#方法一:使用string.Contains方法
string.Contains是大小写敏感的,如果要用该方法来判断一个string是否包含某个关键字keyword,需要把这个string和这个keyword都转成小写或大写再调用Contains方法;
1 string key = "bbb";
2 string temp = "aaaBBBcccDDD";
3 bool isContains= temp.ToLower().Contains(key.ToLower());//true
#方法二:使用sring.IndexOf方法
使用string.Index方法,然后通过
StringComparison.OrdinalIgnoreCase
指定查找过程忽略大小写;
1 string key = "bbb";
2 string temp = "aaaBBBcccDDD";
3 bool isContains = temp.IndexOf(key,StringComparison.OrdinalIgnoreCase)>=0;//true
#当设计到大小写的问题时,那什么时候使用Contains的上述方法,什么时候使用IndexOf的上述方法,哪个效率高?
contains方法的源码中其实是使用了IndexOf方法的
,但效率还是有差别的;
1、测试代码:基于.net4.5
注:此测试针对的是拥有大量英文的情况下,并且指定的字符串为英文
每个方法测试1千万次,输出所用时间;
1 class Program
3 private const int N = 10000000;
4 private static Stopwatch watch = new Stopwatch();
5 static void Main(string[] args)
8 string source = "aaabbbcccdddeeefffggghhhiiijjjkkklllmmmnnnooopppqqq";
9 string target = "AAA";
10 Console.WriteLine("目标在开头部分时:");
11 Console.WriteLine("不区分大小写:");
12 TestContains(source, target,true);
13 TestIndexOf(source, target,true);
14 Console.WriteLine("区分大小写:");
15 target = "aaa";
16 TestContains(source, target,false);
17 TestIndexOf(source, target,false);
18 Console.WriteLine();
20 Console.WriteLine("目标在中部时:");
21 Console.WriteLine("不区分大小写:");
22 target = "HHH";
23 TestContains(source, target, true);
24 TestIndexOf(source, target, true);
25 Console.WriteLine("区分大小写:");
26 target = "hhh";
27 TestContains(source, target, false);
28 TestIndexOf(source, target, false);
29 Console.WriteLine();
31 Console.WriteLine("目标在结尾时:");
32 Console.WriteLine("不区分大小写:");
33 target = "QQQ";
34 TestContains(source, target,true);
35 TestIndexOf(source, target,true);
36 Console.WriteLine("区分大小写:");
37 target = "qqq";
38 TestContains(source, target,false);
39 TestIndexOf(source, target,false);
41 Console.WriteLine("执行完毕,按任意键退出...");
42 Console.ReadKey();
44 }
45 private static void TestIndexOf(string source, string target,bool isIgnoreCase)
46 {
47 watch.Reset();
48 watch.Start();
49 for (int i = 0; i < N; i++)
50 {
51 if (isIgnoreCase)
52 source.IndexOf(target, StringComparison.OrdinalIgnoreCase);
53 else
54 source.IndexOf(target);
55 }
56 watch.Stop();
57 Console.WriteLine("IndexOf: " + watch.ElapsedMilliseconds.ToString() + "ms");
58 return;
59 }
61 private static void TestContains(string source, string target,bool isIgnoreCase)
62 {
63 watch.Reset();
64 watch.Start();
65 for (int i = 0; i < N; i++)
66 {
67 if (isIgnoreCase)
68 source.ToLower().Contains(target.ToLower());
69 else
70 source.Contains(target);
71 }
72 watch.Stop();
73 Console.WriteLine("Contains: " + watch.ElapsedMilliseconds.ToString() + "ms");
74 return;
75 }
2、测试结果:
1、从测试结果(大量测试)中能明显看出,当拥有大量英文的字符串中:
*当不区分大小写时,string.IndexOf方法的效率明显高于string.Contains方法;
*当区分大小写时,string.Contains方法的效率明显高于string.IndexOf方法;
*如果判断的是中文,没有大小写之分,还是string.Contains方法的效率高;
2、综合上述总结,定义了一个String扩展方法,该方法包含一个StringComparison参数,返回值为是否包含子字符串:
参考:https://docs.microsoft.com/zh-cn/dotnet/api/system.string.contains?redirectedfrom=MSDN&view=netframework-4.5#System_String_Contains_System_String_
1 using System;
3 public static class StringExtensions
5 public static bool Contains(this String str, String substring,
6 StringComparison comp)
8 if (substring == null)
9 throw new ArgumentNullException("substring",
10 "substring cannot be null.");
11 else if (! Enum.IsDefined(typeof(StringComparison), comp))
12 throw new ArgumentException("comp is not a member of StringComparison",
13 "comp");
15 return str.IndexOf(substring, comp) >= 0;
16 }
1 using System;
3 public class Example
5 public static void Main()
7 String s = "This is a string.";
8 String sub1 = "this";
9 Console.WriteLine("Does '{0}' contain '{1}'?", s, sub1);
10 StringComparison comp = StringComparison.Ordinal;
11 Console.WriteLine(" {0:G}: {1}", comp, s.Contains(sub1, comp));
13 comp = StringComparison.OrdinalIgnoreCase;
14 Console.WriteLine(" {0:G}: {1}", comp, s.Contains(sub1, comp));
15 }
16 }
17 // The example displays the following output:
18 // Does 'This is a string.' contain 'this'?
19 // Ordinal: False
20 // OrdinalIgnoreCase: True