January 2005 - Boost-users - lists.boost.org

Re: [sigc] Re: [Boost-users] Signals & Slots
by Douglas Gregor 07 Jan '05

07 Jan '05

On Jan 7, 2005, at 6:12 AM, Murray Cumming wrote: > 3. In "Slot Binders" > Can you expand on this question: "TODO: answer questions: a) What's up > with the No Clue entry, anyone?", please. In fact, please just ask your > TODO questions on this mailing list. So the intent of retype() and retype_return() is to allow casting of the argument and return types of a function. Are these also required when performing implicit conversions? For instance, will the following work? long Func3(double val, string str); sigc::signal<int, float, string> sig; sig.connect(sigc::ptr_fun(&Func3)); If I'm right in assuming that the code will not compile (because the signatures do not match exactly), then the "No Clue" could be replaced by "Not Applicable", because Signals performs all of the implicit conversions. > 4. Some of the "-ed" comments seem outdated now. It would be nice to > clean these up. Replying to some of the -ed comments: - Regarding implementing the preferred syntax from Boost.Signals in libsigc++: it should be trivial, although support for writing function types is not as portable as we'd like. - Regarding bloat factors: they're probably about the same in both libraries. The only thing we know to do to improve the situation is use function pointers instead of virtual functions, and to try to be careful about factoring our templates properly. - About ptr_fun/mem_fun: you can use them in either library, if you'd like to be more explicit. - About bind: bind is now in the C++ Library TR (an addendum to the standard, which should be approved in the near future), so we're forced to build on it to create any signals & slots library for the standards committee. (We'll have a long, uphill battle if we try to introduce our own special binders and don't support bind). - Regarding libsigc++'s specialization for T_accumulator=nil: We don't need to discuss this in a standards proposal, because it's entirely a quality-of-implementation issue. - Regarding Signals and Function: They don't play well together, but we're going to have to deal with this one way or another because Function is also part of the C++ Library TR. And one minor quibble: if we're going to explicitly qualify Boost.Signals by saying that it was strongly influenced by the work of Karl Nelson (that's true), I think it's only fair to point out that libsigc++-2.0's interface was influenced by Boost.Signals. Doug

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Re: B is_convertible to A<T> for some T
by Perepelitsa Roman 07 Jan '05

07 Jan '05

> Hello, > > how do I express through template metaprogramming or in a similar > way that a class is convertible to a template class for some T1? > I.e., the condition: "There exists some T1 such that B is > convertible to A<T1>". I guess all you need is boost::lambda::detail::is_instance_of_1<B, A>. Best regards.

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Problem using boost program_options on HP-UX
by suresh.t＠philips.com 07 Jan '05

07 Jan '05

hi, I am using the boost/program_options and i had no problem when using with Linux (and gcc). I switched to HP-UX ( using gcc 3.2.2) and the boost part fails to compile. I get a error from "boost/program_options/detail/convert.hpp" related to wstring and wchar_t usage. If someone uses program_options on HP with gcc already , could you please let me know what needs to be done to get it working. Thanks in advance --------------------------------------------------------------------------------------------------------- Suresh

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Serialization demo.cpp: "Undefined reference to boost::archive::detail::basic_iarchive::load_object"
by Maximilian Wilson 06 Jan '05

06 Jan '05

I'm using gcc v 3.3, Red Hat Linux (not sure what version), and Boost 1.32. I'm trying to learn the serialization library, using the demo program from http://boost.org/libs/serialization/example/demo.cpp . I have had a little bit of trouble figuring out the boost install procedure for this library but I think I finally did it with: bjam "-sTOOLS=gcc" install --libdir=/home/max/boost --includedir=/home/max/boost -with-serialization But when I execute "g++ -I/home/max/boost/boost-1_32 -L/home/max/boost demo.cpp demo.o" I get a bunch of linker errors. I'm pretty sure I've messed up this install procedure somewhere, and the Boost docs have tentalizing references to serialization not having "automatic linking," but I can't figure out where to go next. What am I doing wrong? Max Wilson -- Ubi solitudinem faciunt, pacem appellant. They make a desert and call it peace. -Tacitus

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Re: bind (excessive?) argument copying
by Trent Hill 06 Jan '05

06 Jan '05

Hi Peter, Peter Dimov wrote: <snip> >> Four copies - I had hoped to only see a single copy. Logically, there >> doesn't seem to be a need for more than one copy. Is there an >> implementation issue that requires this many copies? > > > Not really, but eliminating the unnecessary copies is (relatively) hard, > at least with the current code base (it has been developed with > portability in mind and supports VC6, among others). The specification > requires one copy. One more is almost unavoidable. The other two can be > eliminated, in theory. But... Ok, thanks. Out of interest, is there a simple explanation for why one more is almost unavoidable. <snip> > ... please note that the copies occur at bind time. In a typical > scenario you bind once and call O(N) times (or bind and store in a > function<> with the associated dynamic memory allocation), so this isn't > usually a problem. And, as others have pointed out, there's always > ref(). ;-) Yes I understand. I guess I'm not using bind typically ;-) FYI and for those suggesting boost::ref, the actual case is using bind for message passing between threads. I have a polymorphic wrapper for bind something like this: class bind_wrapper { public: virtual void execute() = 0; }; template <typename binder_t> class bind_wrapper_impl : public bind_wrapper { public: bind_wrapper_impl(const binder_t &binder_a) : binder_m(binder_a) { } virtual void execute() { binder_m(); } private: binder_t binder_m; }; template <typename binder_t> std::auto_ptr<bind_wrapper> make_bind_wrapper(const binder_t &binder_a) { return std::auto_ptr<bind_wrapper>( new bind_wrapper_impl<binder_t>(binder_a)); } Now the idea is that certain functions transparently transfer work to a worker thread. So for such a function "foo", there would be an internal implementation function: void foo_impl(const std::string &string_a) { // do stuff } and a public proxy that requests foo_impl to be called on the worker thread: future foo_async(const std::string &arg_a) { std::auto_ptr<bind_wrapper> message_l( make_bind_wrapper(boost::bind(&foo_impl, arg_a))); // add message_l to message queue and return future to allow // rendezvous ... } The worker thread will collect this message and call execute(), something like: void worker_thread() { // retrieve from message queue and execute std::auto_ptr<bind_wrapper> message_l = ... message_l->execute(); } So, in this case: 1. Yes, a copy is required - boost::ref is not appropriate. 2. Each bind corresponds to a single call (not O(N) calls) We have a home grown solution (less general than bind of course) requiring only a single copy. I was hoping to replace it with bind but it's hard to justify adding the extra argument copies. Thanks for the info though, Cheers, Trent.

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preprocessor library, unique token for each translational unit
by Sean Kelly 06 Jan '05

06 Jan '05

Hello All, I'm trying to figure out if it is possible to use the preprocessor library to generate a unique token for a given translational unit suitable for use in a variable definition. __FILE__ doesn't work for obvious reasons. The motivation is use the template below to generate a unique function scope static "verbosity" for each translation unit. The extern is necessary to give the non-type template par external linkage but also requires a unique variable name. thanks for any help. -Sean #define INIT_VERBOSITY extern const char BOOST_PP_CAT(file,UNIQUE_TOKEN)[] filename = __FILE__; #define VERBOSITY VerbosityLookup<BOOST_PP_CAT(file,UNIQUE_TOKEN)>::get() template<const char* STR> class VerbosityLookup { static int get() { static int verbosity = initialize(STR); return verbosity; } }

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Boost General Interest mailing list
by Jon Kalb 06 Jan '05

06 Jan '05

Boosters, This message announces the Boost General Interest mailing list, called Boost-Interest. This list is a moderated low-traffic announcement-only list of interest to the Boost community. On topic messages will include announcements of books, magazine articles, papers, talks, seminars, products, tools, events, or conferences on advanced uses of C++, generic/generative/meta-programming, and, of course, the Boost libraries. Off topic will be discussion of any kind and job postings. Yes, this is an opt-in list for announcements, but it is a moderated list and the moderators make you two promises. This list will be low volume and all messages will be on-topic (as defined by the charter above). Subscribe or unsubscribe at the Boost-Interest home page: http://lists.boost.org/mailman/listinfo.cgi/boost-interest Anyone may post to this list, but due to the high potential for abuse, each message is individually moderated. Please anticipate some delays in posting and understand that the list moderators have the final say on what is or is not on-topic. -- Jon Kalb Boost-Interest Moderator Kalb(a)LibertySoft.com

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Serialization with NaN and infinity
by Austin Bingham 06 Jan '05

06 Jan '05

I saw a thread on this topic from a few months ago, and I was wondering if there had been any progress or new thought on the topic. Essentially, it appears that the serialization library can't reliably deserialize the serialized version of NaN and infinity for doubles and floats. This seems to be a result of relying on the, AFAIK, undefined behavior of writing NaN/infinity to a stream; it will work correctly with some standard library implementations, but not all. I think the problem can be addressed with these changes: basic_text_oprimitive::save(float or double): on NaN or Infinity, write out some known, stable string (i.e. "nan" or "inf"); don't rely on std implementation. basic_text_iprimitive::load(float or double): look for the "known values" printed by save(), generating the correct values when they're seen. That's a lot of hand waving, to be sure, but something like this would really help out. Of course, a better solution would be fine with me, but there are definitely cases where it's necessary to serialize these values. Currently, there doesn't seem to be a way to reliably to it. Austin Bingham

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Problem compiling the libraries with Dev-C++
by Phantom 06 Jan '05

06 Jan '05

Greetings, I've hit apon a slight problem when it comes to building the latest version of boost (1.32.0) with the tools which come with Dev-C++ (distro 4.9.9.1). When attempting to build the library with the command line; G:\Programming\SDKs\boost_1_32_0>bjam "-sTOOLS=mingw" "-sMINGW_ROOT_DIRECTORY=D:\Dev-Cpp" install the build process fails with the error : spawn: Invalid argument I googled around for a bit and hit apon putting -d+4 onto the command line, which after building the .obj files (via aload of bat files) reported back; Executing raw command directly Executing command ["D:\Dev-Cpp\bin\g++"] ["-Wl,--enable-auto-image-base"] ["-Wl,--exclude-symbols,_bss_end__:_bss_start_ _:_data_end__:_data_start__"] ["-Wl,--out-implib,bin\boost\libs\date_time\build\boost_date_time.dll\mingw\ debug\boost_da te_time-mgw-d-1_32.lib"] [-g] [-shared] [-Wl,--allow-multiple-definition] [-mno-cygwin] [-o] ["bin\boost\libs\date_time\ build\boost_date_time.dll\mingw\debug\boost_date_time-mgw-d-1_32.dll"] [-L"D:/Dev-Cpp/lib"] ["bin\boost\libs\date_time\b uild\boost_date_time.dll\mingw\debug\greg_month.obj"] ["bin\boost\libs\date_time\build\boost_date_time.dll\mingw\debug\g reg_weekday.obj"] ["bin\boost\libs\date_time\build\boost_date_time.dll\mingw\debug\date_genera tors.obj"] spawn: Invalid argument On the advise of someone from gamedev.net I tried the cleaned up version of the command line myself, and it built the lib and dll ok. the cleaned up version was : D:\Dev-Cpp\bin\g++ -Wl,--enable-auto-image-base -Wl,--exclude-symbols,_bss_e nd__:_bss_start__:_data_end__:_data_start__ -Wl,--out-implib,bin\boost\libs\ date_time\build\boost_date_time.dll\mingw\debug\boost_date_time-mgw-d-1_32.l ib -g -shared -Wl,--allow-multiple-definition -mno-cygwin -o bin\boost\libs\date_time\build\boost_date_time.dll\mingw\debug\boost_date_ti me-mgw-d-1_32.dll -LD:/Dev-Cpp/lib bin\boost\libs\date_time\build\boost_date_time.dll\mingw\debug\greg_month.ob j bin\boost\libs\date_time\build\boost_date_time.dll\mingw\debug\greg_weekday. obj bin\boost\libs\date_time\build\boost_date_time.dll\mingw\debug\date_generato rs.obj So, the tools work fine, just for some reason the bjam building doesnt. Bjam has been used by me to build the VC7.1 version of the library back when the current boost version was released. So, the questionis, does anyone have any idea what I might have done wrong to cause such sillyness? The output directory of C:\boost and the "bin" directory the build makes were both deleted prior to trying to build the libraries with mingw32. For completeness the output from the g++ --version is; D:\Dev-Cpp\bin>g++ --version g++ (GCC) 3.3.1 (mingw special 20030804-1) Any tips or help would be appricated, I dont fancy having to try to link everything by hand... Cheers, Rob

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libboost_regex-vc6-sgd-1_32.lib
by Asha V.G. 06 Jan '05

06 Jan '05

Hi When I try to link the test sample, I am getting the error cannot open file "libboost_regex-vc6-sgd-1_32.lib" I am using vc6 to compile. Could any one please help in getting source compiled? Regards Asha

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