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Random: Using random generators with runtime parameters
by Hans Mull 23 Nov '08

23 Nov '08

Hi! How can I use random generators with multiple parameters such as linear_congruential with parameters that are only known at runtime? Thanks in advance, Hans

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MultiPassInputIterator concept
by Tim Keitt 22 Nov '08

22 Nov '08

I have a question about the requirements of the MultiPassInputIterator concept as used in the Boost Graph Library. Does the ++first_iter == ++second_iter requirement hold across calls to out_edges(vertex, g)? Or put another way, does out_edges always have to return an iterator with same ordering of returned edges? The difference is between: graph_traits<graph>::out_edge_iterator i = out_edges(vertex, g); graph_traits<graph>::out_edge_iterator j = i; ++i == ++j; // clearly required, but sufficient? and graph_traits<graph>::out_edge_iterator i = out_edges(vertex, g); graph_traits<graph>::out_edge_iterator j = out_edges(vertex, g); ++i == ++j; // also required? Strangely enough, I have an application where the second case is (currently) not guaranteed (its a custom graph class where the out_edge_iterator is constructed on-the-fly). THK -- Timothy H. Keitt http://www.keittlab.org/

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[Regex] subexpressions
by Carsten Witzel 22 Nov '08

22 Nov '08

Hi, I'm using the Regex library for the first time with Visual Studio 2008. I've created a simple win32 console project, which works fine. The code is ------------------------------------- const char *pattern = "^(\\w*)\\s*=\\s*(\\w*).*"; const char *text = "Key = Value; Comment"; boost::regex re(pattern); boost::cmatch match; std::cout << pattern << std::endl; std::cout << text << std::endl; if (regex_match(text, match, re)) { std::cout << "--> " << match.size() << std::endl; for (int i = 0; i < match.size(); ++i) { std::cout << i << ": " << match[i] << std::endl; } } ------------------------------------- And the output is as expected: -------------------------------------- ^(\w*)\s*=\s*(\w*).* Key = Value; Comment --> 3 0: Key = Value; Comment 1: Key 2: Value -------------------------------------- However, I've tried to use the same code with the C/C++-API of a commercial software, and here I get the following output: -------------------------------------- ^(\w*)\s*=\s*(\w*).* Key = Value; Comment --> 3 - 0: Key = Value; Comment - 1: Key = Value; Comment - 2: Value; Comment -------------------------------------- Does anybody have an idea what's wrong here? Unfortunately, I'm not allowed to post any header files, so I need some hints where to look for a solution by myself. Thanks for any help! Regards Carsten Witzel

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Boost.Function and Boost.Bind
by Yang Zhang 22 Nov '08

22 Nov '08

I have the following simple test case: #include <boost/bind.hpp> #include <boost/function.hpp> #include <iostream> using namespace boost; using namespace std; void show(int x) { cout << x << endl; } void twice(function0<void> f) { f(); f(); } int main() { // This works... function<void()> f = bind(show, 0); bind(twice, f)(); // ...but this does not compile. // bind(twice, bind(show, 0))(); return 0; } When uncommenting the problematic line and attempting to build, I get: $ g++ -Wall -o boost_function{,.cc} /opt/armed/include/boost/bind.hpp: In member function ‘void boost::_bi::list1<A1>::operator()(boost::_bi::type<void>, F&, A&, int) [with F = void (*)(boost::function0<void, std::allocator<boost::function_base> >), A = boost::_bi::list0, A1 = boost::_bi::bind_t<void, void (*)(int), boost::_bi::list1<boost::_bi::value<int> > >]’: /opt/armed/include/boost/bind/bind_template.hpp:20: instantiated from ‘typename boost::_bi::result_traits<R, F>::type boost::_bi::bind_t<R, F, L>::operator()() [with R = void, F = void (*)(boost::function0<void, std::allocator<boost::function_base> >), L = boost::_bi::list1<boost::_bi::bind_t<void, void (*)(int), boost::_bi::list1<boost::_bi::value<int> > > >]’ boost_function.cc:13: instantiated from here /opt/armed/include/boost/bind.hpp:232: error: conversion from ‘void’ to non-scalar type ‘boost::function0<void, std::allocator<boost::function_base> >’ requested Why can't I put the two on the same line? (I also tried using template<typename T> void twice(T f) { f(); f() }, but that didn't work either.) Thanks in advance for any tips. -- Yang Zhang http://www.mit.edu/~y_z/

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[regex] segfault from construction
by Andrew Troschinetz 22 Nov '08

22 Nov '08

Hello all, I've got what I suspect is a relatively unique problem that's resulting in a segfault whenever I try to construct a boost::regex. First some machine information: Red Hat Enterprise Linux Server release 5.1 (Tikanga) Linux 2.6.18-53.el5, SMP, x86_64 gcc 4.1.2 20070626 (Red Hat 4.1.2-14) boost 1.33.1-10 Here's a small example that shows the problem: #include <boost/algorithm/string/regex.hpp> #include <iostream> #include <string> using namespace std; int main() { string input ("test test1 test2 test3"); string pattern ("\\btest\\b"); erase_regex (input, boost::regex (pattern)); cout << input << endl; // expecting " test1 test2 test3" return 0; } Compile flags (and this is getting to the heart of the problem, I think): -g -m32 -malign-double -O3 -Wall -lboost_regex Put all the above together in a bag, shake it up, and you get this segfault: 0x08066beb in boost::re_detail::basic_regex_parser<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::parse_extended (this=0xffde311c) at /usr/include/boost/regex/v4/basic_regex_parser.hpp:235 235 switch*this->m_traits.syntax_type(*m_position)) (gdb) print m_position $1 = 0x0 (gdb) bt #0 0x08066beb in boost::re_detail::basic_regex_parser<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::parse_extended at /usr/include/boost/regex/v4/basic_regex_parser.hpp:235 #1 0xf7f9e364 in boost ::re_detail::basic_regex_parser<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::parse () from /usr/lib/libboost_regex.so.2 #2 0xf7fa0eba in boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::do_assign () from /usr/lib/ libboost_regex.so.2 #3 0x08050789 in main () at /usr/include/boost/regex/v4/ basic_regex.hpp:254 So the immediate culprit is a dereferencing-null problem. Interestingly, the problem goes away at -O, -O1, and -O2. Or -O3 but without -malign-double. I was wondering if this is a known problem, and if anyone else who's hand is forced to compile with -malign-double has seen this problem and been able to work around it? -- Andrew Troschinetz Applied Research Laboratories

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Boost.Test with a static library
by Moritz Beber 22 Nov '08

22 Nov '08

Hello everyone, after prying for any hints in the documentation and reading frustrating mails in the archives for a while now, I get the feeling that this is a very confusing topic. My aim is to use a static library of boost.test because I need to compile it a lot and the waiting time when using the header is just frustrating. So I added to the "Jamfile.v2" in "libs/test/build" under "requirements" the following line: <define>BOOST_TEST_ALTERNATIVE_INIT_API=1 Then I used boost.build and apart from a few warnings like: ./boost/test/detail/config.hpp:85:1: warning: "BOOST_TEST_ALTERNATIVE_INIT_API" redefined <command-line>: warning: this is the location of the previous definition everything seemed alright. So I'm assuming I now have a static library with this macro defined so it should use the alternative initialiser. Then I tried the following code, which I mostly copied from the documentation, except for adding two macros: #define BOOST_TEST_NO_LIB #define BOOST_TEST_ALTERNATIVE_INIT_API #define BOOST_TEST_MODULE example #include <boost/test/unit_test.hpp> BOOST_AUTO_TEST_SUITE( test_suite1 ) BOOST_AUTO_TEST_CASE( test_case1 ) { BOOST_WARN( sizeof(int) < 4 ); } BOOST_AUTO_TEST_CASE( test_case2 ) { BOOST_REQUIRE_EQUAL( 1, 2 ); BOOST_FAIL( "Should never reach this line" ); } BOOST_AUTO_TEST_SUITE_END() BOOST_AUTO_TEST_SUITE( test_suite2 ) BOOST_AUTO_TEST_CASE( test_case3 ) { BOOST_CHECK( true ); } BOOST_AUTO_TEST_CASE( test_case4 ) { BOOST_CHECK( false ); } BOOST_AUTO_TEST_SUITE_END() When I try to compile, however, I get the following error: /home/engineer/libs/boost/lib/libboost_unit_test_framework-gcc43-mt-1_37.a(unit_test_main.o): In function `main': unit_test_main.cpp:(.text+0x2229): undefined reference to `init_unit_test()' collect2: ld returned 1 exit status Which I thought the macro BOOST_TEST_MODULE would take care of. I also tried using the BOOST_TEST_MAIN and took out the BOOST_TEST_NO_LIB. Nothing made a change to the compiler error. Can anyone help? Or give me a link to some proper documentation of how to resolve this issue? Thanks, Moritz

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Boost.Statechart and Simulink
by Derek Ditch 22 Nov '08

22 Nov '08

I was wondering if there were any known issues with compiling using Matlab's mex compiler (which in turn uses and links with gcc) and using Boost.Statechart. When I implemented my statechart, I tested it using a separate main() file and it works 100%. When I compile using mex into a Matlab MEX file, I seem to lose the functionality of the event triggers. I've tried several things to figure out what is happening, but all I can ascertain is that if I use the iterators state_begin() and state_end() to access all internal states, the loop never executes. I tried to dereference state_begin(), but got a segfault. My initial approach was to use the state_downcast<>(), but this didn't work in SImulink either. My final suspicion was that it had something to do with the extern "C" business, but admittedly, I don't understand the effects of this statement other than how the symbol appears in the library (i.e. avoiding mangling). I get this same behavior on OS X 10.5 w/ gcc 4.0.1 as well as on Linux x86_64 with gcc 4.2.4. If anyone wants to have my Simulink model to test, I could send that as well. I've attached the following files: ctrl_machine.[ch]pp - My state machine implementation/declaration. main.cpp - My test program air_controller.cpp - The C++ SFunction implementation used in Simulink. mex uses the following compilation steps with gcc/g++ -> g++-4.2 -c -I/opt/matlab/extern/include -I/opt/matlab/simulink/include -DMATLAB_MEX_FILE -ansi -D_GNU_SOURCE -fPIC -fno-omit-frame-pointer -pthread -DMX_COMPAT_32 -O -DNDEBUG "ctrl_machine.cpp" -> g++-4.2 -c -I/opt/matlab/extern/include -I/opt/matlab/simulink/include -DMATLAB_MEX_FILE -ansi -D_GNU_SOURCE -fPIC -fno-omit-frame-pointer -pthread -DMX_COMPAT_32 -O -DNDEBUG "air_controller.cpp" -> gcc-4.2 -c -I/opt/matlab/extern/include -I/opt/matlab/simulink/include -DMATLAB_MEX_FILE -ansi -D_GNU_SOURCE -fexceptions -fPIC -fno-omit-frame-pointer -pthread -DMX_COMPAT_32 -O -DNDEBUG "/opt/matlab/extern/src/mexversion.c" -> g++-4.2 -O -pthread -shared -Wl,--version-script,/opt/matlab/extern/lib/glnxa64/mexFunction.map -Wl,--no-undefined -o "ctrl_machine.mexa64" ctrl_machine.o air_controller.o mexversion.o -Wl,-rpath-link,/opt/matlab/bin/glnxa64 -L/opt/matlab/bin/glnxa64 -lmx -lmex -lmat -lm -lm ----- Thanks, Derek Ditch

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Re: [Boost-users] boost test with assert()
by Hicham Mouline 21 Nov '08

21 Nov '08

Hello, Any ideas re this issue? Can the assert from <cassert> be caught somehow? Regards,

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std::vector and default constructor
by peter_foelsche＠agilent.com 21 Nov '08

21 Nov '08

It would be helpful to have something like std::vector which allows one to pass some argument which is in turn passed to the constructor of every element so that not the default constructor is being called. This would be helpful for e.g. objects located in memory created by memory mapped files. Peter "The first point (using an init() function in preference to a constructor) is bogus. Using constructors and exception handling is a more general and systematic way of dealing with resource acquisition and initialization errors. This style is a relic of pre-exception C++." -- Stroustrup

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[test] new g++ compilation warnings on trunk
by Robert Mecklenburg 21 Nov '08

21 Nov '08

Compiling against the boost trunk I'm getting hundreds of these: g++ -Wall -Wextra -Wno-missing-braces -g -ftrapv -DBOOST_1_36_0 -Iboost-1_37 -MMD -MP -DUSE_TRAPV -c -o src/test/BlobTest.o src/test/BlobTest.cpp boost/test/floating_point_comparison.hpp:224: warning: 'boost::test_tools::<unnamed>::check_is_close' defined but not used boost/test/floating_point_comparison.hpp:246: warning: 'boost::test_tools::<unnamed>::check_is_small' defined but not used Any chance we can fix this? If you need a tester for g++ 4.2.3, I can do it. Thanks, -- Robert

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