Regex Match.Value returning entire value, not the

问题:

I am currently trying to achieve the relatively simple task of capturing values from a string which exist between sets of curly braces using a regular expression. The expression I have written works fine on a number of online tools I have tested it on, however this is not the case in .NET.

String str= "{Value1}-{Value2}.{Value3}";
Regex regex = new Regex( @"\{(\w+)\}");

MatchCollection matches = regex.Matches(str);

foreach(Match match in matches)
{
    Console.WriteLine(match.Value);
}

I would expect to get 3 matches of "Value1", "Value2", "Value3". However .NET is also returning the brackets, i.e. "{Value1}", "{Value2}", "{Value3}".

Any help on how this can be achieved would be great.

回答1:

You used capturing groups (...), so what you want is in the Groups[1]:

Regex regex = new Regex(@"\{(\w+)\}");

MatchCollection matches = regex.Matches(str);

foreach (Match match in matches) {
    Console.WriteLine(match.Groups[1].Value);
} 

Another way is to use zero-width assertions:

Regex regex = new Regex(@"(?<=\{)(\w+)(?=\})");

MatchCollection matches = regex.Matches(str);

foreach (Match match in matches) {
    Console.WriteLine(match.Value);
} 

In this way the Regex will search for \w+ that is preceded and followed by the { and }, but these two characters won't be part of the match.

回答2:

You can use lookarounds:

Regex regex = new Regex( @"(?<=\{)(\w+)(?=\})");

or use matched group #1.

回答3:

You can use

Console.WriteLine(match.Groups[1].Value);

From MSDN:

If the regular expression engine can find a match, the first element of the GroupCollection object (the element at index 0) returned by the Groups property contains a string that matches the entire regular expression pattern. Each subsequent element, from index one upward, represents a captured group, if the regular expression includes capturing groups.

So match.Groups[0].Value is {Value1} itself and match.Groups[1].Value is Value1.