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  • Inheriting and static members

    - by Bruce
    Here is my code - #include <iostream> #include <conio.h> using namespace std; class Base { public: int a; }; //int Base::a = 5; class Derived : public Base { public: int static a; }; int main() { Derived d; cout<<d.a; getch(); return 0; } I get a linker error here. But when I do it the other way round - class Base { public: int static a; }; int Base::a = 5; class Derived : public Base { public: int a; }; I get no error. Can someone please explain what is happening here.

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  • Unresolved symbol when inheriting interface

    - by LeopardSkinPillBoxHat
    It's late at night here and I'm going crazy trying to solve a linker error. If I have the following abstract interface: class IArpPacketBuilder { public: IArpPacketBuilder(const DslPortId& aPortId); virtual ~IArpPacketBuilder(); // Other abstract (pure virtual methods) here... }; and I instantiate it like this: class DummyArpPacketBuilder : public IArpPacketBuilder { public: DummyArpPacketBuilder(const DslPortId& aPortId) : IArpPacketBuilder(aPortId) {} ~DummyArpPacketBuilder() {} }; why am I getting the following error when linking? Unresolved symbol references: IArpPacketBuilder::IArpPacketBuilder(DslPortId const&): ppc603_vxworks/_arpPacketQueue.o IArpPacketBuilder::~IArpPacketBuilder(): ppc603_vxworks/_arpPacketQueue.o typeinfo for IArpPacketBuilder: ppc603_vxworks/_arpPacketQueue.o *** Error code 1 IArpPacketBuilder is an abstract interface, so as long as I define the constructors and destructions in the concrete (derived) interface, I should be fine, no? Well it appears not.

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  • Inheriting the main method

    - by Eric
    I want to define a base class that defines a main method that instantiates the class, and runs a method. There are a couple of problems though. Here is the base class: public abstract class Strategy { abstract void execute(SoccerRobot robot); public static void main(String args) { Strategy s = new /*Not sure what to put here*/(); s.execute(new SoccerRobot()) } } And here is an example derived class: public class UselessStrategy { void execute(SoccerRobot robot) { System.out.println("I'm useless") } } It defines a simple execute method, which should be called in a main method upon usage as a the main application. However, in order to do so, I need to instantiate the derived class from within the base class's main method. Which doesn't seem to be possible. I'd rather not have to repeat the main method for every derived class, as it feels somewhat unnessary. Is there a right way of doing this?

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  • Interface(s) inheriting other interface(s) in WCF services.

    - by avance70
    In my solution there's a few WCF services, each of them implementing it's own callback interface. Let's say they are called: Subscribe1, with ISubscribe1 and ICallback1, etc. It happens there are a few methods shared among ICallbacks, so I made a following interface: interface ICallback { [OperationContract] CommonlyUsedMethod(); } and i inherited it in all: ICallback1 : ICallback, ICallback2 : ICallback, etc. And deleted the CommonlyUsedMethod() from all callback interfaces. Now, on the service-side code, everything compiles fine and services can start working as usual. But, when I updated the service references for the client, CommonlyUsedMethod() dissapeared from the reference.cs file (the ISubscribeCallback part), and could no longer be used to send data to back to the client.

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  • Trait, FunctionN, or trait-inheriting-FunctionN in Scala?

    - by Willis Blackburn
    I have a trait in Scala that has a single method. Call it Computable and the single method is compute(input: Int): Int. I can't figure out whether I should Leave it as a standalone trait with a single method. Inherit from (Int = Int) and rename "compute" to "apply." Just get rid of Computable and use (Int = Int). A factor in favor of it being a trait is that I could usefully add some additional methods. But of course if they were all implemented in terms of the compute method then I could just break them out into a separate object. A factor in favor of just using the function type is simplicity and the fact that the syntax for an anonymous function is more concise than that for an anonymous Computable instance. But then I've no way to distinguish objects that are actually Computable instances from other functions that map Int to Int but aren't meant to be used in the same context as Computable. How do other people approach this type of problem? No right or wrong answers here; I'm just looking for advice.

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  • ASP.NET MVC NullReferenceException when inheriting from a Base Controller

    - by rockinthesixstring
    I've got a base controller that I inherit all of my Controllers from. It's job is to basically set caching and error handling as well as check for mobile browsers. My UI works fine, but my Unit Tests are failing. Imports System.Web.Mvc <HandleError()> _ <CompressFilter()> _ <OutputCache(Duration:=30, VaryByParam:="id")> _ Public Class BaseController : Inherits System.Web.Mvc.Controller Protected Overrides Function View(ByVal viewName As String, ByVal masterName As String, ByVal model As Object) As System.Web.Mvc.ViewResult Dim ismobile As Nullable(Of Boolean) = Request.Browser.IsMobileDevice If ismobile Then Return MyBase.View(viewName, "Mobile", model) Else Return MyBase.View(viewName, "Site", model) End If End Function End Class The error I'm getting in my Unit test is on Dim ismobile As Nullable(Of Boolean) = Request.Browser.IsMobileDevice saying Object Reference Not Set To An Instance Of An Object.

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  • Java method get the inheriting type

    - by DrDro
    I have several classes that extend C and I would need a method that accepts any argument of type C. But in this method I would like to know if I'm dealing with A or B. * public A extends C public B extends C public void goForIt(C c)() If I cast how can I retrieve the type in a clean way (I just read using getClass or instanceof is often not the best way). PS: Fell free to edit an explicit title. *Sorry but I can't type closing braces

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  • PyQt - QLabel inheriting

    - by Ockonal
    Hello, i wanna inherit QLabel to add there click event processing. I'm trying this code: class NewLabel(QtGui.QLabel): def __init__(self, parent): QtGui.QLabel.__init__(self, parent) def clickEvent(self, event): print 'Label clicked!' But after clicking I have no line 'Label clicked!' EDIT: Okay, now I'm using not 'clickEvent' but 'mousePressEvent'. And I still have a question. How can i know what exactly label was clicked? For example, i have 2 edit box and 2 labels. Labels content are pixmaps. So there aren't any text in labels, so i can't discern difference between labels. How can i do that? EDIT2: I made this code: class NewLabel(QtGui.QLabel): def __init__(self, firstLabel): QtGui.QLabel.__init__(self, firstLabel) def mousePressEvent(self, event): print 'Clicked' #myLabel = self.sender() # None =) self.emit(QtCore.SIGNAL('clicked()'), "Label pressed") In another class: self.FirstLang = NewLabel(Form) QtCore.QObject.connect(self.FirstLang, QtCore.SIGNAL('clicked()'), self.labelPressed) Slot in the same class: def labelPressed(self): print 'in labelPressed' print self.sender() But there isn't sender object in self. What i did wrong?

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  • Java method: retrieve the inheriting type

    - by DrDro
    I have several classes that extend C and I would need a method that accepts any argument of type C. But in this method I would like to know if I'm dealing with A or B. * public A extends C public B extends C public void goForIt(C c)() If I cast how can I retrieve the type in a clean way (I just read using getClass or instanceof is often not the best way). *Sorry but I can't type closing braces

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  • Inheriting System.Windows.Controls.Panel

    - by modosansreves
    I use the Panel to provide custom layout of UIElements. For this, I override MeasureOverride and ArrangeOverride. In ArrangeOverride proper locations are given to Children. In my application, there is a bunch of rather heavy (by number of visuals) children inside the panel, but only 2 of them are located inside the visible region at a time. Working with my application I feel like all the visuals are drown. I need to introduce a kind of 'virtualization' and make the children render (or take CPU cycles) selectively. How do I?

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  • Qt inheriting from QGraphicsEllipseItem

    - by JHollanti
    I was trying to inherit from QGraphicsEllipseItem 'cause i wanted to add some functionality to it. However i was faced with this error, which probably has something to do with the compiler/precompiler or moc? error: 'staticMetaObject' is not a member of 'QGraphicsEllipseItem' And here's the class code: class MyEllipseItem : public QGraphicsEllipseItem { Q_OBJECT public: MyEllipseItem (const QRectF & outline) : QGraphicsEllipseItem(outline) { } };

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  • Inheriting XML files and modifying values

    - by Veehmot
    This is a question about concept. I have an XML file, let's call it base: <base id="default"> <tags> <tag>tag_one</tag> <tag>tag_two</tag> <tag>tag_three</tag> </tags> <data> <data_a>blue</data_a> <data_b>3</data_b> </data> </base> What I want to do is to be able to extend this XML in another file, modifying individual properties. For example, I want to inherit that file and make a new one with a different data/data_a node: <base id="green" import="default"> <data> <data_a>green</data_a> </data> </base> So far it's pretty simple, it replaces the old data/data_a with the new one. I even can add a new node: <base id="ext" import="default"> <moredata> <data>extended version</data> </moredata> </base> And still it's pretty simple. The problem comes when I want to delete a node or deal with XML Lists (like the tags node). How should I reference a particular index on a list? I was thinking doing something like: <base id="diffList" import="default"> <tags> <tag index="1">this is not anymore tag_two</tag> </tags> </base> And for deleting a node / array index: <base id="deleting" import="default"> <tags> <tag index="2"/> </tags> <data/> </base> <!-- This will result in an XML containing these values: --> <base> <tag>tag_one</tag> <tag>tag_two</tag> </base> But I'm not happy with my solutions. I don't know anything about XSLT or other XML transformation tools, but I think someone must have done this before. The key goal I'm looking for is ease to write the XML by hand (both the base and the "extended"). I'm open to new solutions besides XML, if they are easy to write manually. Thanks for reading.

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  • Inheriting from multiple classes in Java (and possibly not using interface)

    - by sheidaei
    So, let's say we have classes A, B and C and I want to inherit from all those classes and have another class called D, it can be done using implements and interfaces in Java. But let's say we don't want to use this simple solution, would you be able to inherit class D from classes A, B and C in any other way in Java? (This question might be related to design patterns, it has been brought up after challenging my colleague at lunch discussing design patterns) I don't think there is any other way to have multiple inheritance in Java other than using multiple interfaces.

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  • Inheriting database connection in PHP OOP

    - by vrode
    My abstract class Database is made for database interaction and any child of this class (UserDatabase, ActionDatabase, EventDatabase) inherits its database connection which is defined as static. `abstract class Database { static $connection = mysql_connect( ); } class UserDatabase extends Database { ... public function __construct( ) { $connection ? "connected" : "not connected"; $this-table = "users"; mysql_query( "FROM " . $this-table . " SELECT *" ); } } ` Does that mean, that my database connection is only set up and stored in memory once and passed on to subclasses as reference without being replicated for each instance? Is this how you would implement you OOP-correct database interface?

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  • inheriting scope from a has_many relationship

    - by hb922
    I am using ruby on rails 3.1 and have 2 models, an event and a group. Each event has_many groups, but has to have at least one "master" group, where the column :is_master = true Class Group < ActiveRecord::Base has_many :users belongs_to :event scope :master, where (:is_master => true) end Class Event< ActiveRecord::Base has_many :groups def master_group groups.master end end I want to be able to default all properties of the master group to the event, so for example, event.users.count should be the same as event.master_group.users.count. Is there any way to do something like this? Can I do a has_many :through = master_group? Am I approaching this the wrong way? Thanks!

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  • ASP.NET MVC Inheriting from ProfileBase

    - by Glen
    I have 2 related issues. I inherited from ProfileBase and I have a couple of properites as such public SomeType PropertyName { get { return (SomeType)base["PropertyName"]; } set { base["PropertyName"] = value; Save(); } } I also have a User class (UserId, UserName, Profile, LastActivityDate) that has 2 additional properties out of the profile that I retrieve in my View to show a list of Users (i.e. @Model.Profile.PropertyName). However, everytime I access a property (from my View) it seems to update the LastActivityDate in the aspnet_Users table because when I show the LastActivityDate as well as the profile properties on my screen the LastActivtyDate is out of sync with the database. Also there is a LastActivityDate property available in my profile which unfortunately is not available and is in fact set to null and throws an exception when accessing it saying the property UserName is null. So the static Create method provided by ProfileBase seems to retrieve the correct profile properties but does not set the base's UserName property even though you pass in a UserName parameter to the Create method. Is this a internal bug? I was kind of hoping if by accessing the property because the LastActivityDate is updated then I could store that value to update my LastActivityDate in my User class before it is rendered to the page. The only way I can think of doing it is: public SomeType PropertyName { get { SomeType result = (SomeType)base["PropertyName"]; OnLastActivityDateChanged(); return result; } set { base["PropertyName"] = value; } } then in my User class: ... public MyProfile() { Profile.LastActivityDateChanged += Profile_LastActivityDateChanged(); } ~MyProfile() { Profile.LastActivityDateChanged -= Profile_LastActivityDateChanged(); } ... void Profile_LastActivityDateChanged(object sender, EventArgs e) { //Run a query to get the latest LastActivityDate this.LastActivityDate = ... } It seems I have to make 1 call to retrieve the full list to my aspnet_Users table then another call for each row just to get the latest activity date. ARGGGGHHH!!! Am I going about this the wrong way! I put an ajax refresh hyperlink next to each User row and when I click it, immediately after loading the page, the value changes. Therefore my suspision is valid that calling a property via the inherited profilebase class updates the value. Is there a workaround? It is a bit miss leading when my page says User Smith has no activity for 4 days then I click my ajax refresh link (or refresh the whole page for that matter) and now it says Smith was active but it was just me meally showing the page that indirectly caused an activity read event.

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  • Accessing and inheriting Windows Message for other Windows Message in Delphi

    - by HX_unbanned
    I am using WMSysCommand messages to modify Caption bar button ( Maximize / Minimize ) behaivor and recent update requiered to use WMNCHitTest, but I do not want to split these two related messages in multiplie procedures because of lengthy code. Can I access private declaration ( message ) from other message? And if I can - How to do it? procedure TForm1.WMNCHitTest(var Msg: TWMNCHitTest) ; begin SendMessage(Handle, HTCAPTION, WM_NCHitTest, 0); // or other wParam or lParam ???? end; procedure TForm1.WMSysCommand; begin if (Msg.CmdType = SC_MAXIMIZE or 61488) or (Msg.Result = htCaption or 2) then // if command is Maximize or reciever message of Caption Bar click begin if CheckWin32Version(6, 0) then Constraints.MaxHeight := 507 else Constraints.MaxHeight := 499; Constraints.MaxWidth := 0; end else if (Msg.CmdType = SC_MINIMIZE or 61472) or (Msg.Result = htCaption or 2) then // if command is Minimize begin if (EnsureRange(Width, 252, 510) >= (510 / 2)) then PreviewOpn.Caption := '<' else PreviewOpn.Caption := '>'; end; DefaultHandler(Msg); // reset Message handler to default ( Application ) end; Soo ... do I think correctly and sipmly do not know correct commands or I am thinking total bullsh*t? Regards. Thanks for any help...

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  • Custom authentication module inheriting IHttpModule issue.

    - by Chandan Khatwani
    LoginPage.aspx:- protected void Button1_Click(object sender, EventArgs e) { Context.Items["Username"] = txtUserId.Text; Context.Items["Password"] = txtPassword.Text; // FormsAuthenticationTicket ticket = new FormsAuthenticationTicket(1, Context.Items["Username"].ToString(), DateTime.Now, DateTime.Now.AddMinutes(10), true, "users", FormsAuthentication.FormsCookiePath); // Encrypt the cookie using the machine key for secure transport string hash = FormsAuthentication.Encrypt(ticket); HttpCookie cookie = new HttpCookie( FormsAuthentication.FormsCookieName, // Name of auth cookie hash); // Hashed ticket // Set the cookie's expiration time to the tickets expiration time if (ticket.IsPersistent) cookie.Expires = ticket.Expiration; Response.Cookies.Add(cookie); Response.Redirect("Default.aspx"); } Global.asax file:- void Application_AuthenticateRequest(object sender, EventArgs e) { if (HttpContext.Current.User != null) { if (HttpContext.Current.User.Identity.IsAuthenticated) { if (HttpContext.Current.User.Identity is FormsIdentity) { FormsIdentity id = (FormsIdentity)HttpContext.Current.User.Identity; FormsAuthenticationTicket ticket = id.Ticket; // Get the stored user-data, in this case, our roles string userData = ticket.UserData; string[] roles = userData.Split(','); HttpContext.Current.User = new System.Security.Principal.GenericPrincipal(id, roles); Response.Write(HttpContext.Current.User.Identity.Name); Response.Redirect("Default.aspx"); } } } } I get the following error after signing in This webpage has a redirect loop. The webpage at http://localhost:1067/Default.aspx has resulted in too many redirects. Clearing your cookies for this site or allowing third-party cookies may fix the problem. If not, it is possibly a server configuration issue and not a problem with your computer.

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  • Having troubles inheriting base class

    - by Nick
    When I inherit the base class, it's telling me there is no such class This is enhanced.h: class enhanced: public changeDispenser // <--------where error is occuring { public: void changeStatus(); // Function: Lets the user know how much of each coin is in the machine enhanced(int); // Constructor // Sets the Dollar amount to what the User wants void changeLoad(int); // Function: Loads what change the user requests into the Coin Machine int dispenseChange(int); // Function: Takes the users amount of cents requests and dispenses it to the user private: int dollar; }; This is enhanced.cpp: #include "enhanced.h" #include <iostream> using namespace std; enhanced::enhanced(int dol) { dollar = dol; } void enhanced::changeStatus() { cout << dollar << " dollars, "; changeDispenser::changeStatus(); } void enhanced::changeLoad(int d) { dollar = dollar + d; //changeDispenser::changeLoad; } This is changeDispenser.h: class changeDispenser { public: void changeStatus(); // Function: Lets the user know how much of each coin is in the machine changeDispenser(int, int, int, int); // Constructor // Sets the Quarters, Dimes, Nickels, and Pennies to what the User wants void changeLoad(int, int, int, int); // Function: Loads what change the user requests into the Coin Machine int dispenseChange(int); // Function: Takes the users amount of cents requests and dispenses it to the user private: int quarter; int dime; int nickel; int penny; }; I didn't include the driver file or the changeDispenser imp file, but in the driver, these are included #include "changeDispenser.h" #include "enhanced.h"

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  • before_filter not inheriting from parent controller correctly?

    - by Scott
    Sorry if this may be a stupid question but I'm unable get my filters to inherit the way the Rails 3 documentation is saying it should. Specifically I have an Admin controller that was generated via: rails generate controller admin I added only a single action to the admin controller, the before filter & the private filter method class AdminController < ApplicationController before_filter require_admin_creds def index end private def require_admin_creds unless current_user && current_user.admin? flash[:error] = ... redirect_to .... end end end I next then created my nested resources under the admin section with: rails generate scaffold admin/model While my admin index is indeed getting the filter, the admin/model index (or any other actions) are not. What is happening under the hood here that I must have excluded? Thanks in advance.

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  • Inheriting and overriding interfaces in C#

    - by Daniel A. White
    Please note: I am writing this question. I have these interfaces in a library/framework I am working on: interface IRepository<TKey,TModel> { void Remove(TModel entity); } interface IRepository<T> : IRepository<int, T> { } interface ISoftDeleteRepository<TKey,TModel> : IRepository<TKey, TModel> { } interface ISoftDeleteRepository<TModel> : ISoftDeleteRepository<int, TModel>, IRepository<TModel> { } and these implementations class Repository : IRepository { void Remove(TModel entity) { // actually Delete } } interface IRepository<T> : IRepository<int, T> { } interface ISoftDeleteRepository<TKey,TModel> : IRepository<TKey, TModel> { } interface ISoftDeleteRepository<TModel> : ISoftDeleteRepository<int, TModel>, IRepository<TModel> { }

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  • Inheriting a Base Form but Paste/Cut Commands Not Captured

    - by ohu812
    I created a base form that has a specific size and an icon as a base for all forms created in my project (to be consistent in looks). The problem is, for some reason if I add a Text box to the Child form, I can no longer execute shortcuts like Copy (CTRL+C) etc into the Textbox. What should I do to handle this OTHER THAN writing code to capture those on the KeyUp control? This is also the case for RichTextBox control as well. Thanks

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  • Minimal framework in Scala for collections with inheriting return type

    - by Rex Kerr
    Suppose one wants to build a novel generic class, Novel[A]. This class will contain lots of useful methods--perhaps it is a type of collection--and therefore you want to subclass it. But you want the methods to return the type of the subclass, not the original type. In Scala 2.8, what is the minimal amount of work one has to do so that methods of that class will return the relevant subclass, not the original? For example, class Novel[A] /* What goes here? */ { /* Must you have stuff here? */ def reverse/* What goes here instead of :Novel[A]? */ = //... def revrev/*?*/ = reverse.reverse } class ShortStory[A] extends Novel[A] /* What goes here? */ { override def reverse: /*?*/ = //... } val ss = new ShortStory[String] val ss2 = ss.revrev // Type had better be ShortStory[String], not Novel[String] Does this minimal amount change if you want Novel to be covariant? (The 2.8 collections do this among other things, but they also play with return types in more fancy (and useful) ways--the question is how little framework one can get away with if one only wants this subtypes-always-return-subtypes feature.)

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