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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

程序员文章站 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:

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

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:

    参考: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

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