Char.IsSymbol(“*”) is false

Question

I\'m working on a password validation routine, and am surprised to find that VB does not consider \'*\' to be a symbol per the Char.IsSymbol() check. Here is the output from

Answer 1

Maybe you have the compiler option "strict" of, because with

Char.IsSymbol("*")

I get a compiler error

BC30512: Option Strict On disallows implicit conversions from 'String' to 'Char'.

To define a Character literal in VB.NET, you must add a c to the string, like this:

Char.IsSymbol("*"c)

Answer 2

Characters that are symbols in this context: UnicodeCategory.MathSymbol, UnicodeCategory.CurrencySymbol, UnicodeCategory.ModifierSymbol and UnicodeCategory.OtherSymbol from the System.Globalization namespace. These are the Unicode characters designated Sm, Sc, Sk and So, respectively. All other characters return False.

From the .Net source:

internal static bool CheckSymbol(UnicodeCategory uc)
{
    switch (uc)
    {
        case UnicodeCategory.MathSymbol:
        case UnicodeCategory.CurrencySymbol:
        case UnicodeCategory.ModifierSymbol:
        case UnicodeCategory.OtherSymbol:
            return true;
        default:
            return false;
    }
}

or converted to VB.Net:

Friend Shared Function CheckSymbol(uc As UnicodeCategory) As Boolean
    Select Case uc
        Case UnicodeCategory.MathSymbol, UnicodeCategory.CurrencySymbol, UnicodeCategory.ModifierSymbol, UnicodeCategory.OtherSymbol
            Return True
        Case Else
            Return False
    End Select
End Function

CheckSymbol is called by IsSymbol with the Unicode category of the given char.

Since the * is in the category OtherPunctuation (you can check this with char.GetUnicodeCategory()), it is not considered a symbol, and the method correctly returns False.

To answer your question: use char.GetUnicodeCategory() to check which category the character falls in, and decide to include it or not in your own logic.

Answer 3

If you simply need to know that character is something else than digit or letter, use just

!char.IsLetterOrDigit(c) 

preferably with

&& !char.IsControl(c)