Const and readonly usage Summary

In the past, const was used to define constants during development, and readonly was rarely used, because it always felt that the use of const was sufficient. In the past two daysCodeAgain, we can see the use of readonly, and it feels awkward. If a constant is defined in const, it cannot be changed again during use. Otherwise, the value is assigned again in the constructor. Due to the confusion about readonly usage, const and readonly are summarized based on the learning attitude for future reference:

Name	Static constants (Const)	Dynamic constant/read-only variable (readonly)
Scope of use	Global and local	Global
Initial Value	The initial value must be assigned during definition.	No value is assigned during definition.
Assignment Method	Value assignment during definition	Assign values when defining and assign values in Constructors
Access Method	Type access	Instance Object Access
Static	Cannot be used together with static	It can be used together with static. after use, if you want to assign an initial value to the constructor, you must use a static non-argument constructor.
Application Type	Only the value type and string type can be applied.	Any Type

Instance (vs2008)

 1   Using System;
 2   Using System. Collections. Generic;
 3   Using System. LINQ;
 4   Using System. text;
 5  
 6   Namespace Constandreadonly
 7 {
 8       Class Program
 9 {
 10          Static   Void Main ( String [] ARGs)
 11 {
 12 Console. writeline (consttest. Str ); //  Access by type  
  13 Readonlytest RT = New Readonlytest ( "  123456  " );//  Access through instance objects and assign values through Constructors  
  14 Console. writeline (RT. Str );
 15 Console. writeline (RT. strnull );
 16               String [] Str1 = { "  1  " , "  2  " , " 3  " , "  4  " , "  5  " , "  6  " };
 17 Readonlytest rt2 = New Readonlytest (str1 ); //  Assign an array through the constructor 
  18 Console. writeline (rt2.str1. Count ());
 19 Console. Readline ();
 20 }
 21 }
 22       Class Consttest
 23 {
 24           Public   Const   String STR ="  Const Test  " ; //  Unchangeable  
  25 }
 26       Class Readonlytest
 27 {
 28           Public   Readonly   String STR = " Readonly Test  " ;
 29           Public   Readonly   String Strnull; //  No initial value is assigned. The default value is null;  
  30           Public   Readonly   String [] Str1;
 31           Public Readonlytest (String S)
 32 {
 33               This . Strnull = This . STR;
 34               This . Str = s;
 35 }
 36           Public Readonlytest ( String [] S)
 37 {
38               This . Str1 = s;
 39 }
 40 }
 41 }