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  • Does lamda in List.ForEach leads to memory leaks and performance problems ?

    - by Monomachus
    I have a problem which I could solve using something like this sortedElements.ForEach((XElement el) => PrintXElementName(el,i++)); And this means that I have in ForEach a lambda which permits using parameters like int i. I like that way of doing it, but i read somewhere that anonymous methods and delegates with lambda leads to a lot of memory leaks because each time when lambda is executed something is instantiated but is not released. Something like that. Could you please tell me if this is true in this situation and if it is why?

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  • How to create and Expression tree to do the same as "StartsWith"

    - by Jonathan
    Hi to all. Currently, I have this method to compare two numbers Private Function ETForGreaterThan(ByVal query As IQueryable(Of T), ByVal propertyValue As Object, ByVal propertyInfo As PropertyInfo) As IQueryable(Of T) Dim e As ParameterExpression = Expression.Parameter(GetType(T), "e") Dim m As MemberExpression = Expression.MakeMemberAccess(e, propertyInfo) Dim c As ConstantExpression = Expression.Constant(propertyValue, propertyValue.GetType()) Dim b As BinaryExpression = Expression.GreaterThan(m, c) Dim lambda As Expression(Of Func(Of T, Boolean)) = Expression.Lambda(Of Func(Of T, Boolean))(b, e) Return query.Where(lambda) End Function It works fine and is consumed in this way query = ETForGreaterThan(query, Value, propertyInfo) As you can see, I give it an IQueryable collection and it add a where clause to it, base on a property and a value. Y can construct Lessthan, LessOrEqualThan etc equivalents as Expression has this operators predefined. ¿How can I transform this code to do the same with strings? Expression don't give me a predefined operator like "contains" or "startwith" and I'm really noob with Expression trees. Thanks, and please Post your answer in C#/VB. Choose the one that make you feel more confortable.

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  • Lambda expressions in C#?

    - by user30457
    Hey I'm rather new to these could someone explain the significance or prehaps give a link to some useful information on lambda expressions? I encounter the following code in a test and I am wondering why someone would do this: foo.MyEvent += (o, e) = { fCount++; Console.WriteLine(fCount); }; foo.MyEvent -= (o, e) = { fCount++; Console.WriteLine(fCount); }; My instinct tells me it is something simple and not a mistake, but I don't know enough about these expressions to understand why this is being done. Regards,

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  • "Expected initializer before '<' token" in header file

    - by Sarah
    I'm pretty new to programming and am generally confused by header files and includes. I would like help with an immediate compile problem and would appreciate general suggestions about cleaner, safer, slicker ways to write my code. I'm currently repackaging a lot of code that used to be in main() into a Simulation class. I'm getting a compile error with the header file for this class. I'm compiling with gcc version 4.2.1. // Simulation.h #ifndef SIMULATION_H #define SIMULATION_H #include <cstdlib> #include <iostream> #include <cmath> #include <string> #include <fstream> #include <set> #include <boost/multi_index_container.hpp> #include <boost/multi_index/hashed_index.hpp> #include <boost/multi_index/member.hpp> #include <boost/multi_index/ordered_index.hpp> #include <boost/multi_index/mem_fun.hpp> #include <boost/multi_index/composite_key.hpp> #include <boost/shared_ptr.hpp> #include <boost/tuple/tuple_comparison.hpp> #include <boost/tuple/tuple_io.hpp> #include "Parameters.h" #include "Host.h" #include "rng.h" #include "Event.h" #include "Rdraws.h" typedef multi_index_container< // line 33 - first error boost::shared_ptr< Host >, indexed_by< hashed_unique< const_mem_fun<Host,int,&Host::getID> >, // 0 - ID index ordered_non_unique< tag<age>,const_mem_fun<Host,int,&Host::getAgeInY> >, // 1 - Age index hashed_non_unique< tag<household>,const_mem_fun<Host,int,&Host::getHousehold> >, // 2 - Household index ordered_non_unique< // 3 - Eligible by age & household tag<aeh>, composite_key< Host, const_mem_fun<Host,int,&Host::getAgeInY>, const_mem_fun<Host,bool,&Host::isEligible>, const_mem_fun<Host,int,&Host::getHousehold> > >, ordered_non_unique< // 4 - Eligible by household (all single adults) tag<eh>, composite_key< Host, const_mem_fun<Host,bool,&Host::isEligible>, const_mem_fun<Host,int,&Host::getHousehold> > >, ordered_non_unique< // 5 - Household & age tag<ah>, composite_key< Host, const_mem_fun<Host,int,&Host::getHousehold>, const_mem_fun<Host,int,&Host::getAgeInY> > > > // end indexed_by > HostContainer; typedef std::set<int> HHSet; class Simulation { public: Simulation( int sid ); ~Simulation(); // MEMBER FUNCTION PROTOTYPES void runDemSim( void ); void runEpidSim( void ); void ageHost( int id ); int calcPartnerAge( int a ); void executeEvent( Event & te ); void killHost( int id ); void pairHost( int id ); void partner2Hosts( int id1, int id2 ); void fledgeHost( int id ); void birthHost( int id ); void calcSI( void ); double beta_ij_h( int ai, int aj, int s ); double beta_ij_nh( int ai, int aj, int s ); private: // SIMULATION OBJECTS double t; double outputStrobe; int idCtr; int hholdCtr; int simID; RNG rgen; HostContainer allHosts; // shared_ptr to Hosts - line 102 - second error HHSet allHouseholds; int numInfecteds[ INIT_NUM_AGE_CATS ][ INIT_NUM_STYPES ]; EventPQ currentEvents; // STREAM MANAGEMENT void writeOutput(); void initOutput(); void closeOutput(); std::ofstream ageDistStream; std::ofstream ageDistTStream; std::ofstream hhDistStream; std::ofstream hhDistTStream; std::string ageDistFile; std::string ageDistTFile; std::string hhDistFile; std::string hhDistTFile; }; #endif I'm hoping the other files aren't so relevant to this problem. When I compile with g++ -g -o -c a.out -I /Applications/boost_1_42_0/ Host.cpp Simulation.cpp rng.cpp main.cpp Rdraws.cpp I get Simulation.h:33: error: expected initializer before '<' token Simulation.h:102: error: 'HostContainer' does not name a type and then a bunch of other errors related to not recognizing the HostContainer. It seems like I have all the right Boost #includes for the HostContainer to be understood. What else could be going wrong? I would appreciate immediate suggestions, troubleshooting tips, and other advice about my code. My plan is to create a "HostContainer.h" file that includes the typedef and structs that define its tags, similar to what I'm doing in "Event.h" for the EventPQ container. I'm assuming this is legal and good form.

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  • Portable C++ library for IPC (processes and shared memory), Boost vs ACE vs Poco?

    - by user363778
    Hi, I need a portable C++ library for doing IPC. I used fork() and SysV shared memory until now but this limits me to Linux/Unix. I found out that there are 3 major C++ libraries that offer a portable solution (including Windows and Mac OS X). I really like Boost, and would like to use it but I need processes and it seems like that this is only an experimental branch until now!? I have never heard of ACE or POCO before and thus I am stuck I do not know which one to choose. I need fork(), sleep() (usleep() would be great) and shared memory of course. Performance and documentation are also important criteria. Thanks, for your Help!

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  • Using boost.python to import a method with opencv calls but failing due to symbols not being found a

    - by nmz787
    So I don't have the code right now, as I am not home... but i used the boost library for python in C++ to allow python to access a function called something like loadImageIntoMainWindow(string filepath) in the C++ source code the method calls opencv methods that are imported at the top of the file, I included opencv in my Jamroot file, and also found a way to compile and link manually on the command line... in either case when I run my python file it complains that the symbols aren't found for the first function call to an opencv method... I will update as soon as I get home with the C++, the command line compilation lines, the Jamroot, and the python files

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  • Parallel Programming. Boost's MPI, OpenMP, TBB, or something else?

    - by unknownthreat
    Hello, I am totally a novice in parallel programming, but I do know how to program C++. Now, I am looking around for parallel programming library. I just want to give it a try, just for fun, and right now, I found 3 APIs, but I am not sure which one should I stick with. Right now, I see Boost's MPI, OpenMP and TBB. For anyone who have experienced with any of these 3 API (or any other parallelism API), could you please tell me the difference between these? Are there any factor to consider, like AMD or Intel architecture?

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  • Multi-Core Programming. Boost's MPI, OpenMP, TBB, or something else?

    - by unknownthreat
    Hello, I am totally a novice in Multi-Core Programming, but I do know how to program C++. Now, I am looking around for Multi-Core Programming library. I just want to give it a try, just for fun, and right now, I found 3 APIs, but I am not sure which one should I stick with. Right now, I see Boost's MPI, OpenMP and TBB. For anyone who have experienced with any of these 3 API (or any other API), could you please tell me the difference between these? Are there any factor to consider, like AMD or Intel architecture?

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  • How to attach boost::shared_ptr (or another smart pointer) to reference counter of object's parent?

    - by Checkers
    I remember encountering this concept before, but can't find it in Google now. If I have an object of type A, which directly embeds an object of type B: class A { B b; }; How can I have a smart pointer to B, e. g. boost::shared_ptr<B>, but use reference count of A? Assume an instance of A itself is heap-allocated I can safely get its shared count using, say, enable_shared_from_this.

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  • How do I know if a boost thread is done ?

    - by jules
    I am using boost::thread to process messages in a queue. When a first message comes I start a message processing thread. When a second message comes I check if the message processing thread is done. if it is done I start a new one if it is not done I don nothing. How do I know if the thread is done ? I tried with joinable() but it is not working, as when the thread is done, it is still joinable. I also tried to interrupt the process at once, and add an interruption point at the end of my thread, but it did not work. Thanks

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  • How do I insert format str and don't remove the matched regular expression in input string in boost:

    - by Yadollah
    I want to put space between punctuations and other words in a sentence. But boost::regex_replace() replaces the punctuation with space, and I want to keep a punctuation in the sentence! for example in this code the output should be "Hello . hi , " regex e1("[.,]"); std::basic_string<char> str = "Hello.hi,"; std::basic_string<char> fmt = " "; cout<<regex_replace(str, e1, fmt)<<endl; Can you help me?

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  • How to write a code Newton Raphson code in R involving integration and Bessel function

    - by Ahmed
    I have want to estimate the parameters of the function which involves Bessel function and integration. However, when i tried to run it, i got a message that "Error in f(x, ...) : could not find function "BesselI" ". I don't know to fix it and would appreciate any related proposal. library(Bessel) library(maxLik) library(miscTools) K<-300 f <- function(theta,lambda,u) {exp(-u*theta)*BesselI(2*sqrt(t*u*theta*lambda),1)/u^0.5} F <- function(theta,lambda){integrate(f,0,K,theta=theta,lambda=lambda)$value} tt<-function(theta,lambda){(sqrt(lambda)*exp(-t*lambda)/(2*sqrt(t*theta)))(theta(2*t*lambda-1)*F(theta,lambda)} loglik <- function(param) { theta <- param[1] lambda <- param[2] ll <-sum(log(tt(theta,lambda))) } t<-c(24,220,340,620,550,559,689,543) res <- maxNR(loglik, start=c(0.001,0.0005),print.level=1,tol = 1e-08) summary(res)

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  • how to find all occurrences in REGEX with

    - by Vincenzo
    My code is: #include <boost/regex.hpp> boost::cmatch matches; boost::regex_match("alpha beta", matches, boost::regex("([a-z])+")); cout << "found: " matches.size() << endl; And it shows found: 2 which means that only ONE occurrence is found… How to instruct it to find THREE occurrences? Thanks!

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  • Boost.MultiIndex: Are there way to share object between two processes?

    - by Arman
    Hello, I have a Boost.MultiIndex big array about 10Gb. In order to reduce the reading I thought there should be a way to keep the data in the memory and another client programs will be able to read and analyse it. What is the proper way to organize it? The array looks like: struct particleID { int ID;// real ID for particle from Gadget2 file "ID" block unsigned int IDf;// postition in the file particleID(int id,const unsigned int idf):ID(id),IDf(idf){} bool operator<(const particleID& p)const { return ID<p.ID;} unsigned int getByGID()const {return (ID&0x0FFF);}; }; struct ID{}; struct IDf{}; struct IDg{}; typedef multi_index_container< particleID, indexed_by< ordered_unique< tag<IDf>, BOOST_MULTI_INDEX_MEMBER(particleID,unsigned int,IDf)>, ordered_non_unique< tag<ID>,BOOST_MULTI_INDEX_MEMBER(particleID,int,ID)>, ordered_non_unique< tag<IDg>,BOOST_MULTI_INDEX_CONST_MEM_FUN(particleID,unsigned int,getByGID)> > > particlesID_set; Any ideas are welcome. kind regards Arman.

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  • Why there is no scoped locks for multiple mutexes in C++0x or Boost.Thread?

    - by Vicente Botet Escriba
    C++0x thread library or Boost.thread define non-member variadic template function that lock all lock avoiding dead lock. template <class L1, class L2, class... L3> void lock(L1&, L2&, L3&...); While this function avoid help to deadlock, the standard do not includes the associated scoped lock to write exception safe code. { std::lock(l1,l2); // do some thing // unlock li l2 exception safe } That means that we need to use other mechanism as try-catch block to make exception safe code or define our own scoped lock on multiple mutexes ourselves or even do that { std::lock(l1,l2); std::unique_lock lk1(l1, std::adopted); std::unique_lock lk2(l2, std::adopted); // do some thing // unlock li l2 on destruction of lk1 lk2 } Why the standard doesn't includes a scoped lock on multiple mutexes of the same type, as for example { std::array_unique_lock<std::mutex> lk(l1,l2); // do some thing // unlock l1 l2 on destruction of lk } or tuples of mutexes { std::tuple_unique_lock<std::mutex, std::recursive_mutex> lk(l1,l2); // do some thing // unlock l1 l2 on destruction of lk } Is there something wrong on the design?

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  • Setting up separate ctags db's for C/C++ standard libs, boost, and third party libs

    - by Robert S. Barnes
    I want to set up separate ctags databases for various libraries in /usr/include/ for use with OmniCppComplete. The idea is to be able to pull in only the libraries needed for a particular project in the target language - C or C++. For example, I'd like to have one database for the standard C libraries, one for system libraries that might be used by either C or C++ programs ( sockets / networking comes to mind ) one for the standard C++ libs / STL / Boost, and then other databases for various third party libraries such as QT or glib. Then I could pull something in simply by typing set tags+= ~/.vim/somelib.tags in vim. I assume that everything related to the C++ stdlib and STL are in the /usr/include/c++ and that Boost is all in /usr/include/boost. Unfortunately it seems that the standard C libs and system libs are just kind of dumped directly into /usr/include/ with a variety of other stuff. How can I get a list of which files and directories belong to which libs? I'm on Ubuntu 8.04.

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  • Why does Visual Studio 2010 throw this error with Boost 1.42.0?

    - by ra170
    I'm trying to recompile application, that compiles fine with warning level 4 in visual studio 2005 and visual studio 2008. Since the errors (look below) are coming from std:tr1, I'm thinking there's some conflict, but not sure how to fix. My first thought was to remove all references to boost, such as but then I get an error that it can't find format method. So here's one of the errors: (not sure what it means) Any ideas, suggestions, solutions? Thanks! > c:\program files (x86)\microsoft > visual studio > 10.0\vc\include\type_traits(197): error C2752: > 'std::tr1::_Remove_reference<_Ty>' : > more than one partial specialization > matches the template argument list 1> > with 1> [ 1> > _Ty=bool (__cdecl &)(const BlahBlah &) 1> ] 1> c:\program > files (x86)\microsoft visual studio > 10.0\vc\include\xtr1common(356): could be > 'std::tr1::_Remove_reference<_Ty&&>' > 1> c:\program files > (x86)\microsoft visual studio > 10.0\vc\include\xtr1common(350): or 'std::tr1::_Remove_reference<_Ty&>' 1> > c:\program files (x86)\microsoft > visual studio > 10.0\vc\include\type_traits(962) : see reference to class template > instantiation > 'std::tr1::remove_reference<_Ty>' > being compiled 1> with

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  • Using System.DateTime in a C# Lambda expression gives an exception

    - by Samantha J
    I tried to implement a suggestion that came up in another question: Stackoverflow question Snippet here: public static class StatusExtensions { public static IHtmlString StatusBox<TModel>( this HtmlHelper<TModel> helper, Expression<Func<TModel, RowInfo>> ex ) { var createdEx = Expression.Lambda<Func<TModel, DateTime>>( Expression.Property(ex.Body, "Created"), ex.Parameters ); var modifiedEx = Expression.Lambda<Func<TModel, DateTime>>( Expression.Property(ex.Body, "Modified"), ex.Parameters ); var a = "a" + helper.HiddenFor(createdEx) + helper.HiddenFor(modifiedEx); return new HtmlString( "Some things here ..." + helper.HiddenFor(createdEx) + helper.HiddenFor(modifiedEx) ); } } When implemented I am getting the following exception which I don't really understand. The exception points to the line starting with "var createdEx =" System.ArgumentException was unhandled by user code Message=Expression of type 'System.Nullable`1[System.DateTime]' cannot be used for return type 'System.DateTime' Source=System.Core StackTrace: Can anyone help me out and suggest what I could do to resolve the exception?

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  • Summation using Lambda C# 3.0

    - by Newbie
    I have a small thing. public int GetSum(List<int> x) { foreach (int i in x) sum += i; return sum; } where x is a List of integers defined as List<int> l = new List<int>(); l.Add(4); l.Add(2); l.Add(5); l.Add(8); l.Add(6); and has been passed as GetSum(l) Is it possible to rewrite the above foreach loop using a lambda? Reason: I started looking into the lambda stuffs since yesterday and is interested to learn .. however simple it may be. Thanks.

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  • "Cannot use fixed local inside lambda expression"

    - by JulianR
    I have an XNA 3.0 project that compiled just fine in VS2008, but that gives compile errors in VS2010 (with XNA 4.0 CTP). The error: Cannot use fixed local 'depthPtr' inside an anonymous method, lambda expression, or query expression depthPtr is a fixed float* into an array, that is used inside a Parallel.For lambda expression from System.Threading. As I said, this compiled and ran just fine on VS2008, but it does not on VS2010, even when targeting .NET 3.5. Has this changed in .NET 4.0, and even so, shouldn't it still compile when I choose .NET 3.5 as the target framework? Searching for the term "Cannot use fixed local" yields exactly one (useless) result, both in Google and Bing. If this has changed, what is the reason for this? I can imagine capturing a fixed pointer-type in a closure could get a bit weird, is that why? So I'm guessing this is bad practice? And before anyone asks: no, the use of pointers is not absolutely critical here. I would still like to know though :)

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