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by Jiří {x2} Činčura

Concatenating(?) string during compile

28 Apr 2007 1 mins .NET

I’m writing a simple library for reading some data from one Firebird database, it’s not important… For better readability I’m creating CommandText as a string on more lines with some formatting. Because the performance was one of the criterion, I was not so comfortable assigning selects like this (everybody knows, that StringBuilder class is a lot faster when concatenating strings). But as you can expect (and me too), smart compiler creates this string (there’s no variable in it) during compile time as one big, isn’t it? Yeah. However why not to calm down myself with a hundred percent proof?

I’ve created small application only with:

string s = string.Empty;
s = "rrr" +

in Main method. I used ILDasm tool from SDK to convince myself that it’s true:

.method private hidebysig static void Main(string[] args) cil managed
// Code size 14 (0xe)
.maxstack 1
.locals init ([0] string s)
IL_0000: nop
IL_0001: ldsfld string [mscorlib]System.String::Empty
IL_0006: stloc.0
IL_0007: ldstr "rrrrrr"
IL_000c: stloc.0
IL_000d: ret
} // end of method Program::Main

And as you can see, the string is created as one piece, as I (and I hope you too) expected. Well, now I have better sleeping when showing the code of the library.

Note, that:

s += "rrr";
s += "rrr";

are completely different statements (there are two String.Concat commands).

Profile Picture Jiří Činčura is .NET, C# and Firebird expert. He focuses on data and business layers, language constructs, parallelism, databases and performance. For almost two decades he contributes to open-source, i.e. FirebirdClient. He works as a senior software engineer for Microsoft. Frequent speaker and blogger at