February 2012 - Boost-users

[Spirit] qi::parse at translation unit global scope?
by Olaf Meeuwissen 01 Feb '12

01 Feb '12

I noticed this when I played around with wrapping qi::parse() in a parse() function that does some things before and after qi::parse(). My code had been calling qi::parse(), with the `qi::` namespace prefix, everywhere so I removed from a few calls and compiled before adding a parse() declaration. Lo and behold, compilation unexpectedly succeeded. I've reduced the behaviour in a minimalistic sample program (attached). I expect their to be *no* parse() function within the scope of main(). Can anyone clarify why the compiler has no trouble finding one and which one it finds? Adding a global scope operator to the call, i.e. saying ::parse(), does result in the expected compile error. Using Boost 1.46.1, gcc 4.6.2 on Debian wheezy. Thanks in advance, -- Olaf Meeuwissen, LPIC-2 FLOSS Engineer -- AVASYS CORPORATION FSF Associate Member #1962 Help support software freedom http://www.fsf.org/jf?referrer=1962

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problems with C++ integer types
by Robert Ramey 01 Feb '12

01 Feb '12

I'm very confused about a number of things related to C++ standard and boost libraries dealing with numeric types. Here are a few things that I'm not getting. a) The standard says in section 18.3.2.1 "Specializations shall be provided for each arithmetic type, both floating point and integer, including bool. The member is_specialized shall be true for all such specializations of numeric_limits." ... "Non-arithmetic standard types, such as complex<T> (26.4.2), shall not have specializations." and it section 18.3.2.4 numeric_limits members static constexpr bool is_bounded; "True if the set of values representable by the type is finite. [ Note: All built-in types are bounded. This member would be false for arbitrary precision types.-end note ]" So the question is: if one makes a "numeric type" like std::complex (or safe integer which I'm interested in right now). Should one define a specialization for this new type? The working is pretty specific, but then I can't see why "is_bounded" is in there since all built-in arithmetic types are bounded. Oh I see this now: Required by LIA-1. b) boost/type_traits/is_integral.hpp This file just specializes each arithmetic type supported by the implementation. question:Why isn't it just implemented in terms of numeric limits so that every thing is always consistent and never "out of sync" It's implementation returns true for only the built in types so it seems to me it should be repeating what ever happens to already be in numeric_types. c) my real interest is to implement a type "safe_integer" which can be used anywhere an integer is used but will trap errors which occur in the course of implicit conversions and assignements. If I don't specialize numeric_limits for my new "safe_integer" certain type_traits like is_signed won't work for it. If I do - them I"m out of sync with is_integral.hpp and likely out of conformance with the standard - though I'm not sure what the implications of that might be. I'm aware that there is related work going on here - bigint and arbitrary length integers. How do the authors of these libraries plan to address this. There are other cases applications where this would also come up such as modular integer<modulus> , safe_integer_range<max, min> and who know what else. Any useful information/insight would be appreciated. Robert Ramey

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Re: [Boost-users] Need help with Errors in boost MPL tutorials
by Linh Khanh ha 01 Feb '12

01 Feb '12

> There are far more than just two placeholders in Boost. AFAIK Phoenix, > Lambda and Bind come with their own. The mpl placeholder is different > though: It is a placeholder for a type (it's a meta-programming > library after all) and not for a value. Try to write a MPL lambda, > that might clear up some of the confusion. > -- Philipp Moeller, GeometryFactory That clears a lot of confusion from me. So again, mpl::lambda is also different from boost::lambda is that right (and also the lambda from c++11x) ? These are quite new terms for me. Would be great if someone could give me some references why they are different and should be implemented separately.

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Can't dynamically load shared lib that is statically linked to boost thread
by Greg 01 Feb '12

01 Feb '12

Hi, I've run into a problem since adding a dependency on boost_thread. My shared library no longer loads (via dlopen("libmy.so",RTLD_NOW), I get error: undefined symbol: _ZTIN5boost6detail16thread_data_baseE Any ideas on how to resolve this? Details: OS - CentOS 5.4, x86_64 Boost version - 1.47.0 built from source ./bootstrap.sh --with-libraries=exception,filesystem,math,thread --prefix=/usr/local/boost_1_47_0 ./b2 install This worked fine. Although I built the other boost libraries, I'm only using thread at this time. Link line for my shared library which uses boost thread: Building target: libtslib.so Invoking: GCC C++ Linker g++ -L"/usr/local/boost_1_47_0/lib" -L"/opt/xerces-c-3.1.0-x86_64-linux-gcc-3.4/lib" -L"/home/Greg/workspace/geothreadcpp/Release" -L"/home/Greg/workspace/geothreadcpp/Debug" -L"/home/Greg/workspace/geocosmexception/Release" -L"/home/Greg/workspace/geocosmxmllibbasecpp/Release" -L"/home/Greg/workspace/xmllib/Release" -L"/mnt/src/geocosm/matlab/geneticalglib/galibcmplinux_x86_64/distrib" -shared -o"libtslib.so" ./tslibcpp/src/TsLibCpp.o ./tslib/src/tslibresults.o ./tslib/src/tslibsamplematch.o -lmlgalib -lpthread -lgeothreadcpp -lgeocosmexception -lxerces-c-3.1 -lgeocosmxmllibbasecpp -lxmllib Finished building target: libtslib.so note it is relying on the auto link boost feature which seems to correctly use the static lib version of boost_thread as "ldd" does not report a dependency on boost_thread: ldd libtslib.so libmlgalib.so => not found libpthread.so.0 => /lib64/libpthread.so.0 (0x00002aae15ec3000) libgeothreadcpp.so => not found libgeocosmexception.so => not found libxerces-c-3.1.so => not found libgeocosmxmllibbasecpp.so => not found libxmllib.so => not found libstdc++.so.6 => /usr/lib64/libstdc++.so.6 (0x00002aae160e0000) libm.so.6 => /lib64/libm.so.6 (0x00002aae163e0000) libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00002aae16664000) libc.so.6 => /lib64/libc.so.6 (0x00002aae16872000) /lib64/ld-linux-x86-64.so.2 (0x00000036c7a00000) When my application attempts to load my shared library via dlopen I get the undefined symbol error. If I explicitly link to the shared lib version of boost_thread, ldd shows a dependency (which it should). If I then include a copy of boost_thread .so on the ld path my shared library loads without problems. However this is what I wanted to avoid and instead embed lib boost_thread directly into my .so. Thanks for any insight. Greg.

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Boost asio query
by James Barlow-Bignell 01 Feb '12

01 Feb '12

Hiya, Could anyone advise me on the correct way to receive data from a socket into a streambuf with asio? - Read into a new streambuf for each framed TCP message, and pass the streambufs themselves around within the application, or: - Read into a single streambuf for each socket, and copy each message into a std::vector to pass around? Whichever way I'm passing a 'message' around, it would be great if I could parse it easily using istream or similar, but the documentation is a little unclear to me. Any advice greatly appreciated! Cheers.

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Boost.Regex: Iterate over named captures/groups
by NoRulez 01 Feb '12

01 Feb '12

Hi @all, if I have a regex (e.g.: "^Subject: (Re: |Fw: )*(?<subject>.*)") I know I can access them with what["subject"] but is there a way to get a list or whatever of named captures/groups? Maybe something like the following: foreach(const std::string &str, what.namedGroups()) { std::cout << "Group Name: " << what[str] << std::endl; } Thanks in advance Best Regards NoRulez

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Boost::mpl vector product
by Allan Nielsen 01 Feb '12

01 Feb '12

Hi If I have two mpl vectors: v1 and v2 typedef boost::mpl::vector<char, short, int> v1; typedef boost::mpl::range_c<int,0,4> v2; Does boost then provide any tools for constructing the type: boost::mpl::vector< boost::mpl::pair< int_<0>, char >, boost::mpl::pair< int_<1>, char >, boost::mpl::pair< int_<2>, char >, boost::mpl::pair< int_<3>, char >, boost::mpl::pair< int_<0>, short >, boost::mpl::pair< int_<1>, short >, boost::mpl::pair< int_<2>, short >, boost::mpl::pair< int_<3>, short >, boost::mpl::pair< int_<0>, int >, boost::mpl::pair< int_<1>, int >, boost::mpl::pair< int_<2>, int >, boost::mpl::pair< int_<3>, int > > Best regards Allan W. Nielsen

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