Difference between “String” and “string” in .NET and which is best?

Question

In the .NET Framework, at least in the C# language, we have two "versions" of the string type:

• "string"
• "String"

It appears that they are interchangeable, but are they really? If they are not interchangeable, is it generally better to use one instead of the other, and under what circumstances?

Answer 1

Well according to the MSDN

string is an alias for String in the .NET Framework.

Where "String" is in fact System.String.

I would say that they are interchangeable and there is no difference when and where you should use one or the other.

It would be better to be consistent with which one you did use though.

Answer 2

As pointed out, they are the same thing and string is just an alias to String.

For what it's worth, I use string to declare types - variables, properties, return values and parameters. This is consistent with the use of other system types - int, bool, var etc (although Int32 and Boolean are also correct).

I use String when using the static methods on the String class, like String.Split() or String.IsNullOrEmpty(). I feel that this makes more sense because the methods belong to a class, and it is consistent with how I use other static methods.

Answer 3

I'd suggest using lowercase string. Uppercase String will use the first class named String it finds in the imported namespaces ... which is generally System.String. It's possible for your own String class to be used instead.

Answer 4

string is a C# keyword which is simply an alias for the System.String

..but as it's a keyword, your syntax colouring editor/IDE will show it in keyword colour, same as int, double, if, else, etc. Stylistically, you may prefer to use the keyword rather than the System.String type (or just String after you've done using System;).

This is a niche point though, as although bool, char, int, double and string are all keyword aliases for system types, string is an odd-one-out as it is a reference type and the others are value types.

Answer 5

string is just an alias for String, they're ultimately the same.

You can use whichever you prefer, although I generally use string when I'm planning on using it much like a primitive data type (similar to int, float, or bool) and String when I'm planning on using it as an object/class. For example:

string foo = "   ";
if (String.isNullOrWhitespace(foo)) 
{
    // ...
}

In the case above, I'm planning on using foo simply to store some text (effectively as a primitive), so I use string; however, when I call String.isNullOrWhitespace(string) I use String. I do this, because generally the first letter of class names are capitalized (String) while the first letter of primitives (such as int) are not.

Answer 6

String is used with namespace System.String, string is used C# compiler specification, moreover System.String is reference type value. You are preferred to deal with System objects, string for literals purposes only. System and system both working is same.

string TC = new System.String('/', 5);

String is used for comparing, equal and other purposes as well.