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

Interprocess general questions
by Andrej van der Zee 16 Mar '09

16 Mar '09

Hi, I am using Boost.interprocess for the first time and read the documentation. It is difficult for me to decide what construct would best fit my scheme, because of all the options. I hope that somebody could help me find out. I am using Boost 1.38 on Ubuntu 8.10. In my setup, I have one parent process that forks many (could be hundreds) child processes. In the parent process I need to maintain a data-queue. The child processes insert data into the queue and once every X seconds the parent removes all messages from the queue (in order to dump it to a database). The data is one type only and fixed length: A struct with a few doubles, a few integers and a fixed-length string. Because there can be hundreds of child processes that insert into the data-queue many times a second, I guess it would make sense to have multiple data regions in one big shared memory segment, each with it's own synchronization mechanism? I mean, it is important that the child processes are able to insert the data fast and do not suffer lock contention too much (a "little" overhead is fine though). So my question is what components from the Boost.interprocess-library should I use? Any other comments and/or tips before I start coding? Thank you! Andrej van der Zee

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installing boost in linux (help needed urgently) !!!!!!
by ayan sinha 15 Mar '09

15 Mar '09

Hi, I am new to linux and also to boost library.. I am planning to install boost library in linux box (which is a production machine with no net connectivity). i have already got the linux version of boost in that machine and now I am planning to install it. Can please somebody tell me what are the steps needs to be done to install linux.. with commands (I cant use any tool that boost provide to install because ther is no net connectivity in that box). I have gone through the boost website .. but it looks very complicated :) also I have gone through couple of websites but it was not much usefull. I will be really greatfull if somebody can tell me what are the steps (with commands) to install in linux box. Thanks in Advance, Ayan.

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Why "Mixing a dll boost library with a static runtime is a really bad idea..."?
by D M 15 Mar '09

15 Mar '09

Hi, I want (need) to use boost libs as dll with a static run-time library. In this case auto_link.hpp gives me an error "Mixing a dll boost library with a static runtime is a really bad idea...". Why is it a bad idea? I don't think that it's a good idea but requirements in our project demand static-runtime linkage for all modules and they don't want to use regex as static library cause of it's size. What problems could it cause? I know only one problem with a memory allocation in different modules. Any more? Thanks, Vladimir

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Re: [Boost-users] proto: analytical-only math functions
by Hicham Mouline 14 Mar '09

14 Mar '09

> ----- Original Message ----- > From: peter_foelsche(a)agilent.com > To: boost-users(a)lists.boost.org > Subject: Re: [Boost-users] proto: analytical-only math functions > Date: Fri, 6 Mar 2009 12:40:22 -0700 > > > Could the originator of this thread try to explain to me what he wants to > accomplish? > I still cannot figure any use case for proto. > > Peter Step1 is to have a derivative metafunction which computers the nth derivative of a function at compile time. In order to do that, I need a mathematical language to write my functions. so I have constants, variables, basic_functions and user-defined functions that are terminals of my language f(x) = log(x); g(x) = derivative(1, f, x); g(x) will be 1/x; I should manage to run derivative purely in compile time. Later, I will look at stochastic and partial differential equations and write functions to solve them analytically whenever possible... proto will help me define terminals, the grammars for what are acceptable expressions. regards,

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Seekg on a gzip'd file...Is this possible?
by Gerrick Bivins 14 Mar '09

14 Mar '09

Hello all, I¹m switching one of my projects over from java to c++. Basically it¹s a gzip file reader, where I¹d like to parse a bunch of numbers (floats, ints, doubles) and in some instances I¹d like to skip some of the data. I¹m a ³noob² to boost and after getting the file reader working using the boost like this: { .... std::ifstream ormodelFile(filenameForTimeStep.c_str(), std::ios_base::in|std::ios_base::binary); boost::iostreams::filtering_istreambuf compressedFileFilter; compressedFileFilter.push(boost::iostreams::gzip_decompressor()); compressedFileFilter.push(ormodelFile); this->inputFile.rdbuf(&compressedFileFilter); //where inputFile is a an istream. ... //do the file reading } I tried to add the skipping parts to the code by simply calling: { ... double value; this->inputFile->seekg(sizeof(double),ios::cur); ... } the fail bit is set on the inputFile istream. Is it possible to do this using boost? I¹m pretty ³green² with boost so I¹m sure it¹s just my misunderstanding of how to use the lib but I couldn¹t find my way around the docs to well. The best I could find was that I need to somehow make my stream ³seekable² but it wasn¹t too clear to me how to do this. Any help would be greatly appreciated. Gerrick

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Re: [Boost-users] shared_ptr, auto_ptr and enable_shared_from_this confusion
by 张亚霏 14 Mar '09

14 Mar '09

shared_ptr's constructor in line 168 calls 'boost::detail::sp_enable_shared_from_this( pn, p, p );'. 'boost::shared_ptr<IDerived> c(new Derived());' is dispatched to 'sp_enable_shared_from_this' in line 86. pay attension to the second parameter, it can accept all types that inherit 'enable_shared_from_this<T>', so does 'Derived*'. While, 'boost::shared_ptr<IDerived> c((IDerived*)new Derived());' is dispatched to 'sp_enable_shared_from_this' in line 111, bacause the static type IDerived* has nothing to do with 'enable_shared_from_this<T>' and can not be implicitly converted to 'enable_shared_from_this<T>'. Then check out the difference between the two 'sp_enable_shared_from_this'. It is obvious that the second usage shall cause a BOOST_ASSERT failed in 'enable_shared_from_this::shared_from_this', so an exception is raised. However, I think the root reason is not the language nor boost, but the design of class IDerived. Its root and root1 seem a little bit irrational because there is not direct relationship between IDerived and Base(IBase). ------------------ Original ------------------ From: "Ryan McConnehey"<mccorywork(a)gmail.com>; Date: Sat, Mar 14, 2009 04:29 AM To: "Boost-users"<boost-users(a)lists.boost.org>; Subject: [Boost-users] shared_ptr,auto_ptr and enable_shared_from_this confusion I'm having some trouble with using shared_ptr, auto_ptr and enable_shared_from_this with my inheritance layout. The following is how my inheritance is laid out. // Inheritance Layout // // boost::enable_shared_from_this<T> // ^ // | // Base --------> IBase // ^ // | // Derived -----> IDerived In my test code (that I've included with this email) the following two ways to instantiate a shared pointer is equivalent. boost::shared_ptr<IDerived> r (new Derived()); std::auto_ptr<IDerived> k (new Derived); boost::shared_ptr<IDerived> l (k.release()); When creating the shared_ptr, both declaration take me to line 185 of shared_ptr.hpp. Instantiating the shared_ptr directly then takes me to line 105 of shared_ptr.hpp. Though when instantiating by releasing the auto_ptr into the shared_ptr I'm taken to line 129. It seems to me that I should be going to the same line of code. This wouldn't be such a problem except when trying to call shared_from_this() an exception is thrown if my shared_ptr was created from an auto_ptr. Is this behavior correct? Ryan

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(no subject)
by isik bicer 14 Mar '09

14 Mar '09

Hello everybody, I am a newly boost user and have a problem in the following code. Since it is long, i put only the relevant parts. Could anyone help me please? When I try to get the vertices from a vector and put them to add_edge(), i get the following error massage : 'boost::add_edge' : cannot convert parameter 1 from 'char' to 'void *' The problematic part is highlighted. Code:typedefvector<Edge> simpleedgevector; vector<Edge>::iterator s_e_i;for simpleedge = Edge((*(*vec_it1)),(*(*vec_it1+1))); simpleedgevector.push_back(simpleedge);}edge_descriptor e; cout<< tie(e, inserted) = add_edge((*s_e_i).first, (*s_e_i).second, g); }for(s_e_i = simpleedgevector.begin();s_e_i != simpleedgevector.end();s_e_i++){boolinserted;"first part : "<<(*s_e_i).first<<" second part : "<<(*s_e_i).second<<endl;(vec_it1 = output1.begin();vec_it1 !=output1.end();vec_it1++){std::pair<char, char> Edge;

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shared_ptr, auto_ptr and enable_shared_from_this confusion
by Ryan McConnehey 13 Mar '09

13 Mar '09

I'm having some trouble with using shared_ptr, auto_ptr and enable_shared_from_this with my inheritance layout. The following is how my inheritance is laid out. // Inheritance Layout // // boost::enable_shared_from_this<T> // ^ // | // Base --------> IBase // ^ // | // Derived -----> IDerived In my test code (that I've included with this email) the following two ways to instantiate a shared pointer is equivalent. boost::shared_ptr<IDerived> r (new Derived()); std::auto_ptr<IDerived> k (new Derived); boost::shared_ptr<IDerived> l (k.release()); When creating the shared_ptr, both declaration take me to line 185 of shared_ptr.hpp. Instantiating the shared_ptr directly then takes me to line 105 of shared_ptr.hpp. Though when instantiating by releasing the auto_ptr into the shared_ptr I'm taken to line 129. It seems to me that I should be going to the same line of code. This wouldn't be such a problem except when trying to call shared_from_this() an exception is thrown if my shared_ptr was created from an auto_ptr. Is this behavior correct? Ryan #include <iostream> #include <memory> #include <boost/shared_ptr.hpp> #include <boost/enable_shared_from_this.hpp> // Inheritance Layout // // boost::enable_shared_from_this<T> // ^ // | // Base --------> IBase // ^ // | // Derived -----> IDerived class IBase { public: virtual void hello(void) = 0; }; class Base : public IBase, public boost::enable_shared_from_this<Base> { public: Base(void){} ~Base(void){} void hello(void) { std::cout << "Hello" << std::endl; } }; class IDerived { public: virtual void world(void) = 0; static std::auto_ptr<IDerived> createAuto(void); static boost::shared_ptr<IDerived> createShared(void); virtual boost::shared_ptr<Base> root(void) = 0; virtual boost::shared_ptr<IBase> root2(void) = 0; }; class Derived : public IDerived, public Base { public: Derived(void){} ~Derived(void){} void world(void) { std::cout << "World" << std::endl; } virtual boost::shared_ptr<Base> root(void) { return shared_from_this(); } virtual boost::shared_ptr<IBase> root2(void) { return shared_from_this(); } }; std::auto_ptr<IDerived> IDerived::createAuto(void) { return std::auto_ptr<IDerived>(new Derived()); } boost::shared_ptr<IDerived> IDerived::createShared(void) { return boost::shared_ptr<IDerived>(new Derived()); } int main(int argc, char* argv[]) { boost::shared_ptr<IDerived> c = IDerived::createShared(); boost::shared_ptr<IBase> d = c->root2(); std::cout << c.use_count() << std::endl; boost::shared_ptr<IDerived> r (new Derived()); std::auto_ptr<IDerived> k (new Derived); boost::shared_ptr<IDerived> l (k.release()); boost::shared_ptr<IBase> m = l->root2(); std::cout << m.use_count() << std::endl; return 0; }

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using boost :: thread in Linux
by ayansinhas＠gmail.com 13 Mar '09

13 Mar '09

HI, I am using boost::thread for my project. I have extracted only boost::thread through BCP and I have build my multithreading application. It is working properly in my local machine (Windows)now I have to port it over to linux box. I had couple of questions ...?? Is it ok to copy the boost::thread folder (That I have extracted) from my local machine to linux box and run my application?? or is it that I have to install the entire boost library in linux box and then by using bcp I have to extract only boost:thread part which I can use for my application?? Please let me know what can be the possible solution.If there is any other solution please feel free to advice. Thanks In Advance Ayan.

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[signals] Chaining signals
by Remko Tronçon 13 Mar '09

13 Mar '09

Hi, Is it possible to 'chain' boost signals? I.e., connect signal a to signal b, such that whenever signal a fires, all slots of signal b are called. thanks, Remko

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