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Is this c# return statement good/bad in terms of performance?

Answer 1

+10 A:

String concatenation in a single shot will be faster than using a StringBuilder - although if Sb is already a StringBuilder, it might make sense to append to that instead (assuming it's a local variable). Assuming this is actually data which has come from a database, the time taken to fetch it is going to vastly exceed the string concatenation here anyway.

Note that you don't need all these calls to ToString() - this would do just as well:

return (Sb + " " + ds.Tables[1].Rows[0].ItemArray[0] + " " + 
        ds.Tables[2].Rows[0].ItemArray[0]);

Here's the equivalent using the existing builder:

return Sb.Append(" ")
         .Append(ds.Tables[1].Rows[0].ItemArray[0])
         .Append(" ")
         .Append(ds.Tables[2].Rows[0].ItemArray[0])
         .ToString();

This might be slightly faster - it will depend on various things. Personally I'd probably use the concatenation version anyway, as it's slightly simpler IMO. I highly doubt that you'd see much difference in performance. Note that this is a bit of a special case, as you've already got a StringBuilder; in the general case of concatenating a set of items where they can all be specified in one compile-time expression, concatenation can be faster as a single method call can provide all the required information.

I have a page on StringBuilder vs string concatenation if you want more details and guidelines.

Jon Skeet 2010-03-30 07:20:22

Will it really be faster? Might be "best practice" to use StringBuilder though, don't you think?

Filip Ekberg 2010-03-30 07:21:47

@jon ya `sb` is indeed a stringbuilder...

Pandiya Chendur 2010-03-30 07:22:46

@Filip: Yes, it will be faster. It will result in a single call to `String.Concat` which can look at the lengths of *all* the strings involved, work out the exact size of buffer required, copy them all in, and you're done. No extra `StringBuilder` object required; no expanding buffer (potentially involving more reallocations). It's definitely *not* best practice to use `StringBuilder` without understanding why it's *sometimes* more efficient.

Jon Skeet 2010-03-30 07:24:52

@Pandiya Chendur: In that case it *may* be faster to append to the existing `StringBuilder` and call `ToString` at the end. I'll edit the answer.

Jon Skeet 2010-03-30 07:25:28

@jon great explanation in ur article...

Pandiya Chendur 2010-03-30 07:26:43

@Jon, Allright, thanks for clearing that up.

Filip Ekberg 2010-03-30 07:27:48

Good article Jon

Sri Kumar 2010-03-30 07:35:58

Answer 2

+2 A:

If you're calling this in a tight loop, you'll be probably be better off using StringBuilder (but this piece should be profiled nevertheless). Otherwise, concatenation is perfectly fine. I would change it, however, to String.Format() for maintainability/readability reasons.

Anton Gogolev 2010-03-30 07:20:49

Even if you're calling it in a loop, a `StringBuilder` isn't going to help - notice that this is a *return* statement... the result of the concatenation is going to be returned immediately. `StringBuilder` will almost certainly be *slower* (to an almost irrelevant extent, probably) than using concatenation here.

Jon Skeet 2010-03-30 07:23:32

Answer 3

+4 A:

I think this is more readable:

return String.Format("{0} {1} {2}", Sb, ds.Tables[1].Rows[0].ItemArray[0], ds.Tables[2].Rows[0].ItemArray[0]);

About concatenating strings or using StringBuilder:

Concatenating Strings Efficiently
StringBuilder and String Concatenation

tsocks 2010-03-30 07:30:06

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Is this c# return statement good/bad in terms of performance?

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