带+，*的C＃正则表达式\\ w似乎无法正常工作

Question

I've got such a piece of code:

String source = "There will will be";
Regex r = new Regex(@"There \w+ be");
Console.WriteLine(r.Match(source).Value);

And I can't see anything in the output, if the source is There will be, I can see the output. Could anyone explain it to me?

And some extent to a question. How to create a Regex that will find between 1 or 2 (that's an example, I'm writing some kind of parser and need to create my own wildchar that behaves that way) words. I've already tried a few combinations but everything fails. One of my tries:

@"\w+\s{1,2}"

I think it's wrong becouse {1,2} tells that regexp to repeat whitespace 1 or 2 times, not whole \\w+\\s. Do you know how to fix it or make in a different way?

Answer 1

The reason for this is the fact that this code won't match. \\w can be any alphanumerical character and the underscore (so essentially A through Z , 0 through 9 and _ ). Spaces however are their own group (represented by \\s ).

To fix this, you can make the regular expression match both by creating a group where the matching algorithm can pick any element using [] :

There [\\w\\s]+? be

Note that I also added a ? to make this a non-greedy match, trying to match a small as possible part of the text (otherwise you could just skip a be while matching).

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As for the addition, just use a non-matching group (saving some processing time and memory compared to a matching group):

(?:\\w+\\s){1,2}

Answer 2

\\w matches any word character(a-zA-Z0-9 and underscore). There will will be would require \\w+ to match will will . \\w can't match the space, thus the regex doesn't match.

Answer 3

That's because space is not matched within \\w+ . Try using either of the following:

@"There \w+ \w+ be"

or

@"There [\w\s]+ be"

Answer 4

\\w matches all alphanumeric characters and the underscore. In your example it would have to match will will which contains a space and therefore does not match. Your expression will however match There will be with only one will .

Answer 5

\\w matches word characters, so the space between the two 'will' strings prevents the match. You might want to replace it with @"There \\w+(?:\\s+\\w+)* be" instead.