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  • C++: static function member shared between threads, can block all?

    - by mhambra
    Hi all, I have a class, which has static function defined to work with C-style extern C { static void callback(foo bar) { } }. // static is defined in header. Three objects (each in separate pthread) are instantiated from this class, each of them has own loop (in class constructor), which can receive the callback. The pointer to function is passed as: x = init_function(h, queue_id, &callback, NULL); while(1) { loop_function(x); } So each thread has the same pointer to &callback. Callback function can block for minutes. Each thread object, excluding the one which got the blocking callback, can call callback again. If the callback function exists only once, then any thread attempting to callback will also block. This would give me an undesired bug, circa is interesting to ask: can anything in C++ become acting this way? Maybe, due to extern { } or some pointer usage?

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  • Using pipes inside a class in C++

    - by Paul
    I'm trying to use this tutorial to make plots with Gnuplot in C++. However I will be using the pipe to Gnuplot from within a class, but then I run into some problems: I've got a header file where I declare all variables etc. I need to declare the pipe-variable here too, but how do I do that? I've tried doing it straight away, but it doesn't work: Logger.h: class Logger { FILE pipe; } Logger.cpp: Logger::Logger() { //Constructor *pipe = popen("gnuplot -persist","w"); } Gives the error Logger.cpp:28: error: no match for ‘operator=’ in ‘*((Logger*)this)->Logger::pipe = popen(((const char*)"gnuplot -persist"), ((const char*)"w"))’ Suggestions?

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  • Why is there "data" and "newtype" in Haskell?

    - by martingw
    To me it seems that a newtype definition is just a data definition that obeys some restrictions (only one constructor and such), and that due to these restrictions the runtime system can handle newtypes more efficiently. Ok, and the handling of pattern matching for undefined values is slightly different. But suppose Haskell would only knew data definitions, no newtypes: Couldn't the compiler find out for himself whether a given data definition obeys these restrictions, and automatically treat it more efficiently? I'm sure I'm missing out on something, these Haskell designers are so clever, there must be some deeper reason for this...

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  • Question About NerdDinner Controller Constructors

    - by Gavin Draper
    I've been looking at the Nerd Dinner app, more specifically how it handles its unit tests. The following constructors for the RSVPController are confusing my slightly public RSVPController() : this(new DinnerRepository()) { } public RSVPController(IDinnerRepository repository) { dinnerRepository = repository; } From what I can tell the second one is used by the unit tests so it can use Fake repositories. What I cant work out is what the first constructor does. It doesn't seem to ever set the dinnerRepository variable, it seems to imply its inheriting from something but I really don't get it. Can anyone explain? Thanks

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  • Explicitly persist states in Workflow 4.0 rather than everything.

    - by jlafay
    I have ran into an issue with my SQL instance store attached to a WorkflowApplication that is running. When I exit my application I'm calling an Unload() on the WF app to persist it. I didn't think about it during design time, but it does makes sense, it's persisting an arg that was passed in to the WorkflowApplication constructor when instanced. When the application runs, everything in the workflow works as expected. When I call Unload() I get an unhandled exception that states that the arg is not serializable and needs [DataContractAttribute]. What's passed into the workflow is my applications custom logger object that I wrote so that the WF can log to disk in a uniform way that I prefer. How do I prevent the workflow app from persisting this one argument and persist everything else? I'm sure something can be done with extensions but I'm having a hard time finding info on them or finding persistence examples for my scenario.

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  • Change a registry value in vb.net

    - by mhofer
    Hello, I have searched a lot to find a solution for my problem, but I can't find any specific solution. I need to change a value which is stored under HKEY_LOCAL_MACHINE\SOFTWARE\APP_NAME. It is not possible to use .NET's registry functions, since they have drastic restrictions. The following snippet should solve my problem: Dim regKey As RegistryKey Dim ver As Decimal regKey = My.Computer.Registry.LocalMachine.OpenSubKey("HKEY_LOCAL_MACHINE\SOFTWARE\APP_NAME", True) regKey.SetValue("IP", "192.168.10.15:18500") regKey.Close() Unfortunately, I get a NullReferenceExeption when I try to set the value. What should I do? I have imported Microsoft.Win32 and RegistryKey doesn't accept any constructor... cheers mike

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  • Cant append "used" DOMObject in IE

    - by Kein
    I have some objects, that keep created DOMObjects, like here: function category(){ var domBlock; this.block = function(){ if (!domBlock){ // Here dom-object constructor $('<div></div>'); etc } return domBlock; // jquery object, // but i test and native document.createElement } } Then i clear category's area, and append old and new received(with Ajax) objects: area.html(''); for(id in category_list){ area.append( category_list[id].block() ); } where category_list is list that contain category objects. Area is jQuery object. In other browsers (except IE) i get area with all needed categories, but in IE i get only new received categories(that just create DomObject), other old objects that keeped old DomObject not show. I know it possible make with innerHTML, but i wont keep DomObject, not text. Because DomObject keep many events. And it very hard for browser attach events for each DomObject after refresh area.

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  • How do I create static instances of a class inside that class?

    - by wehas
    I have a class Color that holds values for the red, green, and blue channels of a color. The class constructor lets you create a new color by specifying values for the three channels. However, for convenience, I would also like to have some "premade" colors available for the programmer. For example instead of having something like DrawRectangle(new Color(1, 0, 0)); you would be able to say DrawRectangle(Color.Red); Where Color.Red is an instance of Color that lives inside the Color class. How can I declare these instances of Color inside the Color class? If there is a name for this type of technique I'd like to know it as I had no idea what search terms to use when I was looking for help online.

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  • WPF UserControl event called only once?

    - by 742
    Hi Everyone, I need to bind two-way a property of a user control to a property of a containing user control. I also need to set a default value to the property from code in the child (cannot be done easily from XAML tags). If I call my code from the child constructor, the value is set in the parent but the change callback routine is not triggered (my understanding is that the parent doesn't yet exist at the time the child is created). My current workaround is to catch the Loaded event of the child and to call the code from the handler. Howver as Loaded is called more than once, I need to set a flag to set the property only the first time. I don't like this way, but I don't know if there is a single shot event that could be used, or if this can be done otherwise. Any feedback based on your experience?

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  • Bring Control to ToolBox

    - by Mohanavel
    I created a TextBoxControl which is inherited from Infragistics.Win.UltraWinEditors.UltraTextEditor, an Infragistics control. As showed below. public class TextBoxControl : Infragistics.Win.UltraWinEditors.UltraTextEditor { //My Stuff } At some level Infragistics.Win.UltraWinEditors.UltraTextEditor class also inherited from WinForm's "Control" class. My problem is, this control is not appearing in the ToolBox. I done two steps 1. Choose from browse option and select the dll where the class present 2. Drag and drop the dll directly to the ToolBox In-fact both are same, TextBoxControl control is not appearing in the ToolBox, what i missing here. Edit : TextBoxControl class have empty constructor, nothing special in this class.

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  • Quickest way to clone a GregorianCalendar?

    - by wds
    I'm trying to make a deep copy of an object, including a GregorianCalendar instance. I'm always wary of using clone() and it doesn't seem to have been overridden here, so I'm just doing the copy field by field. Ideally, there'd be a copy constructor, which I could use like so: GregorianCalendar newCalendar = new GregorianCalendar(oldCalendar); Unfortunately I can't find any such functionality in the API and am stuck trying to figure out which fields I need to get an exact copy. So, to make a copy of one of these calendars, how would you do it? Am I missing some simple shortcut here?

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  • [Qt] How to make another window pop up that extends QWidget as opposed to QDialog?

    - by Graphics Noob
    So far I've only had my main window pop up other windows that were QDialogs and I'm not getting it to work with a QWidget. The other window I want to display was designed with the Form Editor, then wrapped in a class called ResultViewer which extends QWidget (as opposed to QDialog). What I want is to have the ResultViewer show its ui in a seperate window. Now when I try to display it the ResultViewer ui just pops up in the main window on top of the mainwindow ui. The code I'm using to display it is this (in my mainwindow.cpp file) ResultViewer * rv = new ResultView(this); rv->show(); The constructor for the ResultViewer looks like this ResultViewer::ResultViewer(QWidget * parent) : QWidget(parent), ui(new Ui::ResultViewer) { ui->setupUi(this); } I've looked through the QWidget documentation a bit but the only thing I can find that may be related is the QWidget::window() function, but the explanation isn't very clear, it just gives an example of changing the title of a window.

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  • c++ Array passing dilemma

    - by Thomas
    Hi, I am writing a function that takes a string, string pointer and an int. The function splits the string based on a set of rules and puts each token into an array. I need to return the array out of the function with the number of elements in the int variable etc. I am stuck as to how I return the array as I can not use auto other wise it is destroyed and I am reluctant to use new as I feel this is patchy. I have other ideas on how to go about this but would like to see how other people go about this first. I could also be wrong and it could be possible to pass an auto out of an array. I can also not use vectors so there goes a copy constructor.

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  • Instantiate a javascript module only one time.

    - by Cedric Dugas
    Hey guys, I follow a module pattern where I instantiate components, however, a lot of time a component will only be instantiate one time (example: a comment system for an article). For now I instantiate in the same JS file. but I was wondering if it is the wrong approach? It kind of make no sense to instantiate in the same file and always only once. But at the same time, if this file is in the page I want to have access to my module without instantiate from elsewhere, and IF I need another instance, I just create another from elsewhere... Here is the pattern I follow: ApplicationNamespace.Classname = function() { // constructor function privateFunctionInit() { // private } this.privilegedFunction = function() { // privileged privateFunction(); }; privateFunctionInit() }; ApplicationNamespace.Classname.prototype = { Method: function(){} } var class = new ApplicationNamespace.Classname(); What do you think, wrong approach, or is this good?

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  • Can I use MFC objects in STL containers?

    - by Jesse Stimpson
    The following code doesn't compile for me in MSVC2005: std::vector<CMenu> vec(10); CMenu is an MFC menu object (such as a context menu). Through some testing I learned that CMenu does not have a public copy constructor. To do what I wanted to do, I needed to use a dynamic array. CMenu* menus = new CMenu[10]; // ... delete [] menus; Of course, now I've lost all the benefits of using an STL container. Do I have any other options?

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  • How to order my objects in a C++ class correctly

    - by Julen
    Hello, I have been coding regurlarly in C++ in the past months. I am getting used to it step by step... but there are things that confuse me about formatting. I know there is a lot of legacy from C that I supousee mixes with C++. This time I have doubts about how to order properly my members and functions within in a class. Also considering their access modifiers. How is the convention in this? Until know I am doing everything "public" and writing first constructor of class, then destructor, next members and finally functions. It this correct? What happens when introducing "private" and "protected" access modifiers or "virtual" functions? From the documents I have look in the Internet there is different ways of doing things. But my questions aims to get the knowledge from a community that develops in C++ that I want to blend into. ;-) Thanks a lot!!!

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  • are Hierarchical SIngletons in Java possible?

    - by Zach H
    I've been toying with an interesting idea (No idea if I'll include it in any code, but it's fun to think about) Let's say we have a program that requires a large number of classes, all of a certain subclass. And those classes all need to be singletons. Now, we could write the singleton pattern for each of those classes, but it seems wasteful to write the same code over and over, and we already have a common base class. It would be really nice to create a getSingleton method of A that when called from a subclass, returns a singleton of the B class (cast to class A for simplicity) class A{ public A getSingleton(){ //Wizardry } } class B extends A{ } A blargh = B.getSingleton() A gish = B.getSingleton() if(A == B) System.out.println("It works!") It seems to me that the way to do this would be to recognize and call B's default constructor (assuming we don't need to pass anything in.) I know a little of the black magic of reflection in Java, but i'm not sure if this can be done. Anyone interested in puzzling over this?

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  • Is this a valid, lazy, thread-safe Singleton implementation for C#?

    - by Matthew
    I implemented a Singleton pattern like this: public sealed class MyClass { ... public static MyClass Instance { get { return SingletonHolder.instance; } } ... static class SingletonHolder { public static MyClass instance = new MyClass (); } } From Googling around for C# Singleton implementations, it doesn't seem like this is a common way to do things in C#. I found one similar implementation, but the SingletonHolder class wasn't static, and included an explicit (empty) static constructor. Is this a valid, lazy, thread-safe way to implement the Singleton pattern? Or is there something I'm missing?

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  • C++ performance, optimizing compiler, empty function in .cpp

    - by Dodo
    I've a very basic class, name it Basic, used in nearly all other files in a bigger project. In some cases, there needs to be debug output, but in release mode, this should not be enabled and be a NOOP. Currently there is a define in the header, which switches a makro on or off, depending on the setting. So this is definetely a NOOP, when switched off. I'm wondering, if I have the following code, if a compiler (MSVS / gcc) is able to optimize out the function call, so that it is again a NOOP. (By doing that, the switch could be in the .cpp and switching will be much faster, compile/link time wise). --Header-- void printDebug(const Basic* p); class Basic { Basic() { simpleSetupCode; // this should be a NOOP in release, // but constructor could be inlined printDebug(this); } }; --Source-- // PRINT_DEBUG defined somewhere else or here #if PRINT_DEBUG void printDebug(const Basic* p) { // Lengthy debug print } #else void printDebug(const Basic* p) {} #endif

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  • Syncing JS+PHP time

    - by meder
    Since the Date constructor is based on your PC's timezone and server-side is obviously dependent on the server's time settings... What procedures can I do to ensure that the timestamps I generate are consistent on both ends? I have a jQuery datepicker setup and I do a lot of work, I also have my own datepicker that's generated from server-side code which looks up db availability for bookings. I'm saving arrival/departure times on the server-side and the days are off by one because the JS is local timezone ( mine is Eastern ) . Is my only option doing something like making the JS call PHP to grab a timestamp?

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  • Call an AsyncTask inside a Thread

    - by Arun
    I am working in an android application and I want to call an AsyncTask from my UI main thread. For that I want to call my AsyncTask from a thread. This is the method that I call from my main UI thread. This is working correctly CommonAysnk mobjCommonAysnk = new CommonAysnk(this, 1); mobjCommonAysnk.execute(); CommonAysnk is my AsyncTask class.I want to pass my activity and an integer parameter to the AsyncTask constructor. How can I call this from a thread as shown below method. Thread t = new Thread() { public void run() { try { CommonAysnk mobjCommonAysnk = new CommonAysnk(this, 1); mobjCommonAysnk.execute(); } catch (Exception ex) { }}}; t.start(); When I tried to call it from a Thread and I am not able to pass the activity parameter correctly. How can we sole this. Thanks

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  • How do I obtain an HtmlHelper<TModel> instance for a model in ASP.NET MVC?

    - by DanM
    Let's say I have an Index view. The model I pass in is actually a collection of models, so the Html property is of type HtmlHelper<List<MyModel>>. If I want to call extension methods (e.g., Display() or DisplayFor() on the individual items in the list, however, I think I need to obtain an HtmlHelper<MyModel>. But how? I tried using the HtmlHelper<TModel> constructor, which looks like this: HtmlHelper<TModel>(ViewContext, IViewDataContainer) But I'm not having any luck with that. I don't know how to obtain the IViewDataContainer for the item, and the documentation on these things is very sparse. A lot of magic apparently happens when I do... return View(List<MyModel>); ...in my controller. How do I recreate that magic on individual items in a list/collection?

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  • Do I really have to call Focus in OnMouseDown of my custom Control?

    - by Thomas
    I'm implementing a custom control that inherits from Control. I want it to be focusable (it's a kind of list box). In the constructor, I do SetStyle(ControlStyles.Selectable, true); I can now use Tab to navigate to the control. However, when the control receives a mouse click, it does not automatically claim focus. I can work around this, of course: protected override void OnMouseDown(MouseEventArgs e) { Focus(); base.OnMouseDown(e); } But this feels like a kludge that should not be necessary. Is this really the way to go? Or is there some way to tell Control to claim focus automatically when it receives a mouse click?

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  • contain new elements of an "instance" in javascript

    - by iamnotmad
    Hi, so I know there are tons of ways to simulate inheritance and other OO features. I have chosen one to use for my project and am wondering if I can create an instance and add stuff to it and keep it contained (within braces). Consider the following: function BaseClass(){ <this.stuff here> } function SubClass(){ this.superClass = BaseClass(); this.superClass(); <this.other stuff here> } myObj = new SubClass(); so myObj is an instance of SubClass. I can add things to myObj like: myObj.blah = "funtimes"; What I would like is to be able to add stuff to the "instance" and keep it organized in braces much like the constructor. psuedo code like: myObj = new SubClass() { var blah = "funtimes" <more instance specific stuff here> } Is something like this possible? Thanks!

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  • Circle class in java

    - by user292395
    I need to get the Java code for the below problem asap. Create a class Circle that will allow us to define a circle with a specific radius. Your class should include the following methods: A constructor that can create a circle with a specified radius. A method setRadius that sets a specific value as a new radius for an existing circle. A method getRadius that returns the radius of an existing circle. A method toString that returns a String with all the information about an existing circle. A method computeArea that computes the area of a circle A method computePerimeter that computes the perimeter of a circle.

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