How using try catch for exception handling is best practice

Question

while maintaining my colleague s code from even someone who claims to be a senior developer  I often see the following code  try       do something   catch       Do nothing    or sometimes they write logging information to log files like following try catch block try       do some work   catch Exception exception       WriteException2LogFile exception      I am just wondering if what they have done is the best practice  It makes me confused because in my thinking users should know what happens with the system

User · Answer

The better approach is the second one  the one in which you specify the exception type   The advantage of this is that you know that this type of exception can occur in your code  You are handling this type of exception and you can resume  If any other exception came  then that means something is wrong which will help you find bugs in your code  The application will eventually crash  but you will come to know that there is something you missed  bug  which needs to be fixed

User · Answer

I know this is an old question  but nobody here mentioned the MSDN article  and it was the document that actually cleared it up for me  MSDN has a very good document on this  you should catch exceptions when the following conditions are true    You have a good understanding of why the exception might be thrown  and you can implement a specific recovery  such as prompting the user to enter a new file name when you catch a FileNotFoundException object   You can create and throw a new  more specific exception     int GetInt int   array  int index        try               return array index             catch System IndexOutOfRangeException e                throw new System ArgumentOutOfRangeException               quot Parameter index is out of range  quot               You want to partially handle an exception before passing it on for additional handling  In the following example  a catch block is used to add an entry to an error log before re-throwing the exception        try          Try to access a resource    catch  System UnauthorizedAccessException e           Call a custom error logging procedure      LogError e          Re-throw the error      throw          I d suggest reading the entire  quot Exceptions and Exception Handling quot  section and also Best Practices for Exceptions

User · Answer

Best practice is to throw an Exception when the error occurs  Because an error has occurred and it should not be hidden   But in real life you can have several situations when you want to hide this   You rely on third party component and you want to continue the program in case of error  You have a business case that you need to continue in case of error

User · Answer

The only time you should worry your users about something that happened in the code is if there is something they can or need to do to avoid the issue   If they can change data on a form  push a button or change a application setting in order to avoid the issue then let them know   But warnings or errors that the user has no ability to avoid just makes them lose confidence in your product    Exceptions and Logs are for you  the developer  not your end user   Understanding the right thing to do when you catch each exception is far better than just applying some golden rule or rely on an application-wide safety net   Mindless coding is the ONLY kind of wrong coding   The fact that you feel there is something better that can be done in those situations shows that you are invested in good coding  but avoid trying to stamp some generic rule in these situations and understand the reason for something to throw in the first place and what you can do to recover from it

User · Answer

My exception-handling strategy is   To catch all unhandled exceptions by hooking to the Application ThreadException event  then decide   For a UI application  to pop it to the user with an apology message  WinForms  For a Service or a Console application  log it to a file  service or console     Then I always enclose every piece of code that is run externally in try catch    All events fired by the WinForms infrastructure  Load  Click  SelectedChanged     All events fired by third party components  Then I enclose in  try catch   All the operations that I know might not work all the time  IO operations  calculations with a potential zero division      In such a case  I throw a new ApplicationException  quot custom message quot   innerException  to keep track of what really happened  Additionally  I try my best to sort exceptions correctly  There are exceptions which   need to be shown to the user immediately  require some extra processing to put things together when they happen to avoid cascading problems  ie  put  EndUpdate in the finally section during a TreeView fill   the user does not care  but it is important to know what happened  So I always log them   In the event log  or in a  log file on the disk   It is a good practice to design some static methods to handle exceptions in the application top level error handlers  I also force myself to try to   Remember ALL exceptions are bubbled up to the top level  It is not necessary to put exception handlers everywhere  Reusable or deep called functions does not need to display or log exceptions   they are either bubbled up automatically or rethrown with some custom messages in my exception handlers   So finally  Bad     DON T DO THIS  ITS BAD try             catch          only air       Useless     DON T DO THIS  IT S USELESS try             catch Exception ex        throw ex     Having a try finally without a catch is perfectly valid  try       listView1 BeginUpdate            If an exception occurs in the following code  then the finally will be executed        and the exception will be thrown           finally          I WANT THIS CODE TO RUN EVENTUALLY REGARDLESS AN EXCEPTION OCCURRED OR NOT     listView1 EndUpdate       What I do at the top level     i e When the user clicks on a button try             catch Exception ex        ex Log       Log exception      -- OR --          ex Log   Display       Log exception  then show it to the user with apologies       What I do in some called functions     Calculation module try             catch Exception ex           Add useful information to the exception     throw new ApplicationException  quot Something wrong happened in the calculation module  quot   ex         IO module try             catch Exception ex        throw new ApplicationException string Format  quot I cannot write the file  0  to  1  quot   fileName  directoryName   ex      There is a lot to do with exception handling  Custom Exceptions  but those rules that I try to keep in mind are enough for the simple applications I do  Here is an example of extensions methods to handle caught exceptions a comfortable way  They are implemented in a way they can be chained together  and it is very easy to add your own caught exception processing     Usage   try          boom   catch Exception ex           Only log exception     ex Log         -- OR --         Only display exception     ex Display         -- OR --         Log  then display exception     ex Log   Display         -- OR --         Add some user-friendly message to an exception     new ApplicationException  quot Unable to calculate   quot   ex  Log   Display          Extension methods  internal static Exception Log this Exception ex        File AppendAllText  quot CaughtExceptions quot    DateTime Now ToString  quot yyyy-MM-dd quot      quot  log quot   DateTime Now ToString  quot HH mm ss quot      quot    quot    ex Message    quot  n quot    ex ToString      quot  n quot        return ex     internal static Exception Display this Exception ex  string msg   null  MessageBoxImage img   MessageBoxImage Error        MessageBox Show msg    ex Message   quot  quot   MessageBoxButton OK  img       return ex

User · Answer

To me  handling exception can be seen as business rule  Obviously  the first approach is unacceptable  The second one is better one and it might be 100  correct way IF the context says so  Now  for example  you are developing an Outlook Addin  If you addin throws unhandled exception  the outlook user might now know it since the outlook will not destroy itself because of one plugin failed  And you have hard time to figure out what went wrong  Therefore  the second approach in this case  to me  it is a correct one  Beside logging the exception  you might decide to display error message to user - i consider it as a business rule

User · Answer

Best practice is that exception handling should never hide issues  This means that try-catch blocks should be extremely rare   There are 3 circumstances where using a try-catch makes sense    Always deal with known exceptions as low-down as you can  However  if you re expecting an exception it s usually better practice to test for it first  For instance parse  formatting and arithmetic exceptions are nearly always better handled by logic checks first  rather than a specific try-catch  If you need to do something on an exception  for instance logging or roll back a transaction  then re-throw the exception  Always deal with unknown exceptions as high-up as you can - the only code that should consume an exception and not re-throw it should be the UI or public API    Suppose you re connecting to a remote API  here you know to expect certain errors  and have things to in those circumstances   so this is case 1   try        remoteApi Connect     catch ApiConnectionSecurityException ex            User s security details have expired     return false     return true    Note that no other exceptions are caught  as they are not expected   Now suppose that you re trying to save something to the database  We have to roll it back if it fails  so we have case 2   try       DBConnection Save      catch          Roll back the DB changes so they aren t corrupted on ANY exception     DBConnection Rollback            Re-throw the exception  it s critical that the user knows that it failed to save     throw      Note that we re-throw the exception - the code higher up still needs to know that something has failed   Finally we have the UI - here we don t want to have completely unhandled exceptions  but we don t want to hide them either  Here we have an example of case 3   try          Do something   catch Exception ex            Log exception for developers     WriteException2LogFile ex           Display message to users     DisplayWarningBox  An error has occurred  please contact support         However  most API or UI frameworks have generic ways of doing case 3  For instance ASP Net has a yellow error screen that dumps the exception details  but that can be replaced with a more generic message in the production environment  Following those is best practice because it saves you a lot of code  but also because error logging and display should be config decisions rather than hard-coded   This all means that case 1  known exceptions  and case 3  one-off UI handling  both have better patterns  avoid the expected error or hand error handling off to the UI    Even case 2 can be replaced by better patterns  for instance transaction scopes  using blocks that rollback any transaction not committed during the block  make it harder for developers to get the best practice pattern wrong    For instance suppose you have a large scale ASP Net application  Error logging can be via ELMAH  error display can be an informative YSoD locally and a nice localised message in production  Database connections can all be via transaction scopes and using blocks  You don t need a single try-catch block   TL DR  Best practice is actually to not use try-catch blocks at all

User · Answer

Sometimes you need to treat exceptions which say nothing to users   My way is    To catch uncaughted exceptions on application level  ie  in global asax  for critical exceptions  application can not be useful   These exeptions I am not catching on the place  Just log them on app level and let system do its job  Catch  on place  and show some useful info to user  entered wrong number  can t parse   Catch on place and do nothing on marginal problems like  I will check for update info on the background  but the service is not running     It definitely does not have to be best practice   -

User · Answer

I can tell you something   Snippet  1 is not acceptable because it s ignoring exception   it s swallowing it like nothing happened    So do not add catch block that do nothing or just rethrows   Catch block should add some value  For example output message to end user or log error   Do not use exception for normal flow program logic  For example   e g input validation   lt - This is not valid exceptional situation  rather you should write method IsValid myInput   to check whether input item is valid or not   Design code to avoid exception  For example   int Parse string input     If we pass value that cannot be parsed to int  this method would throw and exception  instead of that we might write something like this   bool TryParse string input out int result    lt - this method would return boolean indicating if parse was successfull   Maybe this is little bit out of scope of this question  but I hope this will help you to make right decisions when it s about try    catch     and exceptions

User · Answer

With Exceptions  I try the following   First  I catch special types of exceptions like division by zero  IO operations  and so on and write code according to that   For example  a division by zero  depending the provenience of the values I could alert the user  example a simple calculator in that in a middle calculation  not the arguments  arrives in a division by zero  or to silently treat that exception  logging it and continue processing   Then I try to catch the remaining exceptions and log them   If possible allow the execution of code  otherwise alert the user that a error happened and ask them to mail a error report   In code  something like this   try        Some code here   catch DivideByZeroException dz       AlerUserDivideByZerohappened      catch Exception e       treatGeneralException e     finally        if a IO operation here i close the hanging handlers for example

User · Answer

The second approach is a good one   If you don t want to show the error and confuse the user of application by showing runtime exception i e  error  which is not related to them  then just log error and the technical team can look for the issue and resolve it   try       do some work   catch Exception exception       WriteException2LogFile exception    it will write the or log the error in a text file     I recommend that you go for the second approach for your whole application

User · Answer

The catch without any arguments is simply eating the exception and is of no use   What if a fatal error occurs   There s no way to know what happened if you use catch without argument   A catch statement should catch more specific Exceptions like FileNotFoundException and then at the very end you should catch Exception which would catch any other exception and log them

User · Answer

You should consider these Design Guidelines for Exceptions   Exception Throwing Using Standard Exception Types Exceptions and Performance   https   docs microsoft com en-us dotnet standard design-guidelines exceptions

User · Answer

An exception is a blocking error    First of all  the best practice should be don t throw exceptions for any kind of error  unless it s a blocking error   If the error is blocking  then throw the exception  Once the exception is already thrown  there s no need to hide it because it s exceptional  let the user know about it  you should reformat the whole exception to something useful to the user in the UI    Your job as software developer is to endeavour to prevent an exceptional case where some parameter or runtime situation may end in an exception  That is  exceptions mustn t be muted  but these must be avoided   For example  if you know that some integer input could come with an invalid format  use int TryParse instead of int Parse  There is a lot of cases where you can do this instead of just saying  if it fails  simply throw an exception    Throwing exceptions is expensive    If  after all  an exception is thrown  instead of writing the exception to the log once it has been thrown  one of best practices is catching it in a first-chance exception handler  For example    ASP NET  Global asax Application Error Others  AppDomain FirstChanceException event    My stance is that local try catches are better suited for handling special cases where you may translate an exception into another  or when you want to  mute  it for a very  very  very  very  very special case  a library bug throwing an unrelated exception that you need to mute in order to workaround the whole bug    For the rest of the cases    Try to avoid exceptions  If this isn t possible  first-chance exception handlers  Or use a PostSharp aspect  AOP     Answering to  thewhiteambit on some comment      thewhiteambit said      Exceptions are not Fatal-Errors  they are Exceptions  Sometimes they   are not even Errors  but to consider them Fatal-Errors is completely   false understanding of what Exceptions are    First of all  how an exception can t be even an error    No database connection    exception  Invalid string format to parse to some type    exception Trying to parse JSON and while input isn t actually JSON    exception Argument null while object was expected    exception Some library has a bug    throws an unexpected exception There s a socket connection and it gets disconnected  Then you try to send a message    exception       We might list 1k cases of when an exception is thrown  and after all  any of the possible cases will be an error   An exception is an error  because at the end of the day it is an object which collects diagnostic information -- it has a message and it happens when something goes wrong    No one would throw an exception when there s no exceptional case  Exceptions should be blocking errors because once they re thrown  if you don t try to fall into the use try catch and exceptions to implement control flow they mean your application service will stop the operation that entered into an exceptional case   Also  I suggest everyone to check the fail-fast paradigm published by Martin Fowler  and written by Jim Shore   This is how I always understood how to handle exceptions  even before I got to this document some time ago            consider them Fatal-Errors is completely false understanding of what exceptions are    Usually exceptions cut some operation flow and they re handled to convert them to human-understandable errors  Thus  it seems like an exception actually is a better paradigm to handle error cases and work on them to avoid an application service complete crash and notify the user consumer that something went wrong   More answers about  thewhiteambit concerns     For example in case of a missing Database-Connection the program could   exceptionally continue with writing to a local file and send the   changes to the Database once it is available again  Your invalid   String-To-Number casting could be tried to parse again with   language-local interpretation on Exception  like as you try default   English language to Parse  1 5   fails and you try it with German   interpretation again which is completely fine because we use comma   instead of point as separator  You see these Exceptions must not even   be blocking  they only need some Exception-handling     If your app might work offline without persisting data to database  you shouldn t use exceptions  as implementing control flow using try catch is considered as an anti-pattern  Offline work is a possible use case  so you implement control flow to check if database is accessible or not  you don t wait until it s unreachable  The parsing thing is also an expected case  not EXCEPTIONAL CASE   If you expect this  you don t use exceptions to do control flow   You get some metadata from the user to know what his her culture is and you use formatters for this   NET supports this and other environments too  and an exception because number formatting must be avoided if you expect a culture-specific usage of your application service       An unhandled Exception usually becomes an Error  but Exceptions itself   are not codeproject com Articles 15921 Not-All-Exceptions-Are-Errors   This article is just an opinion or a point of view of the author    Since Wikipedia can be also just the opinion of articule author s   I wouldn t say it s the dogma  but check what Coding by exception article says somewhere in some paragraph            Using these exceptions to handle specific errors that arise to   continue the program is called coding by exception  This anti-pattern can quickly degrade software in performance and maintainability    It also says somewhere   Incorrect exception usage     Often coding by exception can lead to further issues in the software   with incorrect exception usage  In addition to using exception   handling for a unique problem  incorrect exception usage takes this   further by executing code even after the exception is raised  This   poor programming method resembles the goto method in many software   languages but only occurs after a problem in the software is detected    Honestly  I believe that software can t be developed don t taking use cases seriously  If you know that      Your database can go offline    Some file can be locked    Some formatting might be not supported    Some domain validation might fail    Your app should work in offline mode    whatever use case         you won t use exceptions for that  You would support these use cases using regular control flow    And if some unexpected use case isn t covered  your code will fail fast  because it ll throw an exception  Right  because an exception is an exceptional case   In the other hand  and finally  sometimes you cover exceptional cases throwing expected exceptions  but you don t throw them to implement control flow  You do it because you want to notify upper layers that you don t support some use case or your code fails to work with some given arguments or environment data properties

User · Answer

Leave blank catch block is the worse thing to do  If there is an error the best way to handle it is to    Log it into file database etc   Try to fix it on the fly  maybe trying alternative way of doing that operation  If we cannot fix that  notify the user that there is some error and of course abort the operation

[c#] How using try catch for exception handling is best practice

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