Safest way to check for integer.

Question

This is probally more of an elegance question than functionality. I am looking for the absolutely safest way to check for an integer from a string and an object,

Using most of the built in functions for this in .net seem to generate a first chance exception, displayed in the Immediate window, and over time they just build up. what are the implications of these exceptions as they don't seem to affect the operation of the system.

Here are my two attempts, both feel clunky and I know there has to be a better way than using VB.IsDBNull and Integer.TryParse... Or am I just being anal.

(to integer from object)

    Dim nInteger As Integer = 0
    If oData Is Nothing OrElse VB.IsDBNull(oData) Then
    Else
        If bThrowErrorIfInvalid Then
        Else
            On Error Resume Next
        End If
        nInteger = CType(oData, Integer)
    End If
    Return nInteger

(to integer from string)

    Dim nInteger As Integer = 0
    If sText Is Nothing Then
    Else
        If bThrowErrorIfInvalid Then
        Else
            On Error Resume Next
        End If
        Integer.TryParse(sText, nInteger) 
    End If
    Return nInteger

Answer 1

You can try this:

Dim i as Integer
Try
    i = Convert.ToInt32(obj)
Catch
    ' This ain't an int
End Try

Convert is in the System namespace.

EDIT: Note: If you are going to put any other code in the Try block, make sure to specify that the only exception the Catch should catch is the exception thrown by Convert.ToInt32 if/when it fails - otherwise you could end up with a nasty problem if something else in that try/catch should fail.

Answer 2

Whats wrong with using the Integer.TryParse? Thats what it was made for...

int i = 0;
string toTest = "not number";
if(int.TryParse(toTest, out i))
{
   // it worked

}

How is that clunky? (C# not VB i know, but same diff)

EDIT: Added if you want to check from an object as well (since TryParse relies on a string) and im not too sure on how you actually plan to use it. Does that cover your concerns a little since this one method will check for both of your cases?

    static bool TryParseInt(object o, out int i)
    {
        i = 0;

        if (o.GetType() == typeof(int))
        {
            i = (int)o;
            return true;
        }
        else if (o.GetType() == typeof(string))
        {
            return int.TryParse(o as string, out i);
        }

        return false;
    }

Answer 3

Integer.TryParse is designed to be the safe way to do this: that's why it was put into the framework in the first place. For an Object, you could always just call ToString() before using TryParse.

I'd also avoid using On Error Resume Next in favor of a Try-Catch block if you need to swallow an error for some reason, as it's much less likely to cause an unwanted side effect.

Answer 4

Since it's VB you can also use the IsNumeric function

Answer 5

it seems in your second example, you have a unnecessary check for bThrowErrorIfInvalid because Integer.TryParse never throws an error. Something Like

If bThrowErrorIfInvalid And Not Integer.TryParse(sText, nInteger) Then
   Throw New ArgumentException()
EndIf