C# Check if Regex is a match, returns True instead of False

Question

I'm not familiar with Regex so, I hope someone can help me with this. I'm using Regex and I'm checking further in the code if that specific Regex is a match or not.

Regex I use and want to check for:

• Regex InitialGForKj = new Regex("[Y[\\s\\S]|E[BILPRSY]|I[BELN]]", RegexOptions.Compiled); .

Now the code where I check if it is a match is as followed:

else if (i == 0 && InitialGForKj.IsMatch(upperLetters.Substring(1, 3)))
        {
            dmetaphoneKeyResultPrimary.Append("K");
            dmetaphoneKeyResultSecondary.Append("J");
            i += 2;
        }

• i is the current Character (In this case it is 'G').
• upperLetters = The Word what will be checked (In this case: Garçon).
• dmetaphoneKeyResultPrimary and dmetaphoneKeyResultSecondary are the replacements for the Letter 'G' (Both are Stringbuilders).

I Also checked with Console.WriteLine() what the substring its value is (Which returns "arç"). So, now the question is, why does the code see this as true and not as False ? Which I think it must be False .

Or am I doing it completely wrong?

Answer 1

You must write it as

var InitialGForKj = new Regex("Y.|E[BILPRSY]|I[BELN]", RegexOptions.Compiled | RegexOptions.Singleline);

See the regex demo . Note that . matches any char including a newline since the RegexOptions.Singleline option is passed to the Regex constructor.

The current [Y[\\s\\S]|E[BILPRSY]|I[BELN]] pattern matches 3 alternatives:

• [Y[\\s\\S] - a Y , [ , whitespace or non-whitespace (this matches any char there is!)
• | - or
• E[BILPRSY] - E and then one letter from the class
• | - or
• I[BELN]] - a I followed with B , E , L , N , and then ] .

As you see, you corrupted it by enclosing the whole pattern with [ and ] .

Answer 2

First of all, this is your current expression:

As you see, the outer [ ] will be recognized as chars. So drop them!

Because \\s\\S is recognised as whitespace or non-whitespace, so pretty much as everything, Garcon is a valid match.