<<字符串高级截取和统计>>一文的C#正则实现

using System;
using System.Text.RegularExpressions;

namespace SubStringDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            string source = "123412355123559912323399";
            string destString = "123";
            Console.WriteLine("SubString count:" + SubString(source, destString));
            Console.WriteLine("SubString 2th:" + SubString(source, destString, 2));
            Console.WriteLine("" + SubString(source, destString, 4, 5));
            Console.ReadLine();
        }
        
        /// <summary>
        /// 统计源字符串中包含多少目标字符串
        /// </summary>
        /// <param name="source">源字符串</param>
        /// <param name="dest">目标字符串</param>
        /// <returns>出现次数</returns>
        private static int SubString(string source, string dest)
        {
            MatchCollection mc = Regex.Matches(source, dest);
            return mc.Count;
        }

        /// <summary>
        /// 获取目标字符串在源字符串中指定出现次数的索引
        /// </summary>
        /// <param name="source">源字符串</param>
        /// <param name="dest">目标字符串</param>
        /// <param name="ordinalNumber">出现序数</param>
        /// <returns>出现位置索引</returns>
        private static int SubString(string source, string dest, int ordinalNumber )
        {
            MatchCollection mc = Regex.Matches(source, dest);
            if (mc.Count < ordinalNumber)
            {
                return -1;
            }
            else
            {
                return mc[ordinalNumber - 1].Index;
            }
        }

        /// <summary>
        /// 获取源字符串中在指定序数的目标字符串之后的字符串
        /// </summary>
        /// <param name="source">源字符串</param>
        /// <param name="dest">目标字符串</param>
        /// <param name="ordinalNumber">出现序数</param>
        /// <param name="returnStringlength">返回字符串的长度</param>
        /// <returns>获取的字符串，不成功为null</returns>
        private static string SubString(string source, string dest, int ordinalNumber, int returnStringlength)
        {
            int pos = SubString(source, dest, ordinalNumber);
            if(pos != -1)
            {
                return source.Substring(pos + dest.Length, returnStringlength);
            }
            else
            {
                return null;
            }
        }
    }

} 

执行结果：

SubString count:4
SubString 2th:4
23399