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.NET Forum / .NET Framework / Performance / March 2008Better coding
Which code is really better in term of performance, A or B? A) list_of_strings[0] == "" B) list_of_strings[0].Length.Equals(0) > Which code is really better in term of performance, A or B? > A) list_of_strings[0] == "" > B) list_of_strings[0].Length.Equals(0) The difference is negligible. Do whatever is most readable or follows convention for your team. In theory, checking the length should be quicker, but some say that checking against String.Empty is quicker too. If you are really at that point in optimizing your code, I am jealous :P > Which code is really better in term of performance, A or B? > A) list_of_strings[0] == "" > B) list_of_strings[0].Length.Equals(0) C) list_of_strings[0].Length == 0 :) A string holds its length as part of its structure which is why quering the length carries no overhead, unlike comparing it to another string. However as has been said, comparing two empty strings probably isn't any slower in reality. > > Which code is really better in term of performance, A or B? > > A) list_of_strings[0] == "" [quoted text clipped - 8 lines] > as has been said, comparing two empty strings probably isn't any slower in > reality. Especially as the first thing a string equality comparison is likely to do is compare the lengths. Personally I find if (x=="") easier to read - it conveys the intention of "is x an empty string" better (to me) than if (x.Length==0) Very much a personal preference thing - but I'd make the choice based on readability rather than performance.  SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk > Especially as the first thing a string equality comparison is likely to > do is compare the lengths. [quoted text clipped - 7 lines] > Very much a personal preference thing - but I'd make the choice based > on readability rather than performance. I see where you're coming from, but I haven't seen the "==" op code so don't know if it has a special case for comparing empty strings. I don't know if it says "both strings are 0 length so return true" or if it initiates a "foreach" loop anyway. Even if it compares both string lengths to see if they are 0 and return true, that is still two comparisons. Whereas I know that just checking if the length is 0 is only one comparison. Another reason I dislike comparison with an empty string is that some people (read: other developers) don't appreciate that you get the odd stray spaces and that "" != " ". The fact that you are checking a zero length string makes it more obvious (to me anyway) that rogue spaces are not to be tolerated. > > Very much a personal preference thing - but I'd make the choice based > > on readability rather than performance. [quoted text clipped - 5 lines] > they are 0 and return true, that is still two comparisons. Whereas I know > that just checking if the length is 0 is only one comparison. Show me *any* production application where that makes any significant difference, and I'll buy you several pints. It's really not worth bothering about. > Another reason I dislike comparison with an empty string is that some people > (read: other developers) don't appreciate that you get the odd stray spaces > and that "" != " ". The fact that you are checking a zero length string > makes it more obvious (to me anyway) that rogue spaces are not to be > tolerated. Okay, it reads pretty clearly to me - but this is where the personal preference business kicks in. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk > Show me *any* production application where that makes any significant > difference, and I'll buy you several pints. It's really not worth > bothering about. I've admitted it doesn't make a difference, it just comes down to personal choice. However it seems you're not too keen when other's personal choice differs from your personal choice! > > Show me *any* production application where that makes any significant > > difference, and I'll buy you several pints. It's really not worth [quoted text clipped - 3 lines] > choice. However it seems you're not too keen when other's personal choice > differs from your personal choice! Not at all - I'm perfectly happy if people choose to use a different approach based on their personal preference due to differing ideas of readability. If people choose to use one approach based on *performance* however, they're using a completely bogus reason - and I'll call them on that. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk jsh02_nova schrieb: > Which code is really better in term of performance, A or B? > A) list_of_strings[0] == "" > B) list_of_strings[0].Length.Equals(0) Depending on what exactly you want to check, you could also use String.IsNullOrEmpty(list_of_strings[0]) or list_of_strings[0] == string.Empty This avoids constructing a temporary string object that holds the emtpy string for comparison. Norbert > jsh02_nova schrieb: > > Which code is really better in term of performance, A or B? [quoted text clipped - 8 lines] > This avoids constructing a temporary string object that holds the emtpy > string for comparison. There would be no temporary string object. There'd be a single interned empty string for every occurrence of the string literal "" in your AppDomain. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk Is that correct? string interning isn't on by default is it? Signature-- Regards, Alvin Bruney [MVP ASP.NET] [Shameless Author plug] The O.W.C. Black Book, 2nd Edition Exclusively on www.lulu.com/owc $19.99 >> jsh02_nova schrieb: >> > Which code is really better in term of performance, A or B? [quoted text clipped - 12 lines] > empty string for every occurrence of the string literal "" in your > AppDomain. > Is that correct? string interning isn't on by default is it? For C#, it's guaranteed by the language specification. Section 2.4.4.5 (unified C# 3.0 spec): <quote> Each string literal does not necessarily result in a new string instance. When two or more string literals that are equivalent according to the string equality operator (§7.9.7) appear in the same program, these string literals refer to the same string instance. </quote> That also includes "x"+"y" being the same reference as "xy" btw. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk I think Fx Cop says to use .Length I like then Length myself. Schneider <"Alvin Bruney [ASP.NET MVP]" <www.lulu.com/owc>> wrote: > Is that correct? string interning isn't on by default is it? For C#, it's guaranteed by the language specification. Section 2.4.4.5 (unified C# 3.0 spec): <quote> Each string literal does not necessarily result in a new string instance. When two or more string literals that are equivalent according to the string equality operator (§7.9.7) appear in the same program, these string literals refer to the same string instance. </quote> That also includes "x"+"y" being the same reference as "xy" btw. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk If I remember correctly all unique strings are cache, at what level I'm not sure... Schneider >I think Fx Cop says to use .Length > [quoted text clipped - 17 lines] > > That also includes "x"+"y" being the same reference as "xy" btw. > If I remember correctly all unique strings are cache, at what level I'm not > sure... No, only those which are interned - which includes all string literals. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk Correct, I was under the impression it was automatic. Seems there is some GC issues related to them also. http://msdn2.microsoft.com/en-us/library/system.string.intern.aspx >> If I remember correctly all unique strings are cache, at what level I'm >> not >> sure... > > No, only those which are interned - which includes all string literals. > Correct, I was under the impression it was automatic. Seems there is some GC > issues related to them also. > http://msdn2.microsoft.com/en-us/library/system.string.intern.aspx Automatically interning *every* string to ever be created would be a memory nightmare. Basically it would make it impossible for an application to stay up for any significant length of time, if it was doing any string processing. SignatureJon Skeet - <skeet@pobox.com> http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet World class .NET training in the UK: http://iterativetraining.co.uk uh huh. i had it backward. that jogged my memory. Signature-- Regards, Alvin Bruney [MVP ASP.NET] [Shameless Author plug] The O.W.C. Black Book, 2nd Edition Exclusively on www.lulu.com/owc $19.99 >> Is that correct? string interning isn't on by default is it? > [quoted text clipped - 10 lines] > > That also includes "x"+"y" being the same reference as "xy" btw. Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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