April 2010 - Boost-users - lists.preview.boost.org

[Random] Passing an arbitrary uniform random number generator to a function
by Joseph Wakeling 08 May '10

08 May '10

Hello, Suppose that I have a function that takes a uniform random number generator as an argument, e.g. double foo(mt19937 &urng) { double x = uniform_real<double> (0.0, 10.0) (urng); double y = uniform_real<double> (5.0, 7.0) (urng); return (x*y); } Is there a way to make the choice of random number generator arbitrary (i.e. not limited to mt19937) without making the function a template? Alternatively, is there a better way of passing around the basic uniform random number generator? The reason for the no-template rule is that I would like to pass a URNG to a virtual function in a class, and I would really not like to have to make the class itself a template dependent on the type of URNG. Can someone recommend a solution? Thanks and best wishes, -- Joe

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[units] (controlled) implicit conversion
by alfC 05 May '10

05 May '10

Hi, I took much labour in defining an extra system of units (atomic units). It works very well and it also defines (optionaly) default conversion from atomic to SI units. The problem that I have now is that all the conversion has to be done explicitly. I understand that this way of doing thing is by design. But for some formulas I would like to allow implicit conversion, for example when adding energies in SI and energies in atomic units (I don't care which direction the conversion is done since I will transform to one of the two at the end of the formula). On top of that the Units Manual says: "Safety and the potential for unintended conversions leading to precision loss and hidden performance costs. Options are provided for forcing implicit conversions between specific units to be allowed. " The question is which are the "Options provided for forcing implicit conversion"? What follow is an example: What I want is some controlled implicit conversion (even better is this conversion are allowed inside a certain program scope). Note that line 4 doesn't work: quantity<si::energy> e1(3.*si::joules); quantity<atomic::energy> e2(4.*atomic::hartree); quantity<atomic::energy> e3(e1); //works e1 = e2; //doesn't work e1 = quantity<si::energy>(e2); //works cout<<e1<<'\n'<<e2<<'\n'<<e3<<endl; note that the third line works because somewhere I defined a conversion_factor plus a default_conversion between units in the different systems. And it works because the conversion is explicit. Now the fourth line doesn't work, it gives an error (see at end). comenting the third line compiles. I even tried defining a conversion for this particular units, but still doesn't work. BOOST_UNITS_DEFINE_CONVERSION_FACTOR( boost::units::atomic::energy, boost::units::si::energy, double, 4.359744e-18 ); BOOST_UNITS_DEFAULT_CONVERSION( boost::units::atomic::energy, boost::units::si::energy ); error caused by line 4: In file included from /usr/include/boost/units/io.hpp:28, from /home/alfc/prj/mag/Qbox//units/systems/ atomic.hpp:187, from eos.cpp:8: /usr/include/boost/units/quantity.hpp: In member function ‘boost::units::quantity<Unit, Y>& boost::units::quantity<Unit, Y>::operator=(const boost::units::quantity<Unit2, YY>&) [with Unit2 = boost::units::unit<boost::units::list<boost::units::dim<boost::units::length_base_dimension, boost::units::static_rational<2l, 1l> >, boost::units::list<boost::units::dim<boost::units::mass_base_dimension, boost::units::static_rational<1l, 1l> >, boost::units::list<boost::units::dim<boost::units::time_base_dimension, boost::units::static_rational<-0x00000000000000002l, 1l> >, boost::units::dimensionless_type> > >, boost::units::homogeneous_system<boost::units::list<boost::units::atomic::electron_mass_base_unit, boost::units::list<boost::units::atomic::elementary_charge_base_unit, boost::units::list<boost::units::atomic::reduced_planck_constant_base_unit, boost::units::list<boost::units::atomic::coulomb_force_constant_base_unit, boost::units::list<boost::units::atomic::boltzman_constant_base_unit, boost::units::dimensionless_type> > > > > >, void>, YY = double, Unit = boost::units::unit<boost::units::list<boost::units::dim<boost::units::length_base_dimension, boost::units::static_rational<2l, 1l> >, boost::units::list<boost::units::dim<boost::units::mass_base_dimension, boost::units::static_rational<1l, 1l> >, boost::units::list<boost::units::dim<boost::units::time_base_dimension, boost::units::static_rational<-0x00000000000000002l, 1l> >, boost::units::dimensionless_type> > >, boost::units::homogeneous_system<boost::units::list<boost::units::si::meter_base_unit, boost::units::list<boost::units::scaled_base_unit<boost::units::cgs::gram_base_unit, boost::units::scale<10l, boost::units::static_rational<3l, 1l> > >, boost::units::list<boost::units::si::second_base_unit, boost::units::list<boost::units::si::ampere_base_unit, boost::units::list<boost::units::si::kelvin_base_unit, boost::units::list<boost::units::si::mole_base_unit, boost::units::list<boost::units::si::candela_base_unit, boost::units::list<boost::units::angle::radian_base_unit, boost::units::list<boost::units::angle::steradian_base_unit, boost::units::dimensionless_type> > > > > > > > > >, void>, Y = double]’: eos.cpp:115: instantiated from here /usr/include/boost/units/quantity.hpp:234: error: invalid application of ‘sizeof’ to incomplete type ‘boost::STATIC_ASSERTION_FAILURE<false>’ /usr/include/boost/units/quantity.hpp:234: error: invalid application of ‘sizeof’ to incomplete type ‘boost::STATIC_ASSERTION_FAILURE<false>’ Thank you, Alfredo

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Can BOOST libraries be integrated with c++/CLR .net?
by Joe Pagliarulo 05 May '10

05 May '10

Hi, my name is Joe and I am new to the Boost libraries. Here's my question: Can BOOST libraries be integrated with c++/CLR .net? Does is work with clr/.NET? Thanks, Joe Pagliarulo

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[ASIO] native back into local::stream_protocol
by Etienne Philip Pretorius 04 May '10

04 May '10

Hello List, I just need some guidance here. I have a parent process fork off a child and pass the int value to the child indicating what the native socket file descriptor it should use to receive communication from the parent process. I am just not able to get it placed back into a boost::asio::local::stream_protocol::socket object. Here is the code below, from the child process loaded via execlp: for(int i = 3; i < static_cast<unsigned char>(~0); i++) { if(i == boost::lexical_cast<int>(argv[0])) { continue; } close(i); } boost::asio::io_service io_service; boost::asio::local::stream_protocol::socket parent_(io_service); parent_.assign(boost::asio::local::stream_protocol, boost::lexical_cast<int>(argv[0])); Compiler error: g++ -c -g -MMD -MP -MF build/Debug/GNU-Linux-x86/main.o.d -o build/Debug/GNU-Linux-x86/main.o main.cpp main.cpp: In function ‘int main(int, char**)’: main.cpp:30: error: expected primary-expression before ‘,’ token Thank you, Etienne -- This message has been scanned for viruses and dangerous content by Pinpoint, and is believed to be clean.

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[iostreams] Inconsistent state of stream
by Nicola 03 May '10

03 May '10

Hi, can someone tell me if the behaviour of the enclosed example is a bug? In my test, the last two assertions fail, but I don't understand why (Boost 1.42.0). Thanks, Nicola #include <boost/iostreams/copy.hpp> #include <boost/iostreams/filtering_stream.hpp> #include <boost/iostreams/filter/bzip2.hpp> #include <cassert> #include <fstream> #include <sstream> struct bz2istream : public boost::iostreams::filtering_stream<boost::iostreams::input> { public: bz2istream(std::string const& path) : pBz2file(path.c_str(), std::ios_base::in | std::ios_base::binary) { push(boost::iostreams::bzip2_decompressor()); push(pBz2file); } private: std::ifstream pBz2file; }; int main() { bz2istream bzippedfile("foo.bz2"); std::ostringstream os; boost::iostreams::copy(bzippedfile, os); assert(!(bzippedfile.rdstate() & std::ios_base::goodbit)); // Ok assert(bzippedfile.rdstate() & std::ios_base::eofbit); // Fails assert(!(bzippedfile.good())); // Fails }

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[UTF] Let my debugger catch unhandled exceptions
by Adam Nielsen 03 May '10

03 May '10

Hi all, I'm trying to track down a problem in my code that the Boost test framework has isolated, however I'm finding it difficult to track it back to a line in the source. The Boost test framework likes to catch all exceptions, which means when you run the code through a debugger it doesn't break at the point the exception becomes unhandled, so you can't do a backtrace to see where it came from. There is the option --catch_system_errors=no which works for some exceptions, but not these ones. I'm using gdb and telling it to "catch throw" is painful because there are dozens of exceptions thrown around correctly before it gets to the unhandled one I'm interested in. Is there some easy way I can tell UTF not to catch any exceptions? Many thanks, Adam.

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How do you use the find_iterator to do in-place replacements?
by G S 01 May '10

01 May '10

Hi all. I have the split_iterator working as intended on a string, but I don't see how to use the range it returns to change the string directly without copying it. For example, I want to do an erase_all on a range, but that function won't take a range. Anybody have an example of how to do this? Thanks!

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Boost Graph: determining type of bundled property
by Trevor Harmon 30 Apr '10

30 Apr '10

Hi, I wrote some Boost Graph code that uses a custom pointer type as the vertex: adjacency_list<vecS, vecS, directedS, Foo*, property<edge_index_t, std::size_t> > I now need to expand the graph so that the Foo pointer is just one of several vertex properties. I assume bundled properties are the way to go: http://www.boost.org/doc/libs/1_42_0/libs/graph/doc/bundles.html I also need my vertices to be of different types (but all as children of a base type), such that my vertex bundles look something like this: class BaseVertex { }; class EntryVertex : public BaseVertex { }; class ExitVertex : public BaseVertex { }; class FooVertex : public BaseVertex { Foo *foo; // ... other properties follow ... }; My goal is to be able to iterate through the vertices and perform different actions depending on the type of vertex. (e.g., if vertex type is EntryVertex do this, if vertex type is ExitVertex do that, etc.) However, I don't know how to determine a vertex's type. The bundles document mentions something about vertex_bundle_type<Graph>::type, but I have no idea how to use this. I couldn't find any code in the Boost examples that use it, either. Any tips to get me started? Also, note that I've added an index property to my graph's edges, declared explicitly in the adjacency_list instantiation (as seen above). Would it make sense to convert this to a bundled property as well, or should I leave it as-is? (I don't think I'll ever need any edge properties other than the index.) Thanks, Trevor

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handling of daylight saving time...
by Archie14 30 Apr '10

30 Apr '10

My software records time events on the computer and it does it using whatever timezone and daylight saving time settings are on this computer. I realized too late that, while storing timestamps, I am not accounting for this daylight adjustment process. So, if hypothetically speaking, the daylight adjustment happens today at 9:00 am and I am writing my timestamps every second I will have something like that: … 8.58 8.59 9.00 10.01 (without timesaving should be 9.01) 10.02 (without timesaving should be 9.02) … When I am reading my timestamps back I am constructing timezone and using it for timestamps manipulation std::string gmt = (boost::format("TMZ%1% TMS1:00:00,M3.2.0/02:00:00,M11.1.0/02:00:00") % gmtoffset).str(); , but this one-hour gap persists, as I now think it should. The question is: is it possible to do manipulation with datetime library to remove this gap without hard-coding one hour removal after specific date/time of daylight saving time?

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Detect generic base class
by Francesco Biscani 30 Apr '10

30 Apr '10

Hi list, how can I detect if a class inherits from a generic class? E.g., template <class Derived> class base {}; class final: public base<final> {}; I would like to specialise a type trait for all classes deriving from base<whatever>, possibly using enable_if and is_base_of: template <class T, class Enable = void> class trait: boost::false_type {}; // What syntax here? Something like this (which does not work): template <class T, class Derived> class trait<T,typename boost::enable_if<boost::is_base_of<base<Derived>,T> >::type>: boost::true_type {}; The best I've come up with has been putting a typedef for Derived in base, and then using SFINAE: template <class Derived> class base { public: typename Derived derived; }; template <class T> class trait<T,typename boost::enable_if<boost::is_base_of<base<typename T::derived>,T> >::type>: boost::true_type {}; But this is ugly and I'm sure there are much better ways of doing this :) Thanks in advance, Francesco

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