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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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• 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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• C++ enum casting and templates

  - by JP

  I get the following error with VS2008: Conversion to enumeration type requires an explicit cast (static_cast, C-style cast or function-style cast) When casting a down casting a ClassA to ClassA_1 and ClassA_1 is a templated class that received an enum for parameter such as: ClassA { virtual ~ClassA(){}; } template <class Param1> ClassA_1 : public ClassA { public: //constructor ClassA_1(Param1 p1) { _p1 = p1; } Param1 _p1; } So I have a upcasted ClassA a = new ClassA_1<myenum>(); When I need to do this: ClassA_1<myenum> a1 = (ClassA_1<myenum> a); // This fails ... The only way it works is: ClassA_1<int> a1 = (ClassA_1<int> a); but this break my template as it must always deal with int... How to properly cast a enum that is now a int, back into the enum?

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• Why does coffeescript generate classes like this?

  - by ryeguy

  Given the following coffeescript code: class Animal constructor: (@name) -> speak: (things) -> "My name is #{@name} and I like #{things}" This is generated: var Animal = (function() { function Animal(name) { this.name = name; } Animal.prototype.speak = function(things) { return "My name is " + this.name + " and I like " + things; }; return Animal; })(); But why isn't this more idiomatic code generated? var Animal = function Animal(name) { this.name = name; }; Animal.prototype.speak = function(things) { return "My name is " + this.name + " and I like " + things; }; I know that coffeescript wraps a lot of stuff in anonymous functions to control scope leak, but what could leak here?

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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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• Communication between Multiple Threads in a WPF Application

  - by Robert

  I'm creating a WPF application that uses a custom object to populate all the controls. The constructor of that object is initiated by an EventHandler that waits for an API. The problem I'm having is when I try to access any information from that object using a button for example, it returns an error saying "The calling thread cannot access this object because a different thread owns it". I'm assuming this is because the EventHandler creates a new thread which doesn't allow the Main Thread to have access to it. Any ideas on how to get around this? I'm basically having the error "The calling thread cannot access this object because a different thread owns it" when trying to get or set a CollectionViewSource.

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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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• Copy method optimization in compilers

  - by Dženan

  Hi All! I have the following code: void Stack::operator =(Stack &rhs) { //do the actual copying } Stack::Stack(Stack &rhs) //copy-constructor { top=NULL; //initialize this as an empty stack (which it is) *this=rhs; //invoke assignment operator } Stack& Stack::CopyStack() { return *this; //this statement will invoke copy contructor } It is being used like this: unsigned Stack::count() { unsigned c=0; Stack copy=CopyStack(); while (!copy.empty()) { copy.pop(); c++; } return c; } Removing reference symbol from declaration of CopyStack (returning a copy instead of reference) makes no difference in visual studio 2008 (with respect to number of times copying is invoked). I guess it gets optimized away - normally it should first make a copy for the return value, then call assignment operator once more to assign it to variable sc. What is your experience with this sort of optimization in different compilers? Regards, Dženan

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• MVC Pages that require the user to be logged in

  - by keithjgrant

  I'm working on a little MVC framework and I'm wondering what the "best way" is to structure things so secure pages/controllers always ensure the user is logged in (and thus automatically redirects to a login page--or elsewhere--if not). Obviously, there are a lot of ways to do it, but I'm wondering what solution(s) are the most common or are considered the best practice. Some ideas I had: Explicitly call user->isLoggedIn() at the beginning of your controller action method? (Seems far too easy to forget and leave an important page unsecure on accident) Make your controller extend a secureController that always checks for login in the constructor? Do this check in the model when secure information is requested? (Seems like redundant calls would be made) Something else entirely? Note: I'm working in PHP, though the question is not language-dependent.

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• Real-world examples of populating a GWT CellTable using a clean MVP pattern?

  - by piehole

  We are using the GWT-Presenter framework and attempting to use CellTable to put together an updateable grid. It seems as though several of the GWT constructs for CellTable don't lend themselves to easily breaking up the logic into clean view and presenter code. Examples: 1) Within the View's constructor, the CellTable is defined and each column is created by anonymous inner classes that extend the Column class to provide the onValue() method. 2) The FieldUpdater interface must be implemented to provide logic to execute when a user alters data in a cell. This seems like it would best fit in the Presenter's onBind() method, but FieldUpdaters often need access to the Cell or Column which belong in the view. CellTable does not have accessor methods to get hold of the Columns or Cells, so it seems the only way for the Presenter to get them is for me to create a multitude of member variables on the View and accessors on my Display interface. Can anyone provide good examples for dealing with CellTable in GWT-Presenter or a comparable MVP

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• Java - Confused by the one class per file rule

  - by Mark

  The one class per file rule in Java has me a bit confused. I writing an Android app and trying to implement the accepted answer to this question: Common class for AsyncTask in Android? which calls for an interface definition which class A implements and class B accepts as an argument to its constructor. So I need an A.java and a B.java, but where does the interface go? Does it need a separate java file itself? Do I have to define it inside both A and B? If not how to import it? Also I will have about 10 different AsyncTask classes, but I don't want to bother creating a new file for each one. What would you recommend? Is there a way to put all 10 classes in one file? Or should I create a big if/then block inside the class and pass an argument telling it which of the 10 different tasks I want it to do?

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• WPF Prism deactivate ?

  - by 2Fast4YouBR

  Hi all, I have an problem and would like to know if it is common problem or jsut with me. I am using Wpf with Prism and Unity, all with the pattern MvvM. I am loading a viewModel that has a reference to a dropdown with few items, my idea is that each time that the user click in some place to open the view that has this dropdown is that the dropdown will be shown with diferent values. The problem is that I see is that after I show the view for the first time and after the first DEACTIVATE, when I try to load it again looks like it is already in the memory (was not deactivated/disposed), so as is already in memory, it not call the constructor again of the modelView and the dropdown is shown with tha same old values. public BranchSelectionViewModel(IUnityContainer unityContainer) { this.unityContainer = unityContainer; User user = this.unityContainer.Resolve<User>(); this.branches = new ObservableCollection<Department>(user.Departments .Where(department => department.DepartmentId != user.SelectedDepartment.DepartmentId)); }

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• What could the negative effects be of attaching to a process as a debugger?

  - by I_like_traffic_lights

  Background A client of mine has a major problem. They have a CRM system, which was created by a single person over a period of 9 years. Unfortunatelly, a few weeks ago, this person died. I believe the company has learned their lesson, and they have started a project of rewriting the CRM system to a modern platform. I have been hired to create a solution in the meantime to make adaptations to the CRM system. I have given up understanding the code, as this would take too long. My solution, is therefore, to make a window and show this on top of the CRM system, whenever this CRM system is showing. This part works fine, but my major problem is extracting the data from the CRM system. Proposed solution After excluding 6 approaches, including runtime code injection, memory searching, database integration, I have arrived at attaching to the process as a debugger, so I get notified about event, and use this in combination with reading from process memory. This approach seems to work, but I am worried about possible side-effects of this approach. Question What are the dangers of using this in a production environment, where there are 250 employees utilizing the system. Needless to say, I cannot risk reducing the already shaky stability of the system.

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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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• C++: use array of strings wrapped in namespace?

  - by John D.

  I got the following code, wishing to wrap a group of strings nicely in a namespace: namespace msgs { const int arr_sz = 3; const char *msg[arr_sz] = {"blank", "blank", "blank" }; msg[0] = "Welcome, lets start by getting a little info from you!\n"; msg[1] = "Alright, bla bla bla.."; msg[2] = "etc."; } The code inside works nicely inside a function, but I don't know how to return an array from it. The namespace idea LOOKS fine, but it returns on the last three lines: error: expected constructor, destructor, or type conversion before ‘=’ token Why can't I define the array inside a namespace, do I need to do something first? It's nice because I can call it like printf(msgs::msg[1]) etc. I want to do this I just can't wrap my head around what's wrong :(

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• OBject access from different functions in VC++

  - by sijith

  Hi, I have 3 function in my class B. These three function have to access member function of other class A. I did this by creating object of class A in class B constructor and tried to access that object in functions of class B. But its showing error. How can i assess the same object in these three functions. Where i have to create object of class A B::B() { A a; } B:: function() { a.fun(); //fun belongs to class A } B:: function1() { a.fun1(); //fun1 belongs to class A } I am getting error, How can i implement the same where i can access object a in both function.

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• Java - Does null variable require space in memory

  - by Yatendra Goel

  class CheckStore { private String displayText; private boolean state; private String meaningfulText; private URL url; public CheckStore(String text, boolean state) { this.displayText = text; this.state = state; } : : } As I am initializing only two variables (displayText and state) in the constructor, Will the rest two variables (meaningfulText and url which will have the value null) will require space in memory to store null value. Q1. I think they will require space. If they will, then how much memory does a null value takes in the memory (like int takes 4 bytes). Q2. How much space a string takes in memory. I guess it will depend on the length of the string. So how much space a string takes of how much length?

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• Potential Django Bug In QuerySet.query?

  - by Mike

  Disclaimer: I'm still learning Django, so I might be missing something here, but I can't see what it would be... I'm running Python 2.6.1 and Django 1.2.1. (InteractiveConsole) >>> from myproject.myapp.models import * >>> qs = Identifier.objects.filter(Q(key="a") | Q(key="b")) >>> print qs.query SELECT `app_identifier`.`id`, `app_identifier`.`user_id`, `app_identifier`.`key`, `app_identifier`.`value` FROM `app_identifier` WHERE (`app_identifier`.`key` = a OR `app_identifier`.`key` = b ) >>> Notice that it doesn't put quotes around "a" or "b"! Now, I've determined that the query executes fine. So, in reality, it must be doing so. But, it's pretty annoying that printing out the query prints it wrong. Especially if I did something like this... >>> qs = Identifier.objects.filter(Q(key=") AND") | Q(key="\"x\"); DROP TABLE `app_identifier`")) >>> print qs.query SELECT `app_identifier`.`id`, `app_identifier`.`user_id`, `app_identifier`.`key`, `app_identifier`.`value` FROM `app_identifier` WHERE (`app_identifier`.`key` = ) AND OR `app_identifier`.`key` = "x"); DROP TABLE `app_identifier` ) >>> Which, as you can see, not only creates completely malformed SQL code, but also has the seeds of a SQL injection attack. Now, obviously this wouldn't actually work, for quite a number of reasons (1. The syntax is all wrong, intentionally, to show the oddity of Django's behavior. 2. Django won't actually execute the query like this, it will actually put quotes and slashes and all that in there like it's supposed to). But, this really makes debugging confusing, and it makes me wonder if something's gone wrong with my Django installation. Does this happen for you? If so/not, what version of Python and Django do you have? Any thoughts?

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• Unity 2.0. How to throw ResolutionFailedException

  - by Andrey Khataev

  Hello, I have my app, using functionality that is based on unity application block. Sometimes I need to throw ResolutionFailedException manually. In v1.2 constructor of ResolutionFailedException had three parameters - typerequested, namerequested and exception. In v2.0 fourth parameter was added - buildercontext. I'm not creating it manually, so I have no reference to it and no idea where I can get it. Roughly speaking, I'm only overriding Resolve method in particular way and I'm not interfere in standard mechanism of policies, strategies and so on. Could anyone help?

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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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• 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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• Not getting image in h:graphicImage in JSF

  - by Nitesh Panchal

  Hello, I have this very strange error with h:graphicImage This code works fine :- <h:graphicImage value="/Common/Images/#{item.templatePicName}"/> And this one doesn't :- <h:graphicImage alt="${app:getCommonImagePath(item.templatePicName)}" value="${app:getCommonImagePath(item.templatePicName)}" /> It only shows alt value /Common/Images/Sunset.jpg which is perfectly fine and works in 1st case. Then why doesn't it work in 2nd case? There are no problems with my images. They are present in right directory. here getCommonImagePath is my custom EL function, whose definition is : package Common; public final class AppDeployment { private AppDeployment(){ //hide constructor } private static String commonImageFolderPath = "/Common/Images/"; public static String getCommonImagePath(String picName){ return commonImageFolderPath + picName; } }

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• C# ToolTip will not re-appear after first use.

  - by Roberto Sebestyen

  I have a Forms C# application where I would like to use a toolTip on one of the text boxes. I Initialize the tool-tip in the constructor of the Form class, and it works the first time. So when I hover over the text box with my mouse it works, but once the toolTip times out and it goes away, it does not re-appear when I move my mouse away and back onto the control. I would expect it to come back and I'm wondering what I'm doing wrong. Here is how I initialize the tooltip: myTip = new ToolTip(); myTip.ToolTipIcon = ToolTipIcon.Info; myTip.IsBalloon = true; myTip.ShowAlways = true; myTip.SetToolTip(txtMyTextBox,"My Tooltip Text");

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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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• Is it a bad idea to create tests that rely on each other within a test fixture?

  - by nbolton

  For example: // NUnit-like pseudo code (within a TestFixture) Ctor() { m_globalVar = getFoo(); } [Test] Create() { a(m_globalVar) } [Test] Delete() { // depends on Create being run b(m_globalVar) } … or… // NUnit-like pseudo code (within a TestFixture) [Test] CreateAndDelete() { Foo foo = getFoo(); a(foo); // depends on Create being run b(foo); } … I’m going with the later, and assuming that the answer to my question is: No, at least not with NUnit, because according to the NUnit manual: The constructor should not have any side effects, since NUnit may construct the class multiple times in the course of a session. ... also, can I assume it's bad practice in general? Since tests can usually be run separately. So the result of Create may never be cleaned up by Delete.

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