July 2009 - Boost-users - lists.boost.org

[Boost.Program_options] extra_parser for config files
by Marti Cuquet 10 Jul '09

10 Jul '09

Hi, I want to implement the --switch / --no-switch behavior. I defined a bool option "switch" and then I parse the command line with an extra parser that sets "switch" to "false" if it finds a --no-switch. myopts.add_options() ("switch", po::value<bool>()->implicit_value(true), "Use switch.") ; po::store (po::command_line_parser(argc, argv).options(all).extra_parser(parse_no_options).run(), vm); The extra parser is: std::pair<std::string, std::string> parse_no_options (const std::string& s, const std::string name) { if (s.find("--switch") != s.npos) { if (s.substr (2, 3) == "no-") return std::make_pair (s.substr (5), std::string("false")); else return std::make_pair (s.substr (2), std::string("true")); } return std::make_pair (std::string(), std::string()); } This works fine for the command line. I also need to implement this for the config file, but I do not know how to pass the extra parser to the parse_config_file. Is there a way? Thanks, Marti

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[Threads] Test for running thread
by Krzysiek 10 Jul '09

10 Jul '09

Hi, I use following code to test running thread. bool isRunning = !thread.timed_join ( boost::posix_time::milliseconds ( 0 ) ); Is it safe and portable? Thanks, Krzysiek

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[interprocess] Container
by Moritz 10 Jul '09

10 Jul '09

Hi, is there a possibility to put something like this into the shared_memory? class A { int a; double d; // ... boost::interprocess string s; } Thanks in advance.

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[asio] Is io_service::run() reentrant?
by bearclaw 10 Jul '09

10 Jul '09

Hi, I cannot figure out from the documentation if I can call io_service::run() from an asynchronous handler, called itsels by run() of the same io_service. If it is possible, should I call reset() or not? I tried and it seems to work under linux, but I need to call run() in a loop as it returns prematurely, even with an io_service::work(), and with/without a reset(). The reason I need to do this is because my asynchronous handlers are calling legacy code that needs to perform synchronous operations. Using synchronous socket operations while this lasts as it was suggested to handle this kind of situations would be possible, but a lot more complicated in my setup. A pseudocode example of what I am trying to do in case I'm not clear: io_service io; tcp::socket s(io); onRead2() { // We got our data, stop inner io::run invocation io.stop(); } onRead(socket& s) { s.write("request"); //we need the result of the request synchronously // I know this looks silly, but it makes more sense in my real-world // use case where the async_read is burried deep. s.async_read(&onRead2); // optional io.reset() here, has no effect. io.run(); // <-- ends prematurely } main() { <connect s > s.async_read(&onRead) io.run(); } Regards, Matthieu

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shared_ptr: struct of 3 shared_ptrs: is operator= for struct required?
by Hicham Mouline 10 Jul '09

10 Jul '09

Hello Copying structs by default means memberwise copy. If I have a struct S { shared_ptr<T1> ptr1; shared_ptr<T2> ptr2; shared_ptr<T3> ptr3; }; and i have 2 instances s1 and s2 s1=s2 will call shared_ptr<T.> 's operator=(), right? Regards,

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[optional] How to make boost::optional throw if trying to access uninitialized value
by dariomt＠gmail.com 10 Jul '09

10 Jul '09

Hi list, I've seen in the docs that boost::optional asserts if you try to access an uninitialized value. Is it possible to make it throw an exception instead? Even in release mode? TIA

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How can I save the values in lambda expression? Can any one with kindness help me?
by fmingu 10 Jul '09

10 Jul '09

I am using Dev-C++ with boost lambda expression, I wrote: .................... int nnumber; int switchvalue; typedef std::map<int, int> IIPrimemap; IIPrimemap primemapvec; # define BetaKGre2 1 # define EqualToOne 2 #define ProductOfKPrime 3 ..................... if_then_else(var(nnumber)==1,var(switchvalue)=EqualToOne, if_then_else(constant(count_if(primemapvec.begin(),primemapvec.end(), bind(&IIPrimemap::value_type::second,_1)>2)>0), var(switchvalue)=BetaKGre2,var(switchvalue)=ProductOfKPrime)); std::cout<<" the var(switchvalue) is "<<var(switchvalue)<<"\n"; .............. and the program ran and showed: the var(switchvalue) is without any expression of var(switchvalue). I do not know how to save the values in lambda expression and where is wrong? Can I use *var(switchvalue) instead of var(switchvalue)? Can anyone with kindness help me?

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bootstrap.sh generates incorrect libdir in project-config.jam
by Andreas Klöckner 10 Jul '09

10 Jul '09

Hi all, When I ran bootstrap.sh --prefix=$HOME/pool, it did generate a broken project- config.jam--it used option.set libdir : /lib ; instead of option.set libdir : /home/andreas/pool/lib ; Has anybody else run into the issue described here? Any chance for fixed tarballs? Thanks, Andreas

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[Boost.Program_options] zero or one tokens with zero_tokens()?
by Marti Cuquet 10 Jul '09

10 Jul '09

Hello, I am trying to use an option that can have either zero or one arguments. I have seen an example in the documentation claiming that the following code would allow the user to provide either zero or one tokens to option 'verbose', but instead it throws an exception "extra parameter" when one token is given. So the question is, does zero_tokens() allow the user to specify a value? options_description desc; desc.add_options() ("help", "produce help message") ("compression", value<string>(), "compression level") ("verbose", value<string>()->zero_tokens(), "verbosity level") ("email", value<string>()->multitoken(), "email to send to") ; Thanks, Marti

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[Tuple] Addressing by named tag?
by Robert Jones 09 Jul '09

09 Jul '09

Am I correct in believing that tuples have to be accessed by element index, as in tuple.get<0>() Multi-Index container has a really nice facility to use named (well typed really) tags in these kind of expressions, but it seems tuples do not. Anyone fancy adding it to tuple? - Rob.

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