Hot to check if a string is numeric?

[littleisharp]

What's the best and most elegant way to test whether a value in a string is numeric? Is there some function in the framework that does it?

 

My solution below is a bit snide:

 

        ' Check if it's a number or a string
       Dim i As Integer
       Dim isNumber As Boolean = True
       For i = 1 To tableName.Length()
           Select Case Microsoft.VisualBasic.Strings.Asc(Strings.Mid(tableName, i, 1))
               Case 48 To 57
                   ' This is a number
               Case Else
                   isNumber = False
                   Exit For
           End Select
       Next i

      If isNumber Then
                    ' If it's a number, enclose in single quotes 
       End If

[wessamzeidan]

Char.IsDigit()

 

checks if a character is a digit

[PlausiblyDamp]

You could use regular expressions try something like

 

   Function IsNumber(ByVal test As String) As Boolean

       If System.Text.RegularExpressions.Regex.IsMatch(test, "^\d*$") Then
           Return True
       Else
           Return False
       End If
   End Function

[mocella]

You could do a regular-expression. I think that using "[0-9]" should tell you if there's numbers in the string. Something like this should work (although there's certainly other approaches that will do the same):

 

Regex expression = new Regex( "[0-9]" );



//perform the search in a match-collection object

MatchCollection matches = expression.Matches( tableName );



if( matches.Count > 0 )

{

	isNumber = true;

}

[/Code]

[mocella]

Damn - PlausiblyDamp beat me to the punch, and with a different approach!

[littleisharp]

Hi guys

 

I found something in the framework after all...

 

Microsoft.VisualBasic.Information.IsNumeric(tableName)

 

works perfectly

 

Thanks

[PlausiblyDamp]

That will only work in VB - if you need to convert to C# that will fail.

[Jaco]

That will only work in VB - if you need to convert to C# that will fail.

 

No, the Microsoft.VisualBasic namespace is a core part of the framework and will work from C# even if VB is not installed. I'm calling this namespace's methods for a few things I can't be bothered to reinvent.

[mocella]

I hope this isn't one of the "can't be bothered to reinvent" items (perhaps you meant some other functions in the VisualBasic namespace though).

 

I don't see having to write one common function to check a string for a given RegEx as a bad thing if you implement it correctly. Once you have a general function written, you only need to update the expression sent in, along with the string to search.

 

For example (forgive the spacing):

public static bool SearchStringForExpression( string textToSearch, string searchExpression )

{



bool expressionFound = false;

Regex expression = new Regex( searchExpression );



//perform the search in a match-collection object

MatchCollection matches = expression.Matches( textToSearch );



if( matches.Count > 0 )

{

	expressionFound = true;

}

else

{

	expressionFound = false;

}



return expressionFound;



}

[/Code]

[Arch4ngel]

int.Parse("125 Miles per hours"); couldn't work also ? Just check if != "".

 

RegEx is powerful however... might lead to much larger result than this simple eg.

[jspencer]

This is the one that works for me:

 

    Public Overloads Function IsNumeric(ByVal Value As String) As Boolean
       Dim myRegEx As New Regex("(\+|-)?[0-9][0-9]*(\.[0-9]*)?")
       If myRegEx.IsMatch(Value) AndAlso myRegEx.Match(Value).Length = Value.Length Then
           Return True
       Else
           Return False
       End If
   End Function

[dynamic_sysop]

on the last post , what would happen if the number contained an E after the dot , eg: 1.E560 , it wouldn't be recognized as a numeric.

here's an example i made a while ago ( i posted this in the codebank of another vb forum when i made it )

private bool IsNumeric(object ValueToCheck)
{
double Dummy = new double();
string InputValue = Convert.ToString(ValueToCheck);

bool Numeric = double.TryParse( InputValue , System.Globalization.NumberStyles.Any , null , out Dummy);
	
return Numeric;
}