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#方法一:使用string.Contains方法
string.Contains是大小寫敏感的,如果要用該方法來判斷一個string是否包含某個關(guān)鍵字keyword,需要把這個string和這個keyword都轉(zhuǎn)成小寫或大寫再調(diào)用Contains方法;
string key = "bbb"; string temp = "aaaBBBcccDDD"; bool isContains= temp.ToLower().Contains(key.ToLower());//true
#方法二:使用sring.Index方法
使用string.Index方法,然后通過StringComparison.OrdinalIgnoreCase
指定查找過程忽略大小寫;
string key = "bbb"; string temp = "aaaBBBcccDDD"; bool isContains = temp.IndexOf(key,StringComparison.OrdinalIgnoreCase)>=0;//true
#那什么時候使用Contains方法,什么時候使用Index方法,哪個效率高?
1、測試代碼:
注:此測試針對的是擁有大量英文的情況下,并且指定的字符串為英文
每個方法測試1千萬次,輸出所用時間;
class Program { private const int N = 10000000; private static Stopwatch watch = new Stopwatch(); static void Main(string[] args) { string source = "aaabbbcccdddeeefffggghhhiiijjjkkklllmmmnnnooopppqqq"; string target = "AAA"; Console.WriteLine("目標在開頭部分時:"); Console.WriteLine("不區(qū)分大小寫:"); TestContains(source, target,true); TestIndexOf(source, target,true); Console.WriteLine("區(qū)分大小寫:"); target = "aaa"; TestContains(source, target,false); TestIndexOf(source, target,false); Console.WriteLine(); Console.WriteLine("目標在中部時:"); Console.WriteLine("不區(qū)分大小寫:"); target = "HHH"; TestContains(source, target, true); TestIndexOf(source, target, true); Console.WriteLine("區(qū)分大小寫:"); target = "hhh"; TestContains(source, target, false); TestIndexOf(source, target, false); Console.WriteLine(); Console.WriteLine("目標在結(jié)尾時:"); Console.WriteLine("不區(qū)分大小寫:"); target = "QQQ"; TestContains(source, target,true); TestIndexOf(source, target,true); Console.WriteLine("區(qū)分大小寫:"); target = "qqq"; TestContains(source, target,false); TestIndexOf(source, target,false); Console.WriteLine("執(zhí)行完畢,按任意鍵退出..."); Console.ReadKey(); } private static void TestIndexOf(string source, string target,bool isIgnoreCase) { watch.Reset(); watch.Start(); for (int i = 0; i < N; i++) { if (isIgnoreCase) source.IndexOf(target, StringComparison.OrdinalIgnoreCase); else source.IndexOf(target); } watch.Stop(); Console.WriteLine("IndexOf: " + watch.ElapsedMilliseconds.ToString() + "ms"); return; } private static void TestContains(string source, string target,bool isIgnoreCase) { watch.Reset(); watch.Start(); for (int i = 0; i < N; i++) { if (isIgnoreCase) source.ToLower().Contains(target.ToLower()); else source.Contains(target); } watch.Stop(); Console.WriteLine("Contains: " + watch.ElapsedMilliseconds.ToString() + "ms"); return; } }
2、測試結(jié)果:
3、總結(jié)
1、從測試結(jié)果(大量測試)中能明顯看出,當擁有大量英文的字符串中:
*當不區(qū)分大小寫時,string.IndexOf方法的效率明顯高于string.Contains方法;
*當區(qū)分大小寫時,string.Contains方法的效率明顯高于string.IndexOf方法;
*如果判斷的是中文,沒有大小寫之分,還是string.Contains方法的效率高;
2、綜合上述總結(jié),定義了一個String擴展方法,該方法包含一個StringComparison參數(shù),返回值為是否包含子字符串:
參考:https://docs.microsoft.com/zh-cn/dotnet/api/system.string.contains?redirectedfrom=MSDN&view=netframework-4.5#System_String_Contains_System_String_
using System; public static class StringExtensions { public static bool Contains(this String str, String substring, StringComparison comp) { if (substring == null) throw new ArgumentNullException("substring", "substring cannot be null."); else if (! Enum.IsDefined(typeof(StringComparison), comp)) throw new ArgumentException("comp is not a member of StringComparison", "comp"); return str.IndexOf(substring, comp) >= ; } } using System; public class Example { public static void Main() { String s = "This is a string."; String sub1 = "this"; Console.WriteLine("Does '{0}' contain '{1}'?", s, sub1); StringComparison comp = StringComparison.Ordinal; Console.WriteLine(" {0:G}: {1}", comp, s.Contains(sub1, comp)); comp = StringComparison.OrdinalIgnoreCase; Console.WriteLine(" {0:G}: {1}", comp, s.Contains(sub1, comp)); } } // The example displays the following output: // Does 'This is a string.' contain 'this'? // Ordinal: False // OrdinalIgnoreCase: True
總結(jié)
以上所述是小編給大家介紹的C#判斷字符串中是否包含指定字符串及contains與indexof方法效率問題,希望對大家有所幫助,如果大家有任何疑問歡迎給我留言,小編會及時回復大家的!
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