April 2002 - Boost-users - lists.preview.boost.org

operator == in shared_ptr
by sashan 30 Apr '02

30 Apr '02

Hi Because the operator== function compares pointers and not what they're pointing to this is what I've had to do to get it to find an integer. Basically I had to wrap the basic int type within another class called Int, as show below. class Int { private: shared_ptr<int> p; public: Int(int i) {p.reset(new int); *p = i;} bool operator==(const Int& r) {return *p.get() == *r.p.get();} ~Int() {}; }; void main() { vector < Int > vec; vec.push_back(Int(1)); vec.push_back(Int(2)); vec.push_back(Int(3)); Int p(4); if (find(vec.begin(), vec.end(), p) == vec.end()) { cout << "Couldn't find it"; } } Is there a better way that doesn't involve 1) having to write a wrapper class around a basic type (or any type) and 2) doesn't involve changing the shared_ptr::operator==. [Non-text portions of this message have been removed]

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boost::function::set()
by Douglas Gregor 29 Apr '02

29 Apr '02

Does anyone use the boost::function::set() methods? I'd like to remove them for Boost.Function v2 to cut down on the size of the interface. If you are using set() and would like to keep using it, please tell me. Doug

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RE: [Boost-Users] iterating over a tuple
by Aleksey Gurtovoy 29 Apr '02

29 Apr '02

Toon Knapen wrote: > On Friday 26 April 2002 13:37, Aleksey Gurtovoy wrote: > > Toon Knapen wrote: > > > I have a list of heterogeneous objects, e.g. > [snip sample code] > > > > And now I want to have a function that can accumulate the > > > value sof all the objects in the tuple, e.g. (pseudocode since > > > my problem is exacly that I can't figure out how to code this) > > > > > > template < typename TypleType > > > > int accumulate_values(const TupleType& t) > > > { > > > int acc = 0; > > > for(int i = 0 ; i < t.size() ; ++i ) acc += (get< i >( > t )).value(); > > > } > > > > > > Can I do this using mpl (mpl looks great but I can't figure > > > out how to do this). > > > > It's not exactly a part of MPL (the library doesn't target > "run-time" stuff > > to that extent yet; I hope it will some day), but "tuple extension" > > components I wrote some time ago > > > (http://groups.yahoo.com/group/boost/files/tuple_ext/tuple_ext-08-nov-01.zip ) > allow one to do exactly these kinds of things: > [snip aleksey's solution] > > Thanks, I like tuple_ext a _lot_ ! I am glad you found it useful. > It would be great to have complete STL-like functionality like this. Yep. The only problem with this is that we are going to end up with 3 STL-like libraries within the same language :) (the original one ("run-time"), the MPL one (pure compile time), and something in between, - HSTL (Heterogeneous Sequences Template Library :)). All three with the same algorithms, just written in different notation :). Emily's heterogeneous lists (www.oonumerics.org/tmpw01/winch.pdf, http://groups.yahoo.com/group/boost/files/alist-feb14-02.zip) 'tuple_ext' components, and MPL's v.2 half-run-time 'for_each' are obviously hanging around that "in between" thing. > Plans on adding this tuple_ext to the CVS ? Some; I think it should be a full-fledged submission that would take the prior art and build a simple framework on it. It's not a large undertaking, though - most of the concepts and some code are already here :). Aleksey

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BGL: "Supergraphs?"
by David A. Greene 29 Apr '02

29 Apr '02

Hi, I've been learning the BGL and porting some existing code over to it. First off, Kudos to Jeremy, Lie-Quan and all the BGL developers. This library is great! I find the filtered_graph potentially very useful for my application except for one case. In some (not rare) instances I need to be able to create a filtered_graph that spans two graphs. In other words, I have two separate graphs. Most of the time the information I need is entirely contained in one graph so a filtered_graph works perfectly. However, sometimes I need to create a filtered_graph from several separate graphs and link them together in a well-defined manner (i.e. I easily know where the edges should go). I need a "supergraph" that is the combination of the two filtered graphs. Right now the application handles this problem by creating a new graph from the existing graphs. But this takes time and memory. I'd like to get rid of this overhead if possible, especially since these are often short-lived graphs. The filtered_graph objects would not be induced subgraphs so a subgraph object wouldn't work (subgraph also doesn't support something that spans multiple graphs anyway). What I need is the opposite of subgraph -- a unified interface to multiple filtered_graphs. This seems very hard to do because each filtered_graph will have its own vertex and edge index mappings. An extra level of indirection would solve the problem but I'm not sure the overhead would be less than simply creating a new graph. Thoughts? Opinions? Thanks again for a great library! -Dave -- "Some little people have music in them, but Fats, he was all music, and you know how big he was." -- James P. Johnson

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Newbie: problems installing under RedHat 7.2
by Benjamin Han 28 Apr '02

28 Apr '02

I'm just trying to install Boost library under RedHat 7.2. I was following the build instructions found on the Boost website, but it seemed to fail for several targets. I'm wondering if it's because RH7.2 uses its version of gcc 2.96. Since my project work needs gcc 3.0+, my question is, what do I need to do in order to use gcc3/g++3 instead of gcc/g++? The build system seems exotic and I just want to get over with the installation asap and start to use the library. (does changing /usr/bin/gcc and /usr/bin/g++ links work?) Here is the build command I tried: jam -sBOOST_ROOT=. -sTOOLS="gcc" Errors (selected): ... libs/thread/build/../src/once.cpp: In function `void boost::call_once (void (*) (), once_flag &)': boost/thread/once.hpp:38: previous declaration of `void boost::call_once (void (*) (), once_flag &)' with C++ linkage libs/thread/build/../src/once.cpp:77: conflicts with new declaration ... MkDir1 libs/python/build/bin/libboost_python_static/gcc/debug/runtime-link-dynam ic/shared-linkable-true gcc-C++-action libs/python/build/bin/libboost_python_static/gcc/debug/runtime-li nk-dynamic/shared-linkable-true/types.o In file included from boost/python/errors.hpp:13, from boost/python/detail/call_object.hpp:8, from libs/python/build/../src/types.cpp:11: boost/python/detail/wrap_python.hpp:24:24: patchlevel.h: No such file or directo ry boost/python/detail/wrap_python.hpp:100:20: Python.h: No such file or directory ... (lots of Python-related errors) ... gcc-C++-action status/bin/is_function_test/gcc/debug/runtime-link-dynamic/is_fun ction_test.o boost/type_traits/function_traits.hpp: In instantiation of `boost::is_function<i nt[]>': status/../libs/type_traits/tests/is_function_test.cpp:68: instantiated from he re boost/type_traits/function_traits.hpp:148: Internal error: Segmentation fault. Please submit a full bug report. See <URL:http://bugzilla.redhat.com/bugzilla/> for instructions. ... &boost::noncopyable::operator= (const boost::noncopyable &)' is private status/../libs/utility/noncopyable_test.cpp:35: within this context ...failed updating 43 targets... ...skipped 24 targets... ...updated 629 targets... The folllowing RPMs are installed on the machine: 1. gcc-2.96-110 2. gcc3-3.1-0.23.1 3. python-1.5.2-38 4. python2-2.2-16 5. glibc-2.2.5-32 6. boost-build-1.0-1 7. boost-jam-3.0-1 Other info: kernel 2.4.18 (manually built) Any comment would be greatly appreciated, Ben

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RE: [Boost-Users] iterating over a tuple
by Aleksey Gurtovoy 28 Apr '02

28 Apr '02

Toon Knapen wrote: > I have a list of heterogeneous objects, e.g. > > struct Foo { > Foo(int v) : value_( v ) {} > int value() const { return value_ ; } > int value_; > }; > > struct Bar { > Bar(int v) : value_( v ) {} > int value() const { return value_ ; } > int value_; > }; > > int main() > { > Foo foo(3); > Bar bar(7); > typedef boost::tuple< Foo, Bar > MyTuple ; > MyTuple my_tuple( foo, bar ); > return 0; > } > > And now I want to have a function that can accumulate the > value sof all the objects in the tuple, e.g. (pseudocode since > my problem is exacly that I can't figure out how to code this) > > template < typename TypleType > > int accumulate_values(const TupleType& t) > { > int acc = 0; > for(int i = 0 ; i < t.size() ; ++i ) acc += (get< i >( t )).value(); > } > > Can I do this using mpl (mpl looks great but I can't figure > out how to do this). It's not exactly a part of MPL (the library doesn't target "run-time" stuff to that extent yet; I hope it will some day), but "tuple extension" components I wrote some time ago (http://groups.yahoo.com/group/boost/files/tuple_ext/tuple_ext-08-nov-01.zip ) allow one to do exactly these kinds of things: // untested! :) template< typename Seq, typename T, typename BinaryOp > T accumulate(Seq const& s, T const& Init, BinaryOp op) { T result = Init; for_each( begin(s) , end(s) , boost::bind<T>(op, boost::ref(result), _1) ); return result; } With the above, you can do something like this: struct get_value { template< typename T > int operator()(T const& x) const { return x.value(); } }; int sum = accumulate( tuple , 0 , boost::bind(std::plus<int>() , _1 , boost::bind<int>(get_value(),_2) ) ); Hope it's not too complicated :). LL might allow to do better on this one. Aleksey

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iterating over a tuple
by Toon Knapen 26 Apr '02

26 Apr '02

I have a list of heterogeneous objects, e.g. struct Foo { Foo(int v) : value_( v ) {} int value() const { return value_ ; } int value_; }; struct Bar { Bar(int v) : value_( v ) {} int value() const { return value_ ; } int value_; }; int main() { Foo foo(3); Bar bar(7); typedef boost::tuple< Foo, Bar > MyTuple ; MyTuple my_tuple( foo, bar ); return 0; } And now I want to have a function that can accumulate the value sof all the objects in the tuple, e.g. (pseudocode since my problem is exacly that I can't figure out how to code this) template < typename TypleType > int accumulate_values(const TupleType& t) { int acc = 0; for(int i = 0 ; i < t.size() ; ++i ) acc += (get< i >( t )).value(); } Can I do this using mpl (mpl looks great but I can't figure out how to do this). thanks, toon

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RE: [Boost-Users] iterating over a tuple
by Aleksey Gurtovoy 26 Apr '02

26 Apr '02

Toon Knapen wrote: > > Hope it's not too complicated :). LL might allow to do > > better on this one. > > Thanks, I'll try it out. Coudl you enlighten me on how to > solve it with the lambda library. I don't see how to iterate over > the different indexes in combination with LL ? Oh, sorry, my last sentence was probably misleading. What I meant is that LL can do a better job on construction of the function object that is passed to tuple's 'accumulate': struct get_value { template< typename T > int operator()(T const& x) const { return x.value(); } }; int sum = accumulate(tuple, 0, _1 + ll::bind(get_value(),_2)); I was also hoping that it could help us to get rid of the ad hoc 'get_value' class, but, thinking about it more, I don't see how :(. HTH, Aleksey

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Redistributing Boost?
by Duane Murphy 26 Apr '02

26 Apr '02

Boost has a reasonably liberal license for use in product both commercial and non-commercial. However I am wondering about redistributing source code. Does the boost license(s?) allow the sources to be redistributed as part of a commercial product? For example, a commericial library or framework that is developed using boost for underlying support and that library is sold in source code form. What are the legalities of distributing boost in this fashion? ...Duane -- "If tyranny and oppression come to this land, it will be in the guise of fighting a foreign enemy." - James Madison

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boost::thread_specific_ptr problem
by svanechel 26 Apr '02

26 Apr '02

Hi there, I've encountered a curious problem when using thread_specific_ptr. We are developing a Win32 Service and for each thread we need an object that stays alive for as long as the thread runs (except for the main thread). So we created a dll and in its DllMain function we did something like this: boost::thread_specific_ptr<SomeClass> someClass; BOOL WINAPI DllMain( HINSTANCE hinstDLL, DWORD fdwReason, LPVOID lpvReserved ) { switch ( fdwReason ) { case DLL_THREAD_ATTACH: someClass.reset( new SomeClass ); // Breakpoint 1 case DLL_THREAD_DETACH: someClass.reset(); // Breakpoint 2 } } And now comes the curious bit: If you build this dll and implicitly link it with the exe the exe's startup code hangs in GetModuleFileName (). This is the call stack upto that point _setargv (STDARGV.C) __getmainargs (CRTLIB.C) WinMainCRTStartup (CRTEXE.C) At that point the code hasn't reached Breakpoint 1 yet (it's still in the exe's startup code in the main thread and we are not interested in the main thread) It is not the class we are allocating. We tried it with an empty class and that produced the same result. However, if we stored an object in a TLS slot allocated with the API, everything works. It probably has nothing to do with the exe being a service either, since the same dll with linked to a normal exe had the same problems. To complicate matters even further we reached Breakpoint 1 in a number of runs, but as soon as we left DllMain in those instances the application hanged again. If you break then you see from the call stack that the code is running somewhere in NTDll. Are we using thread_specific_ptr in a way that it wasn't meant to be used, or did we encounter a real problem here? I've used thread_specific_ptr before and had no problems then. PS: We develop under Windows 2000 on a Compaq Evo W6000 dual processor machine, using MSVC 6, SP 5 and the 08/2001 version of the platform SDK. The service can run both under the Local System Account or under an account with absolutely no privileges at all. Sven Van Echelpoel

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