NetBIOS Name Regular Expression

Question

I have a question according to this link http://support.microsoft.com/kb/188997 ( A computer name can be up to 15 alphanumeric characters with no blank spaces. The name must be unique on the network and can contain the following special characters: ! @ # $ % ^ & ( ) - _ ' { } . ~

The Following characters are not allowed: \ * + = | : ; " ? < > , )

and I am developing in C++

so i used the following code but when i input character which isn't allowed.. it is matched ! why ?

 regex  rgx("[a-zA-Z0-9]*(!|@|#|$|%|^|&|\(|\)|-|_|'|.|~|\\{|\\})*[a-zA-Z0-9]*");


string name;
    cin>>name;

if (regex_match(name, rgx))
{
    cout << " Matched :) " << endl;
}
else
    cout << "Not Matched :(" << endl;

your help will be greatly appreciated :)

Answer 1

Your regular expression will match any string, because all your quantifiers are "none or more characters" (*) and since you're not looking for start and end of the string, you'll match even empty strings. Also you're using an unescaped ^ within one pair of brackets ((...|^|...), which will never match, unless this position is the beginning of a string (which may happen due to the *quantifier as explained above).

It's a lot more easier to achieve what you're trying to though:

regex rgx("^[\\w!@#$%^()\\-'{}\\.~]{1,15}$");

If you're using C++11, you might as well use a raw string for better readability:

regex rgx(R"(^[\w!@#$%^()\-'{}\.~]{1,15}$)");

This should match all valid names containing at least one (and up to) 15 of the selected characters.

• \w matches any "word" character, that is A-Z, a-z, digits, and underscores (and based on your locale and regex engine possibly also umlauts and accented characters). Due to this it might be better to actually replace it with A-Za-z\d_ in the above expression:

  regex rgx("^[A-Za-z\\d_!@#$%^()\\-'{}\\.~]{1,15}$");
  

  Or:

  regex rgx(R"(^[A-Za-z\d_!@#$%^()\-'{}\.~]{1,15}$)");
  

• {a,b} is a quantifier matching the previous expresssion between a and b times (inclusive).

• ^ and $ will force the regular expression to fill the whole string (since they'll match beginning and end).

Answer 2

Look here: http://www.cplusplus.com/reference/regex/ECMAScript/ . There you have something about special characters (with a special meaning for a regex).

For example, ^ has a special meaning in a regex, so you must escape it: \^. Other special characters are: $ \ . * + ? ( ) [ ] { } |.

Also, I thing your regex will not allow names like a-b-c (multiple parts of special characters, or more than two parts of alphanumerical characters).