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  • Copying a Polymorphic object in C++

    - by doron
    I have base-class Base from which is derived Derived1, Derived2 and Derived3. I have constructed an instance for one of the the derived classes which I store as Base* a. I now need to make a deep copy of the object which I will store as Base* b. As far as I know, the normal way of copying a class is to use copy constructors and to overload operator=. However since I don't know whether a is of type Derived1, Derived2 or Derived3, I cannot think of a way of using either the copy constructor or operator=. The only way I can think of to cleanly make this work is to implement something like: class Base { public: virtual Base* Clone() = 0; }; and the implement Clone in in the derived class as in: class Derivedn : public Base { public: Base* Clone() { Derived1* ret = new Derived1; copy all the data members } }; Java tends to use Clone quite a bit is there more of a C++ way of doing this?

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  • Java Spring 3.0 MVC Annotation vs COC. Whats the preferred method in the Java community?

    - by Athens
    I am using Spring's MVC framework for an application I'm hosting on Google's App Engine. So far, my controllers are registered via the @Controller annotation; however, prior to getting into Spring, I evaluated ASP.net MVC 2 which requires no configuration and is based on convention. Is convention over configuration (COC) the current and preferred method in the Java community to implement MVC with Spring. Also, this may be a result of my limited knowledge so far but i noticed that i could only instantiate my Controllers the required constuctor injection if i use the COC method via the ControllerClassNameHandlerMapping. For instance the following controller bean config will fail if i use the defaultannotationhandlermapping. <bean id="c" class="com.domain.TestController"> <constructor-arg ref="service" /> </bean> <bean id="service" class="com.domain.Service" /> My com.domain.TestController controller works fine if i use ControllerClassNameHandlerMapping/COC but it results in an error when i use defaultannotationhandlermapping/Annotations.

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  • PHP & MySQLi timeout

    - by Dt7
    Whenever I try to create a mysqli object, as in; $mysqli = new mysqli(host, user, pass, table); ...the page just loads for around a minute, then stops, showing all the content of the page up until that line. info() says that MySQLi (and MySQL if that matters) are enabled, and I can access the MySQL CLI. I'm also working on a local machine, not a remote server. I feel like I've missed something obvious. Can anyone shed some light on it? Edit: just for clarification, I am actually putting real values into the mysqli constructor :)

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  • C# property definition

    - by Sunny
    For C# properties, I can do this: public class Employee{ public string Name { get; private set; } public Employee(string name){ Name = name; } } which means that the Name property can be set within the class Employee & can be read publicly. But, if I want to restrict the set to only within the constructors of the Employee class, I need to do: public class Employee{ public readonly string Name = String.Empty; public Employee(string name){ Name = name; } } But, for this case, I had to change the property to a field. Is there any reason this is not possible/allowed in C#: public class Employee{ public string Name { get; private readonly set; } public Employee(string name){ Name = name; } } IMO this will allow us to have properties which can be set only in the constructor & does not require us to change properties to fields... Thanks!

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  • How to return radio checked object with jQuery ?

    - by Kim
    HTML <input type="radio" name="rdName" id="uniqueID1" value="1" checked="checked"> <input type="radio" name="rdName" id="uniqueID2" value="2"> <input type="radio" name="rdName" id="uniqueID3" value="3"> jQuery #1 $('input:radio[name=rdName]:checked').val(); jQuery #2 $('input[name=rdName]:checked'); jQuery #1 gets the value of checked radio, but I need to get the whole object to get the ID. jQuery #2 get this (from Chrome Dev console). Object "0" is the actual object I need, but I am unable to just that. 0: HTMLInputElement constructor: function Object() context: HTMLDocument length: 1 prevObject: Object selector: input[name=rdName]:checked __proto__: Object Any ideas how to isolate the needed object ?

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  • In Prism (CAL), how can I RegisterPresenterWithRegion instead of RegisterViewWithRegion

    - by Edward Tanguay
    I have a module in a Prism application and in its initialize method I want to register a presenter instead of a view with a region, i.e. I want to do this: PSEUDO-CODE: regionManager.RegisterPresenterWithRegion( "MainRegion", typeof(Presenters.EditCustomerPresenter)); instead of loading a view like this: regionManager.RegisterViewWithRegion( "MainRegion", typeof(Views.EditCustomerView)); The presenter would of course bring along its own view and ultimately register this view in the region, but it would allow me to bind the presenter to the view in the presenter's constructor instead of binding the two together in XAML (which is more of a decoupled MVVM pattern which I want to avoid here). How can I add a Presenter to a Region instead of a view? namespace Client.Modules.CustomerModule { [Module(ModuleName = "CustomerModule")] public class CustomerModule : IModule { private readonly IRegionManager regionManager; public CustomerModule(IRegionManager regionManager) { this.regionManager = regionManager; } public void Initialize() { regionManager.RegisterViewWithRegion("MainRegion", typeof(Views.EditCustomerView)); } } }

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  • What is "sentry object" in C++?

    - by Romain Hippeau
    I answered this question, and Potatoswatter answered too as The modern C++ equivalent would be a sentry object: construct it at the beginning of a function, with its constructor implementing call(), and upon return (or abnormal exit), its destructor implements I am not familiar with using sentry objects in C++. I thought they were limited to input and output streams. Could somebody explain to me about C++ sentry objects as well as how to use them as an around interceptor for one or more methods in a class ? i.e. How to do this ? Sentry objects are very similar indeed. On the one hand they require explicit instantiation (and being passed this) but on the other hand you can add to them so that they check not only the invariants of the class but some pre/post conditions for the function at hand.

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  • Creating New Objects in JavaScript

    - by Ken Ray
    I'm a relatively newbie to object oriented programming in JavaScript, and I'm unsure of the "best" way to define and use objects in JavaScript. I've seen the "canonical" way to define objects and instantiate a new instance, as shown below. function myObjectType(property1, propterty2) { this.property1 = property1, this.property2 = property2 } // now create a new instance var myNewvariable = new myObjectType('value for property1', 'value for property2'); But I've seen other ways to create new instances of objects in this manner: var anotherVariable = new someObjectType({ property1: "Some value for this named property", property2: "This is the value for property 2" }); I like how that second way appears - the code is self documenting. But my questions are: Which way is "better"? Can I use that second way to instantiate a variable of an object type that has been defined using the "classical"way of defining the object type with that implicit constructor? If I want to create an array of these objects, are there any other considerations? Thanks in advance.

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  • Java: constructing a file from a URI?

    - by AP257
    I need to obtain a File object from a URI, working in Java, but keep getting a length of zero - though I know the file size is not zero. I need the File object to pass to another constructor. I'm not sure if it's because I'm constructing it in the wrong way? Here's my code: File videoFile = new File(videoURI.getPath()); if (videoFile == null) { Log.d(LOG_TAG, "File not found!"); return false; } Log.d(LOG_TAG, "about to upload, filepath: " + videoFile.getPath()); Log.d(LOG_TAG, "File length: " + String.valueOf(videoFile.length())); The log output doesn't spit out 'File not found!', and prints a non-null path, but shows a length of 0.

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  • CodeIgniter's Scaffolding not working

    - by 01010011
    Hi, I keep getting a 404 Page Not Found whenever I try to access CodeIgniter's Scaffolding page in my browser, like so: localhost/codeignitor/index.php/blog/scaffolding/mysecretword I can access localhost/codeignitor/index.php/blog just fine. I followed CodeIgnitor's instructions in their "Create a blog in 20 minutes" by storing my database settings in the database.php file; and automatically connecting to the database by inserting "database" in the core array of the autoload.php; and I've added both parent::Controller(); and $this-load-scaffolding('myTableName') to blog's constructor. It still gives me this 404. Any suggestions?

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  • Static classes in PHP via abstract keyword?

    - by Boldewyn
    According to the PHP manual, a class like this: abstract class Example {} cannot be instantiated. If I need a class without instance, e.g. for a registry pattern: class Registry {} // and later: echo Registry::$someValue; would it be considered good style to simply declare the class as abstract? If not, what are the advantages of hiding the constructor as protected method compared to an abstract class? Rationale for asking: As far as I see it, it could a bit of feature abuse, since the manual refers to abstract classes more as like blueprints for later classes with instantiation possibility.

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  • C++ Allocate Memory Without Activating Constructors

    - by schnozzinkobenstein
    I'm reading in values from a file which I will store in memory as I read them in. I've read on here that the correct way to handle memory location in C++ is to always use new/delete, but if I do: DataType* foo = new DataType[sizeof(DataType) * numDataTypes]; Then that's going to call the default constructor for each instance created, and I don't want that. I was going to do this: DataType* foo; char* tempBuffer=new char[sizeof(DataType) * numDataTypes]; foo=(DataType*) tempBuffer; But I figured that would be something poo-poo'd for some kind of type-unsafeness. So what should I do? And in researching for this question now I've seen that some people are saying arrays are bad and vectors are good. I was trying to use arrays more because I thought I was being a bad boy by filling my programs with (what I thought were) slower vectors. What should I be using???

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  • Beginner having a problem with classes

    - by David
    I'm working through O'Reilly's "Learning Python" and having a problem with classes. I think I understand the concept, but in practice have stumbled upon this problem. Fron page 88-89: >>> class Worker: def __innit__(self, name, pay): self.name=name self.pay=pay def lastName(self): return self.name.split()[-1] def giveRaise(self, percent): self.pay*=(1.0+percent) Then the book says "Calling the class like a function generates instances of a new type ...etc" and gives this example. bob = Worker('Bob Smith', 50000) This gives me this error: TypeError: this constructor takes no arguments. And then I start muttering profanities. So what am I doing wrong here? Thanks for the help.

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  • C++ Linked List - Reading data from a file with a sentinel

    - by Nick
    So I've done quite a bit of research on this and can't get my output to work correctly. I need to read in data from a file and have it stored into a Linked List. The while loop used should stop once it hits the $$$$$ sentinel. Then I am to display the data (by searching by ID Number[user input]) I am not that far yet I just want to properly display the data and get it read in for right now. My problem is when it displays the data is isn't stopping at the $$$$$ (even if I do "inFile.peek() != EOF and omit the $$$$$) I am still getting an extra garbage record. I know it has something to do with my while loop and how I am creating a new Node but I can't get it to work any other way. Any help would be appreciated. students.txt Nick J Cooley 324123 60 70 80 90 Jay M Hill 412254 70 80 90 100 $$$$$ assign6.h file #pragma once #include <iostream> #include <string> using namespace std; class assign6 { public: assign6(); // constructor void displayStudents(); private: struct Node { string firstName; string midIni; string lastName; int idNum; int sco1; //Test score 1 int sco2; //Test score 2 int sco3; //Test score 3 int sco4; //Test score 4 Node *next; }; Node *head; Node *headPtr; }; assign6Imp.cpp // Implementation File #include "assign6.h" #include <fstream> #include <iostream> #include <string> using namespace std; assign6::assign6() //constructor { ifstream inFile; inFile.open("students.txt"); head = NULL; head = new Node; headPtr = head; while (inFile.peek() != EOF) //reading in from file and storing in linked list { inFile >> head->firstName >> head->midIni >> head->lastName; inFile >> head->idNum; inFile >> head->sco1; inFile >> head->sco2; inFile >> head->sco3; inFile >> head->sco4; if (inFile != "$$$$$") { head->next = NULL; head->next = new Node; head = head->next; } } head->next = NULL; inFile.close(); } void assign6::displayStudents() { int average = 0; for (Node *cur = headPtr; cur != NULL; cur = cur->next) { cout << cur->firstName << " " << cur->midIni << " " << cur->lastName << endl; cout << cur->idNum << endl; average = (cur->sco1 + cur->sco2 + cur->sco3 + cur->sco4)/4; cout << cur->sco1 << " " << cur->sco2 << " " << cur->sco3 << " " << cur->sco4 << " " << "average: " << average << endl; } }

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  • Using static mutex in a class

    - by Dmitry Yudakov
    I have a class that I can have many instances of. Inside it creates and initializes some members from a 3rd party library (that use some global variables) and is not thread-safe. I thought about using static boost::mutex, that would be locked in my class constructor and destructor. Thus creating and destroying instances among my threads would be safe for the 3rd party members. class MyClass { static boost::mutex mx; // 3rd party library members public: MyClass(); ~MyClass(); }; MyClass::MyClass() { boost::mutex::scoped_lock scoped_lock(mx); // create and init 3rd party library stuff } MyClass::~MyClass() { boost::mutex::scoped_lock scoped_lock(mx); // destroy 3rd party library stuff } I cannot link because I receive error: undefined reference to `MyClass::mx` Do I need some special initialization of such static member? Is the whole conception of static mutex wrong?

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  • QT drawing without erasing widget

    - by faya
    Hello, If I have a derived object of QWidget class and on slot function in it I have an update(). here is some pseudocode: *.h slot: updateNow(); *.cpp constructor() { setPalllete(QPallete(QColor(250,250,200))); setAUtoFillBackground(true); } updateNow() { update(); } paintEvent() { QPainter painter(this); painter.drawRect(1,2,3,4); } So how should I don't get erased my pallete after update() call? P.S. - Sorry for my English and only pseudocode.

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  • Should i use HttpResponse.End() for a fast webapp?

    - by acidzombie24
    HttpResponse.End() seems to throw an exception according to msdn. Right now i have the choice of returning a value to say end thread (it only goes 2 functions deep) or i can call end(). I know that throwing exceptions is significantly slower (read the comment for a C#/.NET test) so if i want a fast webapp should i consider not calling it when it is trivially easy to not call it? -edit- I do have a function call in certain functions and in the constructor in classes to ensure the user is logged in. So i call HttpResponse.End() in enough places although hopefully in regular site usage it doesn't occur too often.

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  • Java - SwingWorker - problem in done() method

    - by Yatendra Goel
    I am using javax.swing.SwingWorker for the first time. I want to update a JLabel from the interim result published by the swing worker as follows: publish("Published String"); Now to update the JLabel, I have coded the following: process(List<String> chunks) { if (chunks.size() > 0) { String text = chunks.get(chunks.size() - 1); label.setText(text); } } The above code works but my problem(or to be more specific, my doubt) is as follows: The above swing worker task is an annonymous inner class so it can access label field. But what if I want to make the swing worker class a non-inner class. Should I need to pass label as an argument to the constructor of swing worker class so that the process() method can access. Or Is there any other way? What approach does other developer follow to update UI components from the swing worker class' result when the swing worker class is not an inner class?

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  • c++ defining a static member of a template class with type inner class pointer

    - by Jack
    I have a template class like here (in a header) with a inner class and a static member of type pointer to inner class template <class t> class outer { class inner { int a; }; static inner *m; }; template <class t> outer <t>::inner *outer <t>::m; when i want to define that static member i says "error: expected constructor, destructor, or type conversion before '*' token" on the last line (mingw32-g++ 3.4.5)

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  • Flash CS, reference root from external class

    - by Lotus
    Hi, I made this class and I put it in the same package of Timeline.as (the Document Class): package { import flash.utils.Timer; import flash.events.TimerEvent; public class Counter2 extends Timer { public function Counter2(delay:Number, repeatCount:int=0) { super(delay, repeatCount); super.addEventListener(TimerEvent.TIMER, timerHandler); } public override function start():void { super.start(); } public override function stop():void { super.stop(); } public function timerHandler(evt:TimerEvent) { trace(evt.target.currentCount); } } } This class is instanciated in Timeline.as constructor. Is there any way to reference Timeline(root) from this class? And, if so, how? Thanks!

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  • Is the JavaScript RegExp implicit method deprecated?

    - by Eric
    So everyone knows what I mean by "implicit methods"? They're like those default properties from the Windows COM days of yore, where you could type something like val = obj(arguments) and it would be interpreted as val = obj.defaultMethod(arguments) I just found out JavaScript has the same thing: the default method of a RegExp object appears to be 'exec', as in /(\w{4})/('yip jump man')[1] ==> jump This even works when the RegExp object is assigned to a variable, and even when it's created with the RegExp constructor, instead of /.../, which is good news to us fans of referential transparency. Where is this documented, and/or is it deprecated?

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  • Panel is not displaying in JFrame

    - by mallikarjun
    I created a chat panel and added to Jframe but the panel is not displaying. But my sop in the chat panel are displaying in the console. Any one please let me know what could be the problem My Frame public class MyFrame extends JFrame { MyPanel chatClient; String input; public MyFrame() { input = (String)JOptionPane.showInputDialog(null, "Name:", "Connect to chat server", JOptionPane.QUESTION_MESSAGE, null,null, "Test"); input=input.trim(); chatClient = new MyPanel("localhost",input); setVisible(true); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); add(chatClient); } public static void main(String...args){ new MyFrame(); } } MyPanel: public class MyPanel extends JPanel{ ChatClient chatClient; public MyPanel(String host, String uid) { chatClient= new ChatClient(host,uid); add(chatClient.getChatPanel()); this.setVisible(true); } } chat panel: public class ChatClient { Client client; String name; ChatPanel chatPanel; String hostid; public ChatClient(String host,String uid){ client = new Client(); client.start(); System.out.println("in constructor"); Network.register(client); client.addListener(new Listener(){ public void connected(Connection connection){ System.out.println("in client connected method"); Network.RegisterName registerName = new Network.RegisterName(); registerName.name=name; client.sendTCP(registerName); } public void received(Connection connection,Object object){ System.out.println("in client received method"); if (object instanceof Network.UpdateNames) { Network.UpdateNames updateNames = (Network.UpdateNames)object; //chatFrame.setNames(updateNames.names); System.out.println("got it message"); return; } if (object instanceof Network.ChatMessage) { Network.ChatMessage chatMessage = (Network.ChatMessage)object; //chatFrame.addMessage(chatMessage.text); System.out.println("send it message"); return; } } }); // end of listner name=uid.trim(); hostid=host.trim(); chatPanel = new ChatPanel(hostid,name); chatPanel.setSendListener(new Runnable(){ public void run(){ Network.ChatMessage chatMessage = new Network.ChatMessage(); chatMessage.chatMessage=chatPanel.getSendText(); client.sendTCP(chatMessage); } }); new Thread("connect"){ public void run(){ try{ client.connect(5000, hostid,Network.port); }catch(IOException e){ e.printStackTrace(); } } }.start(); }//end of constructor static public class ChatPanel extends JPanel{ CardLayout cardLayout; JList messageList,nameList; JTextField sendText; JButton sendButton; JPanel topPanel,bottomPanel,panel; public ChatPanel(String host,String user){ setSize(600, 200); this.setVisible(true); System.out.println("Chat panel "+host+"user: "+user); { panel = new JPanel(new BorderLayout()); { topPanel = new JPanel(new GridLayout(1,2)); panel.add(topPanel); { topPanel.add(new JScrollPane(messageList=new JList())); messageList.setModel(new DefaultListModel()); } { topPanel.add(new JScrollPane(nameList=new JList())); nameList.setModel(new DefaultListModel()); } DefaultListSelectionModel disableSelections = new DefaultListSelectionModel() { public void setSelectionInterval (int index0, int index1) { } }; messageList.setSelectionModel(disableSelections); nameList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION); } { bottomPanel = new JPanel(new GridBagLayout()); panel.add(bottomPanel,BorderLayout.SOUTH); bottomPanel.add(sendText=new JTextField(),new GridBagConstraints(0,0,1,1,1,0,GridBagConstraints.CENTER,GridBagConstraints.BOTH,new Insets(0,0,0,0),0,0)); bottomPanel.add(sendButton=new JButton(),new GridBagConstraints(1,0,1,1,0,0,GridBagConstraints.CENTER,0,new Insets(0,0,0,0),0,0)); } } sendText.addActionListener(new ActionListener(){ public void actionPerformed(ActionEvent e){ sendButton.doClick(); } }); } public void setSendListener (final Runnable listener) { sendButton.addActionListener(new ActionListener() { public void actionPerformed (ActionEvent evt) { if (getSendText().length() == 0) return; listener.run(); sendText.setText(""); sendText.requestFocus(); } }); } public String getSendText () { return sendText.getText().trim(); } public void setNames (final String[] names) { EventQueue.invokeLater(new Runnable(){ public void run(){ DefaultListModel model = (DefaultListModel)nameList.getModel(); model.removeAllElements(); for(String name:names) model.addElement(name); } }); } public void addMessage (final String message) { EventQueue.invokeLater(new Runnable() { public void run () { DefaultListModel model = (DefaultListModel)messageList.getModel(); model.addElement(message); messageList.ensureIndexIsVisible(model.size() - 1); } }); } } public JPanel getChatPanel(){ return chatPanel; } }

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  • Are returned locals automatically xvalues

    - by mark
    Following on from a comment I made on this: passing std::vector to constructor and move semantics Is the std::move necessary in the following code, to ensure that the returned value is a xvalue? std::vector<string> buildVector() { std::vector<string> local; // .... build a vector return std::move(local); } It is my understanding that this is required. I have often seen this used when returning a std::unique_ptr from a function, however GManNickG made the following comment: It is my understanding that in a return statement all local variables are automatically xvalues (expiring values) and will be moved, but I'm unsure if that only applies to the returned object itself. So OP should go ahead and put that in there until I'm more confident it shouldn't have to be. :) Can anyone clarify if the std::move is necessary? Is the behaviour compiler dependent?

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  • Implementing operator< in C++

    - by Vulcan Eager
    I have a class with a few numeric fields such as: class Class1 { int a; int b; int c; public: // constructor and so on... bool operator<(const Class1& other) const; }; I need to use objects of this class as a key in an std::map. I therefore implement operator<. What is the simplest implementation of operator< to use here?

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  • Strict pointer aliasing: any solution for a specific problem?

    - by doublep
    I have a problem caused by breaking strict pointer aliasing rule. I have a type T that comes from a template and some integral type Int of the same size (as with sizeof). My code essentially does the following: T x = some_other_t; if (*reinterpret_cast <Int*> (&x) == 0) ... Because T is some arbitary (other than the size restriction) type that could have a constructor, I cannot make a union of T and Int. (This is allowed only in C++0x only and isn't even supported by GCC yet). Is there any way I could rewrite the above pseudocode to preserve functionality and avoid breaking strict aliasing rule? Note that this is a template, I cannot control T or value of some_other_t; the assignment and subsequent comparison do happen inside the templated code. (For the record, the above code started breaking on GCC 4.5 if T contains any bit fields.)

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