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I am reviewing some code and I see a large amount of string concatentation but they are all very small strings. Something like this:

public string BuildList()
{
    return "A" + GetCount() + "B" + TotalCount() + "C" + AMountLeft()
         + "D" + DaysLeft + "R" +  Initials() + "E";
}

I am simplifying it but in total the longest string is about 300 characters and the number of + are about 20. I am trying to figure out if its worth to convert it to StringBuilder and do something like this:

public string BuildList()
{
    var sb = new StringBuilder();
    sb.Append("A");
    sb.Append(GetCount());
    sb.Append("B");
    sb.Append(TotalCount());
    sb.Append("C");
    sb.Append(AmountLeft());
    sb.Append("D");

    // etc . . 
}

I can't see a big difference from testing but wanted to see if there is a good breakeven rule about using StringBuilder (either length of string or number of different concatenations)?

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2
  • 1
    possible dup with: stackoverflow.com/questions/1612797/… Commented Apr 12, 2014 at 18:12
  • If you concat strings with + in a loop (such as foreach or while), you should change that to string.Concat, string.Join or similar. If the loop is too complex for that, change to a StringBuilder. If there is no loop statement, it is hardly a problem to use +. In your case there are many + in the very same expression, and that is compiled to a single Concat method call. Commented Apr 12, 2014 at 19:32

2 Answers 2

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5

For such a fixed situation with limited number of variable strings, and with a always-the-same part of text between those values, I would personally use string formatting there. That way, your intention gets a lot more clear and it’s easier to see what’s happening:

return string.Format("A{0}B{1}C{2}D{3}R{4}E",
    GetCount(), TotalCount(), AmountLeft(), DaysLeft(), Initials());

Note that string.Format is slightly slower than string.Concat (which as others said is used when you build a string using +). However, it’s unlikely that string concatenation will be a bottleneck in your application, so you should favor clarity over micro-optimization until that becomes an actual problem.

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4 Comments

@JonSkeet Just realized that myself, no idea what was going on in my head there. Fixed :)
That's a good alternative, but this answer doesn't actually answer the question.
@Guffa The answer to XY problems is rarely the answer someone is asking for. Given that OP wants to improve code during code review, improving its readability is worth more.
@poke: You are missing the point. Your answer looks like a standard answer to anything that has to do with string concatentation, it doesn't really answer anything that is in the question.
4

No, in that case there is no reason to favour a StringBuilder over string concatenation.

Your first code will become a single call to String.Concat, which would be marginally more efficient that using a StringBuilder.

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1 Comment

We were just playing around with ildasm when we saw this question and yeah we can see that indeed just concatenating the string results in one cal to IL_0006: call string [mscorlib]System.String::Concat(string, string, string, string)

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