Most efficent way of joining strings

Question

I need to concatenate a lot of strings alltogether and put a comma between any of them. I have a list of strings

"123123123213"
"1232113213213"
"123213123"

and I want to get

"123123123213,1232113213213,123213123"

I was wondering what is the best way to achieve that.

I could do this like this:

private List<string> stringList = new List<string> { 
    // a lot of strings in here
    "1234567890", "34343434", "4343434" }; 

string outcome = string.Join(",", stringList.ToArray());

Or maybe:

StringBuilder builder = new StringBuilder();
stringList.ForEach(val => {
    builder.Append(val);
    builder.Append(",");
});

string outcome = builder.ToString();

Which way is better? Do you know better ways to concatenate strings?

Answer 1

As @Ekkehard said, use the string.Join.

However, you do not need the ToArray() because string.Join has an overload for IEnumerable<string>.

List<string> stringList = new List<string> 
    { "1234567890", "34343434", "4343434" }; 

string outcome = string.Join(",", stringList);

EDIT

As @Kobi said, this will work only C# 4.0. In 3.5 I would do.

var s = new StringBuilder(stringList.Count * 8);
foreach (var item in stringList)
{
   s.Append(item);
   s.Append(',');
}
s.Length -= 1;
string outcome = stringList.ToList();

Answer 2

You should use string.Join() because:

a) it's much more readable, maintainable and easy on the eyes.

b) it uses a StringBuilder internally already, so it's very efficient ( you can confirm yourself using Reflector).

Edit:

string.Join() uses a StringBuilder for the general case of an IEnumerable<T> input. If you already have an array on the other hand it uses some voodoo magic (including FastAllocateString() and UnSafeCharBuffer) to be even faster.