What is the difference between String and string?

Stringis the name of the classSystem.String

stringis the alias of System.Stringin C#: string (C# Reference)

At execution level there is no difference since the compiler converts both lines into the same thing.

For example this is what LINQPad generates with the following two statements:

String S = "Hola mundo";
string s = "Hola mundo";

As you can see both lines generate the instruction:

ldstr "Hola mundo"

In the same way, for example, when invoking one of its methods

String.Format("Hola");
string.Format("Hola");

Both lines refer to the same class System.Stringand generate the same code

Effectively, stringit's an alias of System.String . Microsoft does not favor either Microsoft MSDN C# string nomenclature in its documentation .

string vs. System.String

In C#, the string keyword is an alias for String. Therefore, String and string are equivalent, and you can use whatever naming convention you prefer. The String class provides numerous methods for safely creating, manipulating, and comparing strings. , the C# language overloads some operators to simplify common operations on strings.

I remember seeing an MSDN Channel 9 video where they recommended stringfor local variables, and String especially for parameters and return types. Unfortunately, I am unable to find the video right now. And besides, it seems to me an unnecessary distinction and one that will probably be very difficult to carry out.

string in C# is an alias of the .NET Framework Type (CLR type) System.String

(Idem for example to System.Int32 & int )

You can use it as an alias, but sometimes in organizations coding policies are used to, for example, use the class (and not the alias) in the constructor, no matter how much you can use it.

Example:

const char char1 = 'a';
var cadena1 = new string(char1, 1);
var cadena2 = new String(char1, 1);

But for example you can't create string aliases. Example of aliases:

using alias1 = string;  //Error de compilacion
using CodigoBarraCadena = System.String;
using NombreDescriptivoCadena = System.String;

To be used for better code compression

var tupla1 = new Tuple<CodigoBarraCadena, NombreDescriptivoCadena>("1", "2"); //Mas descriptivo

var tupla2 = new Tuple<string, string>("1", "2"); //Menos descriptivo

stringis an alias in C#for System.String, in its documentation Microsoft uses it stringin its examples.