c# -\d的效率不及[0-9]

昨天，我对一个答案发表了评论，该答案是有人在regular expression中使用[0123456789]而不是[0-9]或\d。我说过使用范围或数字说明符可能比使用字符集更有效。

我决定今天进行测试，令我惊讶的是，(至少在C#正则表达式引擎中)\d的效率似乎比其他两个似乎相差不大的效率低。这是我的测试输出，超过10000个随机字符串，包含1000个随机字符，其中5077个实际上包含一个数字:

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

令我惊讶的有两个原因:

我以为该范围将比集合有效得多。

我无法理解\d为什么比[0-9]更糟糕。除了\d的简写之外，[0-9]还有更多的功能吗？

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 one character 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;
        }
    }
}

最佳答案

\d检查所有Unicode数字，而[0-9]限于这10个字符。例如，Persian数字۱۲۳۴۵۶۷۸۹是与\d而不是[0-9]匹配的Unicode数字的示例。

您可以使用以下代码生成所有此类字符的列表:

var sb = new StringBuilder();
for(UInt16 i = 0; i < UInt16.MaxValue; i++)
{
    string str = Convert.ToChar(i).ToString();
    if (Regex.IsMatch(str, @"\d"))
        sb.Append(str);
}
Console.WriteLine(sb.ToString());

产生: