What is the difference between String and string i

Question

Example (note the case):

string s = "Hello world!";
String s = "Hello world!";

What are the guidelines for the use of each? And what are the differences?

Answer 1

string and String are identical in all ways (except the uppercase "S"). There are no performance implications either way.

Lowercase string is preferred in most projects due to the syntax highlighting

Answer 2

C# is a language which is used together with the CLR.

string is a type in C#.

System.String is a type in the CLR.

When you use C# together with the CLR string will be mapped to System.String.

Theoretically, you could implement a C#-compiler that generated Java bytecode. A sensible implementation of this compiler would probably map string to java.lang.String in order to interoperate with the Java runtime library.

Answer 3

string is just an alias for System.String. The compiler will treat them identically.

The only practical difference is the syntax highlighting as you mention, and that you have to write using System if you use String.

Answer 4

This YouTube video demonstrates practically how they differ.

But now for a long textual answer.

When we talk about .NET there are two different things one there is .NET framework and the other there are languages ( C# , VB.NET etc) which use that framework.

"System.String" a.k.a "String" ( capital "S") is a .NET framework data type while "string" is a C# data type.

In short "String" is an alias ( the same thing called with different names) of "string". So technically both the below code statements will give the same output.

String s = "I am String";

or

string s = "I am String";

In the same way there are aliases for other c# data type as shown below:-

object: System.Object, string: System.String, bool: System.Boolean, byte: System.Byte, sbyte: System.SByte, short: System.Int16 and so on

Now the million dollar question from programmer's point of view So when to use "String" and "string"?

First thing to avoid confusion use one of them consistently. But from best practices perspective when you do variable declaration it's good to use "string" ( small "s") and when you are using it as a class name then "String" ( capital "S") is preferred.

In the below code the left hand side is a variable declaration and it declared using "string". At the right hand side we are calling a method so "String" is more sensible.

string s = String.ToUpper() ;

Answer 5

There's a quote on this issue from Daniel Solis' book.

All the predefined types are mapped directly to underlying .NET types. The C# type names (string) are simply aliases for the .NET types (String or System.String), so using the .NET names works fine syntactically, although this is discouraged. Within a C# program, you should use the C# names rather than the .NET names.

Answer 6

I prefer the capitalized .NET types (rather than the aliases) for formatting reasons. The .NET types are colored the same as other object types (the value types are proper objects, after all).

Conditional and control keywords (like if, switch, and return) are lowercase and colored dark blue (by default). And I would rather not have the disagreement in use and format.

Consider:

String someString; 
string anotherString;