How can I throw a FormatException or OverflowException?

Question

This is my syntax so far:

static void Main(string[] args)
{
    // create a writer and open the file
    System.IO.StreamReader reader =
    new System.IO.StreamReader("c:\\Numbers.txt"); ;
    // open file in Output
    using (System.IO.StreamWriter file = new System.IO.StreamWriter(@"C:\Output.txt"))
    {
        string line;
        int Count = 1;
        while ((line = reader.ReadLine()) != null)
        {
            int y = Int32.Parse(line);
            if ((y % 2) == 0)
            {
                file.WriteLine(" Number " + y + " in line " + Count + " is even ");
            }
            else
            {
                file.WriteLine(" Number " + y + " in line " + Count + " is odd ");
            }
            Count++;
        }
        file.Close();
        reader.Close();
    }
}

I need to invoke exceptions that would output the following lines:

FormatException - Input string was not in a correct format., line No.=10, String=ABC

OverflowException - Value was either too large or too small for an Int32., line No.=11, String=123456789012345678901234567890

FormatException - Input string was not in a correct format., line No.=14, String=4.0

Could anyone help on where and how to write these exceptions.

Olivier Jacot-Descombes · Answer 1 · 2014-03-27T20:11:03.357

1

Throw the existing exception System.FormatException or System.OverflowException:

throw new FormatException("my message");

If you only want to display an error message to the user, consider using the message box:

MessageBox.Show("my message");

edited Mar 27 '14 at 20:11

answered Mar 27 '14 at 20:04

Olivier Jacot-Descombes

104,806
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Thank you this seems to be what I was looking for. – user3470207 Mar 27 '14 at 20:37

Manuel Spezzani · Answer 2 · 2014-03-27T20:16:02.550

0

Probably the best way to fix your code is using int.TryParse instead of int.Parse.

http://msdn.microsoft.com/en-us/library/f02979c7(v=vs.110).aspx

If the input is not a string, probably the easiest way is to try parsing into a decimal: - if still fail--> not a number - else it is a number but not an int

edited Mar 27 '14 at 20:16

answered Mar 27 '14 at 20:06

Manuel Spezzani

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7
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score 0 · Answer 3 · edited May 23 '17 at 10:31

My guess would be that you don't want to have exceptions but an output with information about each row containing an error:

while ((line = reader.ReadLine()) != null)
{
    int y;
    if (int.TryParse(line, out y)) {
        if ((y % 2) == 0)
        {
            file.WriteLine(" Number " + y + " in line " + Count + " is even ");
        }
        else
        {
            file.WriteLine(" Number " + y + " in line " + Count + " is odd ");
        }
    } else {
        file.WriteLine(String.Format("Invalid formatted string in line number {0}: {1}", Count, line));
    }

    Count++;
}

Of course you could add some additional checks - but basically you should avoid throwing exceptions if you're kind of expecting some lines to be invalid or if you want to gracefully skip these lines with some comments.

Here's a good answer on when to use exceptions: When to throw an exception?

Yes, I am expecting lines to be invalid but this project entails outputting exceptions. Thank you though for the input. — user3470207, Mar 27 '14 at 20:36

How can I throw a FormatException or OverflowException?

3 Answers3