Use a 'try-finally' block without a 'catch' block

c# .net exception exception-handling

73,842

Solution 1

You would use it to ensure some actions occur after the try content or on an exception, but when you don't wish to consume that exception.

Just to be clear, this doesn't hide exceptions. The finally block is run before the exception is propagated up the call stack.

You would also inadvertently use it when you use the using keyword, because this compiles into a try-finally (not an exact conversion, but for argument's sake it is close enough).

try
{
    TrySomeCodeThatMightException();
}
finally
{
    CleanupEvenOnFailure();
}

Code running in finally is not guaranteed to run, however the case where it isn't guaranteed is fairly edge - I can't even remember it. All I remember is, if you are in that case, chances are very good that not running the finally isn't your biggest problem :-) so basically don't sweat it.

Update from Tobias: finally will not run if the process is killed.

Update from Paddy: Conditions when finally does not execute in a .net try..finally block

The most prevalent example you may see is disposing of a database connection or external resource even if the code fails:

using (var conn = new SqlConnection("")) // Ignore the fact we likely use ORM ;-)
{
    // Do stuff.
}

Compiles into something like:

SqlConnection conn;

try
{
    conn = new SqlConnection("");
    // Do stuff.
}
finally
{
    if (conn != null)
        conn.Dispose();
}

Solution 2

Good Explaination using code:

void MyMethod1()
{
    try
    {
        MyMethod2();
        MyMethod3();
    }
    catch(Exception e)
    {
        //do something with the exception
    }
}


void MyMethod2()
{
    try
    {
        //perform actions that need cleaning up
    }
    finally
    {
        //clean up
    }
}


void MyMethod3()
{
    //do something
}

If either MyMethod2 or MyMethod3 throws an exception, it will be caught by MyMethod1. However, the code in MyMethod2 needs to run clean up code, e.g. closing a database connection, before the exception is passed to MyMethod1.

http://forums.asp.net/t/1092267.aspx?Try+without+Catch+but+with+finally+doesn+t+throw+error+Why+no+syntax+error+

Solution 3

using is equivalent try-finally. You will only use try-finally when you want to do some clean up inside finally and don't care about the exception.

The best approach will be

try
{
   using(resource)
   {
       //Do something here
   }   
}catch(Exception)
{
     //Handle Error
}

Doing so even clean up called by using fails, your code will not fail.

There are some condition when finally will not get executed.

If there is any StackOverflowException or ExecutingEngineException.
Process is killed from external source.

Hope this answers your doubt.

Solution 4

If you have, for example an unmanaged resource you create and use in the try block, you can use the finally block to ensure you release that resource. The finally block will always be executed despite what happens (e.g. exceptions) in the try block.

E.g. the lock(x) statement is really:

System.Threading.Monitor.Enter(x); 
try { ... } 
finally 
{ 
    System.Threading.Monitor.Exit(x); 
}

The finally block will always get called to ensure the exclusive lock is released.

Solution 5

try/finally: when you do not want to handle any exceptions but want to ensure some action(s) occur whether or not an exception is thrown by called code.

View more solutions

73,842