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  • error handling strategies in C?

    - by Leo
    Given the code below: typedef struct {int a;} test_t; arbitrary_t test_dosomething(test_t* test) { if (test == NULL) { //options: //1. print an error and let it crash //e.g. fprintf(stderr, "null ref at %s:%u", __FILE__, __LINE__); //2. stop the world //e.g. exit(1); //3. return (i.e. function does nothing) //4. attempt to re-init test } printf("%d", test->a); //do something w/ test } I want to get a compiler error if test is ever NULL, but I guess that's not possible in C. Since I need to do null checking at runtime, what option is the most proper way to handle it?

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  • Using a general class for execution with try/catch/finally?

    - by antirysm
    I find myself having a lot of this in different methods in my code: try { runABunchOfMethods(); } catch (Exception ex) { logger.Log(ex); } What about creating this: public static class Executor { private static ILogger logger; public delegate void ExecuteThis(); static Executor() { // logger = ...GetLoggerFromIoC(); } public static void Execute(ExecuteThis executeThis) { try { executeThis(); } catch (Exception ex) { logger.Log(ex); } } } And just using it like this: private void RunSomething() { Method1(someClassVar); Method2(someOtherClassVar); } ... Executor.Execute(RunSomething); Are there any downsides to this approach? (You could add Executor-methods and delegates when you want a finally and use generics for the type of Exeception you want to catch...)

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  • .net Attributes that handle exceptions - usage on a property accessor

    - by Mr AH
    Hi, well I know from my asp.net mvc experience that you can have attributes that handle exceptions (HandleErrorAttribute). As far as I can tell the Controller class has some OnException event which may be integral to this behaviour. However, I want to do something similar in my own code: dream example: public String MyProperty { [ExceptionBehaviour(typeof(FormatException), MyExEnum.ClearValue)] set { _thing.prop = Convert.ToThing(value); } } .... The code above obviously makes very little sense, but is close to the kind of thing I wish to do. I want the attribute on the property set accessor to catch some type of exception and then deal with this in some custom way (or even just swallow it). Any ideas guys?

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  • How can I process a form's events in another class in VB.NET?

    - by CowKingDeluxe
    Here's my code: Public Class Form1 End Class Public Class Form1Handler Inherits Form1 Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click MsgBox("I") End Sub End Class I'm trying to get Form1Handler to process Form1's events automatically. How can I do this? Should I use a module instead? I'm doing this in VB 2010.

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  • Catching errors in ANTLR and finding parent

    - by Andreas
    I have found out that I can catch errors during parsing by overwriting displayRecognitionError, but how do I find the parent "node" of this error? ex. if I have the grammar: prog: stat expr; stat: STRING; expr: INTEGER; And give it the input "abc def". Then I will get an error at "def" which should be an integer. At this point I then want to get the parent which is "expr" (since it fails inside the INTEGER part) and it's parent "prog". Kind of like printing stack trace in java. I tried to look at the node from RecognitionException parsed to displayRecognitionError, but it is null, and using CommonErrorNode the parent is null. Should I maybe take a completely different approach?

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  • Detecting and handling third-party library filehandle leaks in Java

    - by tucuxi
    Is there any way to detect and handle whether a Java library is correctly releasing file-handles (via "close") from within a Java program that is using said library, short of having access to the actual library code and inserting the corresponding "finally close" statements? If detection is feasible, is there any way to close those file-handles without a reference to the Reader (or FileInputStream) that was reading the file?

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  • ASP.NET: How can I properly redirect requests with 404 errors?

    - by Adrian Grigore
    Hi, I'd like my ASP.NET MVC application to redirect failed requests to matching action methods of a certain controller. This works fine on my development machine running Windows 7, but not on my production machine running Windows 2008 R2. I set up my web.config as follows: <customErrors mode="On" defaultRedirect="/Error/ServerError/500"> <error statusCode="403" redirect="/Error/AccessDenied" /> <error statusCode="404" redirect="/Error/FileNotFound" /> </customErrors> This customErrors section works fine on both of my machines (production and development) for 500 Internal Server errors. It also works fine for 404 errors on my development machine. However, it does not properly redirect 404 errors on the production machine. Instead of /Error/FileNotFound, I get the standard 404 page that comes with IIS 7. What could be the problem here?

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  • VB.NET: question about "using" block

    - by Craig Johnston
    Consider the code: On Error Goto ErrorHandler Using sr As StreamReader = New StreamReader(OpenFile) str = sr.ReadToEnd sr.Close() End Using Exit Sub ErrorHandler: If there is an error inside the Using block how do you clean up the sr object? The sr object is not in scope in ErrHandler so sr.Close() cannot be called. Does the Using block cleanup any resources automatically even if there is an error?

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  • Handling Corrupted JPEGs in C#

    - by ddango
    We have a process that pulls images from a remote server. Most of the time, we're good to go, the images are valid, we don't timeout, etc. However, every once and awhile we see this error similar to this: Unhandled Exception: System.Runtime.InteropServices.ExternalException: A generic error occurred in GDI+. at System.Drawing.Image.Save(Stream stream, ImageCodecInfo encoder, EncoderPa rameters encoderParams) at ConsoleApplication1.Program.Main(String[] args) in C:\images\ConsoleApplic ation1\ConsoleApplication1\Program.cs:line 24 After not being able to reproduce it locally, we looked closer at the image, and realized that there were artifacts, making us suspect corruption. Created an ugly little unit test with only the image in question, and was unable to reproduce the error on Windows 7 as was expected. But after running our unit test on Windows Server 2008, we see this error every time. Is there a way to specify non-strictness for jpegs when writing them? Some sort of check/fix we can use? Unit test snippet: var r = ReadFile("C:\\images\\ConsoleApplication1\\test.jpg"); using (var imgStream = new MemoryStream(r)) { using (var ms = new MemoryStream()) { var guid = Guid.NewGuid(); var fileName = "C:\\images\\ConsoleApplication1\\t" + guid + ".jpg"; Image.FromStream(imgStream).Save(ms, ImageFormat.Jpeg); using (FileStream fs = File.Create(fileName)) { fs.Write(ms.GetBuffer(), 0, ms.GetBuffer().Length); } } }

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  • Why does Perl's Net::Msmgr hang when I try to authenticate?

    - by codeholic
    There's Net::Msmgr module on CPAN. It's written clean and the code looks trustworthy at the first glance. However this module seems to be beta and there is little documentation and no tests :-/ Has anyone used this module in production? I haven't managed to make it run by now, because it requires all event loop processing to be done in the application and as I've already said there is little documentation and no working examples to study. That's where I've gone so far: #!/usr/bin/perl use strict; use warnings; use Event; use Net::Msmgr::Object; use Net::Msmgr::Session; use Net::Msmgr::User; use constant DEBUG => 511; use constant EVENT_TIMEOUT => 5; # seconds my ($username, $password) = qw/[email protected] my.password/; my $buddy = '[email protected]'; my $user = Net::Msmgr::User->new(user => $username, password => $password); my $session = Net::Msmgr::Session->new; $session->debug(DEBUG); $session->login_handler(\&login_handler); $session->user($user); my $conv; sub login_handler { my $self = shift; print "LOGIN\n"; $self->ui_state_nln; $conv = $session->ui_new_conversation; $conv->invite($buddy); } our %watcher; sub ConnectHandler { my ($connection) = @_; warn "CONNECT\n"; my $socket = $connection->socket; $watcher{$connection} = Event->io(fd => $socket, cb => [ $connection, '_recv_message' ], poll => 're', desc => 'recv_watcher', repeat => 1); } sub DisconnectHandler { my $connection = shift; print "DISCONNECT\n"; $watcher{$connection}->cancel; } $session->connect_handler(\&ConnectHandler); $session->disconnect_handler(\&DisconnectHandler); $session->Login; Event::loop(); That's what it outputs: Dispatch Server connecting to: messenger.hotmail.com:1863 Dispatch Server connected CONNECT Dispatch Server >>>VER 1 MSNP2 CVR0 --> VER 1 MSNP2 CVR0 Dispatch Server >>>USR 2 MD5 I [email protected] --> USR 2 MD5 I [email protected] Dispatch Server <<<VER 1 CVR0 <-- VER 1 CVR0 And that's all, here it hangs. The handler on login is not being triggered. What am I doing wrong?

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  • In FLEX, How can you stop ENTER Key from my Alert being caught by the control that initiated the Al

    - by WeeJavaDude
    I am having an issue where I show an AlertBox message when the user hits ENTER and the focus is in a text area. The pop up works fine, but when the user hits enter the Alert closes as expected, but the TextArea listener receives the ENTER event from the Alert and pops the dialog up again. I have tried a number of ways to catch and eat the event but so far I have not been lucky. Is there way to accomplish this? public function init():void { myTextInput.addEventListener(KeyboardEvent.KEY_UP, handleKeyStrokes); } public function handleKeyStrokes(evt:KeyboardEvent):void { if(evt.keyCode == Keyboard.ENTER) { myAlert = Alert.show("This is a test and only a test", "Title", 4, null, alertCallBack); } } <mx:TextInput id="myTextInput" left="600" top="10"> </mx:TextInput>

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  • Handling close-to-impossible collisions on should-be-unique values

    - by balpha
    There are many systems that depend on the uniqueness of some particular value. Anything that uses GUIDs comes to mind (eg. the Windows registry or other databases), but also things that create a hash from an object to identify it and thus need this hash to be unique. A hash table usually doesn't mind if two objects have the same hash because the hashing is just used to break down the objects into categories, so that on lookup, not all objects in the table, but only those objects in the same category (bucket) have to be compared for identity to the searched object. Other implementations however (seem to) depend on the uniqueness. My example (that's what lead me to asking this) is Mercurial's revision IDs. An entry on the Mercurial mailing list correctly states The odds of the changeset hash colliding by accident in your first billion commits is basically zero. But we will notice if it happens. And you'll get to be famous as the guy who broke SHA1 by accident. But even the tiniest probability doesn't mean impossible. Now, I don't want an explanation of why it's totally okay to rely on the uniqueness (this has been discussed here for example). This is very clear to me. Rather, I'd like to know (maybe by means of examples from your own work): Are there any best practices as to covering these improbable cases anyway? Should they be ignored, because it's more likely that particularly strong solar winds lead to faulty hard disk reads? Should they at least be tested for, if only to fail with a "I give up, you have done the impossible" message to the user? Or should even these cases get handled gracefully? For me, especially the following are interesting, although they are somewhat touchy-feely: If you don't handle these cases, what do you do against gut feelings that don't listen to probabilities? If you do handle them, how do you justify this work (to yourself and others), considering there are more probable cases you don't handle, like a supernonva?

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  • How to pass event to method?

    - by tomaszs
    I would like to create a method that takes as a argument an event an adds eventHandler to it to handle it properly. Like this: I have 2 events: public event EventHandler Click; public event EventHandler Click2; Now i would like to pass particular event to my method like this (pseudocode): public AttachToHandleEvent(EventHandler MyEvent) { MyEvent += Item_Click; } private void Item_Click(object sender, EventArgs e) { MessageBox.Show("lalala"); } ToolStripMenuItem tool = new ToolStripMenuItem(); AttachToHandleEvent(tool.Click); Is it possible or do I not understand it good? Edit: I've noticed with help of you that this code worked fine, and returned to my project and noticed that when I pass event declared in my class it works, but when I pass event from other class id still does not work. Updated above example to reflect this issue. What I get is this error: The event 'System.Windows.Forms.ToolStripItem.Click' can only appear on the left hand side of += or -=

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  • What is a good generic sibling control Javascript communication strategy?

    - by James
    I'm building a webpage that is composed of several controls, and trying to come up with an effective somewhat generic client side sibling control communication model. One of the controls is the menu control. Whenever an item is clicked in here I wanted to expose a custom client side event that other controls can subscribe to, so that I can achieve a loosely coupled sibling control communication model. To that end I've created a simple Javascript event collection class (code below) that acts as like a hub for control event registration and event subscription. This code certainly gets the job done, but my question is is there a better more elegant way to do this in terms of best practices or tools, or is this just a fools errand? /// Event collection object - acts as the hub for control communication. function ClientEventCollection() { this.ClientEvents = {}; this.RegisterEvent = _RegisterEvent; this.AttachToEvent = _AttachToEvent; this.FireEvent = _FireEvent; function _RegisterEvent(eventKey) { if (!this.ClientEvents[eventKey]) this.ClientEvents[eventKey] = []; } function _AttachToEvent(eventKey, handlerFunc) { if (this.ClientEvents[eventKey]) this.ClientEvents[eventKey][this.ClientEvents[eventKey].length] = handlerFunc; } function _FireEvent(eventKey, triggerId, contextData ) { if (this.ClientEvents[eventKey]) { for (var i = 0; i < this.ClientEvents[eventKey].length; i++) { var fn = this.ClientEvents[eventKey][i]; if (fn) fn(triggerId, contextData); } } } } // load new collection instance. var myClientEvents = new bsdClientEventCollection(); // register events specific to the control that owns it, this will be emitted by each respective control. myClientEvents.RegisterEvent("menu-item-clicked"); Here is the part where this code above is consumed by source and subscriber controls. // menu control $(document).ready(function() { $(".menu > a").click( function(event) { //event.preventDefault(); myClientEvents.FireEvent("menu-item-clicked", $(this).attr("id"), null); }); }); <div style="float: left;" class="menu"> <a id="1" href="#">Menu Item1</a><br /> <a id="2" href="#">Menu Item2</a><br /> <a id="3" href="#">Menu Item3</a><br /> <a id="4" href="#">Menu Item4</a><br /> </div> // event subscriber control $(document).ready(function() { myClientEvents.AttachToEvent("menu-item-clicked", menuItemChanged); myClientEvents.AttachToEvent("menu-item-clicked", menuItemChanged2); myClientEvents.AttachToEvent("menu-item-clicked", menuItemChanged3); }); function menuItemChanged(id, contextData) { alert('menuItemChanged ' + id); } function menuItemChanged2(id, contextData) { alert('menuItemChanged2 ' + id); } function menuItemChanged3(id, contextData) { alert('menuItemChanged3 ' + id); }

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  • handling activity destruction in multithreaded android app

    - by Jayesh
    Hi, I have a multithreded app where background threads are used to load data over network or from disk/db. Every once in a while user will perform some action e.g. fetch news over network, which will spawn a background AsyncTask, but for some reason user will quit the app (press back button so that activity gets destroyed). In most such scenarios, I make appropriate checks in the background thread after it returns from n/w i/o, so that it won't crash by accessing members of the activity that is destroyed by now. However some corner cases are left where crashes happen, because the background thread would access some member of activity that is now null. Do other Android developers have some generic/recommended framework to handle such scenarios? These are the times when I wish android would have guaranteed termination of all threads when activity destroys (in the same way that regular linux process cleans up when it's quit)... but I guess Android devs had good reasons for not exposing process lifetimes through the api.

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  • Javascript Prototype Best Practice Event Handlers

    - by nahum
    Hi this question is more a consulting of best practice, Sometimes when I'm building a complete ajax application I usually add elements dynamically for example. When you'r adding a list of items, I do something like: var template = new Template("<li id='list#{id}'>#{value}</li>"); var arrayTemplate = []; arrayOfItem.each(function(item, index){ arrayTemplate.push(template.evaluate( id : index, value : item)) }); after this two options add the list via "update" or "insert" ----- $("elementToUpdate").update("<ul>" + arrayTemplate.join("") + "</ul">); the question is how can I add the event handler without repeat the process of read the array, this is because if you try add a Event before the update or insert you will get an Error because the element isn't still on the DOM. so what I'm doing by now is after insert or update: arrayOfItem.each(function(item, index){ $("list" + index).observe("click", function(){ alert("I see the world"); }) }); so the question is exist a better way to doing this??????

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  • Rescuing a failed WCF call

    - by illdev
    Hello, I am happily using Castle's WcfFacility. From Monorail I know the handy concept of Rescues - consumer friendly results that often, but not necessarily, contain Data about what went wrong. I am creating a Silverlight application right now, doing quite a few WCF service calls. All these request return an implementation of public class ServiceResponse { private string _messageToUser = string.Empty; private ActionResult _result = ActionResult.Success; public ActionResult Result // Success, Failure, Timeout { get { return _result; } set { _result = value; } } public string MessageToUser { get { return _messageToUser; } set { _messageToUser = value; } } } public abstract class ServiceResponse<TResponseData> : ServiceResponse { public TResponseData Data { get; set; } } If the service has trouble responding the right way, I would want the thrown Exception to be intercepted and converted to the expected implementation. base on the thrown exception, I would want to pass on a nice message. here is how one of the service methods looks like: [Transaction(TransactionMode.Requires)] public virtual SaveResponse InsertOrUpdate(WarehouseDto dto) { var w = dto.Id > 0 ? _dao.GetById(dto.Id) : new Warehouse(); w.Name = dto.Name; _dao.SaveOrUpdate(w); return new SaveResponse { Data = new InsertData { Id = w.Id } }; } I need the thrown Exception for the Transaction to be rolled back, so i cannot actually catch it and return something else. Any ideas, where I could hook in?

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  • Several client waiting for the same event

    - by ff8mania
    I'm developing a communication API to be used by a lot of generic clients to communicate with a proprietary system. This proprietary system exposes an API, and I use a particular classes to send and wait messages from this system: obviously the system alert me that a message is ready using an event. The event is named OnMessageArrived. My idea is to expose a simple SendSyncMessage(message) method that helps the user/client to simply send a message and the method returns the response. The client: using ( Communicator c = new Communicator() ) { response = c.SendSync(message); } The communicator class is done in this way: public class Communicator : IDisposable { // Proprietary system object ExternalSystem c; String currentRespone; Guid currentGUID; private readonly ManualResetEvent _manualResetEvent; private ManualResetEvent _manualResetEvent2; String systemName = "system"; String ServerName = "server"; public Communicator() { _manualResetEvent = new ManualResetEvent(false); //This methods are from the proprietary system API c = SystemInstance.CreateInstance(); c.Connect(systemName , ServerName); } private void ConnectionStarter( object data ) { c.OnMessageArrivedEvent += c_OnMessageArrivedEvent; _manualResetEvent.WaitOne(); c.OnMessageArrivedEvent-= c_OnMessageArrivedEvent; } public String SendSync( String Message ) { Thread _internalThread = new Thread(ConnectionStarter); _internalThread.Start(c); _manualResetEvent2 = new ManualResetEvent(false); String toRet; int messageID; currentGUID = Guid.NewGuid(); c.SendMessage(Message, "Request", currentGUID.ToString()); _manualResetEvent2.WaitOne(); toRet = currentRespone; return toRet; } void c_OnMessageArrivedEvent( int Id, string root, string guid, int TimeOut, out int ReturnCode ) { if ( !guid.Equals(currentGUID.ToString()) ) { _manualResetEvent2.Set(); ReturnCode = 0; return; } object newMessage; c.FetchMessage(Id, 7, out newMessage); currentRespone = newMessage.ToString(); ReturnCode = 0; _manualResetEvent2.Set(); } } I'm really noob in using waithandle, but my idea was to create an instance that sends the message and waits for an event. As soon as the event arrived, checks if the message is the one I expect (checking the unique guid), otherwise continues to wait for the next event. This because could be (and usually is in this way) a lot of clients working concurrently, and I want them to work parallel. As I implemented my stuff, at the moment if I run client 1, client 2 and client 3, client 2 starts sending message as soon as client 1 has finished, and client 3 as client 2 has finished: not what I'm trying to do. Can you help me to fix my code and get my target? Thanks!

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  • better way of handling nested list

    - by laspal
    Hi, I have list my_list = [ [1,2,3,4,5,6], [1,3,4],[34,56,56,56]] for item in my_list: var1,var2,var3,var4,var5,var6 = None if len(item) ==1: var1 = item[0] if len(item) == 2: var1 = item[0] var2 = item[1] if len(item) == 3: var1 = item[0] var2 = item[1] var3 = item[2] if len(item) == 4: var1 = item[0] var2 = item[1] var3 = item[2] var4 = item[3] fun(var1,var2,var3,var4,var5,var6) I have a function def fun(var1, var2 = None, var3 = None, var4 = None, var5=None, var6= None) Depending upon the values in my inner list. I am passing it to function. I hope I made it clear. Thanks

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  • error handling in asp.net

    - by user98454
    Hi How can i pass the different types of errors from Data access layer to presentation layer? suppose if we take the northwind database scenario I want to delete the customer, so i selected one customer in ui and clicked the "delete" button.It internally calls the "delete" in data access layer. The prerequisite for deleting the customer is that the customer doesn't have any orders.So in data access layer we wil check whether that customer has any orders.If the customer has orders how can we pass the message from dal to presentation layer that the customer has orders and we don't delete. Am i doing right?is there any other ways to deal with this type? Thanks in advance

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  • nicer way of handling dom than DOMCategory?

    - by IttayD
    I'm trying to create a DSL that can easily use a dom node. Using DOMCategory is nice, but adds the noise of 'use(DOMCategory)'. Is there a way to avoid that? I tried wrapping the script call inside a call to 'use', but this doesn't seem to work in closures.

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