const string vs static readonly string in C

Question

In C   what s the difference between static readonly string MyStr   and const string MyStr

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const public const string MyStr   is a compile time constant  you can use it as the default parameter for a method parameter for example   and it will not be obfuscated if you use such technology static readonly public static readonly string MyStr   is runtime constant  It means that it is evaluated when the application is launched and not before  This is why it can t be used as the default parameter for a method  compilation error  for example  The value stored in it can be obfuscated

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You can change the value of a static readonly string only in the static constructor of the class or a variable initializer  whereas you cannot change the value of a const string anywhere

User · Answer

When you use a const string  the compiler embeds the string s value at compile-time  Therefore  if you use a const value in a different assembly  then update the original assembly and change the value  the other assembly won t see the change until you re-compile it   A static readonly string is a normal field that gets looked up at runtime   Therefore  if the field s value is changed in a different assembly  the changes will be seen as soon as the assembly is loaded  without recompiling   This also means that a static readonly string can use non-constant members  such as Environment UserName or DateTime Now ToString     A const string can only be initialized using other constants or literals  Also  a static readonly string can be set in a static constructor  a const string can only be initialized inline   Note that a static string can be modified  you should use static readonly instead

User · Answer

OQ asked about static string vs const  Both have different use cases  although both are treated as static    Use const only for truly constant values  e g  speed of light - but even this varies depending on medium   The reason for this strict guideline is that the const value is substituted into the uses of the const in assemblies that reference it  meaning you can have versioning issues should the const change in its place of definition  i e  it shouldn t have been a constant after all   Note this even affects private const fields because you might have base and subclass in different assemblies and private fields are inherited   Static fields are tied to the type they are declared within  They are used for representing values that need to be the same for all instances of a given type  These fields can be written to as many times as you like  unless specified readonly    If you meant static readonly vs const  then I d recommend static readonly for almost all cases because it is more future proof

User · Answer

Here is a good breakdown of the pros and cons      So  it appears that constants should be used when it is very unlikely that the value will ever change  or if no external apps libs will be using the constant  Static readonly fields should be used when run-time calculation is required  or if external consumers are a factor

[c#] 'const string' vs. 'static readonly string' in C#

`const`

`static readonly`

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