c#点点滴滴(3) 之字符串

[1]字符串比较

第一种比较方法:equals 返回结果:true or false

 1 using System;
 2 using System.Collections.Generic;
 3 public class Equation
 4 {
 5      //确定此 String 实例是否与指定的对象（也必须是 String）具有相同的值。
 6      public static void Main()
 7      {
 8          string str1 = "ABC";
 9          string str2 = "ABC";
          string str3 = "BCD";
          Console.WriteLine(str1.Equals (str2));
          Console.WriteLine(str2.Equals(str3));
      }
 }

result:

True

False

第二种比较方法:==  返回结果:true or false

// from MSDN
using System;
using System.Collections.Generic;
class EqualityOp 
{
    public static void Main() 
    {
        Console.WriteLine( 
            "This example of the String Equality operator\n" +
            "generates the following output.\n" );

        CompareAndDisplay( "ijkl" );
        CompareAndDisplay( "ABCD" );
        CompareAndDisplay( "abcd" );
    }

    static void CompareAndDisplay( string Comparand )
    {
        String  Lower = "abcd";

        Console.WriteLine( 
            "\"{0}\" == \"{1}\" ?  {2}",
            Lower, Comparand, Lower == Comparand );
    }
}

result:

"abcd" == "ijkl" ?  False

"abcd" == "ABCD" ?  False
"abcd" == "abcd" ?  True

 [2]字符串"空"与null

 

 1 using System;
 2 using System.Collections.Generic;
 3 public class StringTest
 4 {
 5     public static void Main()
 6     {
 7         string  str1 = null;
 8         string  str2 = string.Empty;
 9         string  str3 = "";
         if (str1 == str2)
         {
             Console.WriteLine("null is equal to string.Empty");
         }
         else
         {
             Console.WriteLine("null isn't equal to string.Empty");
         }
 
         if (str2 == str3)
         {
             Console.WriteLine("string.Empty is equal to \"\"");
         }
         else
         {
             Console.WriteLine("string.Empty isn't equal to \"\"");
         }
     }
 }

result:

null isn't equal to string.Empty
string.Empty is equal to ""

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