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  • A generic C++ library that provides QtConcurrent functionality?

    - by Lucas
    QtConcurrent is awesome. I'll let the Qt docs speak for themselves: QtConcurrent includes functional programming style APIs for parallel list processing, including a MapReduce and FilterReduce implementation for shared-memory (non-distributed) systems, and classes for managing asynchronous computations in GUI applications. For instance, you give QtConcurrent::map() an iterable sequence and a function that accepts items of the type stored in the sequence, and that function is applied to all the items in the collection. This is done in a multi-threaded manner, with a thread pool equal to the number of logical CPU's on the system. There are plenty of other function in QtConcurrent, like filter(), filteredReduced() etc. The standard CompSci map/reduce functions and the like. I'm totally in love with this, but I'm starting work on an OSS project that will not be using the Qt framework. It's a library, and I don't want to force others to depend on such a large framework like Qt. I'm trying to keep external dependencies to a minimum (it's the decent thing to do). I'm looking for a generic C++ framework that provides me with the same/similar high-level primitives that QtConcurrent does. AFAIK boost has nothing like this (I may be wrong though). boost::thread is very low-level compared to what I'm looking for. I know C# has something very similar with their Parallel Extensions so I know this isn't a Qt-only idea. What do you suggest I use?

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  • Is there a way to find out whether a class is a direct base of another class?

    - by user176168
    Hi I'm wondering whether there is a way to find out whether a class is a direct base of another class i.e. in boost type trait terms a is_direct_base_of function. As far as I can see boost doesn't see to support this kind of functionality which leads me to think that its impossible with the current C++ standard. The reason I want it is to do some validation checking on two macro's that are used for a reflection system to specify that one class is derived from another e.g. header.h: #define BASE A #define DERIVED B class A {}; class B : public A { #include <rtti.h> }; rtti.h: // I want to check that the two macro's are correct with a compile time assert Rtti<BASE, DERIVED> m_rtti; Although the macro's seem unnecessary in this simple example in my real world scenario rtti.h is a lot more complex. One possible avenue would be to compare the size of the this pointer with the size of a this pointer cast to the base type and some how trying to figure out whether its the size of the base class itself away or something (yeah your right I don't know how that would work either! lol)

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  • C++ variable to const expression

    - by user1344784
    template <typename Real> class A{ }; template <typename Real> class B{ }; //... a few dozen more similar template classes class Computer{ public slots: void setFrom(int from){ from_ = from; } void setTo(int to){ to_ = to; } private: template <int F, int T> void compute(){ using boost::fusion::vector; using boost::fusion::at_c; vector<A<float>, B<float>, ...> v; at_c<from_>(v).operator()(at_c<to_>(v)); //error; needs to be const-expression. }; This question isn't about Qt, but there is a line of Qt code in my example. The setFrom() and setTo() are functions that are called based on user selection via the GUI widget. The root of my problem is that 'from' and 'to' are variables. In my compute member function I need to pick a type (A, B, etc.) based on the values of 'from' and 'to'. The only way I know how to do what I need to do is to use switch statements, but that's extremely tedious in my case and I would like to avoid. Is there anyway to convert the error line to a constant-expression?

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  • template specialization for static member functions; howto?

    - by Rolle
    I am trying to implement a template function with handles void differently using template specialization. The following code gives me an "Explicit specialization in non-namespace scope" in gcc: template <typename T> static T safeGuiCall(boost::function<T ()> _f) { if (_f.empty()) throw GuiException("Function pointer empty"); { ThreadGuard g; T ret = _f(); return ret; } } // template specialization for functions wit no return value template <> static void safeGuiCall<void>(boost::function<void ()> _f) { if (_f.empty()) throw GuiException("Function pointer empty"); { ThreadGuard g; _f(); } } I have tried moving it out of the class (the class is not templated) and into the namespace but then I get the error "Explicit specialization cannot have a storage class". I have read many discussions about this, but people don't seem to agree how to specialize function templates. Any ideas?

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  • Is it possible to create ostream object, which outputs to multiple destinations?

    - by fiktor
    In 0-th approximation I have a class class MyClass{ public: ... std::ostream & getOStream(){return f;} private: ofstream f; ... }; Which is used sometimes in the following way: MyClass myclass; myclass.getOStream()<<some<<information<<printed<<here; But now I want to change the class MyClass, so that information will be printed both to f and to std::out, i.e. I want the above line to be equivalent to myclass.f<<some<<information<<printed<<here; std::cout<<some<<information<<printed<<here; I don't know any good way to do that. Do you? Is there any standard solution (for example in stl or in boost)? P.S. I tried to search on this, but it seems that I don't know good keywords. Words multiple, output, ostream, C++, boost seem to be too general.

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  • Confused about std::runtime_error vs. std::logic_error

    - by David Gladfelter
    I recently saw that the boost program_options library throws a logic_error if the command-line input was un-parsable. That challenged my assumptions about logic_error vs. runtime_error. I assumed that logic errors (logic_error and its derived classes) were problems that resulted from internal failures to adhere to program invariants, often in the form of illegal arguments to internal API's. In that sense they are largely equivalent to ASSERT's, but meant to be used in released code (unlike ASSERT's which are not usually compiled into released code.) They are useful in situations where it is infeasible to integrate separate software components in debug/test builds or the consequences of a failure are such that it is important to give runtime feedback about the invalid invariant condition to the user. Similarly, I thought that runtime_errors resulted exclusively from runtime conditions outside of the control of the programmer: I/O errors, invalid user input, etc. However, program_options is obviously heavily (primarily?) used as a means of parsing end-user input, so under my mental model it certainly should throw a runtime_error in the case of bad input. Where am I going wrong? Do you agree with the boost model of exception typing?

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  • Change value of adjacent vertices and remove self loop

    - by StereoMatching
    Try to write a Karger’s algorithm with boost::graph example (first column is vertice, other are adjacent vertices): 1 2 3 2 1 3 4 3 1 2 4 4 2 3 assume I merge 2 to 1, I get the result 1 2 3 2 1 1 3 4 2 1 3 4 3 1 2 4 4 2 3 first question : How could I change the adjacent vertices("2" to "1") of vertice 1? my naive solution template<typename Vertex, typename Graph> void change_adjacent_vertices_value(Vertex input, Vertex value, Graph &g) { for (auto it = boost::adjacent_vertices(input, g); it.first != it.second; ++it.first){ if(*it.first == value){ *(it.first) = input; //error C2106: '=' : left operand must be l-value } } } Apparently, I can't set the value of the adjacent vertices to "1" by this way The result I want after "change_adjacent_vertices_value" 1 1 3 1 1 1 3 4 2 1 3 4 3 1 2 4 4 2 3 second question : How could I pop out the adjacent vertices? Assume I want to pop out the consecutive 1 from the vertice 1 The result I expected 1 1 3 1 3 4 2 1 3 4 3 1 2 4 4 2 3 any function like "pop_adjacent_vertex" could use?

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  • BLAS and CUBLAS

    - by Nils
    I'm wondering about Nvidia's CUBLAS Library. Does anybody have experience with it? For example if I write a C program using BLAS will I be able to replace the calls to BLAS with calls to CUBLAS? Or even better implement a mechanism which let's the user choose at runtime? What about if I use the BLAS Library provided by Boost with C++?

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  • C++ type-checking at compile-time

    - by Masterofpsi
    Hi, all. I'm pretty new to C++, and I'm writing a small library (mostly for my own projects) in C++. In the process of designing a type hierarchy, I've run into the problem of defining the assignment operator. I've taken the basic approach that was eventually reached in this article, which is that for every class MyClass in a hierarchy derived from a class Base you define two assignment operators like so: class MyClass: public Base { public: MyClass& operator =(MyClass const& rhs); virtual MyClass& operator =(Base const& rhs); }; // automatically gets defined, so we make it call the virtual function below MyClass& MyClass::operator =(MyClass const& rhs); { return (*this = static_cast<Base const&>(rhs)); } MyClass& MyClass::operator =(Base const& rhs); { assert(typeid(rhs) == typeid(*this)); // assigning to different types is a logical error MyClass const& casted_rhs = dynamic_cast<MyClass const&>(rhs); try { // allocate new variables Base::operator =(rhs); } catch(...) { // delete the allocated variables throw; } // assign to member variables } The part I'm concerned with is the assertion for type equality. Since I'm writing a library, where assertions will presumably be compiled out of the final result, this has led me to go with a scheme that looks more like this: class MyClass: public Base { public: operator =(MyClass const& rhs); // etc virtual inline MyClass& operator =(Base const& rhs) { assert(typeid(rhs) == typeid(*this)); return this->set(static_cast<Base const&>(rhs)); } private: MyClass& set(Base const& rhs); // same basic thing }; But I've been wondering if I could check the types at compile-time. I looked into Boost.TypeTraits, and I came close by doing BOOST_MPL_ASSERT((boost::is_same<BOOST_TYPEOF(*this), BOOST_TYPEOF(rhs)>));, but since rhs is declared as a reference to the parent class and not the derived class, it choked. Now that I think about it, my reasoning seems silly -- I was hoping that since the function was inline, it would be able to check the actual parameters themselves, but of course the preprocessor always gets run before the compiler. But I was wondering if anyone knew of any other way I could enforce this kind of check at compile-time.

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  • dual map structure implementation?

    - by Danra
    Hey, I'm looking for a standard dual-map structure - is there one implemented in std/boost/another standard C++ library? When I say "dual-map" I mean a map which can be indexed efficiently both by the key and the "value" (it actually has two key types instead of one key type and one value type). for example: dualmap<int,string> m; m[1] = "foo"; m["bar"] = 2 int a = m["bar"]; // a = 2 Thanks, Dan

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  • How do I change the value of a dynamic_bitset?

    - by R S
    I am using C++ boost's dynamic_bitset. I have already allocated a variable and I just want to change its value - to construct it anew from an 'unsigned long' like from the constructor, but I don't want to allocate the memory again or to create a temporary variable. What can I do?

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  • What is a good CPU/PC setup to speed up intensive C++/templates compilation?

    - by ApplePieIsGood
    I currently have a machine with an Opteron 275 (2.2Ghz), which is a dual core CPU, and 4GB of RAM, along with a very fast hard drive. I find that when compiling even somewhat simple projects that use C++ templates (think boost, etc.), my compile times can take quite a while (minutes for small things, much longer for bigger projects). Unfortunately only one of the cores is pegged at 100%, so I know it's not the I/O, and it would seem that there is no way to take advantage of the other core for C++ compilation?

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  • gcc c++ command line error-message parser

    - by Autopulated
    Are there any programs for parsing and displaying in a nice format the c++ error messages generated by gcc. I'm really looking for something like less that I can pipe my errors into that will collapse the template parameter lists by default, maybe with some nice highlighting so that my errors are actually readable. (Yes, it's boost's fault I have such incomprehensible errors, in case you were wondering)

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  • Safe Cross Thread Signals/Slot C++

    - by JP
    It seem that the only implementation that provide Safe Cross-Thread Signals for both the Signal class and what's being called in the slot is QT. (Maybe I'm wrong?). But I cannot use QT in the project I'm doing. So how could I provide safe Slots call from a different thread (Using Boost::signals2 for example)? Are mutex inside the slot the only way? I think signals2 protect themself but not what's being done inside the slot. Thanks

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  • Is it possible to create a C++ factory system that can create an instance of any "registered" object

    - by chrensli
    Hello, I've spent my entire day researching this topic, so it is with some scattered knowledge on the topic that i come to you with this inquiry. Please allow me to describe what I am attempting to accomplish, and maybe you can either suggest a solution to the immediate question, or another way to tackle the problem entirely. I am trying to mimic something related to how XAML files work in WPF, where you are essentially instantiating an object tree from an XML definition. If this is incorrect, please inform. This issue is otherwise unrelated to WPF, C#, or anything managed - I solely mention it because it is a similar concept.. So, I've created an XML parser class already, and generated a node tree based on ObjectNode objects. ObjectNode objects hold a string value called type, and they have an std::vector of child ObjectNode objects. The next step is to instantiate a tree of objects based on the data in the ObjectNode tree. This intermediate ObjectNode tree is needed because the same ObjectNode tree might be instantiated multiple times or delayed as needed. The tree of objects that is being created is such that the nodes in the tree are descendants of a common base class, which for now we can refer to as MyBase. Leaf nodes can be of any type, not necessarily derived from MyBase. To make this more challenging, I will not know what types of MyBase derived objects might be involved, so I need to allow for new types to be registered with the factory. I am aware of boost's factory. Their docs have an interesting little design paragraph on this page: o We may want a factory that takes some arguments that are forwarded to the constructor, o we will probably want to use smart pointers, o we may want several member functions to create different kinds of objects, o we might not necessarily need a polymorphic base class for the objects, o as we will see, we do not need a factory base class at all, o we might want to just call the constructor - without #new# to create an object on the stack, and o finally we might want to use customized memory management. I might not be understanding this all correctly, but that seems to state that what I'm trying to do can be accomplished with boost's factory. But all the examples I've located, seem to describe factories where all objects are derived from a base type. Any guidance on this would be greatly appreciated. Thanks for your time!

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  • Methods for implementing and using graphs of nodes in C++?

    - by DistortedLojik
    I am working on a research project that deals with social networks. I have done most of the backbone of the program in C++ and am now wanting to implement a way to create the graph of nodes and the connections as well as a way to visualize the connections between people. I have looked a little into Lemon and the Boost graph library, but was wondering which one would be easier to learn and implement or if I should just code my own.

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  • Do you know of some performances test of the different ways to get thread local storage in C++?

    - by Vicente Botet Escriba
    I'm doing a library that makes extensive use of a thread local variable. Can you point to some benchmarks that test the performances of the different ways to get thread local variables in C++: C++0x thread_local variables compiler extension (Gcc __thread, ...) boost::threads_specific_ptr pthread Windows ... Does C++0x thread_local performs much better on the compilers providing it?

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  • Is there any way to limit the turbo boost speed / intensity on i7 lap?

    - by Anonymous
    I've just got a used i7 laptop, one of these overheating pavilions from HP with quad cores. And I really want to find a compromise between the temp and performance. If I use linpack, or some other heavy benchmark, the temp easily gets to 95+, and having a TJ of 100 Degrees, for a 2630QM model, it really gets me throttling, that no cooling pad or even an industrial fan could solve. I figured later that it is due to turbo boost, and if I set my power settings to use 99% of the CPU instead of 100%, and it seems to disable the turbo boost, so the temp gets better. But then again it loses quite a bit of performance. The regular clock is 2GHz, and in turbo boost it gets to 2.6Ghz, but I just wonder if I could limit it to around 2.3Ghz, that would be a real nice thing. Also there is another question I've hard time getting answer to. It seems to me that clocks are very quickly boosting up to max even when not needed, eg, it's ok if the CPU has 0% load, the clocks get to their 800MHz, but even if it gets to about 5% it quickly jumps to a max and even popping up turbo, which seems very strange to me. So I wonder if there is any way to adjust the sensitivity of the Speed Step feature. I believe it would be more logical to demand increased clock if it hits let's say 50% load. I do understand that most of these features are probably hardwired somewhere in the CPU itself or the MB, which has no tuning options just like on many laptops. But I would appreciate if you could recommend some thing, or some software. Thanks

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