为什么括号使我的正则表达式不匹配？

Question

This matches:

Console.WriteLine(Regex.IsMatch("15, 17-19", @"^\s*\d\d|\d\d\d\d\s*(?:-\s*\d\d|\d\d\d\d\s*)?(?:,\s*\d\d|\d\d\d\d\s*(?:-\s*\d\d|\d\d\d\d\s*)?)*$"));

But when I add parentheses after the ^ and before the $ it doesn't

Console.WriteLine(Regex.IsMatch("15, 17-19", @"^(\s*\d\d|\d\d\d\d\s*(?:-\s*\d\d|\d\d\d\d\s*)?(?:,\s*\d\d|\d\d\d\d\s*(?:-\s*\d\d|\d\d\d\d\s*)?)*)$"));

Can anyone tell me why?

Update:

I see now that my original expression was wrong. I should have had my \\d\\d|\\d\\d\\d\\d portions enclosed in a non-capturing group like this:

^\s*(?:\d\d|\d\d\d\d)\s*(?:-\s*(?:\d\d|\d\d\d\d)\s*)?(?:,\s*(?:\d\d|\d\d\d\d)\s*(?:-\s*(?:\d\d|\d\d\d\d)\s*)?)*$

Which could also be written as

^\s*(?:\d{2}|\d{4})\s*(?:-\s*(?:\d{2}|\d{4})\s*)?(?:,\s*(?:\d{2}|\d{4})\s*(?:-\s*(?:\d{2}|\d{4})\s*)?)*$

This would allow me to add additional parentheses as needed without changing the behavior. Thanks.

Answer 1

表达式中有管道 - 它会在您添加括号时更改表达式的工作方式。

Answer 2

The second pattern with the parentheses makes the ^ and $ metacharacters apply to the entire pattern, which means the entire string must match the pattern. In other words:

• Match beginning of string ( ^ )
• Your pattern
• Match end of string ( $ )

Your first pattern was passing because it is actually being interpreted as ^pattern1 or pattern2$ , thus it was partially matching the input rather than doing so entirely. The breakdown for this pattern is:

• Match beginning of string and first alternate (from ^ upto the pipe symbol)
• Or match the second alternate and the end of the string (after the pipe symbol till $ )