Method not throwing an exception despite the conditions

Question

This is the method I use to retrieve MAC address from my user.

To reproduce a scenario where a MAC address does not get retrieved, I intentionally disabled my network card. This should not return a MAC address, using this method:

public static string returnMAC1()
{
    try
    {
        ManagementObjectSearcher searcher = new ManagementObjectSearcher("Select MACAddress, PNPDeviceID FROM Win32_NetworkAdapter WHERE MACAddress IS NOT NULL AND PNPDEVICEID IS NOT NULL");
        ManagementObjectCollection mObject = searcher.Get();

        foreach (ManagementObject obj in mObject)
        {
            string pnp = obj["PNPDeviceID"].ToString();
            if (pnp.Contains("PCI\\"))
            {
                string mac = obj["MACAddress"].ToString();
                mac = mac.Replace(":", string.Empty);

                if (string.IsNullOrEmpty(mac))
                {
                    throw new System.Exception("Invalid PCI MAC");
                }

                return mac;
            }
        }
        return string.Empty;
    }
    catch (Exception ex)
    {
        Console.WriteLine("Error Message: " + ex.Message);
    }
    return string.Empty;
}

With this said, despite my exception handler in place to throw an error, I am unable to get it to throw an error despite my output being like this:

enter image description here

Note: It should say: Error Message: Invalid PCI MAC.

Is there any way to check what that "blank" is? Apparently it's not a "", or string.Empty, or null, or null.

Try `string.IsNullOrWhiteSpace()`? Because it could be one (or more) space. — Chi Chan, Feb 21 '14 at 21:30
You could just set a breakpoint and inspect the value. That said, is it possible there are no items in `mObject`? Is it possible that there _are_ values but none of the `PNPDeviceID`s contain `"PCI\\"`? — canon, Feb 21 '14 at 21:30
@ChiChan I have tried that as well -- no throw. @canon, let me try `mObject` — theGreenCabbage, Feb 21 '14 at 21:32
Thinking about it, shouldn't `string.Empty` be returned instead? — theGreenCabbage, Feb 21 '14 at 21:33
Some hex values may appear as empty/blank/spaces on console. When all else fails, try to display the hex value returned using ascii to hex converter function as in: http://stackoverflow.com/questions/15920741/convert-from-string-ascii-to-string-hex — NoChance, Feb 21 '14 at 21:38
Hm.. But IsNullOrWhiteSpace should already handle all of \n\r\v\t: http://www.dotnetperls.com/isnullorwhitespace. Could it be somewhere else in your code? — Chi Chan, Feb 21 '14 at 21:42
Hi @ChiChan is `IsNullOrWhiteSpace` better or `IsNullOrEmpty`? — theGreenCabbage, Feb 21 '14 at 22:02
@theGreenCabbage, it depends on usage. But imagine if you want to check for an empty user input and it's a textarea. The person can type new line characters, spaces and tabs and it's very annoying to check for all of those. In that case you want to use `IsNullOrWhiteSpace`. — Chi Chan, Feb 22 '14 at 18:54

score 2 · Accepted Answer · answered Feb 21 '14 at 21:37

To reproduce a scenario where a MAC address does not get retrieved, I intentionally disabled my network card. This should not return a MAC address, using this method: ...

Could it be that after disabling the card, the following condition is always false

if (pnp.Contains("PCI\\"))

In such case nothing happens within foreach loop and function returns string.Empty?

score 0 · Answer 2 · answered Feb 21 '14 at 21:35

0

you can use .Lenght to be sure

if (string.IsNullOrEmpty(mac) || mac.Trim().Length == 0)
{
    throw new System.Exception("Invalid PCI MAC");
}

answered Feb 21 '14 at 21:35

Maryam Arshi

1,974
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`string.IsNullOrWhiteSpace()` could be slightly better, see comment of @ChiChan. – AlexD Feb 21 '14 at 21:54

Method not throwing an exception despite the conditions

2 Answers2