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  • C++ Generic List Assignment

    - by S73417H
    I've clearly been stuck in Java land for too long... Is it possible to do the C++ equivalent of the following Java code: // Method List<Bar> getBars() { return new LinkedList<Bar>(); } // Assignment statement. List<Foo> stuff = getBars(); Where Foo is a sub-class of Bar. So in C++.... std::list<Bar> & getBars() { std::list<Bar> bars; return bars; } std::list<Foo> stuff = getBars(); Hope that makes sense....

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  • Overwriting a range of bits in an integer in a generic way

    - by porgarmingduod
    Given two integers X and Y, I want to overwrite bits at position P to P+N. Example: int x = 0xAAAA; // 0b1010101010101010 int y = 0x0C30; // 0b0000110000110000 int result = 0xAC3A; // 0b1010110000111010 Does this procedure have a name? If I have masks, the operation is easy enough: int mask_x = 0xF00F; // 0b1111000000001111 int mask_y = 0x0FF0; // 0b0000111111110000 int result = (x & mask_x) | (y & mask_y); What I can't quite figure out is how to write it in a generic way, such as in the following generic C++ function: template<typename IntType> IntType OverwriteBits(IntType dst, IntType src, int pos, int len) { // If: // dst = 0xAAAA; // 0b1010101010101010 // src = 0x0C30; // 0b0000110000110000 // pos = 4 ^ // len = 8 ^------- // Then: // result = 0xAC3A; // 0b1010110000111010 } The problem is that I cannot figure out how to make the masks properly when all the variables, including the width of the integer, is variable. Does anyone know how to write the above function properly?

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  • Mapping integers to types using C++ template fails in a specific case

    - by Shailesh Kumar
    I am attempting to compile the following template based code in VC++ 2005. #include <iostream> using namespace std; /* * T is a template which maps an integer to a specific type. * The mapping happens through partial template specialization. * In the following T<1> is mapped to char, T<2> is mapped to long * and T<3> is mapped to float using partial template specializations */ template <int x> struct T { public: }; template<> struct T<1> { public: typedef char xType; }; template<> struct T<2> { public: typedef long xType; }; template<> struct T<3> { public: typedef float xType; }; // We can easily access the specific xType for a specific T<N> typedef T<3>::xType x3Type; /*! * In the following we are attempting to use T<N> inside another * template class T2<R> */ template<int r> struct T2 { //We can map T<r> to some other type T3 typedef T<r> T3; // The following line fails typedef T3::xType xType; }; int main() { T<1>::xType a1; cout << typeid(a1).name() << endl; T<2>::xType a2; cout << typeid(a2).name() << endl; T<3>::xType a3; cout << typeid(a3).name() << endl; return 0; } There is a particular line in the code which doesn't compile: typedef T3::xType xType; If I remove this line, compilation goes fine and the result is: char long float If I retain this line, compilation errors are observed. main.cpp(53) : warning C4346: 'T<x>::xType' : dependent name is not a type prefix with 'typename' to indicate a type main.cpp(54) : see reference to class template instantiation 'T2<r>' being compiled main.cpp(53) : error C2146: syntax error : missing ';' before identifier 'xType' main.cpp(53) : error C4430: missing type specifier - int assumed. Note: C++ does not support default-int I am not able to figure out how to make sure that T::xType can be treated as a type inside the T2 template. Any help is highly appreciated.

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  • algorithms that destruct and copy_construct

    - by FredOverflow
    I am currently building my own toy vector for fun, and I was wondering if there is something like the following in the current or next standard or in Boost? template<class T> void destruct(T* begin, T* end) { while (begin != end) { begin -> ~T(); ++begin; } } template<class T> T* copy_construct(T* begin, T* end, T* dst) { while (begin != end) { new(dst) T(*begin); ++begin; ++dst; } return dst; }

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  • HTML reuse, create template

    - by nanonerd
    After about a year doing Asp.net web forms, I stepped out (for the most part) from the .net world. I'm now working on a webapp that uses a lot of client side scripting and uses WebAPI for data access. I have a HTML section that allows note taking. I would like to make this HTML section into a template that I can reuse elsewhere on the site (e.g., insert this piece of HTML code into another web page). I'm a bit befuddled on how to go about this. Think of my problem as trying to create a "user control" in asp.net web forms ... only that I am not using web forms. Just good old fashioned HTML, CSS, Javascript, jquery, and knockout. Conceptually, I'd think that others have been in the same spot as myself. Can anyone elaborate a solution or at least provide some pointers? Thanks !

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  • How to save links in Django

    - by xRobot
    I have a simple Blog model with a TextFields. What is the best way to save link ? 1) Saving link in the database in this form: http://www.example.com and then using some filter in the template to trasform it in form: <a rel="nofollow" href="http://www.example.com>http://www.example.com</a> 2) Saving link in the database directly in this form: <a rel="nofollow" href="http://www.example.com>http://www.example.com</a>

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  • Template neglects const (why?)

    - by Gabriel
    Does somebody know, why this compiles?? template< typename TBufferTypeFront, typename TBufferTypeBack = TBufferTypeFront> class FrontBackBuffer{ public: FrontBackBuffer( const TBufferTypeFront front, const TBufferTypeBack back): ////const reference assigned to reference??? m_Front(front), m_Back(back) { }; ~FrontBackBuffer() {}; TBufferTypeFront m_Front; ///< The front buffer TBufferTypeBack m_Back; ///< The back buffer }; int main(){ int b; int a; FrontBackBuffer<int&,int&> buffer(a,b); // buffer.m_Back = 33; buffer.m_Front = 55; } I compile with GCC 4.4. Why does it even let me compile this? Shouldn't there be an error that I cannot assign a const reference to a non-const reference?

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  • WPF: In Expression Blend, how to change Foreground of a custom button with a Border on different states?

    - by SubmarineX
    In Expression Blend 4, I want to change the Foreground of a custom button on different states. I'm just able to change the Background and BorderBrush. Just like this: If the state is "Normal", the color of text "Button" is Black, while the state is "Pressed", the color of text "Button" is White. On Brushes Panel under Properties Panel, there're 3 properties but no Foreground property: Who can help me? I'm so perplexed. Edit I find ContentControl have a Foreground property, but ContentPresenter haven't. Wether I should use ContentControl instead of ContentPresenter?

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  • How to assign HTML value to a asp.net string variable

    - by Zerotoinfinite
    I am using asp.net and C#. I want to send mail to my user in HTML format, I have the content in HTML format let say like this <table style="width:100%;"> <tr> <td style="width:20%; background-color:Blue;"></td> <td style="width:80%; background-color:Green;"></td> </tr> </table> Now I am unable to assign this to a string variable, so that I could send it as a mail. Please let me know how can I bind this whole HTML content into a varibale. Also, please note that the above code is only a demo, I have around 100 lines of HTML code.

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  • Template access of symbol in unnamed namespace

    - by Fred Larson
    We are upgrading our XL C/C++ compiler from V8.0 to V10.1 and found some code that is now giving us an error, even though it compiled under V8.0. Here's a minimal example: test.h: #include <iostream> #include <string> template <class T> void f() { std::cout << TEST << std::endl; } test.cpp: #include <string> #include "test.h" namespace { std::string TEST = "test"; } int main() { f<int>(); return 0; } Under V10.1, we get the following error: "test.h", line 7.16: 1540-0274 (S) The name lookup for "TEST" did not find a declaration. "test.cpp", line 6.15: 1540-1303 (I) "std::string TEST" is not visible. "test.h", line 5.6: 1540-0700 (I) The previous message was produced while processing "f<int>()". "test.cpp", line 11.3: 1540-0700 (I) The previous message was produced while processing "main()". We found a similar difference between g++ 3.3.2 and 4.3.2. I also found in g++, if I move the #include "test.h" to be after the unnamed namespace declaration, the compile error goes away. So here's my question: what does the Standard say about this? When a template is instantiated, is that instance considered to be declared at the point where the template itself was declared, or is the standard not that clear on this point? I did some looking though the n2461.pdf draft, but didn't really come up with anything definitive.

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  • Dealing with C++ web views

    - by Jeffrey
    I'm working, as an hobby (before any one rage out of their mind, I'm just trying to study C++ regarding something I love: web. I'm not trying to reinvent your precious wheel, and I'm not trying to create the new web technology. I just have the time to go for it.), creating a web CGI C++ library. I'm at a pretty good point, but in the future I see one big problem: views. I'm used to the great <body><?php echo "Hey!"; ?></body> embedded php, but there's no such thing in C++, so I'm wondering: How would you deal with views? Would you create a simple find-replace-variable templating system and deal with thousands of partial views? For example: View view; view.load("header.html"); view.load("nav.html"); view.load("post_start.html"); for (int i = 0; i < 10; i++) { std::map<std::string, std::string> post; Post p(i); post = p.get(); view.load(post_view.html, post); // p is passed as argument and every `{% varname %}` in the html will be replaced with its value inside the map } view.load(post_end.html); view.load(footer); Would you create a simple templating system? So that we can deal with this C++ code: std::vector<std::map<std::string, std::string>> posts; Posts p; posts = p.getAll(); view.load(posts.html, posts); and then this HTML/TPL: <html> ... <body> <h2> Posts </h2> {% for (i = 0; i < 10; i++): %} <div class="post">...</div> {% endfor %} </body> </html> Is there any other way? What is the best way to do this? (And no, I don't think this is subjective question)

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  • vb.net project template how can I leave the root namesapce empty

    - by Wietze Veld
    I have been tinkering with the VS 2010 template. So far I am able to create a vb.net class library project from my template. However, one small thing is bugging me. In my project template the default assembly name is the same as the default file name. I have left the root namespace empty. But when I create a new project from the template, VS 2010 automatically fills the root namespace with the same name as my assembly name. My template project (vbproj) for the assembly name and root namespace looks like this: <AssemblyName>$safeprojectname$</AssemblyName> <!-- RootNameSpace should always be empty. --> <RootNamespace></RootNamespace> But as said, when I leave this empty it is always overwritten with the assembly name. Even if I create a custom parameter with an empty string as value to replace the root namespace, it is still overridden. Any help is appreciated.

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  • template; operator (int)

    - by Oops
    Hi, regarding my Point struct already mentioned here: http://stackoverflow.com/questions/2794369/template-class-ctor-against-function-new-c-standard is there a chance to replace the function toint() with a cast-operator (int)? namespace point { template < unsigned int dims, typename T > struct Point { T X[ dims ]; //umm??? template < typename U > Point< dims, U > operator U() const { Point< dims, U > ret; std::copy( X, X + dims, ret.X ); return ret; } //umm??? Point< dims, int > operator int() const { Point<dims, int> ret; std::copy( X, X + dims, ret.X ); return ret; } //OK Point<dims, int> toint() { Point<dims, int> ret; std::copy( X, X + dims, ret.X ); return ret; } }; //struct Point template < typename T > Point< 2, T > Create( T X0, T X1 ) { Point< 2, T > ret; ret.X[ 0 ] = X0; ret.X[ 1 ] = X1; return ret; } }; //namespace point int main(void) { using namespace point; Point< 2, double > p2d = point::Create( 12.3, 34.5 ); Point< 2, int > p2i = (int)p2d; //äähhm??? std::cout << p2d.str() << std::endl; char c; std::cin >> c; return 0; } I think the problem is here that C++ cannot distinguish between different return types? many thanks in advance. regards Oops

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  • Imbricated C++ template

    - by gregseth
    I have the following pattern: template <int a, int b> class MyClass { template <int c> MyClass<a, c> &operator*(MyClass<c, b> const &other) const; }; // ../.. template <int a, int b> template <int c> MyClass<a, c> &MyClass<a, b>::operator*(MyClass<c, b> const &other) const { MyClass<a, c> result; // ..do stuff.. return result; } It doesn't compile, the error message is Error C2975. invalid template argument 'number', constant expression expected. If I replace template <int c> by template <int c, int d> and use it accordignly, it works fine. But I want d to be the same value as b. My questions: Why the example doesn't work? How can I enforce d to be the same than b? Thanks.

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  • What does "static" mean in the context of declaring global template functions?

    - by smf68
    I know what static means in the context of declaring global non-template functions (see e.g. What is a "static" function?), which is useful if you write a helper function in a header that is included from several different locations and want to avoid "duplicate definition" errors. So my question is: What does static mean in the context of declaring global template functions? Please note that I'm specifically asking about global, non-member template functions that do not belong to a class. In other words, what is the difference between the following two: template <typename T> void foo(T t) { /* implementation of foo here */ } template <typename T> static void bar(T t) { /* implementation of bar here */ }

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  • need a virtual template member workaround

    - by yurib
    Hello, I need to write a program implementing the visitor design pattern. The problem is that the base visitor class is a template class. This means that BaseVisited::accept() takes a template class as a parameter and since it uses 'this' and i need 'this' to point to the correct runtime instance of the object, it also needs to be virtual. I'd like to know if there's any way around this problem. template <typename T> class BaseVisitor { public: BaseVisitor(); T visit(BaseVisited *visited); virtual ~BaseVisitor(); } class BaseVisited { BaseVisited(); template <typename T> virtual void accept(BaseVisitor<T> *visitor) { visitor->visit(this); }; // problem virtual ~BaseVisited(); }

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  • Django Find Out if User is Authenticated in Custom Tag

    - by greggory.hz
    I'm trying to create a custom tag. Inside this custom tag, I want to be able to have some logic that checks if the user is logged in, and then have the tag rendered accordingly. This is what I have: def user_actions(context): request = template.Variable('request').resolve(context) return { 'auth': request['user'].is_athenticated() } register.inclusion_tag('layout_elements/user_actions.html', takes_context=True)(user_actions) When I run this, I get this error: Caught VariableDoesNotExist while rendering: Failed lookup for key [request] in u'[{}]' The view that renders this ends like this: return render_to_response('start/home.html', {}, context_instance=RequestContext(request)) Why doesn't the tag get a RequestContext object instead of the Context object? How can I get the tag to receive the RequestContext instead of the Context? EDIT: Whether or not it's possible to get a RequestContext inside a custom tag, I'd still be interested to know the "correct" or best way to determine a user's authentication state from within the custom tag. If that's not possible, then perhaps that kind of logic belongs elsewhere? Where?

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  • template specilization using member enums

    - by Altan
    struct Bar { enum { Special = 4 }; }; template<class T, int K> struct Foo {}; template<class T> struct Foo<T::Special> {}; Usage: Foo<Bar> aa; fails to compile using gcc 4.1.2 It complains about the usage of T::Special for partial specilization of Foo. If Special was a class the solution would be to a typename in front of it. Is there something equivalent to it for enums (or integers)? Thanks, Altan

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  • allocating extra memory for a container class.

    - by sil3nt
    Hey there, I'm writing a template container class and for the past few hours have been trying to allocate new memory for extra data that comes into the container (...hit a brick wall..:| ) template <typename T> void Container<T>::insert(T item, int index){ if ( index < 0){ cout<<"Invalid location to insert " << index << endl; return; } if (index < sizeC){ //copying original array so that when an item is //placed in the middleeverything else is shifted forward T *arryCpy = 0; int tmpSize = 0; tmpSize = size(); arryCpy = new T[tmpSize]; int i = 0, j = 0; for ( i = 0; i < tmpSize; i++){ for ( j = index; j < tmpSize; j++){ arryCpy[i] = elements[j]; } } //overwriting and placing item and location index elements[index] = item; //copying back everything else after the location at index int k = 0, l = 0; for ( k =(index+1), l=0; k < sizeC || l < (sizeC-index); k++,l++){ elements[k] = arryCpy[l]; } delete[] arryCpy; arryCpy = 0; } //seeing if the location is more than the current capacity //and hence allocating more memory if (index+1 > capacityC){ int new_capacity = 0; int current_size = size(); new_capacity = ((index+1)-capacityC)+capacityC; //variable for new capacity T *tmparry2 = 0; tmparry2 = new T[new_capacity]; int n = 0; for (n = 0; n < current_size;n++){ tmparry2[n] = elements[n]; } delete[] elements; elements = 0; //copying back what we had before elements = new T[new_capacity]; int m = 0; for (m = 0; m < current_size; m++){ elements[m] = tmparry2[m]; } //placing item elements[index] = item; } else{ elements[index] = item; } //increasing the current count sizeC++; my testing condition is Container cnt4(3); and as soon as i hit the fourth element (when I use for egsomething.insert("random",3);) it crashes and the above doesnt work. where have I gone wrong?

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  • Getting the hang of CodeIgniter - Templating / loading views

    - by kilrizzy
    Attempting to learn CI and going through the docs to get a better understanding. Without getting a separate library, I could make a template by including a list of views like so: $this->load->view('header'); $this->load->view('navigation'); $this->load->view('sidenav_open'); $this->load->view('blocks/userinfo'); $this->load->view('blocks/stats'); $this->load->view('sidenav_close'); $this->load->view('content',$data); $this->load->view('footer'); This makes sense but would I actually have that on each of my controllers (pages)? Not sure if there is a way to include this in the initial controller (welcome) and then in the others somehow reference it? Or perhaps there is something I am missing completely

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