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  • dynimically using pointer

    - by gcc
    Input: 3 1 2 n 4 5 d 1 21 30 x Output: 2: 4 5 21 30 Input: 3 j 3 34 6 22 10 51 n 1 2 j 1 3 4 5 n 6 7 x Output: 1: 1 2 3 4 5 2: 6 7 3: 34 6 22 10 51 'j': (Jump to array# command) 'd': (Delete array# command) 'n': (Next array command) 'x': (Exit command) #: (Integer number) int num_arrays; /* maximum number of arrays */ int **arrays; /* array of array pointers */ int *l_arrays; /* actual lengths of arrays */ int *c_arrays; /* actual capacities of arrays */ how can we write that code

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  • Clear button at uisearchbar not working at all

    - by kevin.ng
    I created a search bar programmatically and added to my view using the codes below: - (void)viewDidLoad { searchBar = [[UISearchBar alloc] initWithFrame:CGRectMake(xPositionForSearchBar, yPositionForSearchBar, widthForSearchBar, heightForSearchBar)]; UIView *bg = [[searchBar subviews] objectAtIndex:0]; searchBar.delegate = self; searchBar.placeholder = @"Search record"; for(UIView *view in searchBar.subviews){ if([view isKindOfClass:[UITextField class]]){ UITextField *tf = (UITextField *)view; tf.delegate = self; break; } } [bg removeFromSuperview]; [self.view addSubview: searchBar]; } The code is implemented with UISearchBarDelegate and UITextFieldDelegate. I have tried using - (void)searchBarCancelButtonClicked:(UISearchBar *)aSearchBar { NSLog(@"cancel clicked"); searchBar.text = @""; [aSearchBar resignFirstResponder]; } - (BOOL)textFieldShouldClear:(UITextField *)textField { NSLog(@"clear"); [self performSelector:@selector(searchBarCancelButtonClicked:) withObject:searchBar afterDelay: 0.1]; return YES; } and yet, the text inside the searchBar is not cleared at all when i click on the "clear button" - a circle with a "X" inside. The clear button works when I implemented it in IB. Wonder why? Kindly advice, many thanks.

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  • Freeing memory with Pointer Arithmetic

    - by Breedly
    C++ newb here. I'm trying to write my own implementation of an array using only pointers, and I've hit a wall I don't know how to get over. My constructor throws this error array.cpp:40:35: error: invalid conversion from ‘int*’ to ‘int’ [-fpermissive] When my array initializes I want it to free up all the spaces in the array for ints. Array::Array(int theSize){ size = theSize; int *arrayPointer = new int; int index = 0; while(theSize > index){ *(arrayPointer + index) = new int; //This is the trouble line. ++index; } } What am I doing wrong stackoverflow?

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  • Easiest solution to sync an offline (local desktop application) database with a central server and multiple pc's?

    - by tyfius
    I have a desktop application which uses a local database. (This can be SQLite, SqlCe, PostgreSQL or any other database I will be able to install locally, I haven't decided which one to use yet.) The plan is to achieve the following: A user can subscribe to some kind of cloud service. If he does his local database should be synced with the online database (one for all users, or one per user, whatever the easiest solution is) so he will be able to sync his local database data between multiple PC's, can access his data online. (Much like dropbox does for files.) What is the best, easiest (and preferably cheapest) solution to achieve this? I am looking into DataObjects.net but I can't find much documentation about their Sync feature. Or, are there other alternatives? For example, I start with some kind of cloud service which allows local caching and use the local caching for users who do not subscribe to the service. Any pointers, tips or experiences are welcome.

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  • I have a question about variable release in global class.

    - by Beomseok
    + (void)findAndCopyOfDatabaseIfNeeded{ NSArray *path = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES); NSString *documentsDirectory = [path objectAtIndex:0]; NSFileManager *fileManager = [NSFileManager defaultManager]; NSString *databasePath = [documentsDirectory stringByAppendingPathComponent:@"DB"]; BOOL success = [fileManager fileExistsAtPath:databasePath]; if(!success){ NSString *resourcePath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"DB"]; [fileManager copyItemAtPath:resourcePath toPath:databasePath error:NULL]; } NSString *tracePath = [documentsDirectory stringByAppendingPathComponent:@"Trace"]; BOOL traceDir = [fileManager fileExistsAtPath:tracePath]; if(!traceDir){ NSString *resourcePath = [[[NSBundle mainBundle] resourcePath] stringByAppendingPathComponent:@"Trace"]; [fileManager copyItemAtPath:resourcePath toPath:tracePath error:NULL]; } NSDateFormatter *dateFormatter = [[NSDateFormatter alloc]init]; [dateFormatter setDateFormat:@"yyyy"]; NSDate *today = [[NSDate alloc]init]; NSString *resultYear = [dateFormatter stringFromDate:today]; NSString *traceYearPath = [tracePath stringByAppendingPathComponent:resultYear]; BOOL yearDir = [fileManager fileExistsAtPath:tracePath]; if (!yearDir) { [fileManager createDirectoryAtPath:traceYearPath attributes:nil]; } //[resultYear release]; ? //[today release]; ? //[dateFormatter release]; ? } I'm using global class like this [ + (void)findAndCopyOfDatabaseIfNeeded ]. hm,, I don't know NSArray, NSString and NSFileManager are released. Variable release or Not release ? please advice for me.

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  • A Null Reference Exception

    - by Alex
    "Object reference not set to an instance of an object." using System; using System.Collections.Generic; using System.Linq; using System.Text; using Microsoft.Xna.Framework; using Microsoft.Xna.Framework.Content; using Microsoft.Xna.Framework.Graphics; namespace XNAdev { class Sprite { //The size of the Sprite public Rectangle Size; //Used to size the Sprite up or down from the original image public float Scale = 1.0f; //The current position of the Sprite public Vector2 Position = new Vector2(115, 0); //The texture object used when drawing the sprite private Texture2D mSpriteTexture; //Load the texture for the sprite using the Content Pipeline public void LoadContent(ContentManager theContentManager, string theAssetName) { mSpriteTexture = theContentManager.Load<Texture2D>(theAssetName); Size = new Rectangle(0, 0, (int)(mSpriteTexture.Width * Scale), (int)(mSpriteTexture.Height * Scale)); } //Draw the sprite to the screen public void Draw(SpriteBatch theSpriteBatch) { theSpriteBatch.Draw(mSpriteTexture, Position, new Rectangle(0, 0, mSpriteTexture.Width, mSpriteTexture.Height), Color.White, 0.0f, Vector2.Zero, Scale, SpriteEffects.None, 0); } } } I am very new at this C# so any help would be great. I have no idea what my error is.

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  • Combining packages from different projects into a single project in eclipse

    - by primal
    Hi, As part of the Android application I am developing in eclipse, I need to combine two packages from different projects into a single project. I tried copying the files in the package of the second project under the src folder of the first folder and copied other files required for second package into the res folder of the first project. But the auto-generated Java files i.e R.java doesn't get updated on copying. I tried right clicking on the project and clicking on Android Tools - Fix Project Properties. But nothing changed. Any pointers on what I am doing wrong much be appreciated.

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  • WPF: issue updating UI from background thread

    - by Ted Shaffer
    My code launches a background thread. The background thread makes changes and wants the UI in the main thread to update. The code that launches the thread then waits looks something like: Thread fThread = new Thread(new ThreadStart(PerformSync)); fThread.IsBackground = true; fThread.Start(); fThread.Join(); MessageBox.Show("Synchronization complete"); When the background wants to update the UI, it sets a StatusMessage and calls the code below: static StatusMessage _statusMessage; public delegate void AddStatusDelegate(); private void AddStatus() { AddStatusDelegate methodForUIThread = delegate { _statusMessageList.Add(_statusMessage); }; this.Dispatcher.BeginInvoke(methodForUIThread, System.Windows.Threading.DispatcherPriority.Send); } _statusMessageList is an ObservableCollection that is the source for a ListBox. The AddStatus method is called but the code on the main thread never executes - that is, _statusMessage is not added to _statusMessageList while the thread is executing. However, once it is complete (fThread.Join() returns), all the stacked up calls on the main thread are executed. But, if I display a message box between the calls to fThread.Start() and fThread.Join(), then the status messages are updated properly. What do I need to change so that the code in the main thread executes (UI updates) while waiting for the thread to terminate? Thanks.

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  • Unexpected behaviour of Process.MainWindowHandle

    - by Ed Guiness
    I've been trying to understand Process.MainWindowHandle. According to MSDN; "The main window is the window that is created when the process is started. After initialization, other windows may be opened, including the Modal and TopLevel windows, but the first window associated with the process remains the main window." (Emphasis added) But while debugging I noticed that MainWindowHandle seemed to change value... which I wasn't expecting, especially after consulting the documentation above. To confirm the behaviour I created a standalone WinForms app with a timer to check the MainWindowHandle of the "DEVENV" (Visual Studio) process every 100ms. Here's the interesting part of this test app... IntPtr oldHWnd = IntPtr.Zero; void GetMainwindowHandle() { Process[] processes = Process.GetProcessesByName("DEVENV"); if (processes.Length!=1) return; IntPtr newHWnd = processes[0].MainWindowHandle; if (newHWnd != oldHWnd) { oldHWnd = newHWnd; textBox1.AppendText(processes[0].MainWindowHandle.ToString("X")+"\r\n"); } } private void timer1Tick(object sender, EventArgs e) { GetMainwindowHandle(); } You can see the value of MainWindowHandle changing when you (for example) click on a drop-down menu inside VS. Perhaps I've misunderstood the documentation. Can anyone shed light?

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  • java.lang.NoClassDefFoundError when the file is there

    - by tsOverflow
    I've tried to look around for postings that might help me, cant find any. I am deploying an ear to JBoss4 server, and I started having this problem since I added a new project. this new project is defined as Java project in eclipse, and the EAR project has an EJB project that has the new Java project as one of the projects as its dependent upon - if deployed on JBoss locally through eclipse, there's no problem and everything goes smoothly But when being deployed to JBoss in test environment (outside eclipse), kept getting java.lang.NoClassDefFoundError on one of the classes that are defined in the new Java project. I looked inside the EAR file to get to the jar (EJB project), and then inside the jar, I can see the directory structure and all the class files from the new Java project - ie. The class that it complains about is right there inside the EAR-JAR and matching the exact structure that it's looking for. I am at lost to what else I can look at. Any pointers are greatly appreciated! Thanks

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  • How to reset keyboard for an entry field?

    - by David.Chu.ca
    I am using tag field as a flag for text fields text view fields for auto-jumping to the next field: - (BOOL)findNextEntryFieldAsResponder:(UIControl *)field { BOOL retVal = NO; for (UIView* aView in mEntryFields) { if (aView.tag == (field.tag + 1)) { [aView becomeFirstResponder]; retVal = YES; break; } } return retVal; } It works fine in terms of auto-jumping to the next field when Next key is pressed. However, my case is that the keyboards are different some fields. For example, one fields is numeric & punctuation, and the next one is default (alphabetic keys). For the numeric & punctuation keyboard is OK, but the next field will stay as the same layout. It requires user to press 123 to go back ABC keyboard. I am not sure if there is any way to reset the keyboard for a field as its keyboard defined in xib? Not sure if there is any APIs available? I guess I have to do something is the following delegate? -(void)textFieldDidBegingEditing:(UITextField*) textField { // reset to the keyboard to request specific keyboard view? .... } OK. I found a solution close to my case by slatvik: -(void) textFieldDidBeginEditing:(UITextField*) textField { textField.keyboardType = UIKeybardTypeAlphabet; } However, in the case of the previous text fields is numeric, the keyboard stays numeric when auto-jumped to the next field. Is there any way to set keyboard to alphabet mode?

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  • MonoTouch Load image in background

    - by user1058951
    I am having a problem trying to load an image and display it using System.Threading.Task My Code is as follows Task DownloadTask { get; set; } public string Instrument { get; set; } public PriceChartViewController(string Instrument) { this.Instrument = Instrument; DownloadTask = Task.Factory.StartNew(() => { }); } private void LoadChart(ChartType chartType) { NSData data = new NSData(); DownloadTask = DownloadTask.ContinueWith(prevTask => { try { UIApplication.SharedApplication.NetworkActivityIndicatorVisible = true; NSUrl nsUrl = new NSUrl(chartType.Uri(Instrument)); data = NSData.FromUrl(nsUrl); } finally { UIApplication.SharedApplication.NetworkActivityIndicatorVisible = false; } }); DownloadTask = DownloadTask.ContinueWith(t => { UIImage image = new UIImage(data); chartImageView = new UIImageView(image); chartImageView.ContentScaleFactor = 2f; View.AddSubview(chartImageView); this.Title = chartType.Title; }, CancellationToken.None, TaskContinuationOptions.OnlyOnRanToCompletion, TaskScheduler.FromCurrentSynchronizationContext()); } The second Continue with does not seem to be being called? Initially my code looked like the following without the background processing and it worked perfectly. private void oldLoadChart(ChartType chartType) { UIApplication.SharedApplication.NetworkActivityIndicatorVisible = true; NSUrl nsUrl = new NSUrl(chartType.Uri(Instrument)); NSData data = NSData.FromUrl(nsUrl); UIImage image = new UIImage(data); chartImageView = new UIImageView(image); chartImageView.ContentScaleFactor = 2f; View.AddSubview(chartImageView); this.Title = chartType.Title; UIApplication.SharedApplication.NetworkActivityIndicatorVisible = false; } Does anyone know what I am doing wrong?

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  • C# object (2 numbers) performing 2 calculations

    - by Chris
    I have a couple questions about creating a object (2 values) and how to "call" it. Initializing the object with: Tweetal t1, t2, t3, t4, t5, t6; t1 = new Tweetal(); //a: 0 , b = 0 t2 = new Tweetal(-2); //a: -2, b = -2 t3 = new Tweetal(5, 17); //a: 5, b = 17 t4 = new Tweetal(t3); //a:5, b = 17 Console.Write("t1 = " + t1); Console.Write("\tt2 = " + t2); Console.Write("\tt3 = " + t3); Console.Write("\tt4 = " + t4); Console.WriteLine("\n"); t1 = t1.Som(t2); t4 = t2.Som(t2); //...... Now the 2 things i want to do with this object are taking the SUM and the SUMNumber: Sum: t4 = t2.sum(t3); (this would result in t4: a:3 (-2+5), b: 15(-2+17) SumNumber: t1 = t3.sum(8) (this would result in t1: a:13 , b:25) Next is my code for the object (in a separate class), but how exactly do i perform the simple sum calculation when i call up for example t2 etc... public class Tweetal: Object { private int a; private int b; public Tweetal() { //??? //Sum(...,...) } public Tweetal(int a) { //??? //Sum(...,...) } public Tweetal(int a, int b) { //??? } public Tweetal(Tweetal //....) // to call upton the object if i request t1, t2, t3,... insteed of a direct number value) { // ???? } public void Sum(int aValue, int bValue) { //a = ??? //b = ??? //Sum(...,...) } public void SumNumber(int aValue, int bValue) { } public override string ToString() { return string.Format("({0}, {1})", a, b); }/*ToString*/ }

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  • How can a class's memory-allocated address be determined from within the contructor?

    - by Jim Fell
    Is it possible to get the memory-allocated address of a newly instantiated class from within that class's constructor during execution of said constructor? I am developing a linked list wherein multiple classes have multiple pointers to like classes. Each time a new class instantiates, it needs to check its parent's list to make sure it is included. If I try to do something like this: MyClass() // contructor { extern MyClass * pParent; for ( int i = 0; i < max; i++ ) { pParent->rels[i] == &MyClass; // error } } I get this error: error C2275: 'namespace::MyClass' : illegal use of this type as an expression Any thoughts or suggestions would be appreciated. Thanks.

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  • OnClickListener cannot be resolved to a type

    - by Webnet
    I'm diving into Java (this is day 1) and I'm trying to create a button that will trigger a notification when I click it... This code is based off of the notification documentation here, and UI events documentation here package com.example.contactwidget; import android.app.Activity; import android.app.Notification; import android.app.NotificationManager; import android.app.PendingIntent; import android.content.Context; import android.content.Intent; import android.os.Bundle; import android.widget.Button; public class ContactWidget extends Activity { /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); Button calc1 = (Button) findViewById(R.id.calc_button_1); calc1.setOnClickListener(buttonListener); setContentView(R.layout.main); } private static final int HELLO_ID = 1; //Error: OnClickListener cannot be resolved to a type private OnClickListener buttonListener = new OnClickListener() { public void onClick (View v) { String ns = Context.NOTIFICATION_SERVICE; NotificationManager mNotificationManager = (NotificationManager) getSystemService(ns); int icon = R.drawable.icon; CharSequence ticketBrief = "Button Pressed Brief"; CharSequence ticketTitle = "Button pressed"; CharSequence ticketText = "You pressed button 1"; long when = System.currentTimeMillis(); Notification notification = new Notification(icon, ticketBrief, when); Intent notificationIntent = new Intent(this, ContactWidget.class); PendingIntent contentIntent = PendingIntent.getActivity(this, 0, notificationIntent, 0); notification.setLatestEventInfo(getApplicationContext(), ticketTitle, ticketText, contentIntent); mNotificationManager.notify(HELLO_ID, notification); } } } I'm running into a problem: OnClickListener cannot be resolved to a type. The problem here is that I don't see any problems with my code in relation to the example I'm using

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  • Interview question : What is the fastest way to generate prime number recursively ?

    - by hilal
    Generation of prime number is simple but what is the fastest way to find it and generate( prime numbers) it recursively ? Here is my solution. However, it is not the best way. I think it is O(N*sqrt(N)). Please correct me, if I am wrong. public static boolean isPrime(int n) { if (n < 2) { return false; } else if (n % 2 == 0 & n != 2) { return false; } else { return isPrime(n, (int) Math.sqrt(n)); } } private static boolean isPrime(int n, int i) { if (i < 2) { return true; } else if (n % i == 0) { return false; } else { return isPrime(n, --i); } } public static void generatePrimes(int n){ if(n < 2) { return ; } else if(isPrime(n)) { System.out.println(n); } generatePrimes(--n); } public static void main(String[] args) { generatePrimes(200); }

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  • Merging and splitting overlapping rectangles to produce non-overlapping ones

    - by uj
    I am looking for an algorithm as follows: Given a set of possibly overlapping rectangles (All of which are "not rotated", can be uniformly represented as (left,top,right,bottom) tuplets, etc...), it returns a minimal set of (non-rotated) non-overlapping rectangles, that occupy the same area. It seems simple enough at first glance, but prooves to be tricky (at least to be done efficiently). Are there some known methods for this/ideas/pointers? Methods for not necessarily minimal, but heuristicly small, sets, are interesting as well, so are methods that produce any valid output set at all.

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  • How do I pass references as method parameters across AppDomains?

    - by Thiado de Arruda
    I have been trying to get the following code to work(everything is defined in the same assembly) : namespace SomeApp{ public class A : MarshalByRefObject { public byte[] GetSomeData() { // } } public class B : MarshalByRefObject { private A remoteObj; public void SetA(A remoteObj) { this.remoteObj = remoteObj; } } public class C { A someA = new A(); public void Init() { AppDomain domain = AppDomain.CreateDomain("ChildDomain"); string currentAssemblyPath = Assembly.GetExecutingAssembly().Location; B remoteB = domain.domain.CreateInstanceFromAndUnwrap(currentAssemblyPath,"SomeApp.B") as B; remoteB.SetA(someA); // this throws an ArgumentException "Object type cannot be converted to target type." } } } What I'm trying to do is pass a reference of an 'A' instance created in the first AppDomain to the child domain and have the child domain execute a method on the first domain. In some point on 'B' code I'm going to call 'remoteObj.GetSomeData()'. This has to be done because the 'byte[]' from 'GetSomeData' method must be 'calculated' on the first appdomain. What should I do to avoid the exception, or what can I do to achieve the same result?

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  • Emacs hide/show support for C++ triple-slash Doxygen markup?

    - by jsyjr
    I use Doxygen's triple-slash syntax to markup my C++ code. There are two important cases which arise: 1) block markup comments which are the sole element on the line and may or may not begin flush left; e.g. class foo /// A one sentence brief description of foo. The elaboration can /// continue on for many lines. { ... }; void foo::bar /// A one sentence brief description of bar. The elaboration can /// continue on for many lines. () const { ... } 2) trailing markup comments which always follow some number of C++ tokens earlier on the first line but may still spill over onto subsequent lines; e.g. class foo { int _var1; ///< A brief description of _var1. int _var2; ///< A brief description of _var2 ///< requiring additional lines. } void foo::bar ( int arg1 ///< A brief description of arg1. , int arg2 ///< A brief description of arg2 ///< requiring additional lines. ) const { ... } I wonder what hide/show support exists to deal with these conventions. The most important cases are the block markup comments. Ideally I would like to be able to eliminate these altogether, meaning that I would prefer not to waste a line simply to indicate presence of a folded block markup comment. Instead I would like a fringe marker, a la http://www.emacswiki.org/emacs/hideshowvis.el /john

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  • calling a function from a set of overloads depending on the dynamic type of an object

    - by Jasper
    I feel like the answer to this question is really simple, but I really am having trouble finding it. So here goes: Suppose you have the following classes: class Base; class Child : public Base; class Displayer { public: Displayer(Base* element); Displayer(Child* element); } Additionally, I have a Base* object which might point to either an instance of the class Base or an instance of the class Child. Now I want to create a Displayer based on the element pointed to by object, however, I want to pick the right version of the constructor. As I currently have it, this would accomplish just that (I am being a bit fuzzy with my C++ here, but I think this the clearest way) object->createDisplayer(); virtual void Base::createDisplayer() { new Displayer(this); } virtual void Child::createDisplayer() { new Displayer(this); } This works, however, there is a problem with this: Base and Child are part of the application system, while Displayer is part of the GUI system. I want to build the GUI system independently of the Application system, so that it is easy to replace the GUI. This means that Base and Child should not know about Displayer. However, I do not know how I can achieve this without letting the Application classes know about the GUI. Am I missing something very obvious or am I trying something that is not possible?

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  • Editable CATextLayer?

    - by Ron
    I have several CATextLayers. When I doubleclick one of them, I want to be able to edit it's string. Think of text as it's handled in Keynote or many other apps. Any ideas? I thought of putting an editable textfield right in front of the layer and then dismiss it on enter, but I didn't get far. :-( I target Mac OS X 10.5 with Objective-C 2.0 and Garbage Collection. Any help or pointers would be greatly appreciated. Thanks in advance!!

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  • How to filter List<T> with LINQ and Reflection

    - by Ehsan Sajjad
    i am getting properties via reflection and i was doing like this to iterate on the list. private void HandleListProperty(object oldObject, object newObject, string difference, PropertyInfo prop) { var oldList = prop.GetValue(oldObject, null) as IList; var newList = prop.GetValue(newObject, null) as IList; if (prop.PropertyType == typeof(List<DataModel.ScheduleDetail>)) { List<DataModel.ScheduleDetail> ScheduleDetailsOld = oldList as List<DataModel.ScheduleDetail>; List<DataModel.ScheduleDetail> ScheduleDetailsNew = newList as List<DataModel.ScheduleDetail>; var groupOldSchedules = ScheduleDetailsOld .GroupBy(x => x.HomeHelpID) .SelectMany(s => s.DistinctBy(d => d.HomeHelpID) .Select(h => new { h.HomeHelpID, h.HomeHelpName })); } } Now i am making it generic because there will be coming different types of Lists and i don't want to put if conditions this way i want to write generic code to handle any type of list. I came up with this way: private void HandleListProperty(object oldObject, object newObject, string difference, PropertyInfo prop) { var oldList = prop.GetValue(oldObject, null) as IList; var newList = prop.GetValue(newObject, null) as IList; var ListType = prop.PropertyType; var MyListInstance = Activator.CreateInstance(ListType); MyListInstance = oldList; } i am able to get the items in MyListInstance but as the type will come at runtime i am not getting how to write linq query to filter them, any ideah how to do.

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  • Will C++0x support __stdcall or extern "C" capture-nothing lambdas?

    - by Daniel Trebbien
    Yesterday I was thinking about whether it would be possible to use the convenience of C++0x lambda functions to write callbacks for Windows API functions. For example, what if I wanted to use a lambda as an EnumChildProc with EnumChildWindows? Something like: EnumChildWindows(hTrayWnd, CALLBACK [](HWND hWnd, LPARAM lParam) { // ... return static_cast<BOOL>(TRUE); // continue enumerating }, reinterpret_cast<LPARAM>(&myData)); Another use would be to write extern "C" callbacks for C routines. E.g.: my_class *pRes = static_cast<my_class*>(bsearch(&key, myClassObjectsArr, myClassObjectsArr_size, sizeof(my_class), extern "C" [](const void *pV1, const void *pV2) { const my_class& o1 = *static_cast<const my_class*>(pV1); const my_class& o2 = *static_cast<const my_class*>(pV2); int res; // ... return res; })); Is this possible? I can understand that lambdas that capture variables will never be compatible with C, but it at least seems possible to me that capture-nothing lambdas can be compatible.

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  • std::bad_cast from parent to child?

    - by polyglot
    For simplicity, class Parent {} class Child1 : Parent {} class Child2 : Parent {} Elsewhere, I created instances of Child1 and Child2 and store it in same vector under Parent: // . . . in .h file, for example vector<Parent> vector_of_parent; // . . . in one particular method Child1 c1(); Child2 c2(); vector_of_parent.push_back(c1); vector_of_parent.push_back(c2); // . . . Then in another method which has access to vector_of_parent, I tried void doSomething(Parent& some_child) { // wrapped in a try block somehow... Child1& c = dynamic_cast<Child1&> some_child; // do something if the cast is successful } void otherMethod() { doSomething(vector_of_parent.at(0)); // vector_of_parent.at(0) is a Child1 } Why is there a std:bad_cast when I call otherMethod()?

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  • operator overloading and inheritance

    - by user168715
    I was given the following code: class FibHeapNode { //... // These all have trivial implementation virtual void operator =(FibHeapNode& RHS); virtual int operator ==(FibHeapNode& RHS); virtual int operator <(FibHeapNode& RHS); }; class Event : public FibHeapNode { // These have nontrivial implementation virtual void operator=(FibHeapNode& RHS); virtual int operator==(FibHeapNode& RHS); virtual int operator<(FibHeapNode& RHS); }; class FibHeap { //... int DecreaseKey(FibHeapNode *theNode, FibHeapNode& NewKey) { FibHeapNode *theParent; // Some code if (theParent != NULL && *theNode < *theParent) { //... } //... return 1; } }; Much of FibHeap's implementation is similar: FibHeapNode pointers are dereferenced and then compared. Why does this code work? (or is it buggy?) I would think that the virtuals here would have no effect: since *theNode and *theParent aren't pointer or reference types, no dynamic dispatch occurs and FibHeapNode::operator< gets called no matter what's written in Event.

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