Separated string created in loop

Question

I'm searching the best way to create a string separated with another in a loop. I mean, for example, SQL reader:

StringBuilder sb = new StringBuilder();
while(reader.Read())
{
  sb.Append(reader[0]);
  sb.Append("<br />");
}
string result = sb.ToString();
result = result.Remove(result.LastIndexOf("<br />")); // <-

or creating SQL query string;

StringBuilder sb = new StringBuilder();
foreach(string v in values)
{
  sb.Append(v);
  sb.Append(",");
}
string query = sb.ToString()
query = query.Remove(query.LastIndexOf(",")); // <-
query = String.Concat("INSERT INTO [foo] ([bar]) VALUES(", query, ")");

This is the best I have found:

List<string> list = new List<string>;
while(reader.Read())
{
  list.Add(reader[0]);
}
string result = String.Join("<br />", list.ToArray());

Edit: I know about StringBuilder, I didn't used it here just for some clarity. My general idea do not use Remove / LastIndexOf !

Answer 1

How's about:

StringBuilder builder;
while (reader.Read())
{
    if( builder == null )
    {
        builder = new StringBuilder(reader[0]);
    }
    else
    {
        builder.Append("<br />");
        builder.Append(reader[0]);
    }
}
string result = builder.ToString();

Answer 2

I am not a fan of StringBuilder unless you really know that you need to worry about performance. It produces ugly code. I would write it this way...

private IEnumerable<string> ReadAllStrings(DataReader reader)
{
    while(reader.Read())
        yield return reader[0];
}


String.Join("<br />", ReadAllStrings(reader).ToArray());

If I were doing it a lot, I might consider an extension method:

public static class Extensions
{
    public static string JoinWith(this IEnumerable<string> strings, string separator)
    {
        return String.Join(separator, strings.ToArray());
    }
}

Then, my code would look like this:

ReadAllStrings(reader).JoinWith("<br />");

Answer 3

This is just a combination of several of the better ideas shown:

public static class Extensions
{

    public static string JoinStrings(this DataReader reader, int ColumnIndex, string delimiter)
    {
        var result = new StringBuidler();
        var delim = String.Empty;
        while (reader.Read())
        {
           result.Append(delim).Append(reader[ColumnIndex].ToString());
           delim = delimiter;
        }
        return result.ToString();
    }
}

Now all you have to do is call it like this:

string result = reader.JoinStrings(0, "<br/>");

Answer 4

Another .Net 2.0 solution - change the order:

reader.Read();
StringBuilder sb = new StringBuilder(reader[0]);
while(reader.Read())
{
  sb.Append("<br />");
  sb.Append(reader[0]);
}
string result = sb.ToString();

Answer 5

public class Separator 
{

    private string sep;
    private bool first = true;

    public Separator(string sep) 
    {
        this.sep = sep;
    }

    public virtual string ToString() 
    {
        string reply = first ? "" : sep;
        first = false;
        return reply;
    }
}

var sep = new Separator("<br/>");
var builder = new StringBuilder();
while (reader.Read())
{
    builder.Append (sep.ToString()) ;
    builder.Append (reader[0]) ;
}