Why is string.Empty more efficient than "" in .Net

Question

I am certain that string.Empty is more efficient than using "" in .Net languages. What I would like to know is WHY is it more efficient?

@Gregory - StyleCop recommends making the change from "" to string.Empty. I like to think there is some reasoning behind this... — JL.
– JL., Commented Dec 11, 2009 at 11:34
But what makes you think the reasoning has to do with efficiency? — Stack Overflow is garbage
– Stack Overflow is garbage, Commented Dec 11, 2009 at 11:39
And what makes you think that StyleCop is always right, and always up-to-date in its recommendations? — Jon Skeet
– Jon Skeet, Commented Dec 11, 2009 at 11:48

Fredrik Mörk · Accepted Answer · 2009-12-11 11:36:03Z

13

I think in most cases there is no difference. In normal cases, when you use "" in your code this string will be interned and the same string instance will be reused. So there will not be more string instances around when using "" as compared to String.Empty.

If you want proof:

Dim a As String
Dim b As String

a = ""
b = ""

Console.WriteLine(Object.ReferenceEquals(a, b)) ' Prints True '

The above code prints True also if you replace one of them with String.Empty, so you can even mix the approaches without creating extra string instances.

Bottom line: the difference is personal taste.

edited Dec 11, 2009 at 11:36

answered Dec 11, 2009 at 11:30

Fredrik Mörk

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3 Comments

JonoW Over a year ago

Is there any overhead accessing an interned string compared to accessing a puplic static string?

JL. Over a year ago

Ok, accepted answer. This is good to know, because a lot of IT geeks frown upon the use of "". I guess this is another StyleCop rule worth ignoring too.

Fredrik Mörk Over a year ago

@JonoW: never measured it, but it would surprise me if there is any difference.

Rik · Accepted Answer · 2009-12-11 11:42:42Z

6

First of all, I'm not sure that it is more efficient. A reason it is a static is, it is basically a constant: there is only one empty string.

A more important issue is that there are some inconsistencies with string interning in .NET, which can result in comparisons with String.empty not always returning the expected result, depending on what version of the runtime you're using. Eric Lippert has written a fascinating blog post about it here.

(Example taken from Eric's post)

object obj = "";
string str1 = "";
string str2 = String.Empty;
Console.WriteLine(obj == str1); // true
Console.WriteLine(str1 == str2); // true
Console.WriteLine(obj == str2); // sometimes true, sometimes false?!

edited Dec 11, 2009 at 11:42

answered Dec 11, 2009 at 11:31

Rik

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1 Comment

John Gietzen Over a year ago

That third line will never be false. Perhaps you mean object.ReferenceEquals?

rahul · Accepted Answer · 2009-12-11 11:27:53Z

2

I don't think there is any performance gain in using string.Empty over "".

Its just a matter of personal preference.

answered Dec 11, 2009 at 11:27

rahul

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3 Comments

Klaus Byskov Pedersen Over a year ago

Agree, but string.Empty is definitely more explicit than ""

JL. Over a year ago

Stylecop recommends using string.Empty, surely this is not just because it is more visually appealing than ""?

thecoop Over a year ago

Sebastian - incorrect. If "" is in code, then all references to "" will be interned to the same instance, just like any other string constant

Konamiman · Accepted Answer · 2009-12-11 11:34:53Z

2

"" will create an instance of an empty string in your application. Sure, .NET interns the string constants, but still, you will create one instance. String.Empty, on the other hand, does not create any instance.

answered Dec 11, 2009 at 11:34

Konamiman

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Comments

Benny · Accepted Answer · 2009-12-11 11:28:18Z

0

string.Empty is a singleton static const string that has been constructed, but "" will create a new string that is empty.

answered Dec 11, 2009 at 11:28

Benny

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6 Comments

ctford Over a year ago

...which also means that it's interned - there's only one copy of the string in memory regardless of how many times it's used.

JL. Over a year ago

So if you're using loads of string manipulation, its way more efficient!

thecoop Over a year ago

It won't create a new instance every time you reference "", it will use a reference to the single interned value of ""

Rob Fonseca-Ensor Over a year ago

wrong, look up string interning. If you use: new string("") however, you'll use more memory...

Jon Skeet Over a year ago

If you use new string("") you'll get a compile-time error - there isn't a string constructor taking just a string.

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