正则表达式不过滤特殊符号

Question

I'm currently using the following line of code:

Regex Regex_Alpha = new Regex(@"[a-zA-Z]+('[a-zA-Z])?[a-zA-Z]*");

What I want to do is filter the input of text fields with the condition that input should only be letters and the apostrophe symbol (actually, I still want to add more, but I'm trying to resolve this first).

Right now, it is accepting ALL characters, even numbers.

With my understanding of Regex, I tried to formulate my own expression in the line of:

Regex Regex_Alpha = new Regex(@"^[a-zA-Z'-"+$);

It filters numbers, but doesn't accept the apostrophe symbol. Tried to remove the @ sign and filter the apostrophe with the backslash escape character, but still no use.

What should be the best approach to filter the input so that it only accepts letters and apostrophe? (I'll do the rest of the symbols once I understand how this one should work)

Answer 1

As I've commented, your first regular expression is a pretty good shot at "letters, with a single apostrophe not at either end". However, it matchs any string with even a single letter because a regular expression looks for any match in the input, not for whether the entire input matches.

You can fix this by doing what you've done in your second regular expression - just put a ^ at the start and a $ at the end. This means the start and end of the expression have to match the start and end of the input, so it ensures the whole input is only made up of letters and a possible apostrophe.

Regarding your second regular expression, you have a few of problems.

• If you want a double-quote in a @"..." string literal, you need to put two double quotes. (I think this might just be a typing mistake in your question, as what you currently have wouldn't even compile.)
• You need to close your character class with a ] , otherwise the [ and everything inside just get treated as a sequence of characters to match, one after the other.
• If you want a hyphen in a character class, it has to go at the start or end, or it gets mistaken for a "between" hyphen (as in AZ ).

The expression @"^[a-zA-Z'""-]+$" should match "any string entirely made of letters, apostrophes, quotes or hyphens".