Performance test on empty string

This post covers strings, focusing specifically on empty strings (strings containing zero characters).

#First question: What is the difference between "" and string.Empty ?

Since .NET 2.0, there is almost no difference. Here is the proof:

string s1 = "";
string s2 = string.Empty;
Console.WriteLine(ReferenceEquals(s1, s2)); //true

With .NET 1.1, the difference was at the allocation level. "" created a new string while string.Empty used the pre-created one.

More recently, the JIT considers both values as strictly equal (JIT: Import string.Empty as "", Delete code related to CompilationRelaxations.NoStringInterning).

#Second question: How to test if a string is empty?

There are four ways to do this:

• Equality test: str == "" or str == string.Empty
• Reference test Object.ReferenceEquals(str, string.Empty)
• Test on the length: str.Length == 0
• Using the function: String.IsNullOrEmpty(str) (not exactly the same, as it also checks null values)

To find the quickest approach, I ran a small benchmark. I used two strings:

string s1 = string.Empty;
string s2 = "foobar";

Here is a table with all the results. The times displayed are in seconds, and are calculated for 2147483647 (int.MaxValue) iterations:

As you can see, the difference is minimal and depends on the target architecture. Unless millions of comparisons are made, all methods are equivalent. Choose whichever you find most readable.

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