Catch multiple exceptions at once

Question

It is discouraged to simply catch System Exception  Instead  only the  quot known quot  exceptions should be caught  Now  this sometimes leads to unnecessary repetitive code  for example  try       WebId   new Guid queryString  quot web quot       catch  FormatException        WebId   Guid Empty    catch  OverflowException        WebId   Guid Empty     I wonder  Is there a way to catch both exceptions and only call the WebId   Guid Empty call once  The given example is rather simple  as it s only a GUID  But imagine code where you modify an object multiple times  and if one of the manipulations fails expectedly  you want to  quot reset quot  the object  However  if there is an unexpected exception  I still want to throw that higher

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The accepted answer seems acceptable  except that CodeAnalysis FxCop will complain about the fact that it s catching a general exception type   Also  it seems the  is  operator might degrade performance slightly   CA1800  Do not cast unnecessarily says to  consider testing the result of the  as  operator instead   but if you do that  you ll be writing more code than if you catch each exception separately   Anyhow  here s what I would do   bool exThrown   false   try          Something   catch  FormatException        exThrown   true    catch  OverflowException        exThrown   true     if  exThrown           Something else

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This is a classic problem every C  developer faces eventually   Let me break your question into 2 questions   The first   Can I catch multiple exceptions at once   In short  no   Which leads to the next question   How do I avoid writing duplicate code given that I can t catch multiple exception types in the same catch   block   Given your specific sample  where the fall-back value is cheap to construct  I like to follow these steps    Initialize WebId to the fall-back value  Construct a new Guid in a temporary variable  Set WebId to the fully constructed temporary variable   Make this the final statement of the try   block    So the code looks like   try       WebId   Guid Empty      Guid newGuid   new Guid queryString  web            More initialization code goes here like         newGuid x   y      WebId   newGuid    catch  FormatException     catch  OverflowException       If any exception is thrown  then WebId is never set to the half-constructed value  and remains Guid Empty   If constructing the fall-back value is expensive  and resetting a value is much cheaper  then I would move the reset code into its own function   try       WebId   new Guid queryString  web            More initialization code goes here    catch  FormatException        Reset WebId     catch  OverflowException        Reset WebId

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If you don t want to use an if statement within the catch scopes  in C  6 0 you can use Exception Filters syntax which was already supported by the CLR in previews versions but existed only in VB NET MSIL   try       WebId   new Guid queryString  web       catch  Exception exception  when  exception is FormatException    ex is OverflowException        WebId   Guid Empty      This code will catch the Exception only when it s a InvalidDataException or ArgumentNullException   Actually  you can put basically any condition inside that when clause   static int a   8        catch  Exception exception  when  exception is InvalidDataException  amp  amp  a    8        Console WriteLine  Catch        Note that as opposed to an if statement inside the catch s scope  Exception Filters cannot throw Exceptions  and when they do  or when the condition is not true  the next catch condition will be evaluated instead   static int a   7   static int b   0        try       throw new InvalidDataException      catch  Exception exception  when  exception is InvalidDataException  amp  amp  a   b    2        Console WriteLine  Catch      catch  Exception exception  when  exception is InvalidDataException    exception is ArgumentException        Console WriteLine  General catch           Output  General catch    When there is more then one true Exception Filter - the first one will be accepted   static int a   8   static int b   4        try       throw new InvalidDataException      catch  Exception exception  when  exception is InvalidDataException  amp  amp  a   b    2        Console WriteLine  Catch      catch  Exception exception  when  exception is InvalidDataException    exception is ArgumentException        Console WriteLine  General catch           Output  Catch    And as you can see in the MSIL the code is not translated to if statements  but to Filters  and Exceptions cannot be throw from within the areas marked with Filter 1 and Filter 2 but the filter throwing the Exception will fail instead  also the last comparison value pushed to the stack before the endfilter command will determine the success failure of the filter  Catch 1 XOR Catch 2 will execute accordingly      Also  specifically Guid has the Guid TryParse method

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Not in C  unfortunately  as you d need an exception filter to do it and C  doesn t expose that feature of MSIL  VB NET does have this capability though  e g   Catch ex As Exception When TypeOf ex Is FormatException OrElse TypeOf ex Is OverflowException   What you could do is use an anonymous function to encapsulate your on-error code  and then call it in those specific catch blocks   Action onError        gt  WebId   Guid Empty  try          something   catch  FormatException        onError      catch  OverflowException        onError

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catch  Exception ex        if             ex is FormatException            ex is OverflowException                 throw            Console WriteLine  Hello

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Catch System Exception and switch on the types  catch  Exception ex                                    if  ex is FormatException    ex is OverflowException                WebId   Guid Empty          return             throw

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In c  6 0 Exception Filters is improvements for exception handling  try       DoSomeHttpRequest      catch  System Web HttpException e        switch  e GetHttpCode                  case 400              WriteLine  Bad Request            case 500              WriteLine  Internal Server Error            default              WriteLine  Generic Error

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in C  6 the recommended approach is to use Exception Filters  here is an example    try          throw new OverflowException        catch Exception e   when   e is DivideByZeroException      e is OverflowException                this will execute iff e is DividedByZeroEx or OverflowEx        Console WriteLine  E

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Wanted to added my short answer to this already long thread   Something that hasn t been mentioned is the order of precedence of the catch statements  more specifically you need to be aware of the scope of each type of exception you are trying to catch   For example if you use a  catch-all  exception as Exception it will preceed all other catch statements and you will obviously get compiler errors however if you reverse the order you can chain up your catch statements  bit of an anti-pattern I think  you can put the catch-all Exception type at the bottom and this will be capture any exceptions that didn t cater for higher up in your try  catch block               try                                  do some work here                           catch  WebException ex                                   catch a web excpetion                           catch  ArgumentException ex                                   do some stuff                           catch  Exception ex                                   you should really surface your errors but this is for example only                 throw new Exception  An error occurred      ex Message                   I highly recommend folks review this MSDN document   Exception Hierarchy

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It is worth mentioning here  You can respond to the multiple combinations  Exception error and exception message     I ran into a use case scenario when trying to cast control object in a datagrid  with either content as TextBox  TextBlock or CheckBox  In this case the returned Exception was the same  but the message varied   try      do something   catch  Exception ex  when  ex Message Equals  the error message1 here        do whatever you like    catch  Exception ex  when  ex Message Equals  the error message2 here        do whatever you like

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Note that I did find one way to do it  but this looks more like material for The Daily WTF   catch  Exception ex        switch  ex GetType   Name                case  System FormatException           case  System OverflowException               WebId   Guid Empty              break          default              throw

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With C  7 the answer from Michael Stum can be improved while keeping the readability of a switch statement   catch  Exception ex        switch  ex                case FormatException            case OverflowException                WebId   Guid Empty              break          default              throw            And with C  8 as switch expression   catch  Exception ex        WebId   ex switch                 when ex is FormatException    ex is OverflowException   gt  Guid Empty              gt  throw ex

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For the sake of completeness  since  NET 4 0 the code can rewritten as   Guid TryParse queryString  web    out WebId     TryParse never throws exceptions and returns false if format is wrong  setting WebId to Guid Empty     Since C  7 you can avoid introducing a variable on a separate line   Guid TryParse queryString  web    out Guid webId     You can also create methods for parsing returning tuples  which aren t available in  NET Framework yet as of version 4 6    bool success  Guid result  TryParseGuid string input    gt       Guid TryParse input  out Guid result   result     And use them like this   WebId   TryParseGuid queryString  web    result     or var tuple   TryParseGuid queryString  web     WebId   tuple success   tuple result   DefaultWebId      Next useless update to this useless answer comes when deconstruction of out-parameters is implemented in C  12

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Cautioned and Warned  Yet another kind  functional style  What is in the link doesn t answer your question directly  but it s trivial to extend it to look like  static void Main           Action body        gt       your code            body Catch lt InvalidOperationException gt              Catch lt BadCodeException gt              Catch lt AnotherException gt  ex   gt       handler               Basically provide another empty Catch overload which returns itself  The bigger question to this is why  I do not think the cost outweighs the gain here

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Micheal  Slightly revised version of your code   catch  Exception ex       Type exType   ex GetType       if  exType    typeof System FormatException             exType    typeof System OverflowException              WebId   Guid Empty       else         throw           String comparisons are ugly and slow

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Exception filters are now available in c  6   You can do  try          WebId   new Guid queryString  web       catch  Exception ex  when ex is FormatException    ex is OverflowException         WebId   Guid Empty      In C  7 0   you can combine this with pattern matching too  try      await Task WaitAll tasks     catch  Exception ex  when  ex is AggregateException ae  amp  amp                             ae InnerExceptions Count  gt  tasks Count 2         More than half of the tasks failed maybe

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I want to suggest shortest answer  one more functional style            Catch lt FormatException  OverflowException gt       gt                                WebId   new Guid queryString  web                                exception   gt                                WebId   Guid Empty                    For this you need to create several  Catch  method overloads  similar to System Action        DebuggerNonUserCode      public static void Catch lt TException1  TException2 gt  Action tryBlock          Action lt Exception gt  catchBlock                CatchMany tryBlock  catchBlock  typeof TException1   typeof TException2                DebuggerNonUserCode      public static void Catch lt TException1  TException2  TException3 gt  Action tryBlock          Action lt Exception gt  catchBlock                CatchMany tryBlock  catchBlock  typeof TException1   typeof TException2   typeof TException3            and so on as many as you wish  But you need to do it once and you can use it in all your projects  or  if you created a nuget package we could use it too    And CatchMany implementation        DebuggerNonUserCode      public static void CatchMany Action tryBlock  Action lt Exception gt  catchBlock          params Type   exceptionTypes                try                       tryBlock                      catch  Exception exception                        if  exceptionTypes Contains exception GetType     catchBlock exception               else throw                    p s  I haven t put null checks for code simplicity  consider to add parameter validations   p s 2  If you want to return a value from the catch  it s necessary to do same Catch methods  but with returns and Func instead of Action in parameters

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Since I felt like these answers just touched the surface  I attempted to dig a bit deeper   So what we would really want to do is something that doesn t compile  say      Won t compile    damn public static void Main         try               throw new ArgumentOutOfRangeException              catch  ArgumentOutOfRangeException      catch  IndexOutOfRangeException                        handle         The reason we want this is because we don t want the exception handler to catch things that we need later on in the process  Sure  we can catch an Exception and check with an  if  what to do  but let s be honest  we don t really want that   FxCop  debugger issues  uglyness   So why won t this code compile - and how can we hack it in such a way that it will   If we look at the code  what we really would like to do is forward the call  However  according to the MS Partition II  IL exception handler blocks won t work like this  which in this case makes sense because that would imply that the  exception  object can have different types    Or to write it in code  we ask the compiler to do something like this  well it s not entirely correct  but it s the closest possible thing I guess       Won t compile    damn try       throw new ArgumentOutOfRangeException      catch  ArgumentOutOfRangeException e        goto theOtherHandler    catch  IndexOutOfRangeException e    theOtherHandler      Console WriteLine  Handle         The reason that this won t compile is quite obvious  what type and value would the   exception  object have  which are here stored in the variables  e    The way we want the compiler to handle this is to note that the common base type of both exceptions is  Exception   use that for a variable to contain both exceptions  and then handle only the two exceptions that are caught  The way this is implemented in IL is as  filter   which is available in VB Net   To make it work in C   we need a temporary variable with the correct  Exception  base type  To control the flow of the code  we can add some branches  Here goes       Exception ex      try               throw new ArgumentException       for demo purposes  won t be caught          goto noCatch            catch  ArgumentOutOfRangeException e            ex   e            catch  IndexOutOfRangeException e            ex   e             Console WriteLine  Handle the exception  ex  here  -            throw ex    noCatch      Console WriteLine  We re done with the exception handling       The obvious disadvantages for this are that we cannot re-throw properly  and -well let s be honest- that it s quite the ugly solution  The uglyness can be fixed a bit by performing branch elimination  which makes the solution slightly better   Exception ex   null  try       throw new ArgumentException      catch  ArgumentOutOfRangeException e        ex   e    catch  IndexOutOfRangeException e        ex   e    if  ex    null        Console WriteLine  Handle the exception here  -         That leaves just the  re-throw   For this to work  we need to be able to perform the handling inside the  catch  block - and the only way to make this work is by an catching  Exception  object    At this point  we can add a separate function that handles the different types of Exceptions using overload resolution  or to handle the Exception  Both have disadvantages  To start  here s the way to do it with a helper function   private static bool Handle Exception e        Console WriteLine  Handle the exception here  -         return true     false will re-throw     public static void Main         try               throw new OutOfMemoryException              catch  ArgumentException e                if   Handle e     throw              catch  IndexOutOfRangeException e                if   Handle e     throw               Console WriteLine  We re done with the exception handling       And the other solution is to catch the Exception object and handle it accordingly  The most literal translation for this  based on the context above is this   try       throw new ArgumentException      catch  Exception e        Exception ex    Exception  e as ArgumentException      e as IndexOutOfRangeException       if  ex    null                Console WriteLine  Handle the exception here  -                throw             else                throw            So to conclude    If we don t want to re-throw  we might consider catching the right exceptions  and storing them in a temporary  If the handler is simple  and we want to re-use code  the best solution is probably to introduce a helper function  If we want to re-throw  we have no choice but to put the code in a  Exception  catch handler  which will break FxCop and your debugger s uncaught exceptions

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So you  re repeating lots of code within every exception-switch  Sounds like extracting a method would be god idea  doesn  t it   So your code comes down to this   MyClass instance  try   instance         catch Exception1 e    Reset instance     catch Exception2 e    Reset instance     catch Exception    throw     void Reset MyClass instance       reset the state of the instance        I wonder why no-one noticed that code-duplication   From C 6 you furthermore have the exception-filters as already mentioned by others  So you can modify the code above to this   try         catch Exception e  when e is Exception1    e is Exception2         Reset instance

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This is a variant of Matt s answer  I feel that this is a bit cleaner    use a method   public void TryCatch            try                 something        return            catch  FormatException         catch  OverflowException          WebId   Guid Empty      Any other exceptions will be thrown and the code WebId   Guid Empty  won t be hit  If you don t want other exceptions to crash your program  just add this AFTER the other two catches       catch  Exception            something  if anything      return     only need this if you follow the example I gave and put it all in a method

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If you can upgrade your application to C  6 you are lucky  The new C  version has implemented Exception filters  So you can write this   catch  Exception ex  when  ex is FormatException    ex is OverflowException        WebId   Guid Empty      Some people think this code is the same as  catch  Exception ex                        if  ex is FormatException    ex is OverflowException            WebId   Guid Empty            throw      But it  s not  Actually this is the only new feature in C  6 that is not possible to emulate in prior versions  First  a re-throw means more overhead than skipping the catch  Second  it is not semantically equivalent  The new feature preserves the stack intact when you are debugging your code  Without this feature the crash dump is less useful or even useless   See a discussion about this on CodePlex  And an example showing the difference

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Update 2015-12-15  See https   stackoverflow com a 22864936 1718702 for C 6  It s a cleaner and now standard in the language   Geared for people that want a more elegant solution to catch once and filter exceptions  I use an extension method as demonstrated below   I already had this extension in my library  originally written for other purposes  but it worked just perfectly for type checking on exceptions   Plus  imho  it looks cleaner than a bunch of    statements   Also  unlike the accepted answer  I prefer explicit exception handling so ex is     had undesireable behaviour as derrived classes are assignable to there parent types    Usage  if  ex GetType   IsAnyOf      typeof FormatException       typeof ArgumentException             Handle   else     throw    IsAnyOf cs Extension  See Full Error Handling Example for Dependancies   namespace Common FluentValidation       public static partial class Validate                    lt summary gt              Validates the passed in parameter matches at least one of the passed in comparisons               lt  summary gt               lt typeparam name  T  gt  lt  typeparam gt               lt param name  p parameter  gt Parameter to validate  lt  param gt               lt param name  p comparisons  gt Values to compare against  lt  param gt               lt returns gt True if a match is found  lt  returns gt               lt exception cref  ArgumentNullException  gt  lt  exception gt          public static bool IsAnyOf lt T gt  this T p parameter  params T   p comparisons                           Validate             p parameter                  CannotBeNull  p parameter                p comparisons                  CannotBeNullOrEmpty  p comparisons                    Test for any match             foreach  var item in p comparisons                  if  p parameter Equals item                       return true                  Return no matches found             return false                      Full Error Handling Example  Copy-Paste to new Console app   using System  using System Collections Generic  using System Linq  using System Text  using Common FluentValidation   namespace IsAnyOfExceptionHandlerSample       class Program               static void Main string   args                           High Level Error Handler  Log and Crash App              try                               Foo                              catch  OutOfMemoryException ex                                Console WriteLine  FATAL ERROR  System Crashing      ex Message                   Console ReadKey                                     static void Foo                            Init             List lt Action lt string gt  gt  TestActions   new List lt Action lt string gt  gt                                   key    gt    throw new FormatException                        key    gt    throw new ArgumentException                        key    gt    throw new KeyNotFoundException                       key    gt    throw new OutOfMemoryException                                      Run             foreach  var FooAction in TestActions                                   Mid-Level Error Handler  Appends Data for Log                  try                                          Init                     var SomeKeyPassedToFoo    FooParam                           Low-Level Handler  Handle Log and Keep going                      try                                               FooAction SomeKeyPassedToFoo                                             catch  Exception ex                                                if  ex GetType   IsAnyOf                              typeof FormatException                               typeof ArgumentException                                                             Handle                             Console WriteLine  ex was  0    ex GetType   Name                               Console ReadKey                                                      else                                                          Add some Debug info                             ex Data Add  SomeKeyPassedToFoo   SomeKeyPassedToFoo ToString                                 throw                                                                                    catch  KeyNotFoundException ex                                           Handle differently                     Console WriteLine ex Message                        int Count   0                      if   Validate IsAnyNull ex  ex Data  ex Data Keys                           foreach  var Key in ex Data Keys                              Console WriteLine                                     0      1       2                                     Count  Key  ex Data Key                         Console ReadKey                                                       namespace Common FluentValidation       public static partial class Validate                    lt summary gt              Validates the passed in parameter matches at least one of the passed in comparisons               lt  summary gt               lt typeparam name  T  gt  lt  typeparam gt               lt param name  p parameter  gt Parameter to validate  lt  param gt               lt param name  p comparisons  gt Values to compare against  lt  param gt               lt returns gt True if a match is found  lt  returns gt               lt exception cref  ArgumentNullException  gt  lt  exception gt          public static bool IsAnyOf lt T gt  this T p parameter  params T   p comparisons                           Validate             p parameter                  CannotBeNull  p parameter                p comparisons                  CannotBeNullOrEmpty  p comparisons                    Test for any match             foreach  var item in p comparisons                  if  p parameter Equals item                       return true                  Return no matches found             return false                          lt summary gt              Validates if any passed in parameter is equal to null               lt  summary gt               lt param name  p parameters  gt Parameters to test for Null  lt  param gt               lt returns gt True if one or more parameters are null  lt  returns gt          public static bool IsAnyNull params object   p parameters                        p parameters                  CannotBeNullOrEmpty  p parameters                 foreach  var item in p parameters                  if  item    null                      return true               return false                     namespace Common FluentValidation       public static partial class Validate                    lt summary gt              Validates the passed in parameter is not null  throwing a detailed exception message if the test fails               lt  summary gt               lt param name  p parameter  gt Parameter to validate  lt  param gt               lt param name  p name  gt Name of tested parameter to assist with debugging  lt  param gt               lt exception cref  ArgumentNullException  gt  lt  exception gt          public static void CannotBeNull this object p parameter  string p name                        if  p parameter    null                  throw                     new                         ArgumentNullException                          string Format  Parameter    0    cannot be null                            p name   default Exception                       namespace Common FluentValidation       public static partial class Validate                    lt summary gt              Validates the passed in parameter is not null or an empty collection  throwing a detailed exception message if the test fails               lt  summary gt               lt typeparam name  T  gt  lt  typeparam gt               lt param name  p parameter  gt Parameter to validate  lt  param gt               lt param name  p name  gt Name of tested parameter to assist with debugging  lt  param gt               lt exception cref  ArgumentNullException  gt  lt  exception gt               lt exception cref  ArgumentOutOfRangeException  gt  lt  exception gt          public static void CannotBeNullOrEmpty lt T gt  this ICollection lt T gt  p parameter  string p name                        if  p parameter    null                  throw new ArgumentNullException  Collection cannot be null  r nParameter Name      p name  default Exception                 if  p parameter Count  lt   0                  throw new ArgumentOutOfRangeException  Collection cannot be empty  r nParameter Name      p name  default Exception                            lt summary gt              Validates the passed in parameter is not null or empty  throwing a detailed exception message if the test fails               lt  summary gt               lt param name  p parameter  gt Parameter to validate  lt  param gt               lt param name  p name  gt Name of tested parameter to assist with debugging  lt  param gt               lt exception cref  ArgumentException  gt  lt  exception gt          public static void CannotBeNullOrEmpty this string p parameter  string p name                        if  string IsNullOrEmpty p parameter                   throw new ArgumentException  String cannot be null or empty  r nParameter Name      p name  default Exception                        Two Sample NUnit Unit Tests  Matching behaviour for Exception types is exact  ie  A child IS NOT a match for any of its parent types    using System  using System Collections Generic  using Common FluentValidation  using NUnit Framework   namespace UnitTests Common Fluent Validations        TestFixture      public class IsAnyOf Tests                Test  ExpectedException typeof ArgumentNullException            public void IsAnyOf ArgumentNullException ShouldNotMatch ArgumentException Test                         Action TestMethod        gt    throw new ArgumentNullException                    try                               TestMethod                              catch  Exception ex                                if  ex GetType   IsAnyOf                      typeof ArgumentException     Note  ArgumentNullException derrived from ArgumentException                       typeof FormatException                       typeof KeyNotFoundException                                             Handle expected Exceptions                     return                                       else throw original                 throw                                    Test  ExpectedException typeof OutOfMemoryException            public void IsAnyOf OutOfMemoryException ShouldMatch OutOfMemoryException Test                         Action TestMethod        gt    throw new OutOfMemoryException                    try                               TestMethod                              catch  Exception ex                                if  ex GetType   IsAnyOf                      typeof OutOfMemoryException                       typeof StackOverflowException                        throw                     else    Handle other exception types  typically by logging to file

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catch  Exception ex        if             ex is FormatException            ex is OverflowException                 throw            Console WriteLine  Hello

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Joseph Daigle s Answer is a good solution  but I found the following structure to be a bit tidier and less error prone   catch Exception ex           if    ex is SomeException    ex is OtherException   throw          Handle exception     There are a few advantages of inverting the expression     A return statement is not necessary The code isn t nested There s no risk of forgetting the  throw  or  return  statements that in Joseph s solution are separated from the expression    It can even be compacted to a single line  though not very pretty   catch Exception ex    if    ex is SomeException    ex is OtherException   throw          Handle exception       Edit   The exception filtering in C  6 0 will make the syntax a bit cleaner and comes with a number of other benefits over any current solution   most notably leaving the stack unharmed   Here is how the same problem would look using C  6 0 syntax   catch Exception ex  when  ex is SomeException    ex is OtherException           Handle exception

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As others have pointed out  you can have an if statement inside your catch block to determine what is going on  C 6 supports Exception Filters  so the following will work   try         catch  Exception e  when  MyFilter e                 The MyFilter method could then look something like this   private bool MyFilter Exception e      return e is ArgumentNullException    e is FormatException      Alternatively  this can be all done inline  the right hand side of the when statement just has to be a boolean expression    try         catch  Exception e  when  e is ArgumentNullException    e is FormatException                This is different from using an if statement from within the catch block  using exception filters will not unwind the stack   You can download Visual Studio 2015 to check this out   If you want to continue using Visual Studio 2013  you can install the following nuget package      Install-Package Microsoft Net Compilers   At time of writing  this will include support for C  6      Referencing this package will cause the project to be built using the   specific version of the C  and Visual Basic compilers contained in the   package  as opposed to any system installed version

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EDIT  I do concur with others who are saying that  as of C  6 0  exception filters are now a perfectly fine way to go  catch  Exception ex  when  ex is        ex is        Except that I still kind of hate the one-long-line layout and would personally lay the code out like the following  I think this is as functional as it is aesthetic  since I believe it improves comprehension  Some may disagree   catch  Exception ex  when       ex is            ex is            ex is         ORIGINAL   I know I m a little late to the party here  but holy smoke     Cutting straight to the chase  this kind of duplicates an earlier answer  but if you really want to perform a common action for several exception types and keep the whole thing neat and tidy within the scope of the one method  why not just use a lambda closure inline function to do something like the following   I mean  chances are pretty good that you ll end up realizing that you just want to make that closure a separate method that you can utilize all over the place  But then it will be super easy to do that without actually changing the rest of the code structurally   Right   private void TestMethod          Action lt Exception gt  errorHandler     ex     gt               write to a log  whatever                try                  try some stuff           catch   FormatException  ex     errorHandler   ex          catch   OverflowException ex     errorHandler   ex          catch   ArgumentNullException ex     errorHandler   ex          I can t help but wonder  warning  a little irony sarcasm ahead  why on earth go to all this effort to basically just replace the following   try          try some stuff   catch  FormatException ex     catch  OverflowException ex     catch  ArgumentNullException ex          with some crazy variation of this next code smell  I mean example  only to pretend that you re saving a few keystrokes      sorta sucks  let s be honest    try          try some stuff   catch  Exception ex         if  ex is FormatException            ex is OverflowException            ex is ArgumentNullException                   write to a log  whatever            return            throw      Because it certainly isn t automatically more readable   Granted  I left the three identical instances of    write to a log  whatever       return  out of the first example   But that s sort of my point   Y all have heard of functions methods  right   Seriously   Write a common ErrorHandler function and  like  call it from each catch block   If you ask me  the second example  with the if and is keywords  is both significantly less readable  and simultaneously significantly more error-prone during the maintenance phase of your project   The maintenance phase  for anyone who might be relatively new to programming  is going to comprise 98 7  or more of the overall lifetime of your project  and the poor schmuck doing the maintenance is almost certainly going to be someone other than you  And there is a very good chance they will spend 50  of their time on the job cursing your name   And of course FxCop barks at you and so you have to also add an attribute to your code that has precisely zip to do with the running program  and is only there to tell FxCop to ignore an issue that in 99 9  of cases it is totally correct in flagging  And  sorry  I might be mistaken  but doesn t that  ignore  attribute end up actually compiled into your app   Would putting the entire if test on one line make it more readable  I don t think so   I mean  I did have another programmer vehemently argue once long ago that putting more code on one line would make it  run faster    But of course he was stark raving nuts  Trying to explain to him  with a straight face--which was challenging  how the interpreter or compiler would break that long line apart into discrete one-instruction-per-line statements--essentially identical to the result if he had gone ahead and just made the code readable instead of trying to out-clever the compiler--had no effect on him whatsoever   But I digress   How much less readable does this get when you add three more exception types  a month or two from now    Answer  it gets a lot less readable    One of the major points  really  is that most of the point of formatting the textual source code that we re all looking at every day is to make it really  really obvious to other human beings what is actually happening when the code runs   Because the compiler turns the source code into something totally different and couldn t care less about your code formatting style   So all-on-one-line totally sucks  too   Just saying        super sucks    catch  Exception ex         if   ex is FormatException    ex is OverflowException    ex is ArgumentNullException                    write to a log  whatever            return            throw

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Maybe try to keep your code simple such as putting the common code in a method  as you would do in any other part of the code that is not inside a catch clause   E g    try                catch  FormatException        DoSomething      catch  OverflowException        DoSomething               private void DoSomething                    Just how I would do it  trying to find the simple is beautiful pattern

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How about  try       WebId   Guid Empty      WebId   new Guid queryString  web       catch  FormatException      catch  OverflowException

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Update for C  9 Using the new pattern matching enhancements made in C  9  you can shorten the expression in the exception filter  Now  catching multiple exceptions is a simple is this  try       WebId   new Guid queryString  quot web quot       catch  Exception e  when  e is FormatException or OverflowException        WebId   Guid Empty

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