try-catch question ...

[Hussam Fattahi]

while using try-catch combination, I've assign a value to a reference type variable within try block, but when I tried to use this variable within catch block it throw an exception (NullRefrenceException) or an error (use of unassigned local variable) occur. my question is: the variables that has been declared, or had values assigned for them in try block, how to deal with them in catch block. the code I'm working on : int i =0; Socket remote; try { remote = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp); i = 5; } catch(Exception ee) { MessageBox.Show(i.ToString()); MessageBox.Show(remote.ToString()); //the error occured here. } and why is that when i used a value type variable it works well.

[Christian Graus]

remote is going to be null, given that you've had an exception, and it's not likely that i=5 threw it.

Christian Graus - Microsoft MVP - C++ Metal Musings - Rex and my new metal blog "I am working on a project that will convert a FORTRAN code to corresponding C++ code.I am not aware of FORTRAN syntax" ( spotted in the C++/CLI forum )

[Hussam Fattahi]

well, that is my qustion. i need to assign a value to 'remote' in try block, and then use that value within catch block. is there any direct way, or trick to do so.

[Christian Graus]

Yes, make a call to the remote constructor which does not fail. There's no rocket science here. It's null going in, your attempt to assign a value is failing, and so it's still null. The fault is in your code, it needs to not make assumptions about things that may not have happened, because you were in a try block.

Christian Graus - Microsoft MVP - C++ Metal Musings - Rex and my new metal blog "I am working on a project that will convert a FORTRAN code to corresponding C++ code.I am not aware of FORTRAN syntax" ( spotted in the C++/CLI forum )

[Scott Dorman]

Hussam Fattahi wrote:

i need to assign a value to 'remote' in try block, and then use that value within catch block.

Usually the only things you would need to do in the catch block are cleanup type activities. If you are trying to show the error message to the user you should be doing something like this:

int i =0;
Socket remote = null;
try
{
remote = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
i = 5;
}
catch(Exception ee)
{
MessageBox.Show(i.ToString());
MessageBox.Show(ee.Message);
}

The Socket remote **= null**; will remove the compiler issue about using an unassigned variable. Any variable that is used inside of a catch block must be explicitly assigned prior to it being used. If the call to remote = new Socket(...) fails for any reason, remote will be null (in all cases), you will take an exception that puts you in your catch handler. At that point, remote is still null, so you are trying to run ToString() on a null reference, which you can't do.

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