CODEWITHSUNDEEP
c#.netexception
mkus
mkus

Reputation: 3497

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

Are there situations where it is appropriate to use a try-finally block without a catch block?

Upvotes: 121

Views: 114717

Answers (10)

Amar Palsapure
Amar Palsapure

Reputation: 9680

using is equivalent to 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.

Upvotes: 5

Parmeshwar karale
Parmeshwar karale

Reputation: 11

1.we can use the try block without catch but we should use the catch/finally, any one of them. 2.We can't use only try block.

Upvotes: 0

jazza1000
jazza1000

Reputation: 4247

Here is a situation where you might want to use try finally: when you would normally use a using statement, but can't because you are calling a method by reflection.

This won't work

using (objMsg  =  Activator.CreateInstance(TypeAssist.GetTypeFromTypeName("omApp.MessagingBO")))
{

}

instead use

           object objMsg = null;
            try
            {
                objMsg
                   = Activator.CreateInstance(TypeAssist.GetTypeFromTypeName("myAssembly.objBO"));

                strResponse = (string)objMsg.GetType().InvokeMember("MyMethod", BindingFlags.Public
                        | BindingFlags.Instance | BindingFlags.InvokeMethod, null, objMsg,
                        new object[] { vxmlRequest.OuterXml });
            }               
            finally
            {
                if (objMsg!=null)
                    ((IDisposable)objMsg).Dispose();
            }

Upvotes: 1

donstack
donstack

Reputation: 2715

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+

Upvotes: 12

Adam Houldsworth
Adam Houldsworth

Reputation: 64527

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();
}

Upvotes: 188

Neil G
Neil G

Reputation: 33252

I don't know anything about C#, but it seems that anything you could do with a try-finally, you could more elegantly do with a using statement. C++ doesn't even have a finally as a result of its RAII.

Upvotes: 0

Jeb
Jeb

Reputation: 3799

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.

Upvotes: 4

Harsh
Harsh

Reputation: 3751

Have a look at the following link: https://softwareengineering.stackexchange.com/questions/131397/why-use-try-finally-without-a-catch-clause

It depends on the architecture of your application and the operation you are performing in the block.

Upvotes: 0

Mitch Wheat
Mitch Wheat

Reputation: 300759

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.

Upvotes: 1

IanNorton
IanNorton

Reputation: 7282

You need a finally block, when no matter which (if any) exceptions are caught or even if none are caught you still want to execute some code before the block exits. For instance, you might want to close an open file.

See Also try-finally

Upvotes: 1

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