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  • .NET and C# Exceptions. What is it reasonable to catch.

    - by djna
    Disclaimer, I'm from a Java background. I don't do much C#. There's a great deal of transfer between the two worlds, but of course there are differences and one is in the way Exceptions tend to be thought about. I recently answered a C# question suggesting that under some circstances it's reasonable to do this: try { some work } catch (Exeption e) { commonExceptionHandler(); } (The reasons why are immaterial). I got a response that I don't quite understand: until .NET 4.0, it's very bad to catch Exception. It means you catch various low-level fatal errors and so disguise bugs. It also means that in the event of some kind of corruption that triggers such an exception, any open finally blocks on the stack will be executed, so even if the callExceptionReporter fuunction tries to log and quit, it may not even get to that point (the finally blocks may throw again, or cause more corruption, or delete something important from the disk or database). May I'm more confused than I realise, but I don't agree with some of that. Please would other folks comment. I understand that there are many low level Exceptions we don't want to swallow. My commonExceptionHandler() function could reasonably rethrow those. This seems consistent with this answer to a related question. Which does say "Depending on your context it can be acceptable to use catch(...), providing the exception is re-thrown." So I conclude using catch (Exception ) is not always evil, silently swallowing certain exceptions is. The phrase "Until .NET 4 it is very bad to Catch Exception" What changes in .NET 4? IS this a reference to AggregateException, which may give us some new things to do with exceptions we catch, but I don't think changes the fundamental "don't swallow" rule. The next phrase really bothers be. Can this be right? It also means that in the event of some kind of corruption that triggers such an exception, any open finally blocks on the stack will be executed (the finally blocks may throw again, or cause more corruption, or delete something important from the disk or database) My understanding is that if some low level code had lowLevelMethod() { try { lowestLevelMethod(); } finally { some really important stuff } } and in my code I call lowLevel(); try { lowLevel() } catch (Exception e) { exception handling and maybe rethrowing } Whether or not I catch Exception this has no effect whatever on the excution of the finally block. By the time we leave lowLevelMethod() the finally has already run. If the finally is going to do any of the bad things, such as corrupt my disk, then it will do so. My catching the Exception made no difference. If It reaches my Exception block I need to do the right thing, but I can't be the cause of dmis-executing finallys

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  • I've caught an exception!! Now what?

    - by Jonesy
    Hi folks, I've started using try catch blocks (bit late i know!) but now im not sure what to do with the exception once i've caught it. What do people usually do here? -- Jonesy Try connection.Open() Dim sqlCmd As New SqlCommand("do some SQL", connection) Dim sqlDa As New SqlDataAdapter(sqlCmd) sqlDa.Fill(dt) Catch ex As SQLException ' ahhhh what to do now!!!? Finally connection.Close() End Try

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  • Where to define exception classes, inside classes or on a higher level?

    - by rve
    Should exception classes be part of the class which may throw them or should they exist on a higher level? For example : class Test { public: class FooException: public ExceptionBase { }; void functionThrowingFooException(); }; or class FooException: public ExceptionBase { }; class Test { public: void functionThrowingFooException(); }; (functionThrowingFooException() is the only function to ever throw a FooException)

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  • It&rsquo;s ok to throw System.Exception&hellip;

    - by Chris Skardon
    No. No it’s not. It’s not just me saying that, it’s the Microsoft guidelines: http://msdn.microsoft.com/en-us/library/ms229007.aspx  Do not throw System.Exception or System.SystemException. Also – as important: Do not catch System.Exception or System.SystemException in framework code, unless you intend to re-throw.. Throwing: Always, always try to pick the most specific exception type you can, if the parameter you have received in your method is null, throw an ArgumentNullException, value received greater than expected? ArgumentOutOfRangeException. For example: public void ArgChecker(int theInt, string theString) { if (theInt < 0) throw new ArgumentOutOfRangeException("theInt", theInt, "theInt needs to be greater than zero."); if (theString == null) throw new ArgumentNullException("theString"); if (theString.Length == 0) throw new ArgumentException("theString needs to have content.", "theString"); } Why do we want to do this? It’s a lot of extra code when compared with a simple: public void ArgChecker(int theInt, string theString) { if (theInt < 0 || string.IsNullOrWhiteSpace(theString)) throw new Exception("The parameters were invalid."); } It all comes down to a couple of things; the catching of the exceptions, and the information you are passing back to the calling code. Catching: Ok, so let’s go with introduction level Exception handling, taught by many-a-university: You do all your work in a try clause, and catch anything wrong in the catch clause. So this tends to give us code like this: try { /* All the shizzle */ } catch { /* Deal with errors */ } But of course, we can improve on that by catching the exception so we can report on it: try { } catch(Exception ex) { /* Log that 'ex' occurred? */ } Now we’re at the point where people tend to go: Brilliant, I’ve got exception handling nailed, what next??? and code gets littered with the catch(Exception ex) nastiness. Why is it nasty? Let’s imagine for a moment our code is throwing an ArgumentNullException which we’re catching in the catch block and logging. Ok, the log entry has been made, so we can debug the code right? We’ve got all the info… What about an OutOfMemoryException – what can we do with that? That’s right, not a lot, chances are you can’t even log it (you are out of memory after all), but you’ve caught it – and as such - have hidden it. So, as part of this, there are two things you can do one, is the rethrow method: try { /* code */ } catch (Exception ex) { //Log throw; } Note, it’s not catch (Exception ex) { throw ex; } as that will wipe all your important stack trace information. This does get your exception to continue, and is the only reason you would catch Exception (anywhere other than a global catch-all) in your code. The other preferred method is to catch the exceptions you can deal with. It may not matter that the string I’m passing in is null, and I can cope with it like this: try{ DoSomething(myString); } catch(ArgumentNullException){} And that’s fine, it means that any exceptions I can’t deal with (OutOfMemory for example) will be propagated out to other code that can deal with it. Of course, this is horribly messy, no one wants try / catch blocks everywhere and that’s why Microsoft added the ‘Try’ methods to the framework, and it’s a strategy we should continue. If I try: int i = (int) "one"; I will get an InvalidCastException which means I need the try / catch block, but I could mitigate this using the ‘TryParse’ method: int i; if(!Int32.TryParse("one", out i)) return; Similarly, in the ‘DoSomething’ example, it might be beneficial to have a ‘TryDoSomething’ that returns a boolean value indicating the success of continuing. Obviously this isn’t practical in every case, so use the ol’ common sense approach. Onwards Yer thanks Chris, I’m looking forward to writing tonnes of new code. Fear not, that is where helpers come into it… (but that’s the next post)

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  • Throwing a C++ exception after an inline-asm jump

    - by SoapBox
    I have some odd self modifying code, but at the root of it is a pretty simple problem: I want to be able to execute a jmp (or a call) and then from that arbitrary point throw an exception and have it caught by the try/catch block that contained the jmp/call. But when I do this (in gcc 4.4.1 x86_64) the exception results in a terminate() as it would if the exception was thrown from outside of a try/catch. I don't really see how this is different than throwing an exception from inside of some far-flung library, yet it obviously is because it just doesn't work. How can I execute a jmp or call but still throw an exception back to the original try/catch? Why doesn't this try/catch continue to handle these exceptions as it would if the function was called normally? The code: #include <iostream> #include <stdexcept> using namespace std; void thrower() { cout << "Inside thrower" << endl; throw runtime_error("some exception"); } int main() { cout << "Top of main" << endl; try { asm volatile ( "jmp *%0" // same thing happens with a call instead of a jmp : : "r"((long)thrower) : ); } catch (exception &e) { cout << "Caught : " << e.what() << endl; } cout << "Bottom of main" << endl << endl; } The expected output: Top of main Inside thrower Caught : some exception Bottom of main The actual output: Top of main Inside thrower terminate called after throwing an instance of 'std::runtime_error' what(): some exception Aborted

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  • Catching specific vs. generic exceptions in c#

    - by Scott Vercuski
    This question comes from a code analysis run against an object I've created. The analysis says that I should catch a more specific exception type than just the basic Exception. Do you find yourself using just catching the generic Exception or attempting to catch a specific Exception and defaulting to a generic Exception using multiple catch blocks? One of the code chunks in question is below: internal static bool ClearFlags(string connectionString, Guid ID) { bool returnValue = false; SqlConnection dbEngine = new SqlConnection(connectionString); SqlCommand dbCmd = new SqlCommand("ClearFlags", dbEngine); SqlDataAdapter dataAdapter = new SqlDataAdapter(dbCmd); dbCmd.CommandType = CommandType.StoredProcedure; try { dbCmd.Parameters.AddWithValue("@ID", ID.ToString()); dbEngine.Open(); dbCmd.ExecuteNonQuery(); dbEngine.Close(); returnValue = true; } catch (Exception ex) { ErrorHandler(ex); } return returnValue; } Thank you for your advice EDIT: Here is the warning from the code analysis Warning 351 CA1031 : Microsoft.Design : Modify 'ClearFlags(string, Guid)' to catch a more specific exception than 'Exception' or rethrow the exception

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  • Does javascript event handling occur inside or outside the program flow?

    - by Carlo Roosen
    This question is related to Javascript event handling and flow control, but it is one step beyond. The question that remains unanswered is: when an event is fired and control is returned to the browser, could the browser decide to handle other events first (fired by other scripts or user action) (A), or will it always handle my event directly (B)? The question is important, because in case (B) you can rely on the fact that nothing has been changed between firing the event and the event handler, while (A) gives no guarantees whatsoever. My first guess is (B), how else could stopPropagation() and preventDefault() work? But giving it a second thought, it is no hard evidence.

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  • unknown exception error in php

    - by fayer
    i wanna catch all exceptions thrown in a script and then check if they have a error code 23000. if they don't i want to rethrow the exception. here is my code: function myException($exception) { /*** If it is a Doctrine Connection Mysql Duplication Exception ***/ if(get_class($exception) === 'Doctrine_Connection_Mysql_Exception' && $exception->getCode() === 23000) { echo "Duplicate entry"; } else { throw $exception; } } set_exception_handler('myException'); $contact = new Contact(); $contact->email = 'peter'; $contact->save(); but i get this error message and i dont know what it means: Fatal error: Exception thrown without a stack frame in Unknown on line 0 i want to be able to rethrow the original error message if it has not the error code 23000. even when i deleted the check errorcode i still get the same message: function myException($exception) { throw $exception; } set_exception_handler('myException'); $contact = new Contact(); $contact->email = 'peter'; $contact->save(); how could i solve this? thanks

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  • Any good idioms for error handling in straight C programs?

    - by Will Hartung
    Getting back in to some C work. Many of my functions look like this: int err = do_something(arg1, arg2, arg3, &result); With the intent the result gets populated by the function, and the return value is the status of the call. The darkside is you get something naive like this: int err = func1(...); if (!err) { err = func2(...); if (!err) { err = func3(...); } } return err; I could macro it I suppose: #define ERR(x) if (!err) { err = (x) } int err = 0; ERR(func1(...)); ERR(func2(...)); ERR(func3(...)); return err; But that only works if I'm chaining function calls, vs doing other work. Obviously Java, C#, C++ have exceptions that work very well for these kinds of things. I'm just curious what other folks do and how other folks do error handling in their C programs nowadays.

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  • 'Installing breakpad exception handler for appid(steam)' while trying to run Steam

    - by Star Diamond
    I installed steam for ubuntu , so I tried to launch it and i get this : ~$ steam Installing breakpad exception handler for appid(steam)/version(1352224866_client) ~$ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 12.10 Release: 12.10 Codename: quantal ~$ lspci | grep VGA 00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09) 01:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI Whistler XT [AMD Radeon HD 6700M Series] (rev ff) What is the problem and how to fix it?

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  • MiniMax function throws null pointer exception

    - by Sven
    I'm working on a school project, I have to build a tic tac toe game with the AI based on the MiniMax algorithm. The two player mode works like it should. I followed the code example on http://ethangunderson.com/blog/minimax-algorithm-in-c/. The only thing is that I get a NullPointer Exception when I run the code. And I can't wrap my finger around it. I placed a comment in the code where the exception is thrown. The recursive call is returning a null pointer, what is very strange because it can't.. When I place a breakpoint on the null return with the help of a if statement, then I see that there ARE still 2 to 3 empty places.. I probably overlooking something. Hope someone can tell me what I'm doing wrong. Here is the MiniMax code (the tic tac toe code is not important): /* * To change this template, choose Tools | Templates * and open the template in the editor. */ package MiniMax; import Game.Block; import Game.Board; import java.util.ArrayList; public class MiniMax { public static Place getBestMove(Board gameBoard, Block.TYPE player) { Place bestPlace = null; ArrayList<Place> emptyPlaces = gameBoard.getEmptyPlaces(); Board newBoard; //loop trough all the empty places for(Place emptyPlace : emptyPlaces) { newBoard = gameBoard.clone(); newBoard.setBlock(emptyPlace.getRow(), emptyPlace.getCell(), player); //no game won and still room to move if(newBoard.getWinner() == Block.TYPE.NONE && newBoard.getEmptyPlaces().size() > 0) { //is an node (has children) Place tempPlace = getBestMove(newBoard, invertPlayer(player)); //ERROR is thrown here! tempPlace is null. emptyPlace.setScore(tempPlace.getScore()); } else { //is an leaf if(newBoard.getWinner() == Block.TYPE.NONE) { emptyPlace.setScore(0); } else if(newBoard.getWinner() == Block.TYPE.X) { emptyPlace.setScore(-1); } else if(newBoard.getWinner() == Block.TYPE.O) { emptyPlace.setScore(1); } //if this move is better then our prev move, take it! if((bestPlace == null) || (player == Block.TYPE.X && emptyPlace.getScore() < bestPlace.getScore()) || (player == Block.TYPE.O && emptyPlace.getScore() > bestPlace.getScore())) { bestPlace = emptyPlace; } } } //This should never be null, but it does.. return bestPlace; } private static Block.TYPE invertPlayer(Block.TYPE player) { if(player == Block.TYPE.X) { return Block.TYPE.O; } return Block.TYPE.X; } }

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  • Unhandled event loop exception "Unknown Mozilla path" with Eclipse 3.7.1

    - by r.bitter
    I installed the Tizen SDK 2.0 which uses Eclipse 3.7.1 as an IDE on Ubuntu 12.10 64bit. When trying to create a Tizen Web Project I got the following error message from Eclipse: Unhandled event loop exception No more handles [Unknown Mozilla path (MOZILLA_FIVE_HOME not set)] The problem is that Eclipse is configured to use Xulrunner as a headless browser inside the IDE. Xulrunner is not in the repositories for Ubuntu 12.10 any more, therefore Eclipse is not able to find the libraries.

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  • Slick & NiftyGUI. Nifty initialize exception

    - by Romeo
    I found my self into trouble when trying to run a Slick game with a Nifty Game State. This is the code: @Override protected void initGameAndGUI(GameContainer container, StateBasedGame game) throws SlickException { initNifty(container, game); } If i run this i get: java.lang.IllegalStateException: The NiftyGUI was already initialized. Its illegal to do so twice. If i delete the call to initNifty() i get another exception:java.lang.IllegalStateException: NiftyGUI was not initialized.

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  • How to deal with checked exceptions that cannot ever be thrown

    - by ammoQ
    Example: foobar = new InputStreamReader(p.getInputStream(), "ISO-8859-1"); Since the encoding is hardcoded and correct, the constructor will never throw the UnsupportedEncodingException declared in the specification (unless the java implementation is broken, in which case I'm lost anyway). Anyway, Java forces me to deal with that exception anyway. Currently, it looks like that try { foobar = new InputStreamReader(p.getInputStream(), "ISO-8859-1"); } catch(UnsupportedEncodingException e) { /* won't ever happen */ } Any ideas how to make it better?

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  • Farm is unavailable exception

    - by H(at)Ni
    I was faced today by an exception saying that "Farm is unavailable" and the call stack which for sure wasn't useful for diagnosing that type of error. My solution to this error was straight forward and below are the steps that I've followed: 1. Open run and type services.msc 2. Search for the SQL server instance and in my case I've found that it's not running, so simply start it :) After that, refresh the page and everything is normal again !

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  • Receiving "Path 'OPTIONS' is forbidden." Exception in ASP.NET website

    - by Greg
    I am getting the error "Path 'OPTIONS' is forbidden." since we moved our website over to a new server setup. I am unable to recreate the error but I am receiving emails for this exception at least a few times a day. Any ideas what could be causing this and how I can fix it? EDIT: Stack Trace: at System.Web.HttpMethodNotAllowedHandler.ProcessRequest(HttpContext context) at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) There are no directories or files named OPTIONS and I believe all permissions are correct. I am finding some information about a possible link to EXCEL getting data from the webserver, but nothing that full explains how or what is happening yet. EDIT AGAIN: Seems this has to do with Excel files opening in Internet Explorer..

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  • HELP! WebClient.UploadFile() throws exception while uploading files to sharepoint

    - by Royson
    In my application i am uploading files to sharepoint 2007. I am using using (WebClient webClient = new WebClient()) { webClient.Credentials = new NetworkCredential(userName, password); webClient.Headers.Add("Content-Type", "application/x-vermeer-urlencoded"); webClient.Headers.Add("X-Vermeer-Content-Type", "application/x-vermeer-urlencoded"); String result = Encoding.UTF8.GetString(webClient.UploadData(webUrl + "/_vti_bin/_vti_aut/author.dll","POST", data.ToArray())); } the code is running successfully..but for some files it throws exception The underlying connection was closed: The connection was closed unexpectedly. at System.Net.WebClient.UploadDataInternal(Uri address, String method, Byte[] data, WebRequest& request) at System.Net.WebClient.UploadData(Uri address, String method, Byte[] data) at System.Net.WebClient.UploadData(String address, String method, Byte[] data) Any Ideas what I have done wrong? I am using VS-2008 2.0

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  • How do I handle all the exceptions in a C# class where both ctor and finalizer throw exceptions?

    - by Frank
    How can I handle all exceptions for a class similar to the following under certain circumstances? class Test : IDisposable { public Test() { throw new Exception("Exception in ctor"); } public void Dispose() { throw new Exception("Exception in Dispose()"); } ~Test() { this.Dispose(); } } I tried this but it doesn't work: static void Main() { Test t = null; try { t = new Test(); } catch (Exception ex) { Console.Error.WriteLine(ex.Message); } // t is still null } I have also tried to use "using" but it does not handle the exception thrown from ~Test(); static void Main() { try { using (Test t = new Test()) { } } catch (Exception ex) { Console.Error.WriteLine(ex.Message); } } Any ideas how can I work around?

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