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  • Using a type parameter and a pointer to the same type parameter in a function template

    - by Darel
    Hello, I've written a template function to determine the median of any vector or array of any type that can be sorted with sort. The function and a small test program are below: #include <algorithm> #include <vector> #include <iostream> using namespace::std; template <class T, class X> void median(T vec, size_t size, X& ret) { sort(vec, vec + size); size_t mid = size/2; ret = size % 2 == 0 ? (vec[mid] + vec[mid-1]) / 2 : vec[mid]; } int main() { vector<double> v; v.push_back(2); v.push_back(8); v.push_back(7); v.push_back(4); v.push_back(9); double a[5] = {2, 8, 7, 4, 9}; double r; median(v.begin(), v.size(), r); cout << r << endl; median(a, 5, r); cout << r << endl; return 0; } As you can see, the median function takes a pointer as an argument, T vec. Also in the argument list is a reference variable X ret, which is modified by the function to store the computed median value. However I don't find this a very elegant solution. T vec will always be a pointer to the same type as X ret. My initial attempts to write median had a header like this: template<class T> T median(T *vec, size_t size) { sort(vec, vec + size); size_t mid = size/2; return size % 2 == 0 ? (vec[mid] + vec[mid-1]) / 2 : vec[mid]; } I also tried: template<class T, class X> X median(T vec, size_t size) { sort(vec, vec + size); size_t mid = size/2; return size % 2 == 0 ? (vec[mid] + vec[mid-1]) / 2 : vec[mid]; } I couldn't get either of these to work. My question is, can anyone show me a working implementation of either of my alternatives? Thanks for looking!

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  • Smart pointers and polymorphism

    - by qwerty
    hello. I implemented reference counting pointers (called SP in the example) and im having problems with polymorphism which i think i shouldn't have. In the following code: SP<BaseClass> foo() { // Some logic... SP<DerivedClass> retPtr = new DerivedClass(); return retPtr; } DerivedClass inherits from BaseClass. With normal pointers this should have worked, but with the smart pointers it says "cannot convert from 'SP<T>' to 'const SP<T>&" and i think it refers to the copy constructor of the smart pointer. How to i allow this kind of polymorphism with reference counting pointer? I'd appreciate code samples cause obviously im doing something wrong here if im having this problem. Thanks! :) [p.s., plz don't tell me to use standart liberary with smart pointers cuz that's impossible at this moment.]

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  • python/django problem with sessions and language

    - by freakish
    Hello everyone! I have the following problem: on the main page I can change language. New language is saved in request.session['django_language']. I also have SESSION_COOKIE_DOMAIN set to my site, so session should be inherited by subdomains. And it is, because after changing language I check request.session['django_language'] in subdomains and it's fine. Then I use django.middleware.locale.LocaleMiddleware to translate my pages. And it works perfectly... only on main site! If I change language and refresh main site - it is ok. However, if I change language and go to a subpage (for example /LogIn), then the page is NOT translated at all. It stays on default language. This is really strange, because if I use {% load i18n %} {% get_current_language as lang %} in this subpage, then lang is good language. There is no mistake. What kind of problem can it be? Some suggestions?

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  • Django - markup parser in template or view?

    - by Amit Ron
    I am building a website where my pages are written in MediaWiki Markup, for which I have a working parser function in Python. Where exactly do I parse my markup: in the view's code, or in the template? My first guess would be something like: return render_to_response( 'blog/post.html', {'post': post, 'content': parseMyMarkup(post.content) }) Is this the usual convention, or should I do something different?

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  • Is it possible top opt-out of INamingContainer if it's implemented by a superclass?

    - by michielvoo
    The UserControl class inherits from TemplateControl which implements INamingContainer. Since this is "only a marker interface" I was wondering if it's possible to opt-out of the behavior that this interface brings with it. I am developing a templated control based on a user control, and I want the controls inside the template to be accessible in the page without using FindControl(id).

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  • Guidelines to an Iterator Class

    - by isurulucky
    Hi, I have a Red Black tree implemented in c++. It supports the functionality of a STL map. Tree nodes contain keys and the values mapped. I want to write an iterator class for this, but I'm stuck with how to do it. Should I make it an inner class of the Tree class? Can anyone give me some guidelines on how to write it + some resources?? Thank You!!

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  • Catching a nested-in-template exception [C++]

    - by Karol
    Hello, I have a problem with writing a catch clause for an exception that is a class nested in a template. To be more specific, I have a following definition of the template and exception: /** Generic stack implementation. Accepts std::list, std::deque and std::vector as inner container. */ template < typename T, template < typename Element, typename = std::allocator<Element> > class Container = std::deque > class stack { public: class StackEmptyException { }; ... /** Returns value from the top of the stack. Throws StackEmptyException when the stack is empty. */ T top() const; ... } I have a following template method that I want exception to catch: template <typename Stack> void testTopThrowsStackEmptyExceptionOnEmptyStack() { Stack stack; std::cout << "Testing top throws StackEmptyException on empty stack..."; try { stack.top(); } catch (Stack::StackEmptyException) { // as expected. } std::cout << "success." << std::endl; } When I compile it (-Wall, -pedantic) I get the following error: In function ‘void testTopThrowsStackEmptyExceptionOnEmptyStack()’: error: expected type-specifier error: expected unqualified-id before ‘)’ token === Build finished: 2 errors, 0 warnings === Thanks in advance for any help! What is interesting, if the stack implementation was not a template, then the compiler would accept the code as it is.

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  • Ant-Ivy-Scala Template: any suggestions on improvements?

    - by luigi-prog
    I just created a template project for Scala using Ant and Apache Ivy. I want to get the communitie's input on any improvements to the Template so it can be improved. The Environment effectively consists of 3 files: build.xml ivy.xml ivysettings.xml running ant init will create all needed directories. I was wondering if there are any Ant or Apache Ivy gurus around that could give some input. The Git Project is Located Here And the Project HomePage here

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  • Codeigniter + Dwoo

    - by RedTruck
    I got problem when implementing my CMS using Codeigniter 1.7.2 and Dwoo. I use Phil Sturgeon Dwoo library. My problem is I want user create template from the admin panel, it means all template will be stored into database including all Dwoo variable and functions.My questions: Is it possible to load dwoo template from database? How to parse dwoo variable or function from database? I tried to load content from database which is include dwoo var and function inside it, and i have tried to do evaluation using dwoo eval() function and phil sturgeon string_parse() but still have no luck. for example: my controller $data['header'] = "<h1>{$header}</h1>"; --> this could be loaded from database $this->parser->parse('header',$data); my view {$header} Thank you,

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  • PHP: Echo function output in function-line, not line of function call

    - by Brill
    I have a problem with my self-coded template system. The content is inserted by Include(). Now I need to add a meta redirect to one page. I know, meta redirect is not the safest way, but I need it because of it's delay possibility. Now i'm looking for a way to influence the wrapping page (template) by the wrapped page (content). So I thought a function can do this job. <?php function test($testvar){ echo $testvar;} ?> <hr /> <?php test("testtext"); ?> Of course the text echos in the line of the function call, not in the function line. Is there a way to make the function echo in the line of the function itself? In this case above the horizontal rule, not below? Of course every other best pratice for this "template problem" ist welcome! THX

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  • Is there any reasonable use of a function returning an anonymous struct?

    - by Akanksh
    Here is an (artificial) example of using a function that returns an anonymous struct and does "something" useful: #include <iostream> template<typename T> T* func( T* t, float a, float b ) { if(!t) { t = new T; t->a = a; t->b = b; } else { t->a += a; t->b += b; } return t; } struct { float a, b; }* foo(float a, float b) { if(a==0) return 0; return func(foo(a-1,b), a, b); } int main() { std::cout << foo(5,6)->a << std::endl; std::cout << foo(5,6)->b << std::endl; void* v = (void*)(foo(5,6)); float* f = (float*)(v); //[1] delete f now because I know struct is floats only. std::cout << f[0] << std::endl; std::cout << f[1] << std::endl; delete[] f; return 0; } There are a few points I would like to discuss: As is apparent, this code leaks, is there anyway I can NOT leak without knowing what the underlying struct definition is? see Comment [1]. I have to return a pointer to an anonymous struct so I can create an instance of the object within the templatized function func, can I do something similar without returning a pointer? I guess the most important, is there ANY (real-world) use for this at all? As the example given above leaks and is admittedly contrived. By the way, what the function foo(a,b) does is, to return a struct containing two numbers, the sum of all numbers from 1 to a and the product of a and b. EDIT: Maybe the line new T could use a boost::shared_ptr somehow to avoid leaks, but I haven't tried that. Would that work?

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  • Creating a simple templated control. Having issues...

    - by Jimock
    Hi, I'm trying to create a really simple templated control. I've never done it before, but I know a lot of my controls I have created in the past would have greatly benefited if I included templating ability - so I'm learning now. The problem I have is that my template is outputted on the page but my property value is not. So all I get is the static text which I include in my template. I must be doing something correctly because the control doesn't cause any errors, so it knows my public property exists. (e.g. if I try to use Container.ThisDoesntExist it throws an exception). I'd appreciate some help on this. I may be just being a complete muppet and missing something. Online tutorials on simple templated server controls seem few and far between, so if you know of one I'd like to know about it. A cut down version of my code is below. Many Thanks, James Here is my code for the control: [ParseChildren(true)] public class TemplatedControl : Control, INamingContainer { private TemplatedControlContainer theContainer; [TemplateContainer(typeof(TemplatedControlContainer)), PersistenceMode(PersistenceMode.InnerProperty)] public ITemplate ItemTemplate { get; set; } protected override void CreateChildControls() { Controls.Clear(); theContainer = new TemplatedControlContainer("Hello World"); this.ItemTemplate.InstantiateIn(theContainer); Controls.Add(theContainer); } } Here is my code for the container: [ToolboxItem(false)] public class TemplatedControlContainer : Control, INamingContainer { private string myString; public string MyString { get { return myString; } } internal TemplatedControlContainer(string mystr) { this.myString = mystr; } } Here is my mark up: <my:TemplatedControl runat="server"> <ItemTemplate> <div style="background-color: Black; color: White;"> Text Here: <%# Container.MyString %> </div> </ItemTemplate> </my:TemplatedControl>

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  • question regarding templatization of virtual function

    - by jan
    Hi, I am new to this forum and sorry If I am repeating this question. I know that you cannot templatize the virtual function and I do understand the concept behind it. But I still need a way to get across some errors I am getting it. I am able to make my stuff work but it doesn't look to me. Here's the deal, I have class called System, #include "Vector.h" class System { virtual void VectorToLocal(Vector<T>& global_dir,const Vector<T>* global_pos = 0) const = 0; }; class UnresolvedSystem : public System { virtual void VectorToLocal(Vector<T>& global_dir,const Vector<T>* global_pos = 0) const { //do something } }; In Vector.h tenplate<typename T> class Vector { //some functions }; See now I want to templatize VectorToLocal in system.h to take just Vector, but I cannot do it as it is a virtual function. I want a work around. I know I can have VectorToLocal take Vector, Vector etc as arguments. But I do not want to do it. Any help would be really appreciated. Thanks in advance, Jan

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  • operator<< cannot output std::endl -- Fix?

    - by dehmann
    The following code gives an error when it's supposed to output just std::endl: #include <iostream> #include <sstream> struct MyStream { std::ostream* out_; MyStream(std::ostream* out) : out_(out) {} std::ostream& operator<<(const std::string& s) { (*out_) << s; return *out_; } }; template<class OutputStream> struct Foo { OutputStream* out_; Foo(OutputStream* out) : out_(out) {} void test() { (*out_) << "OK" << std::endl; (*out_) << std::endl; // ERROR } }; int main(int argc, char** argv){ MyStream out(&std::cout); Foo<MyStream> foo(&out); foo.test(); return EXIT_SUCCESS; } The error is: stream1.cpp:19: error: no match for 'operator<<' in '*((Foo<MyStream>*)this)->Foo<MyStream>::out_ << std::endl' stream1.cpp:7: note: candidates are: std::ostream& MyStream::operator<<(const std::string&) So it can output a string (see line above the error), but not just the std::endl, presumably because std::endl is not a string, but the operator<< definition asks for a string. Templating the operator<< didn't help: template<class T> std::ostream& operator<<(const T& s) { ... } How can I make the code work? Thanks!

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  • initializer_list and move semantics

    - by FredOverflow
    Am I allowed to move elements out of a std::initializer_list<T>? #include <initializer_list> #include <utility> template<typename T> void foo(std::initializer_list<T> list) { for (auto it = list.begin(); it != list.end(); ++it) { bar(std::move(*it)); // kosher? } } Since std::intializer_list<T> requires special compiler attention and does not have value semantics like normal containers of the C++ standard library, I'd rather be safe than sorry and ask.

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  • C# style Action<T>, Func<T,T>, etc in C++0x

    - by Austin Hyde
    C# has generic function types such as Action<T> or Func<T,U,V,...> With the advent of C++0x and the ability to have template typedef's and variadic template parameters, it seems this should be possible. The obvious solution to me would be this: template <typename T> using Action<T> = void (*)(T); however, this does not accommodate for functors or C++0x lambdas, and beyond that, does not compile with the error "expected unqualified-id before 'using'" My next attempt was to perhaps use boost::function: template <typename T> using Action<T> = boost::function<void (T)>; This doesn't compile either, for the same reason. My only other idea would be STL style template arguments: template <typename T, typename Action> void foo(T value, Action f) { f(value); } But this doesn't provide a strongly typed solution, and is only relevant inside the templated function. Now, I will be the first to admit that I am not the C++ wiz I prefer to think I am, so it's very possible there is an obvious solution I'm not seeing. Is it possible to have C# style generic function types in C++?

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  • Call the cast operator of template base class within the derived class

    - by yoni
    I have a template class, called Cell, here the definition: template <class T> class OneCell { ..... } I have a cast operator from Cell to T, here virtual operator const T() const { ..... } Now i have derived class, called DCell, here template <class T> class DCell : public Cell<T> { ..... } I need to override the Cell's cast operator (insert a little if), but after I need to call the Cell's cast operator. In other methods it's should be something like virtual operator const T() const { if (...) { return Cell<T>::operator const T; } else throw ... } but i got a compiler error error: argument of type 'const int (Cell::)()const' does not match 'const int' What can I do? Thank you, and sorry about my poor English.

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  • Architecture for Qt SIGNAL with subclass-specific, templated argument type

    - by Barry Wark
    I am developing a scientific data acquisition application using Qt. Since I'm not a deep expert in Qt, I'd like some architecture advise from the community on the following problem: The application supports several hardware acquisition interfaces but I would like to provide an common API on top of those interfaces. Each interface has a sample data type and a units for its data. So I'm representing a vector of samples from each device as a std::vector of Boost.Units quantities (i.e. std::vector<boost::units::quantity<unit,sample_type> >). I'd like to use a multi-cast style architecture, where each data source broadcasts newly received data to 1 or more interested parties. Qt's Signal/Slot mechanism is an obvious fit for this style. So, I'd like each data source to emit a signal like typedef std::vector<boost::units::quantity<unit,sample_type> > SampleVector signals: void samplesAcquired(SampleVector sampleVector); for the unit and sample_type appropriate for that device. Since tempalted QObject subclasses aren't supported by the meta-object compiler, there doesn't seem to be a way to have a (tempalted) base class for all data sources which defines the samplesAcquired Signal. In other words, the following won't work: template<T,U> //sample type and units class DataSource : public QObject { Q_OBJECT ... public: typedef std::vector<boost::units::quantity<U,T> > SampleVector signals: void samplesAcquired(SampleVector sampleVector); }; The best option I've been able to come up with is a two-layered approach: template<T,U> //sample type and units class IAcquiredSamples { public: typedef std::vector<boost::units::quantity<U,T> > SampleVector virtual shared_ptr<SampleVector> acquiredData(TimeStamp ts, unsigned long nsamples); }; class DataSource : public QObject { ... signals: void samplesAcquired(TimeStamp ts, unsigned long nsamples); }; The samplesAcquired signal now gives a timestamp and number of samples for the acquisition and clients must use the IAcquiredSamples API to retrieve those samples. Obviously data sources must subclass both DataSource and IAcquiredSamples. The disadvantage of this approach appears to be a loss of simplicity in the API... it would be much nicer if clients could get the acquired samples in the Slot connected. Being able to use Qt's queued connections would also make threading issues easier instead of having to manage them in the acquiredData method within each subclass. One other possibility, is to use a QVariant argument. This necessarily puts the onus on subclass to register their particular sample vector type with Q_REGISTER_METATYPE/qRegisterMetaType. Not really a big deal. Clients of the base class however, will have no way of knowing what type the QVariant value type is, unless a tag struct is also passed with the signal. I consider this solution at least as convoluted as the one above, as it forces clients of the abstract base class API to deal with some of the gnarlier aspects of type system. So, is there a way to achieve the templated signal parameter? Is there a better architecture than the one I've proposed?

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  • How to have a policy class implement a virtual function?

    - by dehmann
    I'm trying to design a policy-based class, where a certain interface is implemented by the policy itself, so the class derives from the policy, which itself is a template (I got this kind of thinking from Alexandrescu's book): #include <iostream> #include <vector> class TestInterface { public: virtual void test() = 0; }; class TestImpl1 { public: void test() {std::cerr << "Impl1" << std::endl;} }; template<class TestPolicy> class Foo : public TestInterface, TestPolicy { }; Then, in the main() function, I call test() on (potentially) various different objects that all implement the same interface: int main() { std::vector<TestInterface*> foos; foos.push_back(new Foo<TestImpl1>()); foos[0]->test(); delete foos[0]; return 0; } It doesn't compile, though, because the following virtual functions are pure within ‘Foo<TestImpl1>’: virtual void TestInterface::test() I thought TestInterface::test() is implemented because we derive from TestImpl1?

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  • Register/Include javascript within RenderingTemplate.

    - by Janis Veinbergs
    Is it possible to register (include) javascript within RenderingTemplate? (RenderingTemplates are used to render list forms or fields) By using <SharePoint:RenderingTemplate ID="NewRelatedListItem" runat="server"> <Template> <span id="part1"> <SharePoint:ScriptLink Name="SPFormFieldAssistant.js" Localizable="false" /> ... </span> ... </Template> </SharePoint:RenderingTemplate> it couldn't be done - it didn't include script at HEAD area, but...: Is something wrong with my code? Althought script IS at Layouts folder and I checked with Reflector that it uses Layouts folder if Localizable='False'. I don't want this script to be loaded with every page, but only for forms. Any ideas on how this could be achieved?

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  • Ambiguous access to base class template member function

    - by Johann Gerell
    In Visual Studio 2008, the compiler cannot resolve the call to SetCustomer in _tmain below and make it unambiguous: template <typename TConsumer> struct Producer { void SetConsumer(TConsumer* consumer) { consumer_ = consumer; } TConsumer* consumer_; }; struct AppleConsumer { }; struct MeatConsumer { }; struct ShillyShallyProducer : public Producer<AppleConsumer>, public Producer<MeatConsumer> { }; int _tmain(int argc, _TCHAR* argv[]) { ShillyShallyProducer producer; AppleConsumer consumer; producer.SetConsumer(&consumer); // <--- Ambiguous call!! return 0; } This is the compilation error: // error C2385: ambiguous access of 'SetConsumer' // could be the 'SetConsumer' in base 'Producer<AppleConsumer>' // or could be the 'SetConsumer' in base 'Producer<MeatConsumer>' I thought the template argument lookup mechanism would be smart enough to deduce the correct base Producer. Why isn't it? I could get around this by changing Producer to template <typename TConsumer> struct Producer { template <typename TConsumer2> void SetConsumer(TConsumer2* consumer) { consumer_ = consumer; } TConsumer* consumer_; }; and call SetConsumer as producer.SetConsumer<AppleConsumer>(&consumer); // Unambiguous call!! but it would be nicer if I didn't have to...

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  • syntax help required on templated static member function

    - by omatai
    I have a bunch of containers of object pointers that I want to iterate through in different contexts to produce diagnostics for them. I'm struggling with the syntax required to define the functions... which, on account of these objects filtering through diverse parts of my application, seem best encapsulated in a dedicated diagnostics class thus: // Code sketch only - detail fleshed out below... class ObjectListDiagnoser { public: static void GenerateDiagnostics( /* help required here! */ ); }; ... // Elsewhere in the system... ObjectListDiagnoser::GenerateDiagnostics( /* help required here! */ ); What I'd like to be able to do (in places across my application) is at least this: std::vector<MyObject *> objGroup1; std::list<MyObject *> objGroup2; ObjectListDiagnoser::GenerateDiagnostics( objGroup1.begin(), objGroup1.end() ); ObjectListDiagnoser::GenerateDiagnostics( objGroup2.begin(), objGroup2.end() ); ObjectListDiagnoser::GenerateDiagnostics( objGroup1.rbegin(), objGroup1.rend() ); I have tried to template my function in two ways, with no success: class ObjectListDiagnoser { public: // 1 - nope. template <class ObjIter> static void GenerateDiagnostics( ObjIter first, ObjIter last ); // 2. - nope. template <class Container, class ObjIter> static void GenerateDiagnostics( Container<MyObject *>::ObjIter first, Container<MyObject *>::ObjIter last ); }; Can someone provide the correct syntax for this? The container type will vary, and the direction of iteration will vary, but always for the same type of object.

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  • error: expected constructor, destructor, or type conversion before '(' token

    - by jonathanasdf
    include/TestBullet.h:12: error: expected constructor, destructor, or type conver sion before '(' token I hate C++ error messages... lol ^^ Basically, I'm following what was written in this post to try to create a factory class for bullets so they can be instantiated from a string, which will be parsed from an xml file, because I don't want to have a function with a switch for all of the classes because that looks ugly. Here is my TestBullet.h: #pragma once #include "Bullet.h" #include "BulletFactory.h" class TestBullet : public Bullet { public: void init(BulletData& bulletData); void update(); }; REGISTER_BULLET(TestBullet); <-- line 12 And my BulletFactory.h: #pragma once #include <string> #include <map> #include "Bullet.h" #define REGISTER_BULLET(NAME) BulletFactory::reg<NAME>(#NAME) #define REGISTER_BULLET_ALT(NAME, CLASS) BulletFactory::reg<CLASS>(NAME) template<typename T> Bullet * create() { return new T; } struct BulletFactory { typedef std::map<std::string, Bullet*(*)()> bulletMapType; static bulletMapType map; static Bullet * createInstance(char* s) { std::string str(s); bulletMapType::iterator it = map.find(str); if(it == map.end()) return 0; return it->second(); } template<typename T> static void reg(std::string& s) { map.insert(std::make_pair(s, &create<T>)); } }; Thanks in advance.

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