如何从C＃中的匹配字符串中提取数字？

Question

I want to extract emoji id from the input.

For example, inputs:

`<eid=1>  valid get 1`
`<eid = >  invalid `
`<exd = 1>  invalid` 
`< eid = 1000> valid get 1000`

I know how to match those string, but I have no idea about how to extract those ids from the matched strings.

Answer 1

Use regex

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] inputs = {
                                  "<eid=1>",
                                  "<eid = >",
                                  "<exd = 1>", 
                                  "< eid = 1000>"
                              };
            string pattern = @"\<\s*eid\s*=\s*(?'number'\d+)\s*\>";

            foreach (string input in inputs)
            {
                Match  match = Regex.Match(input, pattern);
                if (match.Success)
                {
                    Console.WriteLine("input : '{0}' Does Match, number = '{1}'", input, match.Groups["number"]);
                }
                else
                {
                    Console.WriteLine("input : '{0}' Does not Match", input);
                }
            }
            Console.ReadLine();
        }
    }
}

Answer 2

You can do something like this. If you don't want to store each item in an array (ex. you have html code), you can store all the values as one string, as use the following:

var input = @"`<eid=1>  valid get 1`
              `<eid = >  invalid `
              `<exd = 1>  invalid` 
              `< eid = 1000> valid get 1000`";
var regex = new Regex(@"(?<open>\=).*?(?<final-open>\>)");
var matches = regex.Matches(input).Cast<Match>().Select(m => m.Groups["final"].Value).Distinct().ToList();

foreach (var match in matches)
{
    // here you have all the matches
    var id = int.Parse(match.Trim());
}

This method sets the opening and closing tags of the matches you want where this is the open tag '\\=' and this is the closing tag '>':

var regex = new Regex(@"(?<open>\=).*?(?<final-open>\>)");

Answer 3

You need to understand what is a match, what is a capture and how can one do match captures of specific data.

---

In the realm of regular expressions there is a difference between a match and a capture and basic grouping .

You want to match the whole value <eid=8> but you want to get the value 8 into a capture . That is done by adding a grouping ( ) pattern to establish 1 to many capture groups. For a match can hold one or more groupings which are indexed starting at 1 to N. Zero is a special group done automatically and explained later.

---

So for the data <eid=8> , to group capture the value use this regex <\\w+=(\\d+)\\> (instead of the viable pattern <\\w+=\\d+\\> ). The grouping is what puts the number into the match capture group of 1 with a value of 8 .

So what are groups exactly?

• Groups[0] is always the whole match such as what you see of <eid=8> .
• Groups[1-N] are individual captures when ( ) construct is specified. So for our example Groups[1].Value is the number of 8 . Nice, that answers your question.
• One can do a named match capture by putting in (<?<{name here}>... ) . By that logic we can change our pattern to <\\w+=(?<TheNumbers>\\d+)\\> and we then can extract with Groups["TheNumbers"].Value or even Groups[1].Value still.