字符串中判断存在的⼏种模式和效率（ains、
string.Index。。。
  通常情况下，我们判断⼀个字符串中是否存在某值常常会⽤ains，其实判断⼀个字符串中存在某值的⽅法有很多种，最常⽤的就是前述所说的ains，相对来说⽐较常⽤的还有string.IndexOf和Regex.Match。直接上代码，后⾯在说些什么吧，通常情况下功能的实现最重要，作者的话，只对有⼼者有效。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
namespace ExistsInString
{
class Program
{
static void Main(string[] args)
{
string str0 = "|456|";
string str1 = "|444|";
string str2 = "|111|222|333|444|555|666|777|888|999|000|";
//------------------------------------------
//String.Contains⽅法
if (str2.Contains(str0))
Console.WriteLine("String.Contains->true");
else
Console.WriteLine("String.Contains->false");
if (str2.Contains(str1))
Console.WriteLine("String.Contains->true");
else
Console.WriteLine("String.Contains->false");
//------------------------------------------
//String.IndexOf⽅法
int val1 = str2.IndexOf(str0);//不存在返回-1
Console.WriteLine("String.IndexOf(no exists)->" + val1);
int val2 = str2.IndexOf(str1);//存在返回str1⾸字符所在str2中的位置(>=0)
Console.WriteLine("String.IndexOf(exists)->" + val2);
//------------------------------------------
//正则匹配⽅法
if (Regex.Match(str2, "[|]456[|]").Success)
Console.WriteLine("Regex.Match(no exists)->true");
else
Console.WriteLine("Regex.Match(no exists)->false");
if (Regex.Match(str2, "[|]444[|]").Success)
Console.WriteLine("Regex.Match(exists)->true");
else
Console.WriteLine("Regex.Match(exists)->false");
Console.ReadKey();
/*
*如果上述三种⽅式都处理⼤量数据，效率如何呢？
*以下循环六组数据说明
*/
int loopCount = (int)10e6;
DateTime lasttime = DateTime.Now;
DateTime nowtime = DateTime.Now;
for (int loop = 1; loop < 7; loop++)
{
Console.WriteLine("\r\nloop " + loop + " >>>>>>>");
//------------------------------------------
//String.Contains⽅法
//no exists
lasttime = DateTime.Now;
for (int i = 0; i < loopCount; i++)
if (str2.Contains(str0)) { };
nowtime = DateTime.Now;
TimeSpan tsStrConNoExists = nowtime - lasttime;
//exists
lasttime = DateTime.Now;
for (int i = 0; i < loopCount; i++)
if (str2.Contains(str1)) { };
nowtime = DateTime.Now;
TimeSpan tsStrConExists = nowtime - lasttime;
//------------------------------------------
//String.IndexOf⽅法
//no exists
lasttime = DateTime.Now;
for (int i = 0; i < loopCount; i++)
if (str2.IndexOf(str0) >= 0) { };//上述已经提到不存在返回-1，存在返回⼀个⾮负整数，这⾥为什么不⽤ == -1 ，⽽是⽤了 >= 0 ，这是⼀个值得深思的问题？                nowtime = DateTime.Now;
TimeSpan tsStrIndNoExists = nowtime - lasttime;
//exists
lasttime = DateTime.Now;
for (int i = 0; i < loopCount; i++)
if (str2.IndexOf(str1) >= 0) { };
nowtime = DateTime.Now;
TimeSpan tsStrIndExists = nowtime - lasttime;
//------------------------------------------
//Regex.Match⽅法
//no exists
Regex Reg0 = new Regex("[|]456[|]");
lasttime = DateTime.Now;
for (int i = 0; i < loopCount; i++)
if (Reg0.Match(str2).Success) { };
nowtime = DateTime.Now;
TimeSpan tsStrRegNoExists = nowtime - lasttime;
//exists
Regex Reg1 = new Regex("[|]444[|]");
lasttime = DateTime.Now;
for (int i = 0; i < loopCount; i++)
if (Reg1.Match(str2).Success) { };
nowtime = DateTime.Now;
TimeSpan tsStrRegExists = nowtime - lasttime;
Console.WriteLine("no exists >>>");
Console.WriteLine("tsStrConNoExists = " + tsStrConNoExists.Milliseconds);
Console.WriteLine("tsStrIndNoExists = " + tsStrIndNoExists.Milliseconds);
Console.WriteLine("tsStrRegNoExists = " + tsStrRegNoExists.Milliseconds);
Console.WriteLine("exists >>>");
Console.WriteLine("tsStrConExists = " + tsStrConExists.Milliseconds);
Console.WriteLine("tsStrIndExists = " + tsStrIndExists.Milliseconds);
Console.WriteLine("tsStrRegExists = " + tsStrRegExists.Milliseconds);
}
Console.ReadKey();
}
}
}
输⼊结果：
String.Contains->false
String.Contains->true
String.IndexOf(no exists)->-1
String.IndexOf(exists)->12
Regex.Match(no exists)->false
Regex.Match(exists)->true
loop 1 >>>>>>>
no exists >>>
tsStrConNoExists = 796
tsStrIndNoExists = 687
tsStrRegNoExists = 171
exists >>>
tsStrConExists = 484
tsStrIndExists = 234
tsStrRegExists = 796
loop 2 >>>>>>>
no exists >>>
tsStrConNoExists = 46
tsStrIndNoExists = 671
tsStrRegNoExists = 234
exists >>>
tsStrConExists = 546
tsStrIndExists = 437
tsStrRegExists = 734
loop 3 >>>>>>>
no exists >>>
tsStrConNoExists = 62
tsStrIndNoExists = 875
tsStrRegNoExists = 171
exists >>>
tsStrConExists = 609
tsStrIndExists = 562
tsStrRegExists = 781
loop 4 >>>>>>>
no exists >>>
tsStrConNoExists = 78
tsStrIndNoExists = 921
tsStrRegNoExists = 218
exists >>>
tsStrConExists = 609
tsStrIndExists = 640
tsStrRegExists = 828
loop 5 >>>>>>>
no exists >>>
tsStrConNoExists = 156
tsStrIndNoExists = 268
tsStrRegNoExists = 265
exists >>>
tsStrConExists = 609
tsStrIndExists = 578
tsStrRegExists = 890
loop 6 >>>>>>>
no exists >>>
tsStrConNoExists = 109
tsStrIndNoExists = 46
tsStrRegNoExists = 546
exists >>>
tsStrConExists = 625
tsStrIndExists = 609
tsStrRegExists = 953
测试结果中不难发现，如果strA中不包括strB，使⽤strA.Contains(strB)更优；反之，如果strA中包括strB，使⽤strA.IndexOf(strB)更优。（Regex.Match在此⽅法中貌似没有体现出任何优势，它更适⽤于模糊匹配）
字符串截取不改变原字符串具体要使⽤string.Contains，或是string.IndexOf要看形势。
之前有看过string下很多⽅法实现的代码（微软的，⾮他⼈），string.Contains是基于string.IndexOf上的⼀个⽅法，使⽤string.Contains的时候，会调⽤
string.IndexOf，按原理，使⽤string.IndexOf的效率是要⾼于string.Contains的，但是这个测试结果让我⼤跌眼镜，应该是我在上述代码中使⽤的判断语句造成的这种⾮理想的测试结果，按照个⼈的意愿，还是希望多使⽤string.IndexOf。
其实⼀次微⼩的改变在当前可能影响不了什么，但是在⽇积⽉累中，它的优势就显⽽易见了。想要快速变得⽐他⼈更强，不需要多么费劲，只需要每天多做⼀点点（千分之⼀）
⼀年之后：（1 + 0.001）365 =  1.44倍
⼗年之后（1 + 0.001）3650 =  38.4倍

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