how to use stream builders using exceptions

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.NET3.5

I made an application to view the text data of a file using one textbox txtdescription
and button display_message and wrote following code on button event

C#

try
{
TextReader tr = new StreamReader("asd.txt");
try
{ txtdescription.Text = tr.ReadToEnd(); }
catch (Exception ex)
{ MessageBox.Show(ex.Message); }
finally
{ tr.Close(); }
}
catch (Exception ex)
{ MessageBox.Show(ex.Message); }

Application is running

C#

catch (Exception ex)
{ MessageBox.Show(ex.Message);

this catch will occur when i "ll define that file which do not exist

but i am not getting the concept of fllowin try catch try

C#

txtdescription.Text = tr.ReadToEnd(); }
catch (Exception ex)
{ MessageBox.Show(ex.Message); }
finally
{ tr.Close(); }

when will this catch occur???

Thanx ion advance

Posted 2-Nov-11 1:54am

shivani 2013

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Nickos_me · Accepted Answer · 2011-11-02T02:16:00

So strange code style.. I think, in your case there is no sence for nested try-catch block.

Maybe it's better to use this:

C#

try
{
   TextReader tr = new StreamReader("asd.txt");
   txtdescription.Text = tr.ReadToEnd();
}
catch (ConcreteException ex)
{ 
   MessageBox.Show(ex.Message); 
}
catch (Exception ex)
{ 
   MessageBox.Show(ex.Message); 
}
finally
{ 
   tr.Close(); 
}

But if you really want to get exception in your code, you can write

C#

tr.Close()

before

C#

txtdescription.Text = tr.ReadToEnd();

Or you can read about TextReader ReadToEnd method[^] and think of case, when this exceptions can be raised.

E.F. Nijboer · Accepted Answer · 2011-11-02T02:20:00

There isn't any logic for the extra surrounding try..catch because the only statement is the declaration and instantiation of a StreamReader class. It would be very bad practice to throw an exception from a constructor so that won't happen. (unless memory is that filled up that this new class will give an out-of-memory but that is not something you need to consider). The outer try.catch therefor can be removed safely.

Maybe a better way is to use "using". This will ensure proper destruction of the object when out of scope (stream will be closed) and that way the finally isn't needed.

C#

class Test
{
    public static void Main()
    {
        try
        {
            // Create an instance of StreamReader to read from a file.
            // The using statement also closes the StreamReader.
            using (StreamReader sr = new StreamReader("TestFile.txt"))
            {
                string line;
                // Read and display lines from the file until the end of
                // the file is reached.
                while ((line = sr.ReadLine()) != null)
                {
                    Console.WriteLine(line);
                }
            }
        }
        catch (Exception e)
        {
            // Let the user know what went wrong.
            Console.WriteLine("The file could not be read:");
            Console.WriteLine(e.Message);
        }
    }
}

Good luck!

how to use stream builders using exceptions

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