February 2007 - Boost-users

[asio] Using tcp::iostreams with Boost.Iostreams filtered_streambuf
by Darren Garvey 14 Feb '07

14 Feb '07

Hi, I was wondering about tcp::iostreams. I need to have the ability to write code like: obj<< "Hello world" and at intervals (of size) have a header attached and then have it written to an open socket. I have been looking into Boost.Iostreams to do this, but I was wondering if rather than implementing the whole streambuf/sink, I could just create a filtering_streambuf (naming convention taken from Boost.Iostreams) - which would attach the header when needed - and just instantiate a tcp::iostream object with that streambuf. I'm still very foggy on the Iostreams library - and streams/buffers in general - but does that sound like it could work? Sorry about the vagueness, Darren

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[signals] rationale for signals::connection::disconnect() const
by Frank Mori Hess 14 Feb '07

14 Feb '07

I just noticed that boost.signals declares signals::connection::disconnect() as a const member function. Can anyone explain to me why that was done? It seems like a non-const operation to me. That's how I declared it in thread_safe_signals, and it doesn't seem to cause any problems there. -- Frank

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How to block a signal
by Dahman 14 Feb '07

14 Feb '07

Hi, I have a signal with many slots connected to it and I have a class object witch want to have the possibility to block this signal at the start and unblock it later, but know nothing about what and how many slots are connected to it (then can't use connection.disconnect()). Is there any solution for this problem? Thanks for any help.

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program_options boost::bad_any_cast: failed conversion using boost::any_cast
by Raiko Albrecht 14 Feb '07

14 Feb '07

Hi, since a while I always get this any-cast error when using program_options with type "std::string". to check it out I'd modified the simple example from boost for program_options a little bit (checking if any_type as it works - does, inserted a string-parameter). Compiling, starting with "--log astring" -> crash. starting without works at expected. (See appended source file) System is Debian etch, X86_64, gcc 4.1.2 20061115 boost: tried with debian package and self build variant. question now is: why? what may I do? As far as I remember on a unstable 32bit with gcc 4.0 it did work, but not sure if I got it running on a 64 bit system later. Hope for help Rajko

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using unit_test_log
by Paez, Juan 14 Feb '07

14 Feb '07

Hello, I new using boost. I am trying to setup a set of test cases to test some api. I would like to be able to use the logging facilities that boost provides through the unit_test_log class. I understand that from the command line you can set the logging parameters. However, I want to be able to set those parameters from inside the my program executing the test cases. any ideas? Specifically, I want to be able to send the log output to specific files (the files change depending on the test suite I am running), the format, level, etc. Thanks, Juan

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spirit and xml
by abir basak 13 Feb '07

13 Feb '07

Hi, I am at present using spirit for parsing unipen file as specified in http://www.unipen.org/dataformats.html . That is great and quite easy to parse, thanks to spirit. Now I am looking to use spirit for parsing an specific xml file ( w3c inkml file). So my intension is not to have a generic xml parser, rather than a specific xml parser (which also have some BNF grammar) . Anyone had used spirit for domain specific xml parsing? I believe using spirit will make it faster. Also I am interested to parse only a portion of the whole document at a time, and generate data from that portion only, rather generating data for whole DOM (The files are large, 4-20 MB typically) my xml file is something like, <page> <trace ref = "1"> 0,1,2,3,4,3,4,3,5,4,3,4 </trace> ... </page> note that inside <trace> the grammar is a BNF (comma sep float pairs mostly) Any comments, or snippets to show how to do it? -- Abir Basak, Member IEEE Software Engineer, Read Ink Technologies B. Tech, IIT Kharagpur email: abir(a)abirbasak.com homepage: www.abirbasak.com

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boost::mutex question
by Anders Sundman 13 Feb '07

13 Feb '07

Hi all! I'm curious about the realization of the boost::mutex class (especially on W32). * How heavy is it to create a mutex object? * Are there any limits (OS recource bound or other) to how many mutex object that can be created? * How costly is it to 're-lock' a recursive mutex? Almost NOP or more costly? Are these questions (and other of the same type) answered somewhere in the docs? Finally, a more concrete question. Consider the following: A list of objects that needs to lock a mutex (all lock the same mutex). vector<CriticalWorker*> foo; ... for ( ... i = each foo ... ) i->doWorkThatLocks(); This code section will lock/unlock repeatedly. If I use a recursive mutex, will the following be much faster (since the locks in 'doWorkThatLocks' will be more light-weight)? lock(); for ( ... i = each foo ... ) i->doWorkThatLocks(); unlock(); Best Regards Anders Sundman

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Preferred syntax on GCC 4.0
by Austin Shoemaker 12 Feb '07

12 Feb '07

I can't find this in the documentation or on the web, surprisingly, so I thought I'd ask here: Should I be able to use "preferred syntax" with boost::signal using GCC 4.0? I get "ISO C++ forbids delcaration of 'signal' with no type" errors, and portable syntax works fine. If it's relevant, I'm using the Apple build of GCC on OS X 10.4.8. Best, Austin

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[lambda] std::string::find
by Bob Quampen 12 Feb '07

12 Feb '07

First, sorry for this total newbie question, i'm trying to do something like this: std::for_each ( std::istream_iterator<std::string>(ss), std::istream_iterator<std::string>(), boost::lambda::if_then ( !(boost::lambda::bind(&std::string::substr, boost::lambda::_1, 0, 1) == _ignore) && !boost::lambda::bind(&std::string::empty, boost::lambda::_1), (boost::lambda::bind(&std::string::find, boost::lambda::_1, _ignore), // compiler complains here ---------------------------------<snip>---------------------------------------------------------------------- i'm getting the following error: Error 23 error C2784: 'const boost::lambda::lambda_functor<boost::lambda::lambda_functor_base<boost::lambda::action<3,boost::lambda::function_action<3,T>>,detail::bind_tuple_mapper<const Arg1,const Arg2,const Arg3>::type>> boost::lambda::bind(const Arg1 &,const Arg2 &,const Arg3 &)' : could not deduce template argument for 'overloaded function type' from 'overloaded function type' am i not supplying the correct amount of parameters to the find method? -- Using Opera's revolutionary e-mail client: http://www.opera.com/mail/

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[OT] Is there a HTTP library in boost?
by Meryl Silverburgh 12 Feb '07

12 Feb '07

Hi, Is there a HTTP library in boost? I am looking for something which can handle http redirect. Thank you.

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