How to know which option in Regex was matched?

问题

I have a Regex that match multiple option.

E.g. ^0x[\da-fA-F]+|-?\d+$ -- a Regex for Match either decimal or hex literals

Is there an option to know which option was eventually match the pattern?

so for...

• -10 - the decimal option was matched
• 0x1Af - the hex option was matched

回答1:

I think you meant this regex:

^(?:-?\d+|0x[\da-fA-F]+)$

with the start and end anchors not part of the alternatives.

You can capture the different alternatives:

^(?:(-?\d+)|(0x[\da-fA-F]+))$

Now you just need to check if a group is not null. If it matches the first alternative, group 1 will be non-null. If it matches the second alternative, group 2 will be non-null:

Match m = Regex.Match(...);
if (m.Groups[1] != null) {
    // first alternative matched!
} else if (m.Groups[2] != null) {
    // second alternative matched!
}

You can also name your groups to make your code more readable:

^(?:(?<decimal>-?\d+)|(?<hex>0x[\da-fA-F]+))$

Now you should check for m.Groups["decimal"] and m.Groups["hex"].

来源：https://stackoverflow.com/questions/55136945/how-to-know-which-option-in-regex-was-matched