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• Impossible to be const-correct when combining data and it's lock?

  - by Graeme

  I've been looking at ways to combine a piece of data which will be accessed by multiple threads alongside the lock provisioned for thread-safety. I think I've got to a point where I don't think its possible to do this whilst maintaining const-correctness. Take the following class for example: template <typename TType, typename TMutex> class basic_lockable_type { public: typedef TMutex lock_type; public: template <typename... TArgs> explicit basic_lockable_type(TArgs&&... args) : TType(std::forward<TArgs...>(args)...) {} TType& data() { return data_; } const TType& data() const { return data_; } void lock() { mutex_.lock(); } void unlock() { mutex_.unlock(); } private: TType data_; mutable TMutex mutex_; }; typedef basic_lockable_type<std::vector<int>, std::mutex> vector_with_lock; In this I try to combine the data and lock, marking mutex_ as mutable. Unfortunately this isn't enough as I see it because when used, vector_with_lock would have to be marked as mutable in order for a read operation to be performed from a const function which isn't entirely correct (data_ should be mutable from a const). void print_values() const { std::lock_guard<vector_with_lock>(values_); for(const int val : values_) { std::cout << val << std::endl; } } vector_with_lock values_; Can anyone see anyway around this such that const-correctness is maintained whilst combining data and lock? Also, have I made any incorrect assumptions here?

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• C++ Declarative Parsing Serialization

  - by Martin York

  Looking at Java and C# they manage to do some wicked processing based on special languaged based anotation (forgive me if that is the incorrect name). In C++ we have two problems with this: 1) There is no way to annotate a class with type information that is accessable at runtime. 2) Parsing the source to generate stuff is way to complex. But I was thinking that this could be done with some template meta-programming to achieve the same basic affect as anotations (still just thinking about it). Like char_traits that are specialised for the different types an xml_traits template could be used in a declaritive way. This traits class could be used to define how a class is serialised/deserialized by specializing the traits for the class you are trying to serialize. Example Thoughs: template<typename T> struct XML_traits { typedef XML_Empty Children; }; template<> struct XML_traits<Car> { typedef boost::mpl::vector<Body,Wheels,Engine> Children; }; template<typename T> std::ostream& Serialize(T const&) { // my template foo is not that strong. // but somthing like this. boost::mpl::for_each<typename XML_Traits<T>::Children,Serialize>(data); } template<> std::ostream& Serialize<XML_Empty>(T const&) { /* Do Nothing */ } My question is: Has anybody seen any projects/decumentation (not just XML) out there that uses techniques like this (template meta-programming) to emulate the concept of annotation used in languges like Java and C# that can then be used in code generation (to effectively automate the task by using a declaritive style). At this point in my research I am looking for more reading material and examples.

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• Visual C++ doesn't operator<< overload

  - by PierreBdR

  I have a vector class that I want to be able to input/output from a QTextStream object. The forward declaration of my vector class is: namespace util { template <size_t dim, typename T> class Vector; } I define the operator<< as: namespace util { template <size_t dim, typename T> QTextStream& operator<<(QTextStream& out, const util::Vector<dim,T>& vec) { ... } template <size_t dim, typename T> QTextStream& operator>>(QTextStream& in,util::Vector<dim,T>& vec) { .. } } However, if I ty to use these operators, Visual C++ returns this error: error C2678: binary '<<' : no operator found which takes a left-hand operand of type 'QTextStream' (or there is no acceptable conversion) A few things I tried: Originaly, the methods were defined as friends of the template, and it is working fine this way with g++. The methods have been moved outside the namespace util I changed the definition of the templates to fit what I found on various Visual C++ websites. The original friend declaration is: friend QTextStream& operator>>(QTextStream& ss, Vector& in) { ... } The "Visual C++ adapted" version is: friend QTextStream& operator>> <dim,T>(QTextStream& ss, Vector<dim,T>& in); with the function pre-declared before the class and implemented after. I checked the file is correctly included using: #pragma message ("Including vector header") And everything seems fine. Doesn anyone has any idea what might be wrong?

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• C++ ambiguous template instantiation

  - by aaa

  the following gives me ambiguous template instantiation with nvcc (combination of EDG front-end and g++). Is it really ambiguous, or is compiler wrong? I also post workaround à la boost::enable_if template<typename T> struct disable_if_serial { typedef void type; }; template<> struct disable_if_serial<serial_tag> { }; template<int M, int N, typename T> __device__ //static typename disable_if_serial<T>::type void add_evaluate_polynomial1(double *R, const double (&C)[M][N], double x, const T &thread) { // ... } template<size_t M, size_t N> __device__ static void add_evaluate_polynomial1(double *R, const double (&C)[M][N], double x, const serial_tag&) { for (size_t i = 0; i < M; ++i) add_evaluate_polynomial1(R, C, x, i); } // ambiguous template instantiation here. add_evaluate_polynomial1(R, C, x, serial_tag());

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• Simplest way to mix sequences of types with iostreams?

  - by Kylotan

  I have a function void write<typename T>(const T&) which is implemented in terms of writing the T object to an ostream, and a matching function T read<typename T>() that reads a T from an istream. I am basically using iostreams as a plain text serialisation format, which obviously works fine for most built-in types, although I'm not sure how to effectively handle std::strings just yet. I'd like to be able to write out a sequence of objects too, eg void write<typename T>(const std::vector<T>&) or an iterator based equivalent (although in practice, it would always be used with a vector). However, while writing an overload that iterates over the elements and writes them out is easy enough to do, this doesn't add enough information to allow the matching read operation to know how each element is delimited, which is essentially the same problem that I have with a single std::string. Is there a single approach that can work for all basic types and std::string? Or perhaps I can get away with 2 overloads, one for numerical types, and one for strings? (Either using different delimiters or the string using a delimiter escaping mechanism, perhaps.)

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• C++ Namespaces & templates question

  - by Kotti

  Hi! I have some functions that can be grouped together, but don't belong to some object / entity and therefore can't be treated as methods. So, basically in this situation I would create a new namespace and put the definitions in a header file, the implementation in cpp file. Also (if needed) I would create an anonymous namespace in that cpp file and put all additional functions that don't have to be exposed / included to my namespace's interface there. See the code below (probably not the best example and could be done better with another program architecture, but I just can't think of a better sample...) Sample code (header) namespace algorithm { void HandleCollision(Object* object1, Object* object2); } Sample code (cpp) #include "header" // Anonymous namespace that wraps // routines that are used inside 'algorithm' methods // but don't have to be exposed namespace { void RefractObject(Object* object1) { // Do something with that object // (...) } } namespace algorithm { void HandleCollision(Object* object1, Object* object2) { if (...) RefractObject(object1); } } So far so good. I guess this is a good way to manage my code, but I don't know what should I do if I have some template-based functions and want to do basically the same. If I'm using templates, I have to put all my code in the header file. Ok, but how should I conceal some implementation details then? Like, I want to hide RefractObject function from my interface, but I can't simply remove it's declaration (just because I have all my code in a header file)... The only approach I came up with was something like: Sample code (header) namespace algorithm { // Is still exposed as a part of interface! namespace impl { template <typename T> void RefractObject(T* object1) { // Do something with that object // (...) } } template <typename T, typename Y> void HandleCollision(T* object1, Y* object2) { impl::RefractObject(object1); // Another stuff } } Any ideas how to make this better in terms of code designing?

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• overloading "<<" with a struct (no class) cout style

  - by monkeyking

  I have a struct that I'd like to output using either 'std::cout' or some other output stream. Is this possible without using classes? Thanks #include <iostream> #include <fstream> template <typename T> struct point{ T x; T y; }; template <typename T> std::ostream& dump(std::ostream &o,point<T> p) const{ o<<"x: " << p.x <<"\ty: " << p.y <<std::endl; } template<typename T> std::ostream& operator << (std::ostream &o,const point<T> &a){ return dump(o,a); } int main(){ point<double> p; p.x=0.1; p.y=0.3; dump(std::cout,p); std::cout << p ;//how? return 0; } I tried different syntax' but I cant seem to make it work.

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• MyMessage<T> throws an exception when calling XmlSerializer

  - by Arthis

  I am very new to nservicebus. I am using version 3.0.1, the last one up to date. And I wonder if my case is a normal limitation of NSB, I am not aware of. I have an asp.net MVC application, I am trying to setup and in my global.asax, I have the following : var configure = Configure.WithWeb() .DefaultBuilder() .ForMvc() .XmlSerializer(); But I have an error with the XmlSerializer when dealing with one of my object: [Serializable] public class MyMessage<T> : IMessage { public T myobject { get; set; } } I pass trough : XmlSerializer() instance.Initialize(types); this.InitType(type, moduleBuilder); this.InitType(info2.PropertyType, moduleBuilder); and then when dealing With T, string typeName = GetTypeName(t); typename is null and the following instruction : if (!nameToType.ContainsKey(typeName)) ends in error. null value not allowed. Is this some limitations to Nservicebus, or am I messing something up?

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• Specializing function templates outside class temp. definition - what is the correct way of doing t

  - by LoudNPossiblyRight

  I am attempting to specialize a function template that is a member of a template class. The two of them have different template parameters. The template function specialization inside the temp. class definition is never called and the one func. spec. outside the class definition does not even compile. Should i expect this to work in the first place, and if so, what do i have to change in this code to both compile and make it work correctly: using VS2010 #include<iostream> using namespace std; template <typename T> class klass{ public: template <typename U> void func(const U &u){ cout << "I AM A TEMPLATE FUNC" << endl; } //THIS NEVER GETS CALLED !!! template <> void klass<T>::func(const string &s){ cout << "I AM A STRING SPECIALIST" << endl; } }; //THIS SPECIALIZATION WILL NOT COMPILE !!! template <typename T> template <> void klass<T>::func(const double &s){ cout << "I AM A DOUBLE SPECIALIST" << endl; } int main(){ double d = 3.14159265; klass<int> k; k.func(1234567890); k.func("string"); k.func(3.14159265); return 0; }

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• Argument type deduction, references and rvalues

  - by uj2

  Consider the situation where a function template needs to forward an argument while keeping it's lvalue-ness in case it's a non-const lvalue, but is itself agnostic to what the argument actually is, as in: template <typename T> void target(T&) { cout << "non-const lvalue"; } template <typename T> void target(const T&) { cout << "const lvalue or rvalue"; } template <typename T> void forward(T& x) { target(x); } When x is an rvalue, instead of T being deduced to a constant type, it gives an error: int x = 0; const int y = 0; forward(x); // T = int forward(y); // T = const int forward(0); // Hopefully, T = const int, but actually an error forward<const int>(0); // Works, T = const int It seems that for forward to handle rvalues (without calling for explicit template arguments) there needs to be an forward(const T&) overload, even though it's body would be an exact duplicate. Is there any way to avoid this duplication?

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• Templates, Function Pointers and C++0x

  - by user328543

  One of my personal experiments to understand some of the C++0x features: I'm trying to pass a function pointer to a template function to execute. Eventually the execution is supposed to happen in a different thread. But with all the different types of functions, I can't get the templates to work. #include `<functional`> int foo(void) {return 2;} class bar { public: int operator() (void) {return 4;}; int something(int a) {return a;}; }; template <class C> int func(C&& c) { //typedef typename std::result_of< C() >::type result_type; typedef typename std::conditional< std::is_pointer< C >::value, std::result_of< C() >::type, std::conditional< std::is_object< C >::value, std::result_of< typename C::operator() >::type, void> >::type result_type; result_type result = c(); return result; } int main(int argc, char* argv[]) { // call with a function pointer func(foo); // call with a member function bar b; func(b); // call with a bind expression func(std::bind(&bar::something, b, 42)); // call with a lambda expression func( [](void)->int {return 12;} ); return 0; } The result_of template alone doesn't seem to be able to find the operator() in class bar and the clunky conditional I created doesn't compile. Any ideas? Will I have additional problems with const functions?

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• Typedef equivalence in function arguments

  - by Warren Seine

  Hi guys, The question is kind of hard to ask without an example so here it is: #include <vector> struct O { }; struct C { template <typename T> void function1(void (C::*callback)(const O*)); template <typename T> void function2(void (C::*callback)(const typename T::value_type)); void print(const O*); }; int main() { C c; c.function1< std::vector<O*> >(&C::print); // Success. c.function2< std::vector<O*> >(&C::print); // Fail. } The error that I am given is: error: no matching function for call to ‘C::function2(void (C::*)(const O*))’. Basically, the only difference between calls is that in function2, I'm more generic since I use the typedef std::vector<O*>::value_type which should resolve to O*, hence similar to function1. I'm using G++ 4.2.1 (I know it's old), but Comeau confirms I'm wrong. Why does the compilation fail?

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• How can I write a function template for all types with a particular type trait?

  - by TC

  Consider the following example: struct Scanner { template <typename T> T get(); }; template <> string Scanner::get() { return string("string"); } template <> int Scanner::get() { return 10; } int main() { Scanner scanner; string s = scanner.get<string>(); int i = scanner.get<int>(); } The Scanner class is used to extract tokens from some source. The above code works fine, but fails when I try to get other integral types like a char or an unsigned int. The code to read these types is exactly the same as the code to read an int. I could just duplicate the code for all other integral types I'd like to read, but I'd rather define one function template for all integral types. I've tried the following: struct Scanner { template <typename T> typename enable_if<boost::is_integral<T>, T>::type get(); }; Which works like a charm, but I am unsure how to get Scanner::get<string>() to function again. So, how can I write code so that I can do scanner.get<string>() and scanner.get<any integral type>() and have a single definition to read all integral types? Update: bonus question: What if I want to accept more than one range of classes based on some traits? For example: how should I approach this problem if I want to have three get functions that accept (i) integral types (ii) floating point types (iii) strings, respectively.

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• static member specialization of templated child class and templated base class

  - by b3nj1

  I'm trying to have a templated class (here C) that inherits from another templated class (here A) and perform static member specialization (of int var here), but I cant get the right syntax to do so (if it's possible #include <iostream> template<typename derived> class A { public: static int var; }; //This one works fine class B :public A<B> { public: B() { std::cout << var << std::endl; } }; template<> int A<B>::var = 9; //This one doesn't works template<typename type> class C :public A<C<type> > { public: C() { std::cout << var << std::endl; } }; //template<> template<typename type> int A<C<type> >::a = 10; int main() { B b; C<int> c; return 0; } I put an example that works with a non templated class (here B) and i can get the static member specialization of var, but for C that just doesn't work. Here is what gcc tells me : test.cpp: In constructor ‘C<type>::C()’: test.cpp:29:26: error: ‘var’ was not declared in this scope test.cpp: At global scope: test.cpp:34:18: error: template definition of non-template ‘int A<C<type> >::a’ I'm using gcc version 4.6.3, thanks for any help

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• C++ Design Question on template types

  - by user231536

  I have a templated class template <typename T> class MyContainerClass For types to be substituted for T, it has to satisfy many requirements: for example, get_id(), int data(), etc. Obviously none of the fundamental types (PODs) are substitutable. One way I can provide this is via wrappers for the PODs that provide these functions. Is this an acceptable way? Another way would be to change the template to: template < typename T, typename C=traits<T> > class MyContainerClass and inside MyContainerClass, call traits::data() instead of data() on T objects. I will specialize traits<int>, traits<const char *> etc. Is this good design ? How do I design such a traits class (completely static methods or allow for inheritance) ? Or are the wrapper classes a good solution? What other alternatives are there?

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• C++: Trouble with dependent types in templates

  - by Rosarch

  I'm having trouble with templates and dependent types: namespace Utils { void PrintLine(const string& line, int tabLevel = 0); string getTabs(int tabLevel); template<class result_t, class Predicate> set<result_t> findAll_if(typename set<result_t>::iterator begin, set<result_t>::iterator end, Predicate pred) // warning C4346 { set<result_t> result; return findAll_if_rec(begin, end, pred, result); } } namespace detail { template<class result_t, class Predicate> set<result_t> findAll_if_rec(set<result_t>::iterator begin, set<result_t>::iterator end, Predicate pred, set<result_t> result) { typename set<result_t>::iterator nextResultElem = find_if(begin, end, pred); if (nextResultElem == end) { return result; } result.add(*nextResultElem); return findAll_if_rec(++nextResultElem, end, pred, result); } } Compiler complaints, from the location noted above: warning C4346: 'std::set<result_t>::iterator' : dependent name is not a type. prefix with 'typename' to indicate a type error C2061: syntax error : identifier 'iterator' What am I doing wrong?

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• Efficiently get the size of a parameter pack up to a certain index

  - by NmdMystery

  I want to be able to determine the number of bytes that are in a subset of a parameter pack from 0 to a given index. Right now I'm using a non-constexpr way of doing this. Below is my code: template <size_t index, typename... args> struct pack_size_index; template <size_t index, typename type_t, typename... args> struct pack_size_index <index, type_t, args...> { static const size_t index_v = index; static const size_t value(void) { if (index_v > 0) { return sizeof(type_t) + pack_size_index<index - 1, args...>::value(); } return 0; } }; template <size_t index> struct pack_size_index <index> { static const size_t index_v = index; static const size_t value(void) { return 0; } }; Usage: //output: 5 (equal to 1 + 4) std::cout << pack_size_index<2, bool, float, int, double>::value() << std::endl; //output: 20 (equal to 8 + 8 + 4) std::cout << pack_size_index<3, double, double, float, int>::value() << std::endl; This gets the job done, but this uses runtime comparison and the resulting executable increases in size rapidly whenever this is used. What's a less expensive way of doing this?

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• Template Syntax in C++

  - by Crystal

  I don't understand templates really and was trying to run a simple find the minimum for ints, doubles, chars. First question, why is template<typename T> sometimes used, and other times template<>? Second question, I do not know what I am doing wrong with the following code below: #include <iostream> template <typename T> T minimum(T arg1, T arg2) { return arg1 < arg2 ? arg1 : arg2; } template <typename T> // first I tried template <> instd of above, but wasn't sure the difference T minimum<const char *>(const char *arg1, const char *arg2) { return strcmp(arg1, arg2) ? arg2 : arg1; } int main() { std::cout << minimum<int>(4, 2) << '\n'; std::cout << minimum<double>(2.2, -56.7) << '\n'; std::cout << minimum(2.2, 2) << '\n'; } Compile Errors: error C2768: 'minimum' : illegal use of explicit template arguments error C2783: 'T minimum(const char *,const char *)' : could not deduce template argument for 'T' : see declaration of 'minimum' : error C2782: 'T minimum(T,T)' : template parameter 'T' is ambiguous : see declaration of 'minimum' Third, in getting familiar with separating .h and .cpp files, if I wanted this minimum() function to be a static function of my class, but it was the only function in that class, would I have to have a template class as well? I originally tried doing it that way instead of having it all in one file and I got some compile errors as well that I can't remember right now and was unsure how I would do that. Thanks!

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• C++ - Conway's Game of Life & Stepping Backwards

  - by Gabe

  I was able to create a version Conway's Game of Life that either stepped forward each click, or just ran forward using a timer. (I'm doing this using Qt.) Now, I need to be able to save all previous game grids, so that I can step backwards by clicking a button. I'm trying to use a stack, and it seems like I'm pushing the old gridcells onto the stack correctly. But when I run it in QT, the grids don't change when I click BACK. I've tried different things for the last three hours, to no avail. Any ideas? gridwindow.cpp - My problem should be in here somewhere. Probably the handleBack() func. #include <iostream> #include "gridwindow.h" using namespace std; // Constructor for window. It constructs the three portions of the GUI and lays them out vertically. GridWindow::GridWindow(QWidget *parent,int rows,int cols) : QWidget(parent) { QHBoxLayout *header = setupHeader(); // Setup the title at the top. QGridLayout *grid = setupGrid(rows,cols); // Setup the grid of colored cells in the middle. QHBoxLayout *buttonRow = setupButtonRow(); // Setup the row of buttons across the bottom. QVBoxLayout *layout = new QVBoxLayout(); // Puts everything together. layout->addLayout(header); layout->addLayout(grid); layout->addLayout(buttonRow); setLayout(layout); } // Destructor. GridWindow::~GridWindow() { delete title; } // Builds header section of the GUI. QHBoxLayout* GridWindow::setupHeader() { QHBoxLayout *header = new QHBoxLayout(); // Creates horizontal box. header->setAlignment(Qt::AlignHCenter); this->title = new QLabel("CONWAY'S GAME OF LIFE",this); // Creates big, bold, centered label (title): "Conway's Game of Life." this->title->setAlignment(Qt::AlignHCenter); this->title->setFont(QFont("Arial", 32, QFont::Bold)); header->addWidget(this->title); // Adds widget to layout. return header; // Returns header to grid window. } // Builds the grid of cells. This method populates the grid's 2D array of GridCells with MxN cells. QGridLayout* GridWindow::setupGrid(int rows,int cols) { isRunning = false; QGridLayout *grid = new QGridLayout(); // Creates grid layout. grid->setHorizontalSpacing(0); // No empty spaces. Cells should be contiguous. grid->setVerticalSpacing(0); grid->setSpacing(0); grid->setAlignment(Qt::AlignHCenter); for(int i=0; i < rows; i++) //Each row is a vector of grid cells. { std::vector<GridCell*> row; // Creates new vector for current row. cells.push_back(row); for(int j=0; j < cols; j++) { GridCell *cell = new GridCell(); // Creates and adds new cell to row. cells.at(i).push_back(cell); grid->addWidget(cell,i,j); // Adds to cell to grid layout. Column expands vertically. grid->setColumnStretch(j,1); } grid->setRowStretch(i,1); // Sets row expansion horizontally. } return grid; // Returns grid. } // Builds footer section of the GUI. QHBoxLayout* GridWindow::setupButtonRow() { QHBoxLayout *buttonRow = new QHBoxLayout(); // Creates horizontal box for buttons. buttonRow->setAlignment(Qt::AlignHCenter); // Clear Button - Clears cell; sets them all to DEAD/white. QPushButton *clearButton = new QPushButton("CLEAR"); clearButton->setFixedSize(100,25); connect(clearButton, SIGNAL(clicked()), this, SLOT(handlePause())); // Pauses timer before clearing. connect(clearButton, SIGNAL(clicked()), this, SLOT(handleClear())); // Connects to clear function to make all cells DEAD/white. buttonRow->addWidget(clearButton); // Forward Button - Steps one step forward. QPushButton *forwardButton = new QPushButton("FORWARD"); forwardButton->setFixedSize(100,25); connect(forwardButton, SIGNAL(clicked()), this, SLOT(handleForward())); // Signals to handleForward function.. buttonRow->addWidget(forwardButton); // Back Button - Steps one step backward. QPushButton *backButton = new QPushButton("BACK"); backButton->setFixedSize(100,25); connect(backButton, SIGNAL(clicked()), this, SLOT(handleBack())); // Signals to handleBack funciton. buttonRow->addWidget(backButton); // Start Button - Starts game when user clicks. Or, resumes game after being paused. QPushButton *startButton = new QPushButton("START/RESUME"); startButton->setFixedSize(100,25); connect(startButton, SIGNAL(clicked()), this, SLOT(handlePause())); // Deletes current timer if there is one. Then restarts everything. connect(startButton, SIGNAL(clicked()), this, SLOT(handleStart())); // Signals to handleStart function. buttonRow->addWidget(startButton); // Pause Button - Pauses simulation of game. QPushButton *pauseButton = new QPushButton("PAUSE"); pauseButton->setFixedSize(100,25); connect(pauseButton, SIGNAL(clicked()), this, SLOT(handlePause())); // Signals to pause function which pauses timer. buttonRow->addWidget(pauseButton); // Quit Button - Exits program. QPushButton *quitButton = new QPushButton("EXIT"); quitButton->setFixedSize(100,25); connect(quitButton, SIGNAL(clicked()), qApp, SLOT(quit())); // Signals the quit slot which ends the program. buttonRow->addWidget(quitButton); return buttonRow; // Returns bottom of layout. } /* SLOT method for handling clicks on the "clear" button. Receives "clicked" signals on the "Clear" button and sets all cells to DEAD. */ void GridWindow::handleClear() { for(unsigned int row=0; row < cells.size(); row++) // Loops through current rows' cells. { for(unsigned int col=0; col < cells[row].size(); col++) // Loops through the rows'columns' cells. { GridCell *cell = cells[row][col]; // Grab the current cell & set its value to dead. cell->setType(DEAD); } } } /* SLOT method for handling clicks on the "start" button. Receives "clicked" signals on the "start" button and begins game simulation. */ void GridWindow::handleStart() { isRunning = true; // It is running. Sets isRunning to true. this->timer = new QTimer(this); // Creates new timer. connect(this->timer, SIGNAL(timeout()), this, SLOT(timerFired())); // Connect "timerFired" method class to the "timeout" signal fired by the timer. this->timer->start(500); // Timer to fire every 500 milliseconds. } /* SLOT method for handling clicks on the "pause" button. Receives "clicked" signals on the "pause" button and stops the game simulation. */ void GridWindow::handlePause() { if(isRunning) // If it is running... this->timer->stop(); // Stops the timer. isRunning = false; // Set to false. } void GridWindow::handleForward() { if(isRunning); // If it's running, do nothing. else timerFired(); // It not running, step forward one step. } void GridWindow::handleBack() { std::vector<std::vector<GridCell*> > cells2; if(isRunning); // If it's running, do nothing. else if(backStack.empty()) cout << "EMPTYYY" << endl; else { cells2 = backStack.peek(); for (unsigned int f = 0; f < cells.size(); f++) // Loop through cells' rows. { for (unsigned int g = 0; g < cells.at(f).size(); g++) // Loop through cells columns. { cells[f][g]->setType(cells2[f][g]->getType()); // Set cells[f][g]'s type to cells2[f][g]'s type. } } cout << "PRE=POP" << endl; backStack.pop(); cout << "OYYYY" << endl; } } // Accessor method - Gets the 2D vector of grid cells. std::vector<std::vector<GridCell*> >& GridWindow::getCells() { return this->cells; } /* TimerFired function: 1) 2D-Vector cells2 is declared. 2) cells2 is initliazed with loops/push_backs so that all its cells are DEAD. 3) We loop through cells, and count the number of LIVE neighbors next to a given cell. --> Depending on how many cells are living, we choose if the cell should be LIVE or DEAD in the next simulation, according to the rules. -----> We save the cell type in cell2 at the same indice (the same row and column cell in cells2). 4) After check all the cells (and save the next round values in cells 2), we set cells's gridcells equal to cells2 gridcells. --> This causes the cells to be redrawn with cells2 types (white or black). */ void GridWindow::timerFired() { backStack.push(cells); std::vector<std::vector<GridCell*> > cells2; // Holds new values for 2D vector. These are the next simulation round of cell types. for(unsigned int i = 0; i < cells.size(); i++) // Loop through the rows of cells2. (Same size as cells' rows.) { vector<GridCell*> row; // Creates Gridcell* vector to push_back into cells2. cells2.push_back(row); // Pushes back row vectors into cells2. for(unsigned int j = 0; j < cells[i].size(); j++) // Loop through the columns (the cells in each row). { GridCell *cell = new GridCell(); // Creates new GridCell. cell->setType(DEAD); // Sets cell type to DEAD/white. cells2.at(i).push_back(cell); // Pushes back the DEAD cell into cells2. } // This makes a gridwindow the same size as cells with all DEAD cells. } for (unsigned int m = 0; m < cells.size(); m++) // Loop through cells' rows. { for (unsigned int n = 0; n < cells.at(m).size(); n++) // Loop through cells' columns. { unsigned int neighbors = 0; // Counter for number of LIVE neighbors for a given cell. // We know check all different variations of cells[i][j] to count the number of living neighbors for each cell. // We check m > 0 and/or n > 0 to make sure we don't access negative indexes (ex: cells[-1][0].) // We check m < size to make sure we don't try to access rows out of the vector (ex: row 5, if only 4 rows). // We check n < row size to make sure we don't access column item out of the vector (ex: 10th item in a column of only 9 items). // If we find that the Type = 1 (it is LIVE), then we add 1 to the neighbor. // Else - we add nothing to the neighbor counter. // Neighbor is the number of LIVE cells next to the current cell. if(m > 0 && n > 0) { if (cells[m-1][n-1]->getType() == 1) neighbors += 1; } if(m > 0) { if (cells[m-1][n]->getType() == 1) neighbors += 1; if(n < (cells.at(m).size() - 1)) { if (cells[m-1][n+1]->getType() == 1) neighbors += 1; } } if(n > 0) { if (cells[m][n-1]->getType() == 1) neighbors += 1; if(m < (cells.size() - 1)) { if (cells[m+1][n-1]->getType() == 1) neighbors += 1; } } if(n < (cells.at(m).size() - 1)) { if (cells[m][n+1]->getType() == 1) neighbors += 1; } if(m < (cells.size() - 1)) { if (cells[m+1][n]->getType() == 1) neighbors += 1; } if(m < (cells.size() - 1) && n < (cells.at(m).size() - 1)) { if (cells[m+1][n+1]->getType() == 1) neighbors += 1; } // Done checking number of neighbors for cells[m][n] // Now we change cells2 if it should switch in the next simulation step. // cells2 holds the values of what cells should be on the next iteration of the game. // We can't change cells right now, or it would through off our other cell values. // Apply game rules to cells: Create new, updated grid with the roundtwo vector. // Note - LIVE is 1; DEAD is 0. if (cells[m][n]->getType() == 1 && neighbors < 2) // If cell is LIVE and has less than 2 LIVE neighbors -> Set to DEAD. cells2[m][n]->setType(DEAD); else if (cells[m][n]->getType() == 1 && neighbors > 3) // If cell is LIVE and has more than 3 LIVE neighbors -> Set to DEAD. cells2[m][n]->setType(DEAD); else if (cells[m][n]->getType() == 1 && (neighbors == 2 || neighbors == 3)) // If cell is LIVE and has 2 or 3 LIVE neighbors -> Set to LIVE. cells2[m][n]->setType(LIVE); else if (cells[m][n]->getType() == 0 && neighbors == 3) // If cell is DEAD and has 3 LIVE neighbors -> Set to LIVE. cells2[m][n]->setType(LIVE); } } // Now we've gone through all of cells, and saved the new values in cells2. // Now we loop through cells and set all the cells' types to those of cells2. for (unsigned int f = 0; f < cells.size(); f++) // Loop through cells' rows. { for (unsigned int g = 0; g < cells.at(f).size(); g++) // Loop through cells columns. { cells[f][g]->setType(cells2[f][g]->getType()); // Set cells[f][g]'s type to cells2[f][g]'s type. } } } stack.h - Here's my stack. #ifndef STACK_H_ #define STACK_H_ #include <iostream> #include "node.h" template <typename T> class Stack { private: Node<T>* top; int listSize; public: Stack(); int size() const; bool empty() const; void push(const T& value); void pop(); T& peek() const; }; template <typename T> Stack<T>::Stack() : top(NULL) { listSize = 0; } template <typename T> int Stack<T>::size() const { return listSize; } template <typename T> bool Stack<T>::empty() const { if(listSize == 0) return true; else return false; } template <typename T> void Stack<T>::push(const T& value) { Node<T>* newOne = new Node<T>(value); newOne->next = top; top = newOne; listSize++; } template <typename T> void Stack<T>::pop() { Node<T>* oldT = top; top = top->next; delete oldT; listSize--; } template <typename T> T& Stack<T>::peek() const { return top->data; // Returns data in top item. } #endif gridcell.cpp - Gridcell implementation #include <iostream> #include "gridcell.h" using namespace std; // Constructor: Creates a grid cell. GridCell::GridCell(QWidget *parent) : QFrame(parent) { this->type = DEAD; // Default: Cell is DEAD (white). setFrameStyle(QFrame::Box); // Set the frame style. This is what gives each box its black border. this->button = new QPushButton(this); //Creates button that fills entirety of each grid cell. this->button->setSizePolicy(QSizePolicy::Expanding,QSizePolicy::Expanding); // Expands button to fill space. this->button->setMinimumSize(19,19); //width,height // Min height and width of button. QHBoxLayout *layout = new QHBoxLayout(); //Creates a simple layout to hold our button and add the button to it. layout->addWidget(this->button); setLayout(layout); layout->setStretchFactor(this->button,1); // Lets the buttons expand all the way to the edges of the current frame with no space leftover layout->setContentsMargins(0,0,0,0); layout->setSpacing(0); connect(this->button,SIGNAL(clicked()),this,SLOT(handleClick())); // Connects clicked signal with handleClick slot. redrawCell(); // Calls function to redraw (set new type for) the cell. } // Basic destructor. GridCell::~GridCell() { delete this->button; } // Accessor for the cell type. CellType GridCell::getType() const { return(this->type); } // Mutator for the cell type. Also has the side effect of causing the cell to be redrawn on the GUI. void GridCell::setType(CellType type) { this->type = type; redrawCell(); // Sets type and redraws cell. } // Handler slot for button clicks. This method is called whenever the user clicks on this cell in the grid. void GridCell::handleClick() { // When clicked on... if(this->type == DEAD) // If type is DEAD (white), change to LIVE (black). type = LIVE; else type = DEAD; // If type is LIVE (black), change to DEAD (white). setType(type); // Sets new type (color). setType Calls redrawCell() to recolor. } // Method to check cell type and return the color of that type. Qt::GlobalColor GridCell::getColorForCellType() { switch(this->type) { default: case DEAD: return Qt::white; case LIVE: return Qt::black; } } // Helper method. Forces current cell to be redrawn on the GUI. Called whenever the setType method is invoked. void GridCell::redrawCell() { Qt::GlobalColor gc = getColorForCellType(); //Find out what color this cell should be. this->button->setPalette(QPalette(gc,gc)); //Force the button in the cell to be the proper color. this->button->setAutoFillBackground(true); this->button->setFlat(true); //Force QT to NOT draw the borders on the button } Thanks a lot. Let me know if you need anything else.

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• Achieving forward compatibility with C++11

  - by mcmcc

  I work on a large software application that must run on several platforms. Some of these platforms support some features of C++11 (e.g. MSVS 2010) and some don't support any (e.g. GCC 4.3.x). I see this situation continuing on for several years (my best guess: 3-5 years). Given that, I would like set up a compatibility interface such that (to whatever degree possible) people can write C++11 code that will still compile with older compilers with a minimum of maintenance. Overall, the goal is to minimize #ifdef's as much as reasonably possible while still enabling basic C++11 syntax/features on the platforms that support them, and provide emulation on the platforms that don't. Let's start with std::move(). The most obvious way to achieve compatibility would be to put something like this in a common header file: #if !defined(HAS_STD_MOVE) namespace std { // C++11 emulation template <typename T> inline T& move(T& v) { return v; } template <typename T> inline const T& move(const T& v) { return v; } } #endif // !defined(HAS_STD_MOVE) This allow people to write things like std::vector<Thing> x = std::move(y); ... with impugnity. It does what they want in C++11 and it does the best it can in C++03. When we finally drop the last of the C++03 compilers, this code can remain as is. However, according to the standard, it is illegal to inject new symbols into the std namespace. That's the theory. My question is, practically speaking, is there any harm in doing this as a way of achieving forward compatibility?

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• How do I repair the corrupted files found by sfc /scannow? "Windows Resource Protection found corrupt files but was unable to fix some of them."

  - by galacticninja

  After running chkdsk C: /F /R and finding out that my hard disk has 24 KB in bad sectors (log is posted below), I decided to run Windows 7's System File Checker utility (sfc /scannow). SFC showed the ff. message after I ran it: "Windows Resource Protection found corrupt files but was unable to fix some of them. Details are included in the CBS.Log windir\Logs\CBS\CBS.log." Since the CBS.log file is too large, I ran findstr /c:"[SR]" %windir%\Logs\CBS\CBS.log >"%userprofile%\Desktop\sfcdetails.txt" (as per Microsoft's KB 928228 article) to only get the log text pertaining to the corrupt files. (log is also posted below) How do I troubleshoot and repair the corrupted files mentioned by sfc /scannow? My OS is Windows 7, 64-bit. chkdsk log Checking file system on C: The type of the file system is NTFS. A disk check has been scheduled. Windows will now check the disk. CHKDSK is verifying files (stage 1 of 5)... 936192 file records processed. File verification completed. 25238 large file records processed. 0 bad file records processed. 4 EA records processed. 44 reparse records processed. CHKDSK is verifying indexes (stage 2 of 5)... 1051640 index entries processed. Index verification completed. 0 unindexed files scanned. 0 unindexed files recovered. CHKDSK is verifying security descriptors (stage 3 of 5)... 936192 file SDs/SIDs processed. Cleaning up 24 unused index entries from index $SII of file 0x9. Cleaning up 24 unused index entries from index $SDH of file 0x9. Cleaning up 24 unused security descriptors. Security descriptor verification completed. 57725 data files processed. CHKDSK is verifying Usn Journal... 36994248 USN bytes processed. Usn Journal verification completed. CHKDSK is verifying file data (stage 4 of 5)... 936176 files processed. File data verification completed. CHKDSK is verifying free space (stage 5 of 5)... 306238 free clusters processed. Free space verification is complete. Adding 1 bad clusters to the Bad Clusters File. Correcting errors in the Volume Bitmap. Windows has made corrections to the file system. 488282111 KB total disk space. 485595420 KB in 766458 files. 401856 KB in 57726 indexes. 24 KB in bad sectors. 1059863 KB in use by the system. 65536 KB occupied by the log file. 1224948 KB available on disk. 4096 bytes in each allocation unit. 122070527 total allocation units on disk. 306237 allocation units available on disk. Internal Info: 00 49 0e 00 81 93 0c 00 34 01 17 00 00 00 00 00 .I......4....... 6b 29 00 00 2c 00 00 00 00 00 00 00 00 00 00 00 k)..,........... 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ sfc /scannow log (through findstr /c:"[SR]" %windir%\Logs\CBS\CBS.log >"%userprofile%\Desktop\sfcdetails.txt") Note: The full log is at http://pastebin.com/raw.php?i=gTEGZmWj . I've only quoted parts of the full log below (mostly from the last part), as the full log won't fit within the character limit for questions. I've added it to serve as a preview. ... 2013-12-28 19:37:50, Info CSI00000542 [SR] Beginning Verify and Repair transaction 2013-12-28 19:37:55, Info CSI00000544 [SR] Verify complete 2013-12-28 19:37:56, Info CSI00000545 [SR] Verifying 95 (0x000000000000005f) components 2013-12-28 19:37:56, Info CSI00000546 [SR] Beginning Verify and Repair transaction 2013-12-28 19:38:03, Info CSI00000548 [SR] Verify complete 2013-12-28 19:38:03, Info CSI00000549 [SR] Repairing 43 (0x000000000000002b) components 2013-12-28 19:38:03, Info CSI0000054a [SR] Beginning Verify and Repair transaction ... 2013-12-28 19:38:15, Info CSI00000730 [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:62{31}]"GroupPolicy-Admin-Gpedit-DL.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI00000733 [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:30{15}]"frs-core-DL.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI00000736 [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:26{13}]"gpmgmt-DL.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI00000739 [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:74{37}]"MediaServer-ASPAdmin-Migration-DL.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI0000073c [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:36{18}]"Ldap-Client-DL.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI0000073f [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:38{19}]"iSNS_Service-DL.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI00000742 [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:76{38}]"MediaServer-Multicast-Migration-DL.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI00000745 [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:78{39}]"Kerberos-Key-Distribution-Center-DL.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI00000748 [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:86{43}]"GroupPolicy-CSE-SoftwareInstallation-DL.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI0000074b [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:28{14}]"ieframe-dl.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI0000074e [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:76{38}]"GroupPolicy-Admin-Gpedit-Snapin-DL.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI00000751 [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:32{16}]"IPSec-Svc-DL.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI00000754 [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:22{11}]"HTTP-DL.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI00000757 [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:56{28}]"MediaServer-Migration-DL.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI0000075a [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:26{13}]"GPBase-DL.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI0000075d [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:38{19}]"IasMigPlugin-DL.man"; source file in store is also corrupted 2013-12-28 19:38:15, Info CSI00000760 [SR] Could not reproject corrupted file [ml:520{260},l:84{42}]"\??\C:\Windows\System32\migwiz\dlmanifests"\[l:50{25}]"International-Core-DL.man"; source file in store is also corrupted 2013-12-28 19:38:16, Info CSI00000762 [SR] Cannot repair member file [l:24{12}]"wbemdisp.dll" of Microsoft-Windows-WMI-Scripting, Version = 6.1.7600.16385, pA = PROCESSOR_ARCHITECTURE_INTEL (0), Culture neutral, VersionScope = 1 nonSxS, PublicKeyToken = {l:8 b:31bf3856ad364e35}, Type neutral, TypeName neutral, PublicKey neutral in the store, hash mismatch 2013-12-28 19:38:16, Info CSI00000763 [SR] This component was referenced by [l:202{101}]"Microsoft-Windows-Foundation-Package~31bf3856ad364e35~amd64~~6.1.7601.17514.WindowsFoundationDelivery" 2013-12-28 19:38:16, Info CSI00000766 [SR] Could not reproject corrupted file [ml:58{29},l:56{28}]"\??\C:\Windows\SysWOW64\wbem"\[l:24{12}]"wbemdisp.dll"; source file in store is also corrupted 2013-12-28 19:38:16, Info CSI00000768 [SR] Cannot repair member file [l:56{28}]"Microsoft.MediaCenter.UI.dll" of Microsoft.MediaCenter.UI, Version = 6.1.7601.17514, pA = PROCESSOR_ARCHITECTURE_MSIL (8), Culture neutral, VersionScope = 1 nonSxS, PublicKeyToken = {l:8 b:31bf3856ad364e35}, Type neutral, TypeName neutral, PublicKey neutral in the store, hash mismatch 2013-12-28 19:38:16, Info CSI00000769 [SR] This component was referenced by [l:176{88}]"Microsoft-Windows-MediaCenter-Package~31bf3856ad364e35~amd64~~6.1.7601.17514.MediaCenter" 2013-12-28 19:38:16, Info CSI0000076c [SR] Could not reproject corrupted file [ml:520{260},l:40{20}]"\??\C:\Windows\ehome"\[l:56{28}]"Microsoft.MediaCenter.UI.dll"; source file in store is also corrupted 2013-12-28 19:38:16, Info CSI0000076e [SR] Cannot repair member file [l:24{12}]"ReAgentc.exe" of Microsoft-Windows-WinRE-RecoveryTools, Version = 6.1.7601.17514, pA = PROCESSOR_ARCHITECTURE_INTEL (0), Culture neutral, VersionScope = 1 nonSxS, PublicKeyToken = {l:8 b:31bf3856ad364e35}, Type neutral, TypeName neutral, PublicKey neutral in the store, hash mismatch 2013-12-28 19:38:16, Info CSI0000076f [SR] This component was referenced by [l:202{101}]"Microsoft-Windows-Foundation-Package~31bf3856ad364e35~amd64~~6.1.7601.17514.WindowsFoundationDelivery" 2013-12-28 19:38:16, Info CSI00000772 [SR] Could not reproject corrupted file [ml:48{24},l:46{23}]"\??\C:\Windows\SysWOW64"\[l:24{12}]"ReAgentc.exe"; source file in store is also corrupted 2013-12-28 19:38:16, Info CSI00000774 [SR] Cannot repair member file [l:82{41}]"System.Management.Automation.dll-Help.xml" of Microsoft-Windows-PowerShell-PreLoc.Resources, Version = 6.1.7600.16385, pA = PROCESSOR_ARCHITECTURE_AMD64 (9), Culture = [l:10{5}]"en-US", VersionScope = 1 nonSxS, PublicKeyToken = {l:8 b:31bf3856ad364e35}, Type neutral, TypeName neutral, PublicKey neutral in the store, hash mismatch 2013-12-28 19:38:16, Info CSI00000775 [SR] This component was referenced by [l:266{133}]"Microsoft-Windows-Client-Features-Package~31bf3856ad364e35~amd64~en-US~6.1.7601.17514.Microsoft-Windows-Client-Features-Language-Pack" 2013-12-28 19:38:16, Info CSI00000778 [SR] Could not reproject corrupted file [ml:520{260},l:104{52}]"\??\C:\Windows\System32\WindowsPowerShell\v1.0\en-US"\[l:82{41}]"System.Management.Automation.dll-Help.xml"; source file in store is also corrupted 2013-12-28 19:38:16, Info CSI0000077a [SR] Cannot repair member file [l:18{9}]"hlink.dll" of Microsoft-Windows-HLink, Version = 6.1.7600.16385, pA = PROCESSOR_ARCHITECTURE_INTEL (0), Culture neutral, VersionScope = 1 nonSxS, PublicKeyToken = {l:8 b:31bf3856ad364e35}, Type neutral, TypeName neutral, PublicKey neutral in the store, hash mismatch 2013-12-28 19:38:16, Info CSI0000077b [SR] This component was referenced by [l:202{101}]"Microsoft-Windows-Foundation-Package~31bf3856ad364e35~amd64~~6.1.7601.17514.WindowsFoundationDelivery" 2013-12-28 19:38:16, Info CSI0000077e [SR] Could not reproject corrupted file [ml:48{24},l:46{23}]"\??\C:\Windows\SysWOW64"\[l:18{9}]"hlink.dll"; source file in store is also corrupted 2013-12-28 19:38:16, Info CSI00000780 [SR] Repair complete 2013-12-28 19:38:16, Info CSI00000781 [SR] Committing transaction 2013-12-28 19:38:19, Info CSI00000785 [SR] Verify and Repair Transaction completed. All files and registry keys listed in this transaction have been successfully repaired

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• which style of member-access is preferable

  - by itwasntpete

  the purpose of oop using classes is to encapsulate members from the outer space. i always read that accessing members should be done by methods. for example: template<typename T> class foo_1 { T state_; public: // following below }; the most common doing that by my professor was to have a get and set method. // variant 1 T const& getState() { return state_; } void setState(T const& v) { state_ = v; } or like this: // variant 2 // in my opinion it is easier to read T const& state() { return state_; } void state(T const& v) { state_ = v; } assume the state_ is a variable, which is checked periodically and there is no need to ensure the value (state) is consistent. Is there any disadvantage of accessing the state by reference? for example: // variant 3 // do it by reference T& state() { return state_; } or even directly, if I declare the variable as public. template<typename T> class foo { public: // variant 4 T state; }; In variant 4 I could even ensure consistence by using c++11 atomic. So my question is, which one should I prefer?, Is there any coding standard which would decline one of these pattern? for some code see here

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• WCF - Automatically create ServiceHost for multiple services

  - by Rajesh Pillai

  WCF - Automatically create ServiceHost for multiple services Welcome back readers!  This blog post is about a small tip that may make working with WCF servicehost a bit easier, if you have lots of services and you need to quickly host them for testing. Recently I was encountered a situation where we were faced to create multiple service host quickly for testing.  Here is the code snippet which is pretty self explanatory.  You can put this code in your service host which in this case is  a console application. class Program   {       static void Main(string[] args)       { // Stores all hosts           List<ServiceHost> hosts = new List<ServiceHost>();           try           { // Get the services element from the serviceModel element in the config file               var section = ConfigurationManager.GetSection("system.serviceModel/services") as ServicesSection;               if (section != null)               {                   foreach (ServiceElement element in section.Services)                   { // NOTE : If the assembly is in another namespace, provide a fully qualified name here in the form // <typename, namespace> // For e.g. Business.Services.CustomerService, Business.Services                       var serviceType = Type.GetType(element.Name); // Get the typeName                        var host = new ServiceHost(serviceType);                       hosts.Add(host); // Add to the host collection                       host.Open(); // Open the host                   }               }               Console.ReadLine();           }           catch (Exception e)           {               Console.WriteLine(e.Message);               Console.ReadLine();           }           finally           {               foreach (ServiceHost host in hosts)               {                   if (host.State == CommunicationState.Opened)                   {                       host.Close();                   }                   else                   {                       host.Abort();                   }               }           }       }   } I hope you find this useful.  You can make this as a windows service if required.

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• what's the difference between Routed Events and Attached Events?

  - by vverma01

  I tried to find through various sources but still unable to understand difference between routed events and attached events in WPF. Most of the places of reference for attached event following example is used: <StackPanel Button.Click="StackPanel_Click"> <Button Content="Click Me!" Height="35" Width="150" Margin="5" /> </StackPanel> Explained as: stack panel do not contain Click event and hence Button.Click event is attached to Stack Panel. Where as msdn says: You can also name any event from any object that is accessible through the default namespace by using a typename.event partially qualified name; this syntax supports attaching handlers for routed events where the handler is intended to handle events routing from child elements, but the parent element does not also have that event in its members table. This syntax resembles an attached event syntax, but the event here is not a true attached event. Instead, you are referencing an event with a qualified name. According to MSDN information as pasted above, the above example of Buttons and StackPanel is actually a routed event example and not true attached event example. In case if above example is truly about usage of attached event (Button.Click="StackPanel_Click") then it's in contradiction to the information as provided at MSDN which says Another syntax usage that resembles typename.eventname attached event syntax but is not strictly speaking an attached event usage is when you attach handlers for routed events that are raised by child elements. You attach the handlers to a common parent, to take advantage of event routing, even though the common parent might not have the relevant routed event as a member. A similar question was raised in this Stack Overflow post, but unfortunately this question was closed before it could collect any response. Please help me to understand how attached events are different from routed events and also clarify the ambiguity as pointed above.

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• C++ function templates, function name confusion. This is funny [migrated]

  - by nashmaniac

  Alright so heres the program and works absolutely right #include <iostream> using namespace std; template <typename T> void Swap(T &a , T &b); int main(){ int i = 10; int j = 20; cout<<"i, j = " << i <<" , " <<j<<endl; Swap(i,j); cout<<"i, j = " << i <<" , " <<j<<endl; } template <typename T> void Swap(T &a , T &b){ T temp; temp = a ; a = b; b= temp; } but when I change the function's name from Swap to swap it generates an error saying error: call of overloaded 'swap(int&, int&)' is ambiguous| note: candidates are: void swap(T&, T&) [with T = int]| ||=== Build finished: 1 errors, 0 warnings ===| what happened is it a rule to start functions using templates to start with a capital letter ?

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