finally block: is possible to know if an exception happened

Dear friends,

I want to discover if an exception happened, but I want to do this inside the finally block.
I could create a boolean variable in the try block and set the value to true on catch block if an exception happened, but I'll have to update all methods to this situation, otherwise, If is possible to detect on finally block the impact is lower.

Here is an example:

Code:

---

    Private Sub Test()
        Try
            'normal code implementation
        Catch ex As Exception
            'Exception Handling
        Finally
            'If happened an exception
            Trace(True)
            'If NOT happened an exception
            Trace(False)
        End Try
    End Sub

    Private Sub Trace(ByVal err As Boolean)
        'normal code implementation
    End Sub

---

Thanks and sorry for my bad English.

I'd use functions for your situation. The function can return a boolean or some customized object containing information about the exception. You then just call the function and retrieve the returned value, examine it and perform appropriate actions from there.

Ok, but I'll have to call this function in the try and catch blocks? I want to call only in the finally block.

Finally block is always executed regardless of the outcome of the Try block. It is meant to be used for cleanups. You can do it the way you had in post#1, but it just looks weird to me. If you turn the sub into a function like this,

Code:

---

Private Function Test() As Boolean
        Try
            'normal code implementation
        Catch ex As Exception
            Return False
        End Try
        Return True
    End Sub

---

Then you just have to call Trace subroutine like this:

Code:

---

Trace(Test())

---

OK, I agree with you, but I would like to get the object Exception.
What the best implementation to the situation down?

Example:

Code:

---

    Private Function Test() As Integer
        Try
            int i = 0;
            'normal code implementation
            'normal code implementation
            return i;
        Catch ex As Exception
            'normal exception Handling
        Finally
            Trace("IT'S a TESTE", true or false ???, how I get the exception ???)
        End Try
    End Sub

    Private Sub Trace(ByVal pAnytext, ByVal err As Boolean, Optional ByVal pException As Exception = nothing)
        If ( err = true ) Then
            'Use pException to get its properties
        End If
    End Sub

---

Why not...

Code:

---


Private Function Test() As Integer
        Dim ex As Exception = Nothing

        Try
                'normal code implementation
                'normal code implementation
        Catch ex
                'normal exception Handling
        Finally
                If Not ex Is Nothing Then

                        Debug.Print(ex.Message)
                End If
        End Try
End Function

---

I have a globlal var call errMess that is a structure of ErrNumber and the ErrorMessage. At the start of the procedure I set the errMess.ErrNum = 0 and errMess.ErrMessage = string.empty.

If there is an error the Catch portion will save the ErrorNumber and ErrorMessage to my structure then I can look at the value in errMess.ErrNum if it is not 0 then I display the error message for the user or write it to a log file to send for support.

GaryMazzone,

Okay, so this is correct? (using C#)

Code:

---

public partial class Form1 : Form
    {

        private Exception _ex;

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            DoTest();
        }

        private int DoTest()
        {
            try
            {
                int i = -1;      //this is only for test
                int j = 0;      //this is only for test
                return i / j;    //this is only for test
            }
            catch (Exception ex)
            {
                _ex = ex;
                return 0;
            }
            finally
            {
                MessageBox.Show("finally Erro: " + _ex.Message);
            }
        }

    }

---

Code:

---

        Dim i As Integer = 0 'test data
        Dim ii As Integer = 1, iii As Integer 'test data
        '
        Dim Flag As Boolean
        Dim ex As Exception
        Try
            Flag = False 'indicate no exception
            iii = ii \ i
        Catch ex
            Flag = True 'indicate exception
        Finally
            Trace(Flag, ex)
        End Try
    End Sub

    Private Function Trace(ByVal err As Boolean, Optional ByVal ex As Exception = Nothing) As Boolean
        If ex Is Nothing Then

        Else
            Debug.WriteLine(ex.Message)
        End If
    End Function

---

dbasnett,

Thanks, but It works to vb.net but not works on C#:

Error 1 The type or namespace name 'ex' could not be found (are you missing a using directive or an assembly reference?) F:\Projetos\Rogerio\C#\ExceptionTeste\Form1.cs 33 20 ExceptionTeste

Code:

---

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            Test();
        }

        private int Test()
        {
            try
            {
                int i = -1;
                int j = 0;
                return i / j;
            }
            catch (ex)
            {
                return 0;
            }
            finally
            {
                MessageBox.Show("finally Erro: " + ex.Message);
            }
        }

---

What are you really getting at here? You have 2 or 3 solutions you can pick from, whats wrong with them.

Personally I really like the idea of creating a small structure to hold the errornumber + message. Most of the time though I will just use a function if I dont need to know what the error message is and just return true and false.

if you need the error message then use a structure. If you dont, use the boolean logic.

The solution shown by dbasnett is satisfactory, but it only works with vb.net, not on C#.

Quote:

---

Originally Posted by roglopes

The solution shown by dbasnett is satisfactory, but it only works with vb.net, not on C#.

---

Of course his solution is in vb.net... you're asking your question in the vb.net section. So (using common sense, something you're probably not too fond of) if you need a solution to be in c#, shouldn't you have posted in the c# section to start with?

Whats wrong with the code you had where you decalred a global variable of type Exception

Your way works fine after testing:

Csharp Code:

static void Main(string[] args)
        {
            Exception _ex;
            _ex = null;
 
            try
            {
                throw new Exception("test exception");
            }
            catch (Exception ex)
            {
                _ex = ex;
            }
            finally 
            {
                Console.WriteLine("Finally happened");
                Console.WriteLine(_ex.Message);
            }
            Console.Read();
        }

to answer the question asked by the OP, in your C# code, you didn't declare a type of exception to catch.

Code:

---

try
{

}
catch (Exception ex)
{

}
finally
{

}

---

as a side note, a finally block should never know or care if an exception was caught in a catch block. it is the job of the finally to do clean up and NOTHING else.

Quote:

---

Originally Posted by masfenix

Your way works fine after testing:

Csharp Code:

static void Main(string[] args)
        {
            Exception _ex;
            _ex = null;
 
            try
            {
                throw new Exception("test exception");
            }
            catch (Exception ex)
            {
                _ex = ex;
            }
            finally 
            {
                Console.WriteLine("Finally happened");
                Console.WriteLine(_ex.Message);
            }
            Console.Read();
        }

---

Yes, I had already tested and worked, but I wanted to know if it would have a way to not declare the exception in the catch block.

To all thanks very much for your support.

Exception is the base type that all other specific exception types inherit from, so if you catch exception, it is basically a global exception handler in terms of the type of exception it will catch when one occurs in the try. Any type of exception thrown will be caught by 'catch (Exception ex)'

sorry i thought this was a vb forum.

dup'ed by accident

To answer the original question: No, you can't do that.

All the solutions that have been posted here have required that something happen in the Catch block. There's a reason for that and Kleinma pointed out what it was. You are trying to make the Finally block act as a pseudo catch block. However, if the Catch block has dones it's job, then there will be no exception by the time the Finally block has been reached. Therefore, you will have to send a signal to the Finally block that the Catch block has been entered, and the only way to do that is to add code to the Catch block, like it or not.

Guys, thanks for the explanations.

Quote:

---

Originally Posted by dbasnett

sorry i thought this was a vb forum.

---

Same here, I guess C# code is best placed in the VB.Net forum, goes to show that C# people need VB's help