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Testing for Empty String

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21 Feb 2008CPOL 47K   12   17
A brief comparison of techniques of testing for empty strings

Background

Every once in a while, someone will post a snippet with code such as...

C#
if ( somestring == "" )

... and in many cases someone else will respond, "Always use if ( somestring.Length == 0 ), it's more efficient."

... or maybe someone will respond, "Always use if ( somestring == System.String.Empty ), it's more efficient."

And neither will back up his claim.

Here are some numbers; performing each test against a provided string (UInt32.MaxValue times) yields:

C:\>StrTest ""
00:01:09.3764731 // if ( providedstring == "" )
00:01:10.3869118 // if ( providedstring == localstaticemptystring )
00:01:10.1249723 // if ( providedstring == System.String.Empty )
00:00:38.1334581 // if ( providedstring.Length == 0 )

C:\>StrTest "abc"
00:01:36.3041617 // if ( providedstring == "" )
00:01:36.6285272 // if ( providedstring == localstaticemptystring )
00:01:35.9541459 // if ( providedstring == System.String.Empty )
00:00:31.6860051 // if ( providedstring.Length == 0 )

The difference between comparing against a literal empty string and a static empty string is negligible. And note that somehow when the provided string isn't empty, those tests take even longer!

Testing the Length of the string is the clear winner here, though it's not as Earth-shattering as some might have you believe.

History

  • 2008-02-21 First submitted

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


Written By
PIEBALDconsult
Software Developer (Senior)
United States United States
BSCS 1992 Wentworth Institute of Technology

Originally from the Boston (MA) area. Lived in SoCal for a while. Now in the Phoenix (AZ) area.

OpenVMS enthusiast, ISO 8601 evangelist, photographer, opinionated SOB, acknowledged pedant and contrarian

---------------

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Comments and Discussions

 
First Prev Next
GeneralHmm Pin
U-P-G-R-A-Y-E-D-D22-Feb-08 5:48
U-P-G-R-A-Y-E-D-D22-Feb-08 5:48 
You should keep in mind that the .Net compiler and VM are tricky beasts, not to mention the JIT. What you write is not always what ends up as IL, because the compiler takes a lot of steps to remove things like unused variables, and unused code blocks. Case in point, if you write an if statement that is empty, in certain situations compiler won't do the comparisons. It will just do the bare minimum to insure any methods that would have been called are called. So, "if (providedString.Length == 0) {}", will be turned into "int v1 = providedString.Length". As far as you know the comparison happened, because .Length was called, but if the if statement was empty it has no reason to generate any jump statements and thus can reduce branching by optimizing out the compare. So you should make sure you do something like set a dummy variable, AND make sure that you do something besides assign a value to that variable, like write it out at the end of the test.

In any event, your numbers are correct, though you missed testing several other cases.

StrTest.exe ""
00:00:13.4399774 : if (providedString == "")
00:00:45.2679716 : if (providedString == String.Empty)
00:00:03.7695695 : if (providedString.Length == 0)
00:00:07.6226158 : if (String.IsNullOrEmpty(providedString))
00:00:05.6808094 : if (providedString == null || providedString.Length == 0)
00:00:46.1933111 : if (String.CompareOrdinal(providedString, String.Empty) == 0)
00:00:13.2321548 : Interned: if (intProvidedString == intEmpty)
00:00:13.1926274 : Interned: if (intProvidedString == intStringDotEmpty)
00:00:03.7688974 : Unsafe: if (ptrProvidedString == ptrEmpty)

StrTest.exe abc
00:00:35.5452142 : if (providedString == "")
00:00:35.5312962 : if (providedString == String.Empty)
00:00:03.8246581 : if (providedString.Length == 0)
00:00:07.7108658 : if (String.IsNullOrEmpty(providedString))
00:00:05.7747759 : if (providedString == null || providedString.Length == 0)
00:00:49.0967074 : if (String.CompareOrdinal(providedString, String.Empty) == 0)
00:00:35.3541753 : Interned: if (intProvidedString == intEmpty)
00:00:35.4164999 : Interned: if (intProvidedString == intStringDotEmpty)
00:00:03.8559366 : Unsafe: if (ptrProvidedString == ptrEmpty)

If you intern the strings, and perform a comparison of the fixed string pointers you can match the speed of the length test.

As for why it took longer when you compared "abc" vs "", it was probably just due to additional branching that occurred because of the difference in the strings, or maybe you had another process taking up cycles. But that's just my guess. Honestly it could have happened for any number of reasons.

Personally I use String.NullOrEmpty() just because I find it much easier to read, and the only additional overhead I'm paying is the method call, as compared to writing if (str == null || str == "") everywhere.

Though, this debate is fairly moot, because if you have to start optimizing your string compares, odds are .Net was not the right choice for the project or you're just a really terrible programmer. Smile | :)
GeneralRe: Hmm Pin
PIEBALDconsult22-Feb-08 7:48
mvePIEBALDconsult22-Feb-08 7:48 
QuestionHave you tested these? Pin
CCMint21-Feb-08 17:44
CCMint21-Feb-08 17:44 
AnswerRe: Have you tested these? Pin
PIEBALDconsult22-Feb-08 7:41
mvePIEBALDconsult22-Feb-08 7:41 
GeneralSo it is not me only... Pin
Oleg Shilo21-Feb-08 16:35
Oleg Shilo21-Feb-08 16:35 
GeneralRe: So it is not me only... Pin
PIEBALDconsult22-Feb-08 7:40
mvePIEBALDconsult22-Feb-08 7:40 
GeneralRe: So it is not me only... Pin
Oleg Shilo24-Feb-08 11:06
Oleg Shilo24-Feb-08 11:06 
GeneralRe: So it is not me only... Pin
Thomas Weller29-Nov-08 18:44
Thomas Weller29-Nov-08 18:44 
GeneralRe: So it is not me only... Pin
PIEBALDconsult30-Nov-08 5:57
mvePIEBALDconsult30-Nov-08 5:57 
GeneralRe: So it is not me only... Pin
Oleg Shilo30-Nov-08 12:10
Oleg Shilo30-Nov-08 12:10 
GeneralRe: So it is not me only... Pin
Thomas Weller30-Nov-08 23:34
Thomas Weller30-Nov-08 23:34 
GeneralRe: So it is not me only... Pin
PIEBALDconsult1-Dec-08 11:08
mvePIEBALDconsult1-Dec-08 11:08 
GeneralRe: So it is not me only... Pin
mm52850430-Jan-09 3:53
mm52850430-Jan-09 3:53 
GeneralRe: So it is not me only... Pin
PIEBALDconsult30-Jan-09 5:22
mvePIEBALDconsult30-Jan-09 5:22 
GeneralRe: So it is not me only... Pin
mm52850431-Jan-09 9:05
mm52850431-Jan-09 9:05 
GeneralRe: So it is not me only... Pin
PIEBALDconsult31-Jan-09 9:18
mvePIEBALDconsult31-Jan-09 9:18 
GeneralRe: So it is not me only... Pin
mm5285041-Feb-09 6:14
mm5285041-Feb-09 6:14 
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Posted 21 Feb 2008

Article Copyright 2008 by PIEBALDconsult
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