var##ns##concept _Tp1> \ struct concept_checking_##type_var##ns##concept { }; \ typedef concept_checking_##type_var##ns##concept< \ BOOST_FPTR ns::concept <type_var>::constraints> \ concept_checking_typedef_##type_var##ns##concept; end code] and at it's usage: [code namespace ns1 { template <class T> struct generic_library_class { BOOST_CLASS_REQUIRES(T, boost, EqualityComparableConcept); // ... }; } end code] that will evaluate to the following: [code namespace ns1 { template <class T> struct generic_library_class { typedef void (boost::EqualityComparableConcept <T>::* funcTboostEqualityComparableConcept)(); ... }; } end code] That's it. Moreover, this solution does not suffer from yet another drawback inherent to the original one, viz, name clashing when using in the same class concept checking classes with the same name, but from different namespaces. The only issue I could see with my suggestion was impossibility to use concept checking classes declared at the global scope, but, I hope nobody would think of such thing, because it's evil (sorry for repetition). I hope the proposed solution will increase usability of the BCCL. Best regards, Igor Bashkirov.

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Upgrade VisC++ compiler
by sen_al2002 20 Aug '02

20 Aug '02

Hi, I am a newbie to all this programmer stuff. I am a physics student doing some computer simulations. I was trying to use the special function atanh from boost libraries but couldn't. The error message reads d:\boost_1_28_0\atanh.hpp(77) : error C2989: 'atanh_helper1_t<T,0>' : template class has already been defined as a non-template class Some advised me to update my VisC++ ver 6.0 compiler. How can I do that? Does anybody out there have any better advise? Thanks sen

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boost python link error
by kiminkim 20 Aug '02

20 Aug '02

I want to export C++ class...use boost lib but link error occured... help me. #include <windows.h> #include <boost/python/class_builder.hpp> #include <string> namespace python = boost::python; class CBaseBox { public: CBaseBox() {}; void move(); private: std::string a; }; void CBaseBox::move() { MessageBox(NULL, "kkm", "kkm", MB_OK); } BOOST_PYTHON_MODULE_INIT(tuesday) { python::module_builder this_module("tuesday"); python::class_builder<CBaseBox> CBaseBox_class(this_module, "CBaseBox"); CBaseBox_class.def(&CBaseBox::move , "move"); } --------------------Configuration: tuesday - Win32 Debug-------------------- Compiling... export.cpp Linking... Creating library pyds\./tuesday_d.lib and object pyds\./tuesday_d.exp export.obj : error LNK2001: unresolved external symbol "class CBaseBox & __cdecl from_python(struct _object *,struct boost::python::type<class CBaseBox &>)" (?from_python@@YAAAVCBaseBox@@PAU_object@@U?$type@AAVCBaseBox@@@python@boost @@@Z) pyds\.\tuesday_d.pyd : fatal error LNK1120: 1 unresolved externals Error executing link.exe.

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Boost Python error handling
by cseymour＠interchange.ubc.ca 19 Aug '02

19 Aug '02

Here is a sample program which shows the problem i've been having (posted in earlier messages). When I import the module "sample" and run the function test(), I get the following output: This is a test Raising an error Aborted When I should get a message saying it caught the error, and then a Python error, instead of it Aborting and quitting Python. /* sample.c */ #include "Python.h" #include "boost/python/class_builder.hpp" namespace py = boost::python; void test() { std::cout << "This is a test" << std::endl; std::cout << "Raising an error" << std::endl; PyErr_SetString(PyExc_TypeError, "This is the error"); throw py::argument_error(); } BOOST_PYTHON_MODULE_INIT(sample) { try { py::module_builder this_module("sample"); this_module.def(test, "test"); } catch (...) { std::cout << "Caught an error" << std::endl; py::handle_exception(); } }

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Newbie and shared_ptr
by Ian Mold 19 Aug '02

19 Aug '02

I have been looking at the shared_ptr class, and I have made a change to include an assignment from a standard pointer. I have done this so that I don't have to create a new shared_ptr just to reassign an existing shared_ptr. // Assignment to a 'normal' pointer. shared_ptr & operator=(T * r) { this_type(r).swap(*this); return *this; } I have a few questions. 1) Is this necessary? 2) Does this do the job? 3) Is there any reason this wasn't included in the first place? I welcome any comments. Regards, IanM

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BGL: Loops in undirected graph
by Tarjei Knapstad 19 Aug '02

19 Aug '02

Is there any "standard best way" of detecting loops in an undirected graph? I had a look at chapter 4.2 in the book (which does an implementation for bidirectional graphs), and tried to adapt this implementation, but with no particular luck :) The graph I've set up in my test suite looks like this (I hope my mail prog. doesn't screw up the formatting) H15 | H8 C2 \ / \ H9-C0-C1 C3-O7-H14 / | | H10 C6 C4 / \ / \ H11 C5 H13 | H12 I'm working with molecules, so the letters denote the type of atom, but that's of no importance here. The numbers are the vertex descriptors. What I'm trying to create is an algorithm that will return the set of vertices [1, 2, 3, 4, 5, 6] defining. Now, my first step is (exactly like in the book) to record every back edge in the graph. As my graph is undirected, and there is allways a path from any one vertex to any other vertex, I thought I could just do a DFS from the first vertex in any such graph and record the back edges. In the above example, starting from 'C0', I'd expect the set of back edges obtained from a DFS to be 1-2, 2-3, 3-4, 4-5, 5-6 and 6-1, a total of 6 edges. The actual result obtained however also includes the following edges: 1-0, 11-6, 12-5, 13-4, 7-3, 14-7, 15-2, 8-0, 9-0 and 10-0. Why is this? I'm assuming there's something I missed out on, regarding graph theory and how the basic DFS works, but I cannot see any logic in this. If so, how could I modify my DFS visitor to record the (in my problem domain) "correct" back edges? This problem also gives me further trouble when trying to detect which vertices are part of each cycle. Does any of you have any suggestion for an effective implementation of the "find vertices that are part of each cycle" part of the algorithm? Any help appreciated. Cheers, -- Tarjei Knapstad

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boost::function/bind Usage Again
by Albrecht Fritzsche 19 Aug '02

19 Aug '02

Here I want to extend simple callbacks so that these callbacks take an argument void fun(int i) { std::cout << "Hi fun " << i << std::endl; } struct Foo { void bar(int i) { std::cout << "Hi bar " << i << std::endl; } }; template <class Value> struct CallFunction { CallFunction(const Value& v) : mValue(value) {} // defined outside void operator()(const boost::function<void, Value>& fun) { if (fun) fun(mValue); } const Value& mValue; }; int main() { std::vector< boost::function<void, int> > funs; Foo foo; funs.push_back(&fun); funs.push_back(boost::bind(&Foo::bar, &foo, _1)); ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ int value = 7; std::for_each(funs.begin(), funs.end(), CallFunction<int>(value)); return 0; } Is this the right usage of the /_1/ here? This code runs (at least on my machine:-), but I'm quite unsure about this place holder. And since the online docu... Ah, now I see - in the online doc there are some links missing. In the files section not only the bind_template.hpp link refers to that very file but also the arg.hpp and placeholders.hpp links and many more. Having checked now the sources makes not everything clear, but at least clearer. So, I would be happy if anyone could let me know if my usage includes some misuse etc... Thanks Ali

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Using gcc's typeof and boost.lambda together.
by Matthew Dempsky 19 Aug '02

19 Aug '02

I was just playing around with the boost.lambda library and thought of playing a bit with it using gcc's typeof extension... this is the code I used (just slightly modified documentation code): typedef typeof(_1 = 1) assign_one; list<int> v(10); for_each(v.begin(), v.end(), assign_one()); I was hoping it would work the same as the documentation's code, but instead it generates a few big errors about lambda_functor_base<...>::lambda_functor_base() not existing. I know typeof is a gnu extension and it's not really portable to use it in code, but does anyone have any ideas of how to get something like this to work correctly? -jivera

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