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• Questions regarding ordering of catch statements in catch block - compiler specific or language stan

  - by Andy

  I am currently using Visual Studio Express C++ 2008, and have some questions about catch block ordering. Unfortunately, I could not find the answer on the internet so I am posing these questions to the experts. I notice that unless catch (...) is placed at the end of a catch block, the compilation will fail with error C2311. For example, the following would compile: catch (MyException) { } catch (...) { } while the following would not: catch (...) { } catch (MyException) { } a. Could I ask if this is defined in the C++ language standard, or if this is just the Microsoft compiler being strict? b. Do C# and Java have the same rules as well? c. As an aside, I have also tried making a base class and a derived class, and putting the catch statement for the base class before the catch statement for the derived class. This compiled without problems. Are there no language standards guarding against such practice please?

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• Trouble binding WPF Menu to ItemsSource

  - by chaiguy

  I would like to avoid having to build a menu manually in XAML or code, by binding to a list of ICommand-derived objects. However, I'm experiencing a bit of a problem where the resulting menu has two levels of menu-items (i.e. each MenuItem is contained in a MenuItem): My guess is that this is happening because WPF is automatically generating a MenuItem for my binding, but the "viewer" I'm using actually already is a MenuItem (it's derived from MenuItem): <ContextMenu x:Name="selectionContextMenu" ItemsSource="{Binding Source={x:Static OrangeNote:Note.MultiCommands}}" ItemContainerStyleSelector="{StaticResource separatorStyleSelector}"> <ContextMenu.ItemTemplate> <DataTemplate> <Viewers:NoteCommandMenuItemViewer CommandParameter="{Binding Source={x:Static OrangeNote:App.Screen}, Path=SelectedNotes}" /> </DataTemplate> </ContextMenu.ItemTemplate> </ContextMenu> (The ItemContainerStyleSelector is from http://bea.stollnitz.com/blog/?p=23, which allows me to have Separator elements inside my bound source.) So, the menu is bound to a collection of ICommands, and each item's CommandParameter is set to the same global target (which happens to be a collection, but that's not important). My question is, is there any way I can bind this such that WPF doesn't automatically wrap each item in a MenuItem?

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• QT: I've inherited from QTreeView. I've inherited from QStandardItem. How do i Style the items?

  - by San Jacinto

  My Google skills must be failing me today. I've inherited from QTreeView to create a TreeView that stores a QStandardItemModel instead of a QAbstractItemModel. I have also inherited from QStandardItem to create a class to store my data in an item as is necessary. I've successfully inserted my derived QStandardItem into my derived QTreeView's QStandardItemModel. Now the trouble is, I can't figure out how to style it. I know that QTreeView has a setStyleSheet(QString) member, but I can't seem to get it working. It may be as simple as I'm not styling the correct attribute. Any pointers would be appreciated. Thanks. For clarity, here are my class defs. class SurveyTreeItem : public QStandardItem { public: SurveyTreeItem(); SurveyTreeItem( const QString & text ); ~SurveyTreeItem(); }; class StandardItemModelTreeView : public QTreeView { public: StandardItemModelTreeView(QWidget* parent = 0); ~StandardItemModelTreeView(); QStandardItemModel* getStandardItemModel(); }; I've tried the following StyleSheets: StandardTreeView::Item { font: 87 12pt 'Arial Black'; } StandardTreeView::QStandardItem { font: 87 12pt 'Arial Black'; } QTreeView::QStandardItem { font: 87 12pt 'Arial Black'; } QTreeView::Item { font: 87 12pt 'Arial Black'; } QTreeView::SurveyTreeItem { font: 87 12pt 'Arial Black'; } StandardTreeView::SurveyTreeItem { font: 87 12pt 'Arial Black'; }

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• SECURITY Flaws in this design for User authentication.

  - by Shao

  SECURITY Flaws in this design for User authentication. From: http://wiki.pylonshq.com/display/pylonscookbook/Simple+Homegrown+Authentication Note: a. Project follows the MVC pattern. b. Only a user with a valid username and password is allowed submit something. Design: a. Have a base controller from which all controllers are derived from. b. Before any of the actions in the derived controllers are called the system calls a before action in the base controller. c. In each controller user hardcodes the actions that need to be verified in an array. d. The before action first looks in the array that has the actions that are protected and sees if a user is logged in or not by peaking into the session. If a user is present then user is allowed to submit otherwise user is redirected to login page. What do you think?

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• Can protobuf-net serialize this combination of interface and generic collection?

  - by tsupe

  I am trying to serialize a ItemTransaction and protobuf-net (r282) is having a problem. ItemTransaction : IEnumerable<KeyValuePair<Type, IItemCollection>></code> and ItemCollection is like this: FooCollection : ItemCollection<Foo> ItemCollection<T> : BindingList<T>, IItemCollection IItemCollection : IList<Item> where T is a derived type of Item. ItemCollection also has a property of type IItemCollection. I am serializing like this: IItemCollection itemCol = someService.Blah(...); ... SerializeWithLengthPrefix<IItemCollection>(stream, itemCol, PrefixStyle.Base128); My eventual goal is to serialize ItemTransaction, but am snagged with IItemCollection. Item and it's derived types can be [de]serialized with no issues, see [1], but deserializing an IItemCollection fails (serializing works). ItemCollection has a ItemExpression property and when deserializing protobuf can't create an abstract class. This makes sense to me, but I'm not sure how to get through it. ItemExpression<T> : ItemExpression, IItemExpression ItemExpression : Expression ItemExpression is abstract as is Expression How do I get this to work properly? Also, I am concerned that ItemTransaction will fail since the IItemCollections are going to be differing and unknown at compile time (an ItemTransaction will have FooCollection, BarCollection, FlimCollection, FlamCollection, etc). What am I missing (Marc) ? [1] http://stackoverflow.com/questions/2276104/protobuf-net-deserializing-across-assembly-boundaries

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• Virtual properties duplicated during serialization when XmlElement attribute used

  - by Laramie

  The Goal: XML serialize an object that contains a list of objects of that and its derived types. The resulting XML should not use the xsi:type attribute to describe the type, to wit the names of the serialized XML elements would be an assigned name specific to the derived type, not always that of the base class, which is the default behavior. The Attempt: After exploring IXmlSerializable and IXmlSerializable with eerie XmlSchemaProvider methods and voodoo reflection to return specialized schemas and an XmlQualifiedName over the course of days, I found I was able to use the simple [XmlElement] attribute to accomplish the goal... almost. The Problem: Overridden properties appear twice when serializing. The exception reads "The XML element 'overriddenProperty' from namespace '' is already present in the current scope. Use XML attributes to specify another XML name or namespace for the element." I attempted using a *Specified property (see code), but it didn't work. Sample Code: Class Declaration using System; using System.Collections.Generic; using System.Xml.Serialization; [XmlInclude(typeof(DerivedClass))] public class BaseClass { public BaseClass() { } [XmlAttribute("virt")] public virtual string Virtual { get; set; } [XmlIgnore] public bool VirtualSpecified { get { return (this is BaseClass); } set { } } [XmlElement(ElementName = "B", Type = typeof(BaseClass), IsNullable = false)] [XmlElement(ElementName = "D", Type = typeof(DerivedClass), IsNullable = false)] public List<BaseClass> Children { get; set; } } public class DerivedClass : BaseClass { public DerivedClass() { } [XmlAttribute("virt")] public override string Virtual { get { return "always return spackle"; } set { } } } Driver: BaseClass baseClass = new BaseClass() { Children = new List<BaseClass>() }; BaseClass baseClass2 = new BaseClass(){}; DerivedClass derivedClass1 = new DerivedClass() { Children = new List<BaseClass>() }; DerivedClass derivedClass2 = new DerivedClass() { Children = new List<BaseClass>() }; baseClass.Children.Add(derivedClass1); baseClass.Children.Add(derivedClass2); derivedClass1.Children.Add(baseClass2); I've been wrestling with this on and off for weeks and can't find the answer anywhere.

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• Validation not bubbling up to my other models.

  - by DJTripleThreat

  Ok, I have a relationship between People, Users and Employees such that All Employees are Users and all Users are People. Person is an abstract class that User is derived from and Employee is derived from that. Now... I have an EmployeesController class and the create method looks like this: def create @employee = Employee.new(params[:employee]) @employee.user = User.new(params[:user]) @employee.user.person = Person.new(params[:person]) respond_to do |format| if @employee.save flash[:notice] = 'Employee was successfully created.' format.html { redirect_to(@employee) } format.xml { render :xml => @employee, :status => :created, :location => @employee } else format.html { render :action => "new" } format.xml { render :xml => @employee.errors, :status => :unprocessable_entity } end end end As you can see, when I'm using the :polymorphic => true clause, the way you access the super class is by doing something like @derived_class_variable.super_class_variable.super_super_etc. The Person class has a validates_presence_of :first_name and when it is satisfied, on my form, everything is OK. However, if I leave out the first name, it won't prevent the employee from being saved. What happens is that the employee record is saved but the person record isn't (because of the validation). How can I get the validation errors to show up in the flash object?

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• How to wrap a thirdparty library COM class for notifications in a C++ project

  - by geocoin

  A thirdparty vendor has provided a COM interface as an external API to their product, and for sending instructions to it, it's fine with the mechanism of generating class wrappers with visual studio by importing from the dll, then creating instances of the created classes, calling their CreateDispatch(), using the access functions and releasing when done. For return notifications, I'd normally create an EventsListener class derived from IDispatch using the Invoke function to handle events returning from the interface. This vendor has created an Events lass which I have to wrap and expose, then explicitly tell the installation where to look. all the example are given is C# where it's really easy, but I'm struggling on how to do it in C++ in the C# example, the interop dll provided is simply added as a reference and derived into a class like so: using System; using System.Runtime.InteropServices; using System.Windows.Forms; using System.Text; using <THIER INTEROP LIB> namespace some.example.namespace { [ComVisible(true)] public class EventViewer : IEvents //where IEvents is their events class { public void OnEvent(EventID EventID, object pData) //overridden function { //event handled here } } } In broad terms I assume that I must create a COM interface, since they require a ProgID from me to instantiate, but how do I derive that's been wrapped by the import and then expose the created class to COM I'm just not sure where to even start, as all the tutorials I've seen so far talk in terms of creating brand new classes not wrapping a third party one

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• Handle cases where Nhibernate subclass does not exist

  - by kaykayman

  I have a scenario where I am using nhibernate to map records from one table to several different derived classes based on a discriminator. public class BaseClass { } public class DerivedClass0 : BaseClass { } public class DerivedClass1 : BaseClass { } public class DerivedClass2 : BaseClass { } I then use nhibernate's DiscriminateSubClassesOnColumn() method and alter the configuration to include <subclass name="DerivedClass0" extends="BaseClass" discriminator-value="discriminator0" /> <subclass name="DerivedClass1" extends="BaseClass" discriminator-value="discriminator1" /> <subclass name="DerivedClass2" extends="BaseClass" discriminator-value="discriminator2" /> so that when mapped, these classes are cast to their derived classes and not BaseClass. However, there are some records in my database which have a discriminator which does not have a corresponding subclass. In these cases, nHibernate throws an error: "Object with id: 'xxx' was not of the specified subclass..." Is there some way I can handle this, so that any records which do not have a corresponding subclass are cast to BaseClass rather than an error being thrown? I have simplified the above as much as possible, however it is worth noting that the XML is edited dynamically which is why I am referencing fluent nhibernate [DiscriminateSubClassesOnColumn()] and XML at the same time. The following things (which would help) are not an option: I cannot correct the data to remove records which are invalid I cannot create subclasses for those records which do not have one I need to handle cases where nHibernate tries to map on a discriminator and finds that one does not exist.

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• git doesn't show where code was removed.

  - by Andrew Myers

  So I was tasked at replacing some dummy code that our project requires for historical compatibility reasons but has mysteriously dropped out sometime since the last release. Since disappearing code makes me nervous about what else might have gone missing but un-noticed I've been digging through the logs trying to find in what commit this handful of lines was removed. I've tried a number of things including "git log -S'add-visit-resource-pcf'", git blame, and even git bisect with a script that simply checks for the existence of the line but have been unable to pinpoint exactly where these lines were removed. I find this very perplexing, particularly since the last log entry (obtained by the above command) before my re-introduction of this code was someone else adding the code as well. commit 0b0556fa87ff80d0ffcc2b451cca1581289bbc3c Author: Andrew Date: Thu May 13 10:55:32 2010 -0400 Re-introduced add-visit-resource-pcf, see PR-65034. diff --git a/spike/hst/scheduler/defpackage.lisp b/spike/hst/scheduler/defpackage.lisp index f8e692d..a6f8d38 100644 --- a/spike/hst/scheduler/defpackage.lisp +++ b/spike/hst/scheduler/defpackage.lisp @@ -115,6 +115,7 @@ #:add-to-current-resource-pcf #:add-user-package-nickname #:add-value-criteria + #:add-visit-resource-pcf #:add-window-to-gs-params #:adjust-derived-resources #:adjust-links-candidate-criteria-types commit 9fb10e25572c537076284a248be1fbf757c1a6e1 Author: Bob Date: Sun Jan 17 18:35:16 2010 -0500 update-defpackage for Spike 33.1 Delivery diff --git a/spike/hst/scheduler/defpackage.lisp b/spike/hst/scheduler/defpackage.lisp index 983666d..47f1a9a 100644 --- a/spike/hst/scheduler/defpackage.lisp +++ b/spike/hst/scheduler/defpackage.lisp @@ -118,6 +118,7 @@ #:add-user-package-nickname #:add-value-criteria #:add-vars-from-proposal + #:add-visit-resource-pcf #:add-window-to-gs-params #:adjust-derived-resources #:adjust-links-candidate-criteria-types This is for one of our package definition files, but the relevant source file reflects something similar. Does anyone know what could be going on here and how I could find the information I want? It's not really that important but this kind of things makes me a bit nervous.

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• Converting currencies via intermediate currencies.

  - by chillitom

  class FxRate { string Base { get; set; } string Target { get; set; } double Rate { get; set; } } private IList<FxRate> rates = new List<FxRate> { new FxRate {Base = "EUR", Target = "USD", Rate = 1.3668}, new FxRate {Base = "GBP", Target = "USD", Rate = 1.5039}, new FxRate {Base = "USD", Target = "CHF", Rate = 1.0694}, new FxRate {Base = "CHF", Target = "SEK", Rate = 8.12} // ... }; Given a large yet incomplete list of exchange rates where all currencies appear at least once (either as a target or base currency): What algorithm would I use to be able to derive rates for exchanges that aren't directly listed? I'm looking for a general purpose algorithm of the form: public double Rate(string baseCode, string targetCode, double currency) { return ... } In the example above a derived rate would be GBP-CHF or EUR-SEK (which would require using the conversions for EUR-USD, USD-CHF, CHF-SEK) Whilst I know how to do the conversions by hand I'm looking for a tidy way (perhaps using LINQ) to perform these derived conversions perhaps involving multiple currency hops, what's the nicest way to go about this?

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• Linq 2 SQL Store inherited classes - not mapped to tables in the database

  - by user348672

  Hi. I'm trying to introduce the Linq2SQL technique into the project and have encountered the following issue: I've created ORM classes based on the Northwind database. In some other application I create several classes derived from the Linq2SQL classes. I'm able to add such a class to EntitySet but the application fails to submit changes. Is there any way around this? Sample code(MyClass is derived from the Order): DataClasses1DataContext northwind = new DataClasses1DataContext(); Product chai = northwind.Products.Single(p => p.ProductName == "Chai"); Product tofu = northwind.Products.Single(p => p.ProductName == "Tofu"); Order myOrder = new Order(); myOrder.OrderDate = DateTime.Now; myOrder.RequiredDate = DateTime.Now.AddDays(1); myOrder.Freight = 34; Order_Detail myItem1 = new Order_Detail(); myItem1.Product = chai; myItem1.Quantity = 12345; Order_Detail myItem2 = new Order_Detail(); myItem2.Product = tofu; myItem2.Quantity = 3; myOrder.Order_Details.Add(myItem1); myOrder.Order_Details.Add(myItem2); Customer myCustomer = northwind.Customers.Single(c => c.CompanyName == "B's Beverages"); MyClass newOrder = new MyClass(); newOrder.OrderDate = DateTime.Now; newOrder.RequiredDate = DateTime.Now.AddDays(31); newOrder.Freight = 35; Order_Detail myItem3 = new Order_Detail(); myItem3.Product = tofu; myItem3.Quantity = 3; newOrder.Order_Details.Add(myItem3); myCustomer.Orders.Add(myOrder); myCustomer.Orders.Add(newOrder); As I said I'm able to add the newOrder object but unable to submit into the database.

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• Python __subclasses__() not listing subclasses

  - by Mridang Agarwalla

  I cant seem to list all derived classes using the __subclasses__() method. Here's my directory layout: import.py backends __init__.py --digger __init__.py base.py test.py --plugins plugina_plugin.py From import.py i'm calling test.py. test.py in turn iterates over all the files in the plugins directory and loads all of them. test.py looks like this: import os import sys import re sys.path.append(os.path.join(os.path.abspath(os.path.dirname(os.path.abspath( __file__ ))))) sys.path.append(os.path.join(os.path.abspath(os.path.dirname(os.path.abspath( __file__ ))), 'plugins')) from base import BasePlugin class TestImport: def __init__(self): print 'heeeeello' PLUGIN_DIRECTORY = os.path.join(os.path.abspath(os.path.dirname(os.path.abspath( __file__ ))), 'plugins') for filename in os.listdir (PLUGIN_DIRECTORY): # Ignore subfolders if os.path.isdir (os.path.join(PLUGIN_DIRECTORY, filename)): continue else: if re.match(r".*?_plugin\.py$", filename): print ('Initialising plugin : ' + filename) __import__(re.sub(r".py", r"", filename)) print ('Plugin system initialized') print BasePlugin.__subclasses__() The problem us that the __subclasses__() method doesn't show any derived classes. All plugins in the plugins directory derive from a base class in the base.py file. base.py looks like this: class BasePlugin(object): """ Base """ def __init__(self): pass plugina_plugin.py looks like this: from base import BasePlugin class PluginA(BasePlugin): """ Plugin A """ def __init__(self): pass Could anyone help me out with this? Whatm am i doing wrong? I've racked my brains over this but I cant seem to figure it out Thanks.

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• NSFetchedResultsController sections localized sorted

  - by Gerd

  How could I use the NSFetchedResultsController with translated sort key and sectionKeyPath? Problem: I have ID in the property "type" in the database like typeA, typeB, typeC,... and not the value directly because it should be localized. In English typeA=Bird, typeB=Cat, typeC=Dog in German it would be Vogel, Katze, Hund. With a NSFetchedResultController with sort key and sectionKeyPath on "type" I receive the order and sections - typeA - typeB - typeC Next I translate for display and everything is fine in English: - Bird - Cat - Dog Now I switch to German and receive a wrong sort order - Vogel - Katze - Hund because it still sorts by typeA, typeB, typeC So I'm looking for a way to localize the sort for the NSFetchedResultsController. I tried the transient property approach, but this doesn't work for the sort key because the sort key need to be in the entity. I have no other idea. But I can't believe that's not possible to use NSFetchedResultsController on a derived attribute required for localization? There are related discussions like http://stackoverflow.com/questions/1384345/using-custom-sections-with-nsfetchedresultscontroller but the difference is that the custom section names and the sort key have probably the same order. Not in my case and this is the main difference. At the end I would need a sort order for the necessary NSSortDescriptor on a derived attribute, I guess. This sort order has also to serve for the sectionKeyPath. Thanks for any hint.

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• Qt and variadic functions

  - by Noah Roberts

  OK, before lecturing me on the use of C-style variadic functions in C++...everything else has turned out to require nothing short of rewriting the Qt MOC. What I'd like to know is whether or not you can have a "slot" in a Qt object that takes an arbitrary amount/type of arguments. The thing is that I really want to be able to generate Qt objects that have slots of an arbitrary signature. Since the MOC is incompatible with standard preprocessing and with templates, it's not possible to do so with either direct approach. I just came up with another idea: struct funky_base : QObject { Q_OBJECT funky_base(QObject * o = 0); public slots: virtual void the_slot(...) = 0; }; If this is possible then, because you can make a template that is a subclass of a QObject derived object so long as you don't declare new Qt stuff in it, I should be able to implement a derived templated type that takes the ... stuff and turns it into the appropriate, expected types. If it is, how would I connect to it? Would this work? connect(x, SIGNAL(someSignal(int)), y, SLOT(the_slot(...))); If nobody's tried anything this insane and doesn't know off hand, yes I'll eventually try it myself...but I am hoping someone already has existing knowledge I can tap before possibly wasting my time on it.

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• Which ORM to use?

  - by Paja

  I'm developing an application which will have these classes: class Shortcut { public string Name { get; } public IList<Trigger> Triggers { get; } public IList<Action> Actions { get; } } class Trigger { public string Name { get; } } class Action { public string Name { get; } } And I will have 20+ more classes, which will derive from Trigger or Action, so in the end, I will have one Shortcut class, 15 Action-derived classes and 5 Trigger-derived classes. My question is, which ORM will best suit this application? EF, NH, SubSonic, or maybe something else (Linq2SQL)? I will be periodically releasing new application versions, adding more triggers and actions (or changing current triggers/actions), so I will have to update database schema as well. I don't know if EF or NH provides any good methods to easily update the schema. Or if they do, is there any tutorial how to do that? I've already found this article about NH schema updating, quoting: Fortunately NHibernate provides us the possibility to update an existing schema, that is NHibernate creates an update script which can the be applied to the database. I've never found how to actually generate the update script, so I can't tell NH to update the schema. Maybe I've misread something, I just didn't found it. Last note: If you suggest EF, will be EF 1.0 suitable as well? I would rather use some older .NET than 4.0.

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• Does QThread::sleep() require the event loop to be running?

  - by suszterpatt

  I have a simple client-server program written in Qt, where processes communicate using MPI. The basic design I'm trying to implement is the following: The first process (the "server") launches a GUI (derived from QMainWindow), which listens for messages from the clients (using repeat fire QTimers and asynchronous MPI receive calls), updates the GUI depending on what messages it receives, and sends a reply to every message. Every other process (the "clients") runs in an infinite loop, and all they are intended to do is send a message to the server process, receive the reply, go to sleep for a while, then wake up and repeat. Every process instantiates a single object derived from QThread, and calls its start() method. The run() method of these classes all look like this: from foo.cpp: void Foo::run() { while (true) { // Send message to the first process // Wait for a reply // Do uninteresting stuff with the reply sleep(3); // also tried QThread::sleep(3) } } In the client's code, there is no call to exec() anywhere, so no event loop should start. The problem is that the clients never wake up from sleeping (if I surround the sleep() call with two writes to a log file, only the first one is executed, control never reaches the second). Is this because I didn't start the event loop? And if so, what is the simplest way to achieve the desired functionality?

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• How to implement an interface class using the non-virtual interface idiom in C++?

  - by andreas buykx

  Hi all, In C++ an interface can be implemented by a class with all its methods pure virtual. Such a class could be part of a library to describe what methods an object should implement to be able to work with other classes in the library: class Lib::IFoo { public: virtual void method() = 0; }; : class Lib::Bar { public: void stuff( Lib::IFoo & ); }; Now I want to to use class Lib::Bar, so I have to implement the IFoo interface. For my purposes I need a whole of related classes so I would like to work with a base class that guarantees common behavior using the NVI idiom: class FooBase : public IFoo // implement interface IFoo { public: void method(); // calls methodImpl; private: virtual void methodImpl(); }; The non-virtual interface (NVI) idiom ought to deny derived classes the possibility of overriding the common behavior implemented in FooBase::method(), but since IFoo made it virtual it seems that all derived classes have the opportunity to override the FooBase::method(). If I want to use the NVI idiom, what are my options other than the pImpl idiom already suggested (thanks space-c0wb0y).

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• What OOP pattern to use when only adding new methods, not data?

  - by Jonathon Reinhart

  Hello eveyone... In my app, I have deal with several different "parameters", which derive from IParameter interface, and also ParamBase abstract base class. I currently have two different parameter types, call them FooParameter and BarParameter, which both derive from ParamBase. Obviously, I can treat them both as IParameters when I need to deal with them generically, or detect their specific type when I need to handle their specific functionality. My question lies in specific FooParameters. I currently have a few specific ones with their own classes which derive from FooParameter, we'll call them FP12, FP13, FP14, etc. These all have certain characteristics, which make me treat them differently in the UI. (Most have names associated with the individual bits, or ranges of bits). Note that these specific, derived FP's have no additional data associated with them, only properties (which refer to the same data in different ways) or methods. Now, I'd like to keep all of these parameters in a Dictionary<String, IParameter> for easy generic access. The problem is, if I want to refer to a specific one with the special GUI functions, I can't write: FP12 fp12 = (FP12)paramList["FP12"] because you can't downcast to a derived type (rightfully so). But in my case, I didn't add any data, so the cast would theoretically work. What type of programming model should I be using instead? Thanks!

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• Improving performance in this query

  - by Luiz Gustavo F. Gama

  I have 3 tables with user logins: sis_login = administrators tb_rb_estrutura = coordinators tb_usuario = clients I created a VIEW to unite all these users by separating them by levels, as follows: create view `login_names` as select `n1`.`cod_login` as `id`, '1' as `level`, `n1`.`nom_user` as `name` from `dados`.`sis_login` `n1` union all select `n2`.`id` as `id`, '2' as `level`, `n2`.`nom_funcionario` as `name` from `tb_rb_estrutura` `n2` union all select `n3`.`cod_usuario` as `id`, '3' as `level`, `n3`.`dsc_nome` as `name` from `tb_usuario` `n3`; So, can occur up to three ids repeated for different users, which is why I separated by levels. This VIEW is just to return me user name, according to his id and level. considering it has about 500,000 registered users, this view takes about 1 second to load. too much time, but is becomes very small when I need to return the latest posts on the forum of my website. The tables of the forums return the user id and level, then look for a name in this VIEW. I have registered 18 forums. When I run the query, it takes one second for each forum = 18 seconds. OMG. This page loads every time somebody enter my website. This is my query: select `x`.`forum_id`, `x`.`topic_id`, `l`.`nome` from ( select `t`.`forum_id`, `t`.`topic_id`, `t`.`data`, `t`.`user_id`, `t`.`user_level` from `tb_forum_topics` `t` union all select `a`.`forum_id`, `a`.`topic_id`, `a`.`data`, `a`.`user_id`, `a`.`user_level` from `tb_forum_answers` `a` ) `x` left outer join `login_names` `l` on `l`.`id` = `x`.`user_id` and `l`.`level` = `x`.`user_level` group by `x`.`forum_id` asc USING EXPLAIN: id select_type table type possible_keys key key_len ref rows Extra 1 PRIMARY <derived2> ALL NULL NULL NULL NULL 6 Using temporary; Using filesort 1 PRIMARY <derived4> ALL NULL NULL NULL NULL 530415 4 DERIVED n1 ALL NULL NULL NULL NULL 114 5 UNION n2 ALL NULL NULL NULL NULL 2 6 UNION n3 ALL NULL NULL NULL NULL 530299 NULL UNION RESULT ALL NULL NULL NULL NULL NULL 2 DERIVED t ALL NULL NULL NULL NULL 3 3 UNION r ALL NULL NULL NULL NULL 3 NULL UNION RESULT ALL NULL NULL NULL NULL NULL Somebody can help me or give a suggestion?

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• Creating PowerShell Automatic Variables from C#

  - by Uros Calakovic

  I trying to make automatic variables available to Excel VBA (like ActiveSheet or ActiveCell) also available to PowerShell as 'automatic variables'. PowerShell engine is hosted in an Excel VSTO add-in and Excel.Application is available to it as Globals.ThisAddin.Application. I found this thread here on StackOverflow and started created PSVariable derived classes like: public class ActiveCell : PSVariable { public ActiveCell(string name) : base(name) { } public override object Value { get { return Globals.ThisAddIn.Application.ActiveCell; } } } public class ActiveSheet : PSVariable { public ActiveSheet(string name) : base(name) { } public override object Value { get { return Globals.ThisAddIn.Application.ActiveSheet; } } } and adding their instances to the current POwerShell session: runspace.SessionStateProxy.PSVariable.Set(new ActiveCell("ActiveCell")); runspace.SessionStateProxy.PSVariable.Set(new ActiveSheet("ActiveSheet")); This works and I am able to use those variables from PowerShell as $ActiveCell and $ActiveSheet (their value change as Excel active sheet or cell change). Then I read PSVariable documentation here and saw this: "There is no established scenario for deriving from this class. To programmatically create a shell variable, create an instance of this class and set it by using the PSVariableIntrinsics class." As I was deriving from PSVariable, I tried to use what was suggested: PSVariable activeCell = new PSVariable("ActiveCell"); activeCell.Value = Globals.ThisAddIn.Application.ActiveCell; runspace.SessionStateProxy.PSVariable.Set(activeCell); Using this, $ActiveCell appears in my PowerShell session, but its value doesn't change as I change the active cell in Excel. Is the above comment from PSVariable documentation something I should worry about, or I can continue creating PSVariable derived classes? Is there another way of making Excel globals available to PowerShell?

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• Why does GCC need extra declarations in templates when VS does not?

  - by Kyle

  template<typename T> class Base { protected: Base() {} T& get() { return t; } T t; }; template<typename T> class Derived : public Base<T> { public: Base<T>::get; // Line A Base<T>::t; // Line B void foo() { t = 4; get(); } }; int main() { return 0; } If I comment out lines A and B, this code compiles fine under Visual Studio 2008. Yet when I compile under GCC 4.1 with lines A and B commented, I get these errors: In member function ‘void TemplateDerived::foo()’: error: ‘t’ was not declared in this scope error: there are no arguments to ‘get’ that depend on a template parameter, so a declaration of ‘get’ must be available Why would one compiler require lines A and B while the other doesn't? Is there a way to simplify this? In other words, if derived classes use 20 things from the base class, I have to put 20 lines of declarations for every class deriving from Base! Is there a way around this that doesn't require so many declarations?

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• C# Virtual method call in constructor - how to refactor?

  - by Cristi Diaconescu

  I have an abstract class for database-agnostic cursor actions. Derived from that, there are classes that implement the abstract methods for handling database-specific stuff. The problem is, the base class ctor needs to call an abstract method - when the ctor is called, it needs to initialize the database-specific cursor. I know why this shouldn't be done, I don't need that explanation! This is my first implementation, that obviously doesn't work - it's the textbook "wrong way" of doing it. The overridden method accesses a field from the derived class, which is not yet instantiated: public abstract class CursorReader { private readonly int m_rowCount; protected CursorReader() { m_rowCount = CreateCursor(sqlCmd); //virtual call ! } protected abstract int CreateCursor(string sqlCmd); } public class SqlCursorReader : CursorReader { private SqlConnection m_sqlConnection; public SqlCursorReader(string sqlCmd, SqlConnection sqlConnection) { m_sqlConnection = sqlConnection; //field initialized here } protected override int CreateCursor(string sqlCmd) { //uses not-yet-initialized member *m_sqlConnection* //so this throws a NullReferenceException var cursor = new CustomCursor(sqlCmd, m_sqlConnection); return cursor.Count(); } } I will follow up with an answer on my attempts to fix this...

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• Best practices for encrypting continuous/small UDP data

  - by temp

  Hello everyone, I am having an application where I have to send several small data per second through the network using UDP. The application need to send the data in real-time (no waiting). I want to encrypt these data and insure that what I am doing is as secure as possible. Since I am using UDP, there is no way to use SSL/TLS, so I have to encrypt each packet alone since the protocol is connectionless/unreliable/unregulated. Right now, I am using a 128-bit key derived from a passphrase from the user, and AES in CBC mode (PBE using AES-CBC). I decided to use a random salt with the passphrase to derive the 128-bit key (prevent dictionary attack on the passphrase), and of course use IVs (to prevent statistical analysis for packets). However I am concerned about few things: Each packet contains small amount of data (like a couple of integer values per packet) which will make the encrypted packets vulnerable to known-plaintext attacks (which will result in making it easier to crack the key). Also, since the encryption key is derived from a passphrase, this will make the key space way less (I know the salt will help, but I have to send the salt through the network once and anyone can get it). Given these two things, anyone can sniff and store the sent data, and try to crack the key. Although this process might take some time, once the key is cracked all the stored data will be decrypted, which will be a real problem for my application. So my question is, what is the best practices for sending/encrypting continuous small data using a connectionless protocol (UDP)? Is my way the best way to do it? ...flowed? ...Overkill? ... Please note that I am not asking for a 100% secure solution, as there is no such thing. Cheers

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• Best practices for encrytping continuous/small UDP data

  - by temp

  Hello everyone, I am having an application where I have to send several small data per second through the network using UDP. The application need to send the data in real-time (on waiting). I want to encrypt these data and insure that what I am doing is as secure as possible. Since I am using UDP, there is no way to use SSL/TLS, so I have to encrypt each packet alone since the protocol is connectionless/unreliable/unregulated. Right now, I am using a 128-bit key derived from a passphrase from the user, and AES in CBC mode (PBE using AES-CBC). I decided to use a random salt with the passphrase to derive the 128-bit key (prevent dictionary attack on the passphrase), and of course use IVs (to prevent statistical analysis for packets). However I am concerned about few things: Each packet contains small amount of data (like a couple of integer values per packet) which will make the encrypted packets vulnerable to known-plaintext attacks (which will result in making it easier to crack the key). Also, since the encryption key is derived from a passphrase, this will make the key space way less (I know the salt will help, but I have to send the salt through the network once and anyone can get it). Given these two things, anyone can sniff and store the sent data, and try to crack the key. Although this process might take some time, once the key is cracked all the stored data will be decrypted, which will be a real problem for my application. So my question is, what is the best practices for sending/encrypting continuous small data using a connectionless protocol (UDP)? Is my way the best way to do it? ...flowed? ...Overkill? ... Please note that I am not asking for a 100% secure solution, as there is no such thing. Cheers

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