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• Library for Dataflow in C

  - by msutherl

  How can I do dataflow (pipes and filters, stream processing, flow based) in C? And not with UNIX pipes. I recently came across stream.py. Streams are iterables with a pipelining mechanism to enable data-flow programming and easy parallelization. The idea is to take the output of a function that turns an iterable into another iterable and plug that as the input of another such function. While you can already do this using function composition, this package provides an elegant notation for it by overloading the operator. I would like to duplicate a simple version of this kind of functionality in C. I particularly like the overloading of the operator to avoid function composition mess. Wikipedia points to this hint from a Usenet post in 1990. Why C? Because I would like to be able to do this on microcontrollers and in C extensions for other high level languages (Max, Pd*, Python). * (ironic given that Max and Pd were written, in C, specifically for this purpose – I'm looking for something barebones)

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• Is the "message" of an exception culturally independent?

  - by Ray Hayes

  In an application I'm developing, I have the need to handle a socket-timeout differently from a general socket exception. The problem is that many different issues result in a SocketException and I need to know what the cause was. There is no inner exception reported, so the only information I have to work with is the message: "A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond" This question has a general and specific part: is it acceptable to write conditional logic based upon the textual representation of an exception? Is there a way to avoid needing exception handling? Example code below... try { IPEndPoint endPoint = null; client.Client.ReceiveTimeout = 1000; bytes = client.Receive(ref endPoint); } catch( SocketException se ) { if ( se.Message.Contains("did not properly respond after a period of time") ) { // Handle timeout differently.. } }

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• Enterprise Library Validation Block - Should validation be placed on class or interface?

  - by Robert MacLean

  I am not sure where the best place to put validation (using the Enterprise Library Validation Block) is? Should it be on the class or on the interface? Things that may effect it Validation rules would not be changed in classes which inherit from the interface. Validation rules would not be changed in classes which inherit from the class. Inheritance will occur from the class in most cases - I suspect some fringe cases to inherit from the interface (but I would try and avoid it). The interface main use is for DI which will be done with the Unity block.

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• UITableView with contact image problems.

  - by prathumca

  As par my app requirement, I'm showing the contact images in a UITableView as shown below. ABRecordRef contact = [self getContact]; if(contact && ABPersonHasImageData(contact)) { UIImage *contactImage = [UIImage imageWithData:(NSData*)ABPersonCopyImageData(contact)]; callImage.image = contactImage; } I've two problems if I use the above code segment. Table Scrolling is too slow. If comment the above code, then UITable responds very fast. Memory Management. My app started using 25 - 30 MB of RAM. Is there any better way to avoid the above two problems?

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• Is it a good practice to create a reference to application context and use it anywhere?

  - by kknight

  I have to use context in many places of my code such as database operations, preference operations, etc. I don't want to pass in context for every method. Is it a good practice to create a reference to application context at the main Activity and use it anywhere such as database operations? So, I don't need some many context in method parameters, and the code can avoid position memory leak due to use of Activity Context. public class MainActivity extends Activity { public static Context s_appContext; /** Called when the activity is first created. */ @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); s_appContext = this.getApplicationContext();

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• Jquery Accordion and multiple slideshows

  - by Dipesh Parmar

  I've been using a lot of slideshows recently on my sites and one thing thats puzzled me is using more than one slideshow per page. I'm currently working on my own site, experimenting with Jquery Accordion. I've managed to adopt a very simple javascript slideshow, see below: http://dvpwebdesign.com/test/accordion/blank.html However i'm unable to either incorporate or use a different multiple slideshow plugin. I dont need slideshow navigation, so the The Cycle plugin works really well and i know you can use multiple slideshows. But if i either use Cycle alongside the current javascript slideshow, or only use the Cycle slideshow to avoid any possible conflict, the Accordion menu stops working. I just cant see what i am doing wrong, can anyone help?

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• asp.net web form Cutom Router Handler

  - by jparram

  I am using a custom route handler for a webforms application. I am using routes to determine localization. ie: if the url has es or fr in the route it will load either spanish or french resources. for example: www.someroute/es/checkstuff/checkstuff.aspx will load: www.someroute/checkstuff/checkstuff.aspx with the spanish resources. I am configuring the custom routes in global.asax via: protected void Application_Start(object sender, EventArgs e) { RegisterRoutes(RouteTable.Routes); } public static void RegisterRoutes(RouteCollection routes) { foreach (var value in _customRoutes) { routes.Add(value.RouteName, new Route(value.Route, new CustomRouteHandler(value.ResolvedRoute))); } } where _customroutes is a list of routes. Is there a way to do this with some kind of pattern matching so I can avoid adding a specific route for each page in the application. While I know I could use a t4 template to generate the routes, I guess I am looking for a dynamic way to create the list

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• how to call a C++ dll from C# windows application project

  - by chathuradd

  I have created a dll in C++ using a Class Library project in Visual Studio. I need to call a method in the dll from a C# application. I got to know there are 2 approches. One is to add the dll project reference to C# project or use DllExport to export method. However when I tried in both ways it always gives the following error when the dll method is called in runtime. An unhandled exception of type 'System.BadImageFormatException' occurred in TestClient.exe Additional information: An attempt was made to load a program with an incorrect format. (Exception from HRESULT: 0x8007000B) Can i know how to avoid this problem ? Thanks in advance!

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• C# - Why can't I enforce derived classes to have parameterless constructors?

  - by FrisbeeBen

  I am trying to do the following: public class foo<T> where T : bar, new { _t = new T(); private T _t; } public abstract class bar { public abstract void someMethod(); // Some implementation } public class baz : bar { public overide someMethod(){//Implementation} } And I am attempting to use it as follows: foo<baz> fooObject = new foo<baz>(); And I get an error explaining that 'T' must be a non-abstract type with a public parameterless constructor in order to use it as parameter 'T' in the generic type or method. I fully understand why this must be, and also understand that I could pass a pre-initialized object of type 'T' in as a constructor argument to avoid having to 'new' it, but is there any way around this? any way to enforce classes that derive from 'bar' to supply parameterless constructors?

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• Can using non primitive Integer/ Long datatypes too frequently in the application, hurt the performance??

  - by Marcos

  I am using Long/Integer data types very frequently in my application, to build Generic datatypes. I fear that using these wrapper objects instead of primitive data types may be harmful for performance since each time it needs to create objects which is an expensive operation. but also it seems that I have no other choice(when I have to use primtives with generics) rather than just using them. However, still it would be great if you can suggest if there is anything I could do to make it better. or any way if I could just avoid it ?? Also What may be the downsides of this ? Suggestions welcomed!

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• Get previous element in IObservable without re-evaluating the sequence

  - by dcstraw

  In an IObservable sequence (in Reactive Extensions for .NET), I'd like to get the value of the previous and current elements so that I can compare them. I found an example online similar to below which accomplishes the task: sequence.Zip(sequence.Skip(1), (prev, cur) => new { Previous = prev, Current = cur }) It works fine except that it evaluates the sequence twice, which I would like to avoid. You can see that it is being evaluated twice with this code: var debugSequence = sequence.Do(item => Debug.WriteLine("Retrieved an element from sequence")); debugSequence.Zip(debugSequence.Skip(1), (prev, cur) => new { Previous = prev, Current = cur }).Subscribe(); The output shows twice as many of the debug lines as there are elements in the sequence. I understand why this happens, but so far I haven't found an alternative that doesn't evaluate the sequence twice. How can I combine the previous and current with only one sequence evaluation?

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• jqGrid: Is it possible to commit a cell change when tabbing off instead of pressing Enter?

  - by The Matt

  I have a simple in-line edit in my grid, and I want to commit the change when the user tabs off the textbox. The default behavior of jqGrid forces the user to press 'Enter' to commit the change, but this is non-intuitive for our users. onSelectRow: function(id) { $(gridCoreGroups).editRow(id, true, undefined, function(response) { alert("hello world"); } } I've worked my way through the events provided, but they all happen as a result of the user pressing 'Enter', which I want to avoid. Is there something I can wire up that would trigger an action when the user tabs off this cell?

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• How to solve this Java type safety warning? (Struts2)

  - by Nicolas Raoul

  Map session = ActionContext.getContext().getSession(); session.put("user", user); This code generates a warning: Type safety: The method put(Object, Object) belongs to the raw type Map. References to generic type Map should be parameterized. Map<String, Serializable> session = (Map<String, Serializable>)ActionContext.getContext().getSession(); session.put("user", user); This code generates a warning: Type safety: Unchecked cast from Map to Map. The getSession method belongs to Struts2 so I can't modify it. I would like to avoid using @SuppressWarnings because other warnings can be useful. I guess all Struts2 users in the world faced the same problem... is there an elegant solution?

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• Can I have fixed typed ArrayList in C#, just like C++?

  - by Kazoom

  I have an ArrayList which contains fixed type of objects. However everytime I need to extract an object a particular index, I need to typecast it to my user defined type from object type. Is there a way in C# to declare ArrayList of fixed types just like Java and C++, or is there a work around to avoid the typecasting everytime? Edit: I apologize I forgot mentioning that I require the datastructure to be thread-safe, which List is not. Otherwise I would have just used a normal Array. But I want to save myself from the effort of explicitly locking and unlocking while writing the array. So I thought of using ArrayList, synchronize it, but it requires typecasting every time.

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• Missing something with Entity Framework for .NET 3.5?

  - by AC

  Is it not possible to have EF create the necessary entities when I have two related tables linked with a FK in .NET3.5SP1? I see where the checkbox to support this is disabled but it is available in .NET4. I've got a DB that has only tables with relationships in it. I need to build a Silverlight app (SL4) that allows management of the data within this app. I can't use .NET4 on the server... only .NET3.5SP1 so FK relationship bit in EF4 isn't available to me. Looking to avoid building as much of the plumbing to get back to the DB from the SL4 app as possible...

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• Is there a way to cause a new C++ class instance to fail, if certain conditions in the contructor ar

  - by Jim Fell

  As I understand it, when a new class is instantiated in C++, a pointer to the new class is returned, or NULL, if there is insufficient memory. I am writing a class that initializes a linked list in the constructor. If there is an error while initializing the list, I would like the class instantiator to return NULL. For example: MyClass * pRags = new MyClass; If the linked list in the MyClass constructor fails to initialize properly, I would like pRags to equal NULL. I know that I can use flags and additional checks to do this, but I would like to avoid that, if possible. Does anyone know of a way to do this? Thanks.

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• Alternative to singleton for unique resources

  - by user1320881

  I keep reading over and over again that one should avoid using singletons for various reasons. I'm wondering how to correctly handle a situation where a class represents a unique system resource. For example, a AudioOutput class using SDL. Since SDL_OpenAudio can only be open once at a time it makes no sense having more then one object of this type and it seems to me preventing accidentally making more then one object would actually be good. Just wondering what experienced programmers think about this, am i missing another option ?

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• UIWebView load remote html page with local images and javascript files

  - by BlueNile

  Im creating application that will display remote page on the UIWebView using local images and javascript/css files for faster loading. I want to avoid using cache because for this to work it must first load all the content. I was searching online for possible solution. Here is what I have: NSURLRequest *urlrequest = [ [NSURLRequest alloc] initWithURL: [NSURL URLWithString:urlString] ]; NSData *returnData = [ NSURLConnection sendSynchronousRequest:urlrequest returningResponse: nil error: nil ]; NSString *HTMLData = [[NSString alloc] initWithData:returnData encoding:NSUTF8StringEncoding]; NSString *resourcePath = [[NSBundle mainBundle] resourcePath]; resourcePath = [resourcePath stringByReplacingOccurrencesOfString:@"/" withString:@"//"]; resourcePath = [resourcePath stringByReplacingOccurrencesOfString:@" " withString:@"%20"]; [webView loadHTMLString:HTMLData baseURL: [NSURL URLWithString: [NSString stringWithFormat:@"file:/%@//",resourcePath] ]]; urlString is defined and I moved files to the app bundle. Code works as I can see the remote page but no images nor javascript files are present.

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• How can I write to the previous line in a log file using Python's Logging module?

  - by turvyc

  Hi all, long-time lurker here, finally emerging from the woodwork. Essentially, what I'm trying to do is have my logger write data like this to the logfile: Connecting to database . . . Done. I'd like the 'Connecting to database . . . ' to be written when the function is called, and the 'Done' written after the function has successfully executed. I'm using Python 2.6 and the logging module. Also, I'd really like to avoid using decorators for this. Any help would be most appreciated!

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• NoneType has no attribute Append

  - by Rosarch

  I'm new to Python. I can't understand why a variable is None at a certain point in my code: class UsersInRoom(webapp.RequestHandler): def get(self): room_id = self.request.get("room_id") username = self.request.get("username") UserInRoom_entities = UserInRoom.gql("WHERE room = :1", room_id).get() if UserInRoom_entities: for user_in_room in UserInRoom_entities: if user_in_room.username == username: user_in_room.put() # last_poll auto updates to now whenenever user_in_room is saved else: user_in_room = UserInRoom() user_in_room.username = username user_in_room.put() UserInRoom_entities = [] UserInRoom_entities.append(user_in_room) // error here # name is `user_at_room` intead of `user_in_room` to avoid confusion usernames = [user_at_room.username for user_at_room in UserInRoom_entities] self.response.out.write(json.dumps(usernames)) The error is: Traceback (most recent call last): File "C:\Program Files\Google\google_appengine\google\appengine\ext\webapp\__init__.py", line 507, in __call__ handler.get(*groups) File "path\to\chat.py", line 160, in get AttributeError: 'NoneType' object has no attribute 'append' How is this possible? I'm setting UserInRoom_entities = [] immediately before that call. Or is something else the None in question?

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• Is it considered bad practice to have ViewModel objects hold the Dispatcher?

  - by stiank81

  My WPF application is structured using the MVVM pattern. The ViewModels will communicate asynchronously with a server, and when the requested data is returned a callback in the ViewModel is triggered, and it will do something with this data. This will run on a thread which is not the UI Thread. Sometimes these callbacks involve work that needs to be done on the UI thread, so I need the Dispatcher. This might be things such as: Adding data to an ObservableCollection Trigger Prism commands that will set something to be displayed in the GUI Creating WPF objects of some kind. I try to avoid the latter, but the two first points here I find to be reasonable things for ViewModels to do. So; is it okay to have ViewModels hold the Dispatcher to be able to Invoke commands for the UI thread? Or is this considered bad practice? And why?

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• How to Execute Base Class's Method Before Implementors's Method?

  - by DaveDev

  I have the following page public partial class GenericOfflineCommentary : OfflineFactsheetBase { } where OfflineFactsheetBase is defined as public class OfflineFactsheetBase : System.Web.UI.Page { public OfflineFactsheetBase() { this.Load += new EventHandler(this.Page_Load); this.PreInit += new EventHandler(this.Page_PreInit); } protected void Page_PreInit(object sender, EventArgs e) { if (Request.QueryString["data"] != null) { this.PageData = StringCompressor.DecompressString(Request.QueryString["data"]); this.ExtractPageData(); } } } OfflineFactsheetBase has the following virtual method: public virtual void ExtractPageData() { // get stuff relevant to all pages that impmement OfflineFactsheetBase } which is implemented in all pages that impmement OfflineFactsheetBase as follows: public partial class GenericOfflineCommentary : OfflineFactsheetBase { public override void ExtractPageData() { // get stuff relevant to an OfflineCommentary page. } } Currently, only GenericOfflineCommentary's ExtractPageData() is firing. How can I modify this to first run OfflineFactsheetBase's ExtractPageData() and then GenericOfflineCommentary's? edit: I'm trying to avoid having to call base.ExtractPageData() in every implementor. Is this possible?

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• How do you escape parentheses in a Binding indexer

  - by Chris S

  I have the following XAML: <Grid x:Name="LayoutRoot" Background="White" DataContext="{Binding Source={StaticResource MyDataKey}}"> <TextBox Name="_myId" Text="{Binding MyDictionary[(Textbox.Name)]" /> </Grid> But it thinks the key in my dictionary is called "(Textbox.Name)", instead of "_myId". The format below works, where I have a property in my class called "_myId": <TextBox Name="_myId" Text="{Binding (Textbox.Name)" /> I've tried using ^ and \ to escape the brackets. Is this syntax supported? I'm trying to avoid duplication of the name in two attributes.

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• Regex to catch all files but those starting with "."

  - by tmslnz

  In a directory with mixed content such as: .afile .anotherfile bfile.file bnotherfile.file .afolder/ .anotherfolder/ bfolder/ bnotherfolder/ How would you catch everything but the files (not dirs) starting with .? I have tried with a negative lookahead ^(?!\.).+? but it doesn't seem to work right. Please note that I would like to avoid doing it by excluding the . by using [a-zA-Z< plus all other possible chars minus the dot >] Any suggestions?

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• Is there a way to intersect/diff a std::map and a std::set?

  - by Jack

  I'm wondering if there a way to intersect or make the differences between two structures defined as std::set<MyData*> and std::map<MyData*, MyValue> with standard algorithms (like std::set_intersect) The problem is that I need to compute the difference between the set and the keyset of the map but I would like to avoid reallocating it (since it's something that is done many times per second with large data structures). Is there a way to obtain a "key view" of the std::map? After all what I'm looking is to consider just the keys when doing the set operation so from an implementation point it should be possible but I haven't been able to find anything.

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