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
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) >= ;
}
writeline教程}
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，如果⼤家有任何疑问欢迎给我留⾔，⼩编会及时回复⼤家的！

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