Difference between string. Empty, string = "" and null

String. Empty is a static constant of the string class;

The difference between string. Empty and string = "is not big, because the internal implementation of string. Empty is:

Public static readonly string empty; // This is string. Empty. It is a read-only member of the string class. What is the default value of the string variable? // String's constructor static string () {empty = ""; // empty is his "" whitespacechars = new char [] {'\ t',' \ n ', '\ V',' \ F', '\ R', '',' \ x0085 ',' \ x00a0 ', 'hangzhou ','','','', 'taobao ','','','','', '\ u2028',' \ u2029 ','',''};}

　　

Let's look at another piece of code:

String S1 = ""; string S2 = string. Empty; If (S1 = S2)
{Console. writeline ("Exactly! ");} // The result is trueconsole. writeline (" ". Equals (string. Empty); console. writeline (object. referenceequals (string. Empty ,""));

Since string. Empty is the same as string = "" and it also needs to occupy memory space, why is string. Empty recommended?

String. Empty only allows the code to be read well and prevents code ambiguity. For example:

String S = ""; string S = ""; this is not very careful, it is difficult to see whether it is a null string or a space character.

 

If you determine whether a string is a Null String, use

If (S = string. Empty) And if (S = ") have the same efficiency, but the most efficient way is if (S. Length = 0)

String. isnullorempty internal implementation:

public static bool IsNullOrEmpty(string value)
{
    if (value != null)    {        return (value.Length == 0);    }    return true;}

String STR = NULL indicates that STR does not point to any object.