我昨天对有人[0123456789]在正则表​​达式而不是[0-9]or中使用的答案发表了评论\d。我说过使用范围或数字说明符可能比字符集更有效。

我决定今天测试一下，我惊讶地发现（至少在 c# regex 引擎中）\d似乎比其他两个似乎没有太大差异的效率低。这是我的测试输出超过 10000
个随机字符串的 1000 个随机字符，其中 5077 实际上包含一个数字：

Regex \d           took 00:00:00.2141226 result: 5077/10000
Regex [0-9]        took 00:00:00.1357972 result: 5077/10000  63.42 % of first
Regex [0123456789] took 00:00:00.1388997 result: 5077/10000  64.87 % of first

有两个原因让我感到惊讶，如果有人能解释一下，我会很感兴趣：

1. 我原以为范围会比集合更有效地实施。
2. 我不明白为什么\d比[0-9]. \d除了简单的简写之外，还有更多的东西[0-9]吗？

这是测试代码：

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

namespace SO_RegexPerformance
{
    class Program
    {
        static void Main(string[] args)
        {
            var rand = new Random(1234);
            var strings = new List<string>();
            //10K random strings
            for (var i = 0; i < 10000; i++)
            {
                //generate random string
                var sb = new StringBuilder();
                for (var c = 0; c < 1000; c++)
                {
                    //add a-z randomly
                    sb.Append((char)('a' + rand.Next(26)));
                }
                //in roughly 50% of them, put a digit
                if (rand.Next(2) == 0)
                {
                    //replace 1 char with a digit 0-9
                    sb[rand.Next(sb.Length)] = (char)('0' + rand.Next(10));
                }
                strings.Add(sb.ToString());
            }

            var baseTime = testPerfomance(strings, @"\d");
            Console.WriteLine();
            var testTime = testPerfomance(strings, "[0-9]");
            Console.WriteLine("  {0:P2} of first", testTime.TotalMilliseconds / baseTime.TotalMilliseconds);
            testTime = testPerfomance(strings, "[0123456789]");
            Console.WriteLine("  {0:P2} of first", testTime.TotalMilliseconds / baseTime.TotalMilliseconds);
        }

        private static TimeSpan testPerfomance(List<string> strings, string regex)
        {
            var sw = new Stopwatch();

            int successes = 0;

            var rex = new Regex(regex);

            sw.Start();
            foreach (var str in strings)
            {
                if (rex.Match(str).Success)
                {
                    successes++;
                }
            }
            sw.Stop();

            Console.Write("Regex {0,-12} took {1} result: {2}/{3}", regex, sw.Elapsed, successes, strings.Count);

            return sw.Elapsed;
        }
    }
}