September 2005 - Boost-users - lists.preview.boost.org

Boost serialization storage question
by Leon Mergen 04 Sep '05

04 Sep '05

Hello, I wondered how the Boost.Serialization library determines how many bytes to read from an input stream to "fill" a class with data. That is, does it read an entire input stream until the end of the stream and use that as the data to fill a class with, or does it perform a sizeof(class) and read that from the stream ? If it is the latter, then out of curiosity, how does it determine the size of an object with different class versions ( so if an object version 1 has been saved and then tries to load version 2 ) ? Does it write some sort of object size at the beginning of the file ? If it reads the entire stream until the end, what would be a good approach to save multiple objects in a single file, and be able to read just a few objects out of the file ? Thanks in advance for any responses. Regards, Leon Mergen

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Compilation problem with date_time and iostream gzip (and bzip2) filters
by tonton 04 Sep '05

04 Sep '05

This simple test fails to compile with gcc 4.0.1 (or 4.0.2, it's the debian unstable version) and boost 1.33.0 if the date_time include is uncommented. Is there any known incompatibility between the two libraries ? #include <boost/iostreams/filtering_stream.hpp> #include <boost/iostreams/filter/gzip.hpp> // #include <boost/date_time/local_time/local_time.hpp> int main() { boost::iostreams::filtering_istream in; in.push(boost::iostreams::gzip_compressor()); return 0; } The full error is attached /usr/include/boost/iostreams/filter/symmetric.hpp: In member function ‘std::streamsize boost::iostreams::symmetric_filter<SymmetricFilter, Alloc>::read(Source&, typename boost::iostreams::char_type_of<T>::type*, std::streamsize) [with Source = boost::iostreams::detail::linked_streambuf<char, std::char_traits<char> >, SymmetricFilter = boost::iostreams::detail::zlib_compressor_impl<std::allocator<char> >, Alloc = std::allocator<char>]’: /usr/include/boost/iostreams/filter/gzip.hpp:199: instantiated from ‘std::streamsize boost::iostreams::basic_gzip_compressor<Alloc>::read(Source&, char*, std::streamsize) [with Source = boost::iostreams::detail::linked_streambuf<char, std::char_traits<char> >, Alloc = std::allocator<char>]’ /usr/include/boost/iostreams/read.hpp:215: instantiated from ‘static std::streamsize boost::iostreams::detail::read_filter_impl<boost::iostreams::multichar_tag>::read(T&, Source&, typename boost::iostreams::char_type_of<T>::type*, std::streamsize) [with T = boost::iostreams::basic_gzip_compressor<std::allocator<char> >, Source = boost::iostreams::detail::linked_streambuf<char, std::char_traits<char> >]’ /usr/include/boost/iostreams/read.hpp:56: instantiated from ‘std::streamsize boost::iostreams::read(T&, Source&, typename boost::iostreams::char_type_of<T>::type*, std::streamsize) [with T = boost::iostreams::basic_gzip_compressor<std::allocator<char> >, Source = boost::iostreams::detail::linked_streambuf<char, std::char_traits<char> >]’ /usr/include/boost/iostreams/detail/adapter/concept_adapter.hpp:247: instantiated from ‘static std::streamsize boost::iostreams::detail::flt_wrapper_impl<boost::iostreams::input>::read(Filter&, Source*, typename boost::iostreams::char_type_of<T>::type*, std::streamsize) [with Filter = boost::iostreams::basic_gzip_compressor<std::allocator<char> >, Source = boost::iostreams::detail::linked_streambuf<char, std::char_traits<char> >]’ /usr/include/boost/iostreams/detail/adapter/concept_adapter.hpp:74: instantiated from ‘std::streamsize boost::iostreams::detail::concept_adapter<T>::read(typename boost::iostreams::char_type_of<T>::type*, std::streamsize, Source*) [with Source = boost::iostreams::detail::linked_streambuf<char, std::char_traits<char> >, T = boost::iostreams::basic_gzip_compressor<std::allocator<char> >]’ /usr/include/boost/iostreams/detail/streambuf/indirect_streambuf.hpp:250: instantiated from ‘typename boost::iostreams::detail::indirect_streambuf<T, Tr, Alloc, Mode>::int_type boost::iostreams::detail::indirect_streambuf<T, Tr, Alloc, Mode>::underflow() [with T = boost::iostreams::basic_gzip_compressor<std::allocator<char> >, Tr = std::char_traits<char>, Alloc = std::allocator<char>, Mode = boost::iostreams::input]’ test.cpp:10: instantiated from here /usr/include/boost/iostreams/filter/symmetric.hpp:112: error: ‘boost::iostreams::symmetric_filter<boost::iostreams::detail::zlib_compressor_impl<std::allocator<char> >, std::allocator<char> >::<anonymous enum>’ is/uses anonymous type /usr/include/boost/iostreams/filter/symmetric.hpp:112: error: trying to instantiate ‘template<class T> struct boost::is_integral’ /usr/include/boost/iostreams/filter/symmetric.hpp:124: error: ‘boost::iostreams::symmetric_filter<boost::iostreams::detail::zlib_compressor_impl<std::allocator<char> >, std::allocator<char> >::<anonymous enum>’ is/uses anonymous type /usr/include/boost/iostreams/filter/symmetric.hpp:124: error: trying to instantiate ‘template<class T> struct boost::is_integral’ /usr/include/boost/iostreams/filter/symmetric.hpp:131: error: ‘boost::iostreams::symmetric_filter<boost::iostreams::detail::zlib_compressor_impl<std::allocator<char> >, std::allocator<char> >::<anonymous enum>’ is/uses anonymous type /usr/include/boost/iostreams/filter/symmetric.hpp:131: error: trying to instantiate ‘template<class T> struct boost::is_integral’

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Renaming boost libraries
by Matt 04 Sep '05

04 Sep '05

Heya Guys, Just wondering if it's possible to rename the boost libraries after they've been built. Specifically, I want to remove the boost version (-1_33) that is appended to all the lib and dll libraries. The reason is twofold; a) our source control system will mark the libs with a label to indicate the version and b) it should make migrating to a new boost version easier. I'm pretty sure it's fine to just physically rename the static libraries but seem to remember that for dynamic libs you can't do that because the matching .lib file indicates which .dll the application should load. Am I mistaken? If not is there any other way to specify that you don't want the boost version appended to the end of the filename? Cheers, Matt

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Re: [Boost-users] Same thing: dynamic bitset as member of struct!?
by Fujinobu Takahashi 04 Sep '05

04 Sep '05

Hello Bronek-san, YATTA! Multi bitsets Works very well. Very helpful suggestion for me and our colleagues. ARIGATOU GOZAIMASU. Fuji On Sat, 03 Sep 2005 22:33:32 +0100 Bronek Kozicki <brok(a)rubikon.pl> wrote: > Hello > > your constructor is incorrectly defined. Following should work: > > #include <iostream> > #include <boost/timer.hpp> > #include <boost/dynamic_bitset.hpp> > using namespace std; > using namespace boost; > > struct multi_bitsets{ > multi_bitsets() : db1(10,1ul), db2(10,2ul) {} > dynamic_bitset<> db1; > dynamic_bitset<> db2; > }; > > int main() > { > multi_bitsets mb1; > cout << "mb1.db1:" << mb1.db1 << endl; > cout << "mb1.db2:" << mb1.db2 << endl; > } > > > Best regards > > > B.

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How to use dynamic bitset as member data of class?
by Fujinobu Takahashi 04 Sep '05

04 Sep '05

Hello again, I enjoy to use the dynamic_bitset for the 1 bit correlation of radio interferometor. Very useful. But how to use the dynamic bitsets as the member data of the class? class multi_bitsets{ const boost::dynamic_bitset<> db1(20,1ul); const boost::dynamic_bitset<> db2(20,1ul); this kind of code always gives me the following errors: $ g++ multi_bitset_test00.cpp multi_bitset_test00.cpp:19: error: expected identifier before numeric constant multi_bitset_test00.cpp:19: error: expected `,' or `...' before numeric constant multi_bitset_test00.cpp:19: error: ISO C++ forbids declaration of `parameter' with no type Please let me know how to use the dynamic bitsets as the member data of the class, thank you. fuji

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[Boost.Python] How is shared_ptr<SubClass> matched with shared_ptr<Base> in signature?
by Nat Goodspeed 03 Sep '05

03 Sep '05

We have a smart_ptr template of our own, sort of cloned from intrusive_ptr. But I'm having trouble with Python code passing subclass objects managed by this smart_ptr to C++ methods accepting smart_ptr<base class>. Consider: class Base: { ... }; class SubClass: public Base { ... }; class Interface { public: void method(smart_ptr<Base> arg) const; }; Of course SubClass* is implicitly convertible to Base*. In C++ code, smart_ptr<SubClass> is even implicitly convertible to smart_ptr<Base>. That is, given the definitions above, this C++ code compiles and runs correctly: Interface worker; smart_ptr<SubClass> objp = new SubClass(); worker.method(objp); We can inform Boost.Python that Base objects -- and, by implication, SubClass as well -- are to be managed using smart_ptr<>. class_<Base, smart_ptr<Base>, boost::noncopyable>("Base", no_init) ... ; class_<SubClass, bases<Base> >("SubClass") ... ; We have many methods that accept smart_ptr<Base> and do appropriately polymorphic things to SubClass and its siblings. However, if a Python caller attempts to pass a SubClass object to a method accepting smart_ptr<Base>: obj = Extension.SubClass() worker = Extension.Interface() worker.method(obj) we get the following runtime error: Boost.Python.ArgumentError: Python argument types in Interface.method(Interface, SubClass) did not match C++ signature: method(class Interface {lvalue}, class smart_ptr<class Base>) That's true for both Boost 1.31 and Boost 1.32. We have not yet tried this with Boost 1.33. We're using MSVC 7.1 on Windows XP Pro. Okay, I know this is our fault, something's wrong with our smart_ptr template definition. I know that because if I recompile with this: #define smart_ptr boost::shared_ptr instead of our own smart_ptr definition, it works just fine! As noted earlier, our smart_ptr is a variant of boost::intrusive_ptr. But it appears that either there's a mysterious requirement on the smart_ptr template that we're not fulfilling, or there's special recognition of boost::shared_ptr and possibly boost::intrusive_ptr in Boost.Python. What must we add to allow Boost.Python to recognize the legal conversion from smart_ptr<SubClass> to smart_ptr<Base> when it does its argument matching? [Your next question is: why not just use one of the Boost smart pointers? Short answer: that's what we WANTED to do! We tried shared_ptr and ran afoul of the second-conversion-from-same-dumb-pointer problem; we tried intrusive_ptr and got completely entangled in new cross-DLL dependencies because intrusive_ptr doesn't deal well with incomplete pointee types. Our smart_ptr is an attempt to trade away both issues, at the cost of a mandatory pointee base class. It almost works, too, except for this baffling bug...] Thanks for your help.

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boost.interval for tracking floating point rounding errors
by Frank Hess 02 Sep '05

02 Sep '05

Hi, I'm curious if it is possible to make boost.interval more convenient to use for tracking floating point rounding errors. Currently, you run into problems if you do naive things like boost::numeric::interval<double> x(0.1); since the 0.1 value gets rounded once by the compiler before the interval constructor ever sees it. Also, things like boost::numeric::interval<double> y(2), z; z = 0.1 * y; have similar problems. -- Frank

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Operators with boost::reference_wrapper
by Edson Tadeu 02 Sep '05

02 Sep '05

Although boost::reference_wrapper has a casting operator to T&, when I use any operator on a reference_wrapper, I get a compiler error stating that "boost::reference_wrapper<T> does not define this operator or a conversion to a type acceptable to the predefined operator". E.g, this should compile, but doesn't: #include <string> #include <iostream> #include <boost/ref.hpp> using namespace std; using namespace boost; void main() { string s1 = "alfa"; string s2 = "beta"; reference_wrapper<string> rs1 (s1); reference_wrapper<string> rs2 (s2); bool test = rs1 < rs2; // Error here cout << rs1; // Error here too } Why is that? I'm using MSVC 7.1.

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Using bind / lambda to create a functor that (1) ignores arguments, and (2) returns a constant
by Stephen Gross 02 Sep '05

02 Sep '05

Is there a way to use bind and/or lambda to create a functor that: (1) Takes as input a single argument (that is ignored), and (2) Returns a constant value. Ideally, something along the lines of: bind(constant(5), _1) // _1 is passed but ignored. Thanks, --Steve Stephen Gross Case Western School of Medicine Cleveland, OH "By Grabthar's hammer, by the sons of Worvan, you shall be avenged." - Dr. Lazarus

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Reference information for lamba
by Stephen Gross 02 Sep '05

02 Sep '05

I'm trying to find reference documentation for the lambda library. I've found the main documentation on boost's website, but not reference information. Is it available somewhere? --Steve

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