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• How do I change the class of an object to a subclass of its current class in C++?

  - by Jared P

  I have an array of pointers to a base class, so that I can make those pointers point to (different) subclasses of the base class, but still interact with them. (really only a couple of methods which I made virtual and overloaded) I'm wondering if I can avoid using the pointers, and instead just make an array of the base class, but have some way to set the class to the subclass of my choosing. I know there must be something there specifying the class, as it needs to use that to look up the function pointer for virtual methods. By the way, the subclasses all have the same ivars and layout. Note: the design is actually based on using a template argument instead of a variable, due to performance increases, so really the abstract base class is just the interface for the subclasses, which are all the same except for their compiled code. Thanks

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• question about quicksort

  - by davit-datuashvili

  i have write code of quicksort from programming pearls here is code public class Quick{ public static void quicksort(int x[], int l,int u) { if (l>=u) return ; int t=x[l]; int i=l; int j=u; do { i++; } while (i<=u && x[i]<t); do { j--; if (i>=j) break; } while ( x[j]>t); swap(x,i,j); swap(x, l,j); quicksort(x, l,j-1); quicksort(x, j+1,u); } public static void main(String[]args){ int x[]=new int[]{55,41,59,26,53,58,97,93}; quicksort(x,0,x.length-1); for (int i=0;i<x.length;i++){ System.out.println(x[i]); } } public static void swap(int x[], int i,int j){ int s=x[i]; x[i]=x[j]; x[j]=s; } } but it does not work here is output 59 41 55 26 53 97 58 93 any idea?

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• Listbox - selected item to call the class method directly using reflection

  - by Karan

  I have a problem scenario like this:- 1) Listbox with values like Car, Scooter and Bike. A button to click. <div> <asp:ListBox ID="lst" runat="server"> <asp:ListItem Text="Bike" Value="Bike"></asp:ListItem> <asp:ListItem Text="Car" Value="Car"></asp:ListItem> <asp:ListItem Text="Scooter" Value="Scooter"></asp:ListItem> </asp:ListBox> <br /> <br /> <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Invoke" /> </div> 2) Now i have three different class like below:- class Car { static string getData() { return "I like cars"; } } class Bike { static string getData() { return "I like Bike"; } } class Scooter { static string getData() { return "I dont like scooter"; } } 3) Now on the button click event handler "Button1_Click", i want to call the getData() method based on the selected value from the listbox using the REFLECTION only. Please help me out.

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• Forward declaring an enum in c++

  - by szevvy

  Hi guys, I'm trying to do something like the following: enum E; void Foo(E e); enum E {A, B, C}; which the compiler rejects. I've had a quick look on Google and the consensus seems to be "you can't do it", but I can't understand why. Can anyone explain? Many thanks. Clarification 2: I'm doing this as I have private methods in a class that take said enum, and I do not want the enum's values exposed - so, for example, I do not want anyone to know that E is defined as enum E { FUNCTIONALITY_NORMAL, FUNCTIONALITY_RESTRICTED, FUNCTIONALITY_FOR_PROJECT_X } as project X is not something I want my users to know about. So, I wanted to forward declare the enum so I could put the private methods in the header file, declare the enum internally in the cpp, and distribute the built library file and header to people. As for the compiler - it's GCC.

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• Thread-Safe lazy instantiating using MEF

  - by Xaqron

  // Member Variable private static readonly object _syncLock = new object(); // Now inside a static method foreach (var lazyObject in plugins) { if ((string)lazyObject.Metadata["key"] = "something") { lock (_syncLock) { // It seems the `IsValueCreated` is not up-to-date if (!lazyObject.IsValueCreated) lazyObject.value.DoSomething(); } return lazyObject.value; } } Here I need synchronized access per loop. There are many threads iterating this loop and based on the key they are looking for, a lazy instance is created and returned. lazyObject should not be created more that one time. Although Lazy class is for doing so and despite of the used lock, under high threading I have more than one instance created (I track this with a Interlocked.Increment on a volatile static int and log it somewhere). The problem is I don't have access to definition of Lazy and MEF defines how the Lazy class create objects. I should notice the CompositionContainer has a thread-safe option in constructor which is already used. My questions: 1) Why the lock doesn't work ? 2) Should I use an array of locks instead of one lock for performance improvement ?

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• Making Extension method Generic

  - by Ian

  In this post there's a very interesting way of updating UI threads using a static extension method. public static void InvokeIfRequired(this Control c, Action<Control> action) { if(c.InvokeRequired) { c.Invoke(() => action(c)); } else { action(c); } } What I want to do, is to make a generic version, so I'm not constrained by a control. This would allow me to do the following for example (because I'm no longer constrained to just being a Control) this.progressBar1.InvokeIfRequired(pb => pb.Value = e.Progress); I've tried the following: public static void InvokeIfRequired<T>(this T c, Action<T> action) where T : Control { if (c.InvokeRequired) { c.Invoke(() => action(c)); } else { action(c); } } But I get the following error that I'm not sure how to fix. Anyone any suggestions? Error 5 Cannot convert lambda expression to type 'System.Delegate' because it is not a delegate type

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• naming a method - using set() when *not* setting a property?

  - by user151841

  Is setX() method name appropriate for only for setting class property X? For instance, I have a class where the output is a string of an html table. Before you can you can call getTable, you have to call setTable(), which just looks at a other properties and decides how to construct the table. It doesn't actually directly set any class property -- only causes the property to be set. When it's called, the class will construct strHtmlTable, but you can't specify it. So, calling it setTable breaks the convention of get and set being interfaces for class properties. Is there another naming convention for this kind of method? Edit: in this particular class, there are at least two ( and in total 8 optional ) other methods that must be called before the class knows everything it needs to to construct the table. I chose to have the data set as separate methods rather than clutter up the __construct() with 8 optional parameters which I'll never remember the order of.

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• Why Enumerable doesn't inherits from IEnumerable<T>

  - by sajjadlove

  Hi All I'm very confused about this issue and can't to underestand it.In the Enumerable Documentation, I readed this: that implement System.Collections.Generic.IEnumerable and some methods like Select() return IEnumerable that we can use from other methods like Where() after using that.for example: names.Select(name => name).Where(name => name.Length > 3 ); but Enumerable doesn't inherits from IEnumerable and IEnumerable doesn't contain Select(),Where() and etc too... have i wrong ? or exists any reason for this?

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• Is it bad practice to use Reflection in Unit testing?

  - by Sebi

  During the last years I always thought that in Java, Reflection is widely used during Unit testing. Since some of the variables/methods which have to be checked are private, it is somehow necessary to read the values of them. I always thought that the Reflection API is also used for this purpose. Last week i had to test some packages and therefore write some JUnit tests. As always i used Reflection to access private fields and methods. But my supervisor who checked the code wasn't really happy with that and told me that the Reflection API wasn't meant to use for such "hacking". Instead he suggested to modifiy the visibility in the production code. Is it really bad practice to use Reflection? I can't really believe that

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• select i th smallest element from array

  - by davit-datuashvili

  i have divide and conqurer method to find i th smalles element from array here is code public class rand_select{ public static int Rand_partition( int a[],int p,int q,int i){ //smallest in a[p..q] if ( p==q) return a[p]; int r=partition (a,p,q); int k=r-p+1; if (i==k) return a[r]; if (i<k){ return Rand_partition(a,p,r-1,i); } return Rand_partition(a,r-1,q,i-k); } public static void main(String[]args){ int a[]=new int []{6,10,13,15,8,3,2,12}; System.out.println(Rand_partition(a,0,a.length-1,7)); } public static int partition(int a[],int p,int q){ int m=a[0]; while ( p<q){ while (p<q && a[p++] <m){ p++; } while (q>p && a[q--]>m){ q--; } int t=a[p]; a[p]=a[q]; a[q]=t; } int k=0; for (int i=0;i<a.length;i++){ if ( a[i]==m){ k=i; } } return k; } } but here is problem java.lang.ArrayIndexOutOfBoundsException please help me

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• Is there anything wrong with taking immediate actions in constructors?

  - by pestaa

  I have classes like this one: class SomeObject { public function __construct($param1, $param2) { $this->process($param1, $param2); } ... } So I can instantly "call" it as some sort of global function just like new SomeObject($arg1, $arg2); which has the benefits of staying concise, being easy to understand, but might break unwritten rules of semantics by not waiting till a method is called. Should I continue to feel bad because of a bad practice, or there's really nothing to worry about? Clarification: I do want an instance of the class. I do use internal methods of the class only. I initialize the object in the constructor, but call the "important" action-taker methods too. I am selfish in the light of these sentences.

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• lstrcpy not updating passed in string

  - by Rorschach

  I'm trying to use kernel32.dll's lstrcpy to get a string from a pointer in C#, but it isn't working. lstrlenA IS working, it gives me the length of the string, so I'm hitting the kernel32.dll at least. lstrcpy is working in the VB6 app I'm converting, so I know it CAN work, but I don't have a clue why it isn't here. The string s never gets filled with the actual string, it just returns the initial padded string. [DllImport("kernel32.dll", EntryPoint = "lstrlenA", CharSet = CharSet.Ansi)] private static extern int lstrlen( int StringPointer ); [DllImport( "kernel32.dll",EntryPoint = "lstrcpyA", CharSet = CharSet.Ansi )] private static extern int lstrcpy(string lpString1, int StringPointer ); private static string StringFromPointer(int pointer) { //.....Get the length of the LPSTR int strLen = lstrlen(pointer); //.....Allocate the NewString to the right size string s = ""; for (int i = 0; i < strLen; i++) s += " "; //.....Copy the LPSTR to the VB string lstrcpy(s, pointer); return s; }

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• list all files from directories and subdirectories in Java

  - by Adnan

  What would be the fastest way to list the names of files from 1000+ directories and sub-directories? EDIT; The current code I use is: import java.io.File; public class DirectoryReader { static int spc_count=-1; static void Process(File aFile) { spc_count++; String spcs = ""; for (int i = 0; i < spc_count; i++) spcs += " "; if(aFile.isFile()) System.out.println(spcs + "[FILE] " + aFile.getName()); else if (aFile.isDirectory()) { System.out.println(spcs + "[DIR] " + aFile.getName()); File[] listOfFiles = aFile.listFiles(); if(listOfFiles!=null) { for (int i = 0; i < listOfFiles.length; i++) Process(listOfFiles[i]); } else { System.out.println(spcs + " [ACCESS DENIED]"); } } spc_count--; } public static void main(String[] args) { String nam = "D:/"; File aFile = new File(nam); Process(aFile); } }

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• SSIS Script Component + Helper Assemblies (.dll's)

  - by Nev_Rahd

  I got a script component which does Transformation / DataType conversions / Creating some calculated columns. All the transform validations / datatype conversion methods and for new column generation is put into custom .dll. As this script component would be same for all other tables, only thing is to define input / ouput columns and apply validation methods on required columns. This all works fine. On production server where do I need to deploy my .dll. Would just putting it into GAC will be enough or need to do something else. Regards

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• Limiting what a .net plugin can access

  - by David Hogue

  I have a web application that can load plugins through reflection. It currently uses Assembly.LoadFrom() and Activator.CreateInstance() to get this done. Right now plugins are loaded into the same AppDomain and have access to anything in my app and anything my app could access. What I'm looking for is a way to limit what classes and methods the plugin can access for security purposes. I want to have all of my classes and methods throw an exception when called unless they are whitelisted. I'd be whitelisting basically all the functions in an API class and a few data transfer objects. I also don't want the plugin to be able to access the filesystem or the database on it's own. I think I can do that with trust levels in a separate AppDomain though. Does anyone out there have any good ideas or resources? Is this something that could be done with Code Access Security or the new Security-Transparent Code features in .net 4?

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• Using iPhone Core Data to many Relationship

  - by BLeB

  When I define a to many relationship between entities in Xcode and then generate the data class from the entity I get a header with the following methods defined: @interface PriceList (CoreDataGeneratedAccessors) - (void)addItemsObject:(PriceListItem *)value; - (void)removeItemsObject:(PriceListItem *)value; - (void)addItems:(NSSet *)value; - (void)removeItems:(NSSet *)value; @end When I attempt to call addItemsObject with the following code a doesNotRecognizeSelector exception is thrown. PriceListItem *item = [NSEntityDescription insertNewObjectForEntityForName:@"PriceListItem" inManagedObjectContext:managedObjectContext]; item.cat = [attributeDict valueForKey:@"c"]; item.sel = [attributeDict valueForKey:@"s"]; [self addItemsObject:item]; From what I have read I do not have to implement these methods and that they are generated at runtime. Any ideas?

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• Java: over-typed structures? To have many types in Object[]?

  - by HH

  Term over-type structure = a data structure that accepts different types, can be primitive or user-defined. I think ruby supports many types in structures such as tables. I tried a table with types 'String', 'char' and 'File' in Java but errs. How can I have over-typed structure in Java? How to show types in declaration? What about in initilization? Suppose a structure: INDEX VAR FILETYPE //0 -> file FILE //1 -> lineMap SizeSequence //2 -> type char //3 -> binary boolean //4 -> name String //5 -> path String Code import java.io.*; import java.util.*; public class Object { public static void print(char a) { System.out.println(a); } public static void print(String s) { System.out.println(s); } public static void main(String[] args) { Object[] d = new Object[6]; d[0] = new File("."); d[2] = 'T'; d[4] = "."; print(d[2]); print(d[4]); } } Errors Object.java:18: incompatible types found : java.io.File required: Object d[0] = new File("."); ^ Object.java:19: incompatible types found : char required: Object d[2] = 'T'; ^

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• What is the point declaring variables at the end of class?

  - by serhio

  I saw multiple examples in MSDN that uses to declare the internal fields at the end of the class. What is the point? I find this a little embarrassing, because each time Visual Studio adds a method it adds it to the end of the class, so there is need every time to move it... class A { public A(){} // Methods, Properties, etc ... private string name; } class A { private string name; public A(){} // Methods, Properties, etc ... }

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• Xcode method navigation

  - by Bill

  In Xcode 4, I can press Ctrl-6 to get a list of all the methods in the current file. The problem is, if I have private methods declared at the top of my implementation file, say: @interface Foo () -(void)tap:(id)sender; @end @implementation Foo ... -(void)tap:(id)sender { ... } then starting to type "tap" while the method list is visible will just take me to the declaration, since it comes first in the file, when what I really want is the implementation. Is there any way to exclude these declarations from the method list or do I need to resort to separate Foo.h and Foo+Private.h headers? Thanks!

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• Use AttachedProperty in Style in ControlTemplate

  - by Andrey

  Here is my simple app: <Window x:Class="WpfApplication1.Window1" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:app="clr-namespace:WpfApplication1" Title="Window1" Height="300" Width="300"> <Window.Resources> <Style x:Key="Test"> <Setter Property="Button.Template"> <Setter.Value> <ControlTemplate> <Border BorderBrush="Blue" BorderThickness="3" Background="Black" CornerRadius="{Binding app:Extras.CornerRadius}" > </Border> </ControlTemplate> </Setter.Value> </Setter> </Style> </Window.Resources> <Grid> <Button Height="23" HorizontalAlignment="Left" Margin="29,26,0,0" Name="button1" VerticalAlignment="Top" Width="75" app:Extras.CornerRadius="10" Style="{StaticResource Test}" >Button</Button> </Grid> </Window> Here is my AttachedPropery: namespace WpfApplication1 { public class Extras { public static readonly DependencyProperty CornerRadiusProperty = DependencyProperty.RegisterAttached( "CornerRadius", typeof(double), typeof(Button), new FrameworkPropertyMetadata(1.0d, FrameworkPropertyMetadataOptions.AffectsRender) ); public static void SetCornerRadius(UIElement element, double value) { element.SetValue(CornerRadiusProperty, value); } public static double GetCornerRadius(UIElement element) { return (double)element.GetValue(CornerRadiusProperty); } } } CornerRadius="{Binding app:Extras.CornerRadius}" this of course doesn't work. so how can I get value from here app:Extras.CornerRadius="10" thanks in advance!

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• question about quicksort 3 way partition

  - by davit-datuashvili

  i want implement quicksort 3 way partition here is code public class quick3{ public static void quicksort3(int a[],int l,int r){ int k; int v=a[r]; if (r<=l) return; int i=l; int j=r; int p=l-1; int q=r; for (;;) { while (a[++i]<v); while (v<a[--j]) if (j==i) break; if (i>=j) break; swap( a,i, j); if (a[i]==v){ p++; swap(a,p,i);} if (v==a[j]){ q--; swap( a,q,j); } } swap(a,i,r); j=i-1; i=i+1; for (k=1;k<=p;k++,j--) swap(a,k,j); for (k=r-1;k>=q;k--,i++) swap(a,k,i); quicksort3(a,l,j); quicksort3(a,i,r); } public static void main(String[]args){ int a[]=new int[]{4,6,5,9,7,8,3}; quicksort3(a,0,a.length-1); for (int i=0;i<a.length;i++){ System.out.println(a[i]); } } public static void swap(int a[],int i,int j){ int t=a[i]; a[i]=a[j]; a[j]=t; } } after change result is 4 8 7 6 3 5 9 any suggestion?please help

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• Unit testing with Data Access Layer

  - by chobo

  Hi, what is a good way to write unit tests with a LINQ to SQL DAL? Currently I am doing some database testing and need to create helper methods that access the database, but I don't want those methods in my main repo's. So what I have is two copies of the DAL, one in my main project and one in the Test project. Is it easier to manage these things if I create a separate project for the data layer? I'm not sure which way is a better way to approach this. If I do create a data layer project would I move all my repo's to that project as well? I'm not sure how to properly setup the layers. Thanks

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• Playing a .wav sound file in JPanel/JFrame using javax (Swing)

  - by JavaIceCream

  I need some code example on how I would use a filepath from a harddrive location to then play a .wav sound file when opened in swing GUI. I don't need it to show a play button, or pause or stop. I just want it to play when I select the 'Sound' option from my 'Files' in my window (I know how to do that already, no need to explain that). So basically, just how to play a .wav sound file from a filepath (i.e. c:/cake/thereisnone.wav) inside of a JFrame. And how can I easily apply methods to that sound file afterwards. Also, if anyone knows how to apply methods on a BufferedImage in a JFrame, that would be helpful too. Thank you very much everyone!

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• Should properties in C# perform a lot of work?

  - by Hamish Grubijan

  When a property is read from or is assigned to, one would not expect it to perform a lot of work. When setSomeValue(...) and getSomeValue(...) methods are used instead, one should not be that surprised that something non-trivial might be going on under the hood. However, now that C# gave the world Properties, it seems silly to use getter and setter methods instead. What is your take on this? Should I mark this Q as a community wiki? Thanks.

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• R: Change the fields' (slots') values of the class assigning a value to some other field

  - by Max Li

  Assgning a value to one field, how can I make the other fields changing. Consider the following R5 class C<-setRefClass("C", fields=list(a="numeric",b="numeric") , methods=list( seta = function(x){ a<<-x b<<-x+10 cat("The change took place!") } ) # end of the methods list ) # end of the class Now create the instance of the class c<-C$new() This command c$seta(10) will result in that c$a is 10 and c$b is 20. So it actually works, however, I want to achieve this result by the command c$a<-10 (i.e. after that I want c$b to be equal to 20 as defined in the class in the logic of seta() function) How can I do it?

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