Unable to compare int? to null

Question

Look at this code which I surrounded by textchanged event of a text box:

        string testString = comboIPAddress.Text;
        string[] parts = testString.Split('.');
        int? ipclass = int.Parse(parts[0]);
        if (ipclass == null)
        {
            //do nothing
        }

        if (ipclass >= 1 && ipclass <= 126)
        {
            comboSubnet.Text = "255.0.0.0";
        }
        if (ipclass >= 192 && ipclass <= 223)
        {
            comboSubnet.Text = "255.255.255.0";
        }
        if (ipclass >= 128 && ipclass <= 191)
        {
            comboSubnet.Text = "255.255.0.0";
        }
        else
        {
            comboSubnet.Text = "";
        }

While executing the exe if I delete everything from IPAddress combo box, it is giving error(Input string was not in a correct format.). I don't know the other way to compare an int to null. Please help.

You should read this: http://msdn.microsoft.com/en-us/library/b3h1hf19.aspx — Bertrand Marron, May 25 '13 at 12:59

score 3 · Accepted Answer · answered May 25 '13 at 12:52

3

Use non-nullable int and check if parsable with int.TryParse()...

int ipclass;
if (!int.TryParse(parts[0], out ipclass))
{
    //do nothing
}

answered May 25 '13 at 12:52

davmos

9,324
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It only needed copy and paste. Thanks Man – gujju_sale May 25 '13 at 13:17

score 1 · Answer 2 · edited May 23 '17 at 12:05

1

Have you considered using a MaskedTextBox for the IP? You can then parse the input easily using the System.Net.IPAddress Parse method as shown in this SO answer.

edited May 23 '17 at 12:05

Community

1
1

answered May 25 '13 at 13:07

keenthinker

7,645
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score 0 · Answer 3 · edited May 25 '13 at 13:14

0

You should test if(!string.IsNullOrEmpty(testString)) before trying to split it, followed by int.TryParse

edited May 25 '13 at 13:14

Soner Gönül

97,193
102
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364

answered May 25 '13 at 12:53

Voicu

1

Unable to compare int? to null

3 Answers3