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  • Passing objects by reference or not in C#

    - by Piku
    Suppose I have a class like this: public class ThingManager { List<SomeClass> ItemList; public void AddToList (SomeClass Item) { ItemList.Add(Item); } public void ProcessListItems() { // go through list one item at a time, get item from list, // modify item according to class' purpose } } Assume "SomeClass" is a fairly large class containing methods and members that are quite complex (List<s and arrays, for example) and that there may be a large quantity of them, so not copying vast amounts of data around the program is important. Should the "AddToList" method have "ref" in it or not? And why? It's like trying to learn pointers in C all over again ;-) (which is probably why I am getting confused, I'm trying to relate these to pointers. In C it'd be "SomeClass *Item" and a list of "SomeClass *" variables)

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  • Why am I getting this error when overriding an inherited method?

    - by Sergio Tapia
    Here's my parent class: public abstract class BaseFile { public string Name { get; set; } public string FileType { get; set; } public long Size { get; set; } public DateTime CreationDate { get; set; } public DateTime ModificationDate { get; set; } public abstract void GetFileInformation(); public abstract void GetThumbnail(); } And here's the class that's inheriting it: public class Picture:BaseFile { public override void GetFileInformation(string filePath) { FileInfo fileInformation = new FileInfo(filePath); if (fileInformation.Exists) { Name = fileInformation.Name; FileType = fileInformation.Extension; Size = fileInformation.Length; CreationDate = fileInformation.CreationTime; ModificationDate = fileInformation.LastWriteTime; } } public override void GetThumbnail() { } } I thought when a method was overridden, I could do what I wanted with it. Any help please? :)

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  • For loop index out of range ArgumentOutOfRangeException when multithreading

    - by Lirik
    I'm getting some strange behavior... when I iterate over the dummyText List in the ThreadTest method I get an index out of range exception (ArgumentOutOfRangeException), but if I remove the threads and I just print out the text, then everything works fine. This is my main method: public static Object sync = new Object(); static void Main(string[] args) { ThreadTest(); Console.WriteLine("Press any key to continue."); Console.ReadKey(); } This method throws the exception: private static void ThreadTest() { Console.WriteLine("Running ThreadTest"); Console.WriteLine("Running ThreadTest"); List<String> dummyText = new List<string>() { "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten"}; for (int i = 0; i < dummyText.Count; i++) { Thread t = new Thread(() => PrintThreadName(dummyText[i])); // <-- Index out of range?!? t.Name = ("Thread " + (i)); t.IsBackground = true; t.Start(); } } private static void PrintThreadName(String text) { Random rand = new Random(DateTime.Now.Millisecond); while (true) { lock (sync) { Console.WriteLine(Thread.CurrentThread.Name + " running " + text); Thread.Sleep(1000+rand.Next(0,2000)); } } } This does not throw the exception: private static void ThreadTest() { Console.WriteLine("Running ThreadTest"); List<String> dummyText = new List<string>() { "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten"}; for (int i = 0; i < dummyText.Count; i++) { Console.WriteLine(dummyText[i]); // <-- No exception here } } Does anybody know why this is happening?

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  • What's the performance penalty of weak_ptr?

    - by Kornel Kisielewicz
    I'm currently designing a object structure for a game, and the most natural organization in my case became a tree. Being a great fan of smart pointers I use shared_ptr's exclusively. However, in this case, the children in the tree will need access to it's parent (example -- beings on map need to be able to access map data -- ergo the data of their parents. The direction of owning is of course that a map owns it's beings, so holds shared pointers to them. To access the map data from within a being we however need a pointer to the parent -- the smart pointer way is to use a reference, ergo a weak_ptr. However, I once read that locking a weak_ptr is a expensive operation -- maybe that's not true anymore -- but considering that the weak_ptr will be locked very often, I'm concerned that this design is doomed with poor performance. Hence the question: What is the performance penalty of locking a weak_ptr? How significant is it?

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  • Unresolved external symbol error in c++

    - by Crystal
    I am trying to do a simple hw problem involving namespace, static data members and functions. I am getting an unresolved external symbol error Error 1 error LNK2001: unresolved external symbol "private: static double JWong::SavingsAccount::annualInterestRate" (?annualInterestRate@SavingsAccount@JWong@@0NA) SavingsAccount.obj SavingsAccount And I don't see why I am getting this error. Maybe I don't know something about static variables compared to regular data members that is causing this error. Here is my code: SavingsAccount.h file #ifndef JWONG_SAVINGSACCOUNT_H #define JWONG_SAVINGSACCOUNT_H namespace JWong { class SavingsAccount { public: // default constructor SavingsAccount(); // constructor SavingsAccount(double savingsBalance); double getSavingsBalance(); void setSavingsBalance(double savingsBalance); double calculateMonthlyInterest(); // static functions static void modifyInterestRate(double newInterestRate); static double getAnnualInterestRest(); private: double savingsBalance; // static members static double annualInterestRate; }; } #endif SavingsAccount.cpp file #include <iostream> #include "SavingsAccount.h" // default constructor, set savingsBalance to 0 JWong::SavingsAccount::SavingsAccount() : savingsBalance(0) {} // constructor JWong::SavingsAccount::SavingsAccount(double savingsBalance) : savingsBalance(savingsBalance) {} double JWong::SavingsAccount::getSavingsBalance() { return savingsBalance; } void JWong::SavingsAccount::setSavingsBalance(double savingsBalance) { this->savingsBalance = savingsBalance; } // returns monthly interest and sets savingsBalance to new amount double JWong::SavingsAccount::calculateMonthlyInterest() { double monthlyInterest = savingsBalance * SavingsAccount::annualInterestRate / 12; setSavingsBalance(savingsBalance + monthlyInterest); return monthlyInterest; } void JWong::SavingsAccount::modifyInterestRate(double newInterestRate) { SavingsAccount::annualInterestRate = newInterestRate; } double JWong::SavingsAccount::getAnnualInterestRest() { return SavingsAccount::annualInterestRate; }

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  • C++. How to define template parameter of type T for class A when class T needs a type A template parameter?

    - by jaybny
    Executor class has template of type P and it takes a P object in constructor. Algo class has a template E and also has a static variable of type E. Processor class has template T and a collection of Ts. Question how can I define Executor< Processor<Algo> > and Algo<Executor> ? Is this possible? I see no way to defining this, its kind of an "infinite recursive template argument" See code. template <class T> class Processor { map<string,T> ts; void Process(string str, int i) { ts[str].Do(i); } } template <class P> class Executor { Proc &p; Executor(P &p) : Proc(p) {} void Foo(string str, int i) { p.Process(str,i); } Execute(string str) { } } template <class E> class Algo { static E e; void Do(int i) {} void Foo() { e.Execute("xxx"); } } main () { typedef Processor<Algo> PALGO; // invalid typedef Executor<PALGO> EPALGO; typedef Algo<EPALGO> AEPALGO; Executor<PALGO> executor(PALGO()); AEPALGO::E = executor; }

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  • Moving UIButton around

    - by pbcoder
    I've tried to move a UIButton up and down in a menu. The problem I've got with the following solution is that the timer is not accurate. Sometimes the Button is moved up 122px, sometimes only 120px. How I can fix this? -(IBAction)marketTabClicked:(id)sender { if (marketTabExtended) { NSLog(@"marketTabExtended = YES"); return; } else { if (iPhoneAppsExtended) { timer = [NSTimer scheduledTimerWithTimeInterval:0.005 target: self selector: @selector(animateItemApps) userInfo: nil repeats: YES]; } else { if (homepageExtended) { timer = [NSTimer scheduledTimerWithTimeInterval:0.005 target: self selector: @selector(animateItemHomepage) userInfo: nil repeats: YES]; } else { timer = [NSTimer scheduledTimerWithTimeInterval:0.005 target: self selector: @selector(animateItemMarketing) userInfo: nil repeats: YES]; } } } [self performSelector:@selector(stopTimer) withObject:self afterDelay:0.605]; iPhoneAppsExtended = NO; homepageExtended = NO; marketTabExtended = NO; marketTabExtended = YES; } -(void)animateItemApps { CGPoint movement; movement = CGPointMake(0, -1); homepage.center = CGPointMake(homepage.center.x, homepage.center.y + movement.y); } -(void)animateItemHomepage { CGPoint movement; movement = CGPointMake(0, 1); homepage.center = CGPointMake(homepage.center.x, homepage.center.y + movement.y); //marketTab.center = CGPointMake(marketTab.center.x, marketTab.center.y + movement.y); } -(void)animateItemMarketing { CGPoint movement; movement = CGPointMake(0, -1); //marketTab.center = CGPointMake(marketTab.center.x, marketTab.center.y + movement.y); homepage.center = CGPointMake(homepage.center.x, homepage.center.y + movement.y); } -(void)stopTimer { [timer invalidate]; }

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  • How can I remove a JPanel from a JFrame?

    - by Roman
    Recently I asked here how to add a new JPanel to JFrame. The answer helped me to get a working code. But not I have a related question: "How can I remove an old JPanel". I need that because of the following problem. A new JPanel appears appears when I want (either time limit is exceeded or user press the "Submit" button). But in several seconds some element of the old JPanel appears together with the component of the new JPanel. I do not understand why it happens. I thought that it is because I have to other threads which update the window. But the first thread just add the old panel once (so, it should be finished). And in the second thread I have a loop which is broken (so, it also should be finished). Here is my code: private Thread controller = new Thread() { public void run() { // First we set the initial pane (for the selection of partner). SwingUtilities.invokeLater(new Runnable() { public void run() { frame.getContentPane().add(generatePartnerSelectionPanel()); frame.invalidate(); frame.validate(); } }); // Update the pane for the selection of the parnter. for (int i=40; i>0; i=i-1) { final int sec = i; SwingUtilities.invokeLater(new Runnable() { public void run() { timeLeftLabel.setText(sec + " seconds left."); } }); try {Thread.sleep(1000);} catch (InterruptedException e) {} if (partnerSubmitted) {break;} } // For the given user the selection phase is finished (either the time is over or form was submitted). SwingUtilities.invokeLater(new Runnable() { public void run() { frame.getContentPane().add(generateWaitForGamePanel()); frame.invalidate(); frame.validate(); } }); } };

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  • flash as3, Error #1009

    - by smerels
    I'm making a website that exist out of linked pages. All the pages are on the time line and all the code is in an as3 file. The first page with links works but if I want to place a link on the second frame I get the 1009 error Cannot access a property or method of a null object reference. Because the link doesn't exist on the first frame. This is my code. package { import flash.display.MovieClip; import flash.events.MouseEvent; public class Honger extends MovieClip { public function Honger():void { weten.buttonMode = true; weten.addEventListener(MouseEvent.CLICK, onClickWeten); spelen.buttonMode = true; spelen.addEventListener(MouseEvent.CLICK, onClickSpelen); antwoorden.buttonMode = true; antwoorden.addEventListener(MouseEvent.CLICK, onClickAntwoorden); } public function onClickWeten(e:MouseEvent):void { this.gotoAndStop("vragen"); } public function onClickSpelen(e:MouseEvent):void{ this.gotoAndStop("spel"); } public function onClickAntwoorden(e:MouseEvent):void{ this.gotoAndStop("sp"); } } } Does anyone know how to solve this problem within the code?

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  • Preprocessor Conditionals

    - by Mike
    I was wondering if it would be possible to have a define which changes values at some point in the code be used in a conditional. Basically something like this: //////////////////////////////////////////// SomeFile.cpp #define SHUTDOWN false while(window->isOpen()) { if(SHUTDOWN) window->close(); // Rest of the main loop } //////////////////////////////////////////// SomeOtherFile.cpp if(Escape.isPressed()) { #undef SHUTDOWN #define SHUTDOWN true } Thus causing the app to close. If it's not, would having a function like RenderWindow* getWindow() { return window; } and then calling if(Escape.isPressed()) getWindow()->close(); The best way to do it? I'd rather not go that route because the classes that are calling the key event are members of the class controlling the main loop and the window, so I'd have to set pointers to the containing class in the smaller classes to call getWindow() and it just seems like a more complicated method. But if I can't do it with preprocessor directives I'll just have to use pointers to the parent class.

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  • Using array of Action() in a lambda expression

    - by Sean87
    I want to do some performance measurement for a method that does some work with int arrays, so I wrote the following class: public class TimeKeeper { public TimeSpan Measure(Action[] actions) { var watch = new Stopwatch(); watch.Start(); foreach (var action in actions) { action(); } return watch.Elapsed; } } But I can not call the Measure mehotd for the example below: var elpased = new TimeKeeper(); elpased.Measure( () => new Action[] { FillArray(ref a, "a", 10000), FillArray(ref a, "a", 10000), FillArray(ref a, "a", 10000) }); I get the following errors: Cannot convert lambda expression to type 'System.Action[]' because it is not a delegate type Cannot implicitly convert type 'void' to 'System.Action' Cannot implicitly convert type 'void' to 'System.Action' Cannot implicitly convert type 'void' to 'System.Action' Here is the method that works with arrays: private void FillArray(ref int[] array, string name, int count) { array = new int[count]; for (int i = 0; i < array.Length; i++) { array[i] = i; } Console.WriteLine("Array {0} is now filled up with {1} values", name, count); } What I am doing wrong?

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  • Trying to make a plugin system in C++/Qt

    - by Pirate for Profit
    I'm making a task-based program that needs to have plugins. Tasks need to have properties which can be easily edited, I think this can be done with Qt's Meta-Object Compiler reflection capabilities (I could be wrong, but I should be able to stick this in a QtPropertyBrowser?) So here's the base: class Task : public QObject { Q_OBJECT public: explicit Task(QObject *parent = 0) : QObject(parent){} virtual void run() = 0; signals: void taskFinished(bool success = true); } Then a plugin might have this task: class PrinterTask : public Task { Q_OBJECT public: explicit PrinterTask(QObject *parent = 0) : Task(parent) {} void run() { Printer::getInstance()->Print(this->getData()); // fictional emit taskFinished(true); } inline const QString &getData() const; inline void setData(QString data); Q_PROPERTY(QString data READ getData WRITE setData) // for reflection } In a nutshell, here's what I want to do: // load plugin // find all the Tasks interface implementations in it // have user able to choose a Task and edit its specific Q_PROPERTY's // run the TASK It's important that one .dll has multiple tasks, because I want them to be associated by their module. For instance, "FileTasks.dll" could have tasks for deleting files, making files, etc. The only problem with Qt's plugin setup is I want to store X amount of Tasks in one .dll module. As far as I can tell, you can only load one interface per plugin (I could be wrong?). If so, the only possible way to do accomplish what I want is to create a FactoryInterface with string based keys which return the objects (as in Qt's Plug-And-Paint example), which is a terrible boilerplate that I would like to avoid. Anyone know a cleaner C++ plugin architecture than Qt's to do what I want? Also, am I safely assuming Qt's reflection capabilities will do what I want (i.e. able to edit an unknown dynamically loaded tasks' properties with the QtPropertyBrowser before dispatching)?

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  • C++ STL type_traits question.

    - by Kim Sun-wu
    I was watching the latest C9 lecture and noticed something interesting.. In his introduction to type_traits, Stephan uses the following (as he says, contrived) example: template <typename T> void foo(T t, true_type) { std::cout << t << " is integral"; } template <typename T> void foo(T t, false_type) { std::cout << t << " is not integral"; } template <typename T> void bar(T t) { foo(t, typename is_integral<T>::type()); } This seems to be far more complicated than: template <typename T> void foo(T t) { if(std::is_integral<T>::value) std::cout << "integral"; else std::cout << "not integral"; } Is there something wrong with the latter way of doing it? Is his way better? Why? Thanks.

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  • Is there a general-purpose printf-ish routine defined in any C standard

    - by supercat
    In many C libraries, there is a printf-style routine which is something like the following: int __vgprintf(void *info, (void)(*print_function(void*, char)), const char *format, va_list params); which will format the supplied string and call print_function with the passed-in info value and each character in sequence. A function like fprintf will pass __vgprintf the passed-in file parameter and a pointer to a function which will cast its void* to a FILE* and output the passed-in character to that file. A function like snprintf will create a struct holding a char* and length, and pass the address of that struct to a function which will output each character in sequence, space permitting. Is there any standard for such a function, which could be used if e.g. one wanted a function to output an arbitrary format to a TCP port? A common approach is to allocate a buffer one hopes is big enough, use snprintf to put the data there, and then output the data from the buffer. It would seem cleaner, though, if there were a standard way to to specify that the print formatter should call a user-supplied routine with each character.

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  • Starting an STA thread, but with parameters to the final function

    - by DRapp
    I'm a bit weak on how some delegates behave, such as passing a method as the parameter to be invoked. While trying to do some NUnit test scripts, I have something that I need to run many test with. Each of these tests requires a GUI created and thus the need for an STA thread. So, I have something like public class MyTest { // the Delegate "ThreadStart" is part of the System.Threading namespace and is defined as // public delegate void ThreadStart(); protected void Start_STA_Thread(ThreadStart whichMethod) { Thread thread = new Thread(whichMethod); thread.SetApartmentState(ApartmentState.STA); //Set the thread to STA thread.Start(); thread.Join(); } [Test] public void Test101() { // Since the thread issues an INVOKE of a method, I'm having it call the // corresponding "FromSTAThread" method, such as Start_STA_Thread( Test101FromSTAThread ); } protected void Test101FromSTAThread() { MySTA_RequiredClass oTmp = new MySTA_RequiredClass(); Assert.IsTrue( oTmp.DoSomething() ); } } This part all works fine... Now the next step. I now have a different set of tests that ALSO require an STA thread. However, each "thing" I need to do requires two parameters... both strings (for this case). How do I go about declaring proper delegate so I can pass in the method I need to invoke, AND the two string parameters in one shot... I may have 20+ tests to run with in this pattern and may have future of other similar tests with different parameter counts and types of parameters too. Thanks.

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  • How can change my code to can user insert numbers of year and days ?

    - by MANAL
    I make code to calculate the date of today and the date for two years ago before the day of today and also calculate day before 5 days. I want user insert the numbers of years and days to make compare between date of today . import java.util.Date; import java.util.Calendar; import java.text.SimpleDateFormat; import java.util.Scanner; public class Calendar1 { private static void doCalendarTime() { System.out.print("*************************************************"); Date now = Calendar.getInstance().getTime(); System.out.print(" \n Calendar.getInstance().getTime() : " + now); System.out.println(); } private static void doSimpleDateFormat() { System.out.print("*************************************************"); System.out.print("\n\nSIMPLE DATE FORMAT\n"); System.out.print("*************************************************"); // Get today's date Calendar now = Calendar.getInstance(); SimpleDateFormat formatter = new SimpleDateFormat("E yyyy.MM.dd 'at' hh:mm:ss a zzz"); System.out.print(" \n It is now : " + formatter.format(now.getTime())); System.out.println(); } private static void doAdd() { System.out.println("ADD / SUBTRACT CALENDAR / DATEs"); System.out.println("================================================================="); // Get today's date Calendar now = Calendar.getInstance(); Calendar working; SimpleDateFormat formatter = new SimpleDateFormat("E yyyy.MM.dd 'at' hh:mm:ss a zzz"); working = (Calendar) now.clone(); working.add(Calendar.DAY_OF_YEAR, - (365 * 2)); System.out.println (" Two years ago it was: " + formatter.format(working.getTime())); working = (Calendar) now.clone(); working.add(Calendar.DAY_OF_YEAR, + 5); System.out.println(" In five days it will be: " + formatter.format(working.getTime())); System.out.println(); } public static void main(String[] args) { System.out.println(); doCalendarTime(); doSimpleDateFormat(); doAdd(); } } help me .

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  • How can I remove the present view when I have added more than one subView ?

    - by srikanth rongali
    How can I remove the present view when I touched the close button. I did [self.view removeFromSuperView] when I added only one subView. It worked. But, I have now added another subView to the previous subView. I need to to get the parent view . How can I do it. My code of adding the subView is here. When I did the following only one view is removed. //FirstViewController: UIViewController -(void)libraryFunction:(id)sender { LibraryController *libraryController = [[LibraryController alloc]init]; [self.view addSubview:libraryController.view]; } //LibraryController: UIViewController -(void)viewDidLoad{ RootViewController *rootViewController = [[RootViewController alloc] initWithStyle:UITableViewStylePlain]; UINavigationController *aNavigationController = [[UINavigationController alloc] initWithRootViewController:rootViewController]; self.navController = aNavigationController; [aNavigationController release]; [rootViewController release]; [self.view addSubview:navController.view]; } //RootViewController: UITableViewController - (void)viewDidLoad { [super viewDidLoad]; self.navigationItem.rightBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"Close" style:UIBarButtonItemStyleBordered target:self action:@selector(close:)]; } -(void)close:(id)sender { [self.view removeFromSuperview]; } Thank You.

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  • How to build a control programatically?

    - by W_K
    I have custom control written in Java. For the sake of simplicity lets assume that it looks like this: public class HelloworldControl extends UIComponentBase { @Override public void decode(FacesContext context) { String cid = this.getClientId(context); ... super.decode(context); } @Override public void encodeBegin(FacesContext context) throws IOException { ResponseWriter writer = context.getResponseWriter(); writer.writeText("Hello world!", this); // I want a view!! } @Override public void encodeEnd(FacesContext context) throws IOException { ResponseWriter writer = context.getResponseWriter(); ... } public void restoreState(FacesContext context, Object state) { Object values[] = (Object[]) state; ... super.restoreState(context, values[0]); } public Object saveState(FacesContext context) { Object values[] = ... } } I would like to add programatically child control to it. For example I would like a child view control to render a view just under the Hellow world text. How can i do this? What is the standard procedure to build dynamically a control? To put it simply - I want programatically build a hierarchy of standard components and I want to attach it to my control.

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  • What is the purpose of unit testing an interface repository

    - by ahsteele
    I am unit testing an ICustomerRepository interface used for retrieving objects of type Customer. As a unit test what value am I gaining by testing the ICustomerRepository in this manner? Under what conditions would the below test fail? For tests of this nature is it advisable to do tests that I know should fail? i.e. look for id 4 when I know I've only placed 5 in the repository I am probably missing something obvious but it seems the integration tests of the class that implements ICustomerRepository will be of more value. [TestClass] public class CustomerTests : TestClassBase { private Customer SetUpCustomerForRepository() { return new Customer() { CustId = 5, DifId = "55", CustLookupName = "The Dude", LoginList = new[] { new Login { LoginCustId = 5, LoginName = "tdude" }, new Login { LoginCustId = 5, LoginName = "tdude2" } } }; } [TestMethod] public void CanGetCustomerById() { // arrange var customer = SetUpCustomerForRepository(); var repository = Stub<ICustomerRepository>(); // act repository.Stub(rep => rep.GetById(5)).Return(customer); // assert Assert.AreEqual(customer, repository.GetById(5)); } } Test Base Class public class TestClassBase { protected T Stub<T>() where T : class { return MockRepository.GenerateStub<T>(); } } ICustomerRepository and IRepository public interface ICustomerRepository : IRepository<Customer> { IList<Customer> FindCustomers(string q); Customer GetCustomerByDifID(string difId); Customer GetCustomerByLogin(string loginName); } public interface IRepository<T> { void Save(T entity); void Save(List<T> entity); bool Save(T entity, out string message); void Delete(T entity); T GetById(int id); ICollection<T> FindAll(); }

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  • Constructor Overload Problem in C++ Inheritance

    - by metdos
    Here my code snippet: class Request { public: Request(void); ……….. } Request::Request(void) { qDebug()<<"Request: "<<"Hello World"; } class LoginRequest :public Request { public: LoginRequest(void); LoginRequest(QDomDocument); …………… } LoginRequest::LoginRequest(void) { qDebug()<<"LoginRequest: "<<"Hello World"; requestType=LOGIN; requestId=-1; } LoginRequest::LoginRequest(QDomDocument doc){ qDebug()<<"LoginRequest: "<<"Hello World with QDomDocument"; LoginRequest::LoginRequest(); xmlDoc_=doc; } When call constructor of Overrided LoginRequest LoginRequest *test=new LoginRequest(doc); I came up with this result: Request: Hello World LoginRequest: Hello World with QDomDocument Request: Hello World LoginRequest: Hello World Obviously both constructor of LoginRequest called REquest constructor. Is there any way to cape with this situation? I can construct another function that does the job I want to do and have both constructors call that function. But I wonder is there any solution?

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  • List of functions references

    - by Ockonal
    Hello, I'm using boost::function for making references to the functions. Can I make a list of references? For example: boost::function<bool (Entity &handle)> behaviorRef; And I need in a list of such pointers. For example: std::vector<behaviorRef> listPointers; Of course it's wrong code due to behaviorRef isn't a type. So the question is: how can I store a list of pointers for the function?

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  • Java Concurrency in practice sample question

    - by andy boot
    I am reading "Java Concurrency in practice" and looking at the example code on page 51. This states that if a thread has references to a shared object then other threads may be able to access that object before the constructor has finished executing. I have tried to put this into practice and so I wrote this code thinking that if I ran it enough times a RuntimeException("World is f*cked") would occur. But it isn't doing. Is this a case of the Java spec not guaranting something but my particular implementation of java guaranteeing it for me? (java version: 1.5.0 on Ubuntu) Or have I misread something in the book? Code: (I expect an exception but it is never thrown) public class Threads { private Widgit w; public static void main(String[] s) throws Exception { while(true){ Threads t = new Threads(); t.runThreads(); } } private void runThreads() throws Exception{ new Checker().start(); w = new Widgit((int)(Math.random() * 100) + 1); } private class Checker extends Thread{ private static final int LOOP_TIMES = 1000; public void run() { int count = 0; for(int i = 0; i < LOOP_TIMES; i++){ try { w.checkMe(); count++; } catch(NullPointerException npe){ //ignore } } System.out.println("checked: "+count+" times out of "+LOOP_TIMES); } } private static class Widgit{ private int n; private int n2; Widgit(int n) throws InterruptedException{ this.n = n; Thread.sleep(2); this.n2 = n; } void checkMe(){ if (n != n2) { throw new RuntimeException("World is f*cked"); } } } }

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  • SWT Problem with MouseTrackListener and Shell

    - by Krt_Malta
    Hi! I'm developing an Eclipse plug-in and I have a problem which is reproduced in this small SWT application: public static void main(String[] args) { Display display = new Display(); Shell shell = new Shell(display); Text text = new Text(shell, SWT.MULTI | SWT.WRAP | SWT.READ_ONLY | SWT.V_SCROLL); text.setText("Hello"); shell.setLayout(new FillLayout()); shell.addMouseTrackListener(new MouseTrackListener() { public void mouseEnter(MouseEvent arg0) { System.out.println("mouseEnter"); } public void mouseExit(MouseEvent arg0) { System.out.println("mouseExit"); } public void mouseHover(MouseEvent arg0) { System.out.println("mouseHover"); } }); // Display the window shell.open(); while (!shell.isDisposed()) { if (!display.readAndDispatch()) { display.sleep(); } } display.dispose(); } As you can see I'm creating a shell and putting a Textbox inside it and putting it all across the shell. Then I attach a MouseTrackListener to the shell. The events don't fire (as in when I hover in the shell "mouseHover" is not printed etc). When I remove the Textbox the events fire. Can anyone tell me where the problem lies please? I don't want to attach a listener to the textbox but to the shell. I'll really appreciate the help because I've been trying to trace it for quite some time now. Thanks and regards, Krt_Malta

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  • Function template accepting nothing less than a bidirectional iterator or a pointer

    - by san
    I need a function template that accepts two iterators that could be pointers. If the two arguments are random_access iterators I want the return type to be an object of std::iterator<random_access_iterator_tag, ...> type else a std::iterator<bidirectional_iterator_tag, ...> type. I also want the code to refuse compilation if the arguments are neither a bidirectional iterator, nor a pointer. I cannot have dependency on third party libraries e.g. Boost Could you help me with the signature of this function so that it accepts bidirectional iterators as well as pointers, but not say input_iterator, output_iterator, forward_iterators. One partial solution I can think of is the following template<class T> T foo( T iter1, T iter2) { const T tmp1 = reverse_iterator<T>(iter1); const T tmp2 = reverse_iterator<T>(iter2); // do something } The idea is that if it is not bidirectional the compiler will not let me construct a reverse_iterator from it.

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  • How to force inclusion of an object file in a static library when linking into executable?

    - by Brian Bassett
    I have a C++ project that due to its directory structure is set up as a static library A, which is linked into shared library B, which is linked into executable C. (This is a cross-platform project using CMake, so on Windows we get A.lib, B.dll, and C.exe, and on Linux we get libA.a, libB.so, and C.) Library A has an init function (A_init, defined in A/initA.cpp), that is called from library B's init function (B_init, defined in B/initB.cpp), which is called from C's main. Thus, when linking B, A_init (and all symbols defined in initA.cpp) is linked into B (which is our desired behavior). The problem comes in that the A library also defines a function (Af, defined in A/Afort.f) that is intended to by dynamically loaded (i.e. LoadLibrary/GetProcAddress on Windows and dlopen/dlsym on Linux). Since there are no references to Af from library B, symbols from A/Afort.o are not included into B. On Windows, we can artifically create a reference by using the pragma: #pragma comment (linker, "/export:_Af") Since this is a pragma, it only works on Windows (using Visual Studio 2008). To get it working on Linux, we've tried adding the following to A/initA.cpp: extern void Af(void); static void (*Af_fp)(void) = &Af; This does not cause the symbol Af to be included in the final link of B. How can we force the symbol Af to be linked into B?

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