C#判断字符串中是否包含指定字符串及contains与indexof方法效率问题
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2023-12-10 18:43:04
正文
#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...
正文
#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;
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,然后通过stringcomparison.ordinalignorecase
指定查找过程忽略大小写;
string key = "bbb"; string temp = "aaabbbcccddd"; bool iscontains = temp.indexof(key,stringcomparison.ordinalignorecase)>=0;//true
#那什么时候使用contains方法,什么时候使用index方法,哪个效率高?
1、测试代码:
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;
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("目标在开头部分时:"); console.writeline("不区分大小写:"); testcontains(source, target,true); testindexof(source, target,true); console.writeline("区分大小写:"); target = "aaa"; testcontains(source, target,false); testindexof(source, target,false); console.writeline(); console.writeline("目标在中部时:"); console.writeline("不区分大小写:"); target = "hhh"; testcontains(source, target, true); testindexof(source, target, true); console.writeline("区分大小写:"); target = "hhh"; testcontains(source, target, false); testindexof(source, target, false); console.writeline(); console.writeline("目标在结尾时:"); console.writeline("不区分大小写:"); target = "qqq"; testcontains(source, target,true); testindexof(source, target,true); console.writeline("区分大小写:"); target = "qqq"; testcontains(source, target,false); testindexof(source, target,false); console.writeline("执行完毕,按任意键退出..."); 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、测试结果:
3、总结
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:
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
总结
以上所述是小编给大家介绍的c#判断字符串中是否包含指定字符串及contains与indexof方法效率问题,希望对大家有所帮助