Reputation: 8295

Best way to remove the last character from a string built with stringbuilder

I have the following

data.AppendFormat("{0},",dataToAppend);

The problem with this is that I am using it in a loop and there will be a trailing comma. What is the best way to remove the trailing comma?

Do I have to change data to a string and then substring it?

Upvotes: 134

Answers (13)

CodingYoshi

Reputation: 27039

Gotcha!!

Most of the answers on this question won't work if you use AppendLine like below:

var builder = new StringBuilder();
builder.AppendLine("One,");
builder.Length--; // Won't work
Console.Write(builder.ToString());

builder = new StringBuilder();
builder.AppendLine("One,");
builder.Length += -1; // Won't work
Console.Write(builder.ToString());

builder = new StringBuilder();
builder.AppendLine("One,");
Console.Write(builder.TrimEnd(',')); // Won't work

Fiddle Me

WHY??? @(&**(&@!!

The issue is simple but took me a while to figure it out: Because there are 2 more invisible characters at the end CR and LF (Carriage Return and Line Feed). Therefore, you need to take away 3 last characters:

var builder = new StringBuilder();
builder.AppendLine("One,");
builder.Length -= 3; // This will work
Console.WriteLine(builder.ToString());

In Conclusion

Use Length-- or Length -= 1 if the last method you called was Append. Use Length -= 3 if you the last method you called AppendLine.

Upvotes: 5

Pankaj

Reputation: 2754

How about this..

string str = "The quick brown fox jumps over the lazy dog,";
StringBuilder sb = new StringBuilder(str);
sb.Remove(str.Length - 1, 1);

Upvotes: 17

gouravm

Reputation: 321

Simply shortens the stringbuilder length by 1;

 StringBuilder sb = new StringBuilder();
 sb.Length--;

i know this is not the effective way as it translates to sb = sb-1;

Alternative Effective solution

sb.Remove(starting_index, how_many_character_to_delete);

for our case it would be

sb.Remove(sb.length-1,1)

Upvotes: 0

Vlad

Reputation: 35594

Just use

string.Join(",", yourCollection)

This way you don't need the StringBuilder and the loop.

Long addition about async case. As of 2019, it's not a rare setup when the data are coming asynchronously.

In case your data are in async collection, there is no string.Join overload taking IAsyncEnumerable<T>. But it's easy to create one manually, hacking the code from string.Join:

public static class StringEx
{
    public static async Task<string> JoinAsync<T>(string separator, IAsyncEnumerable<T> seq)
    {
        if (seq == null)
            throw new ArgumentNullException(nameof(seq));

        await using (var en = seq.GetAsyncEnumerator())
        {
            if (!await en.MoveNextAsync())
                return string.Empty;

            string firstString = en.Current?.ToString();

            if (!await en.MoveNextAsync())
                return firstString ?? string.Empty;

            // Null separator and values are handled by the StringBuilder
            var sb = new StringBuilder(256);
            sb.Append(firstString);

            do
            {
                var currentValue = en.Current;
                sb.Append(separator);
                if (currentValue != null)
                    sb.Append(currentValue);
            }
            while (await en.MoveNextAsync());
            return sb.ToString();
        }
    }
}

If the data are coming asynchronously but the interface IAsyncEnumerable<T> is not supported (like the mentioned in comments SqlDataReader), it's relatively easy to wrap the data into an IAsyncEnumerable<T>:

async IAsyncEnumerable<(object first, object second, object product)> ExtractData(
        SqlDataReader reader)
{
    while (await reader.ReadAsync())
        yield return (reader[0], reader[1], reader[2]);
}

and use it:

Task<string> Stringify(SqlDataReader reader) =>
    StringEx.JoinAsync(
        ", ",
        ExtractData(reader).Select(x => $"{x.first} * {x.second} = {x.product}"));

In order to use Select, you'll need to use nuget package System.Interactive.Async. Here you can find a compilable example.

Upvotes: 55

Mike Perrenoud

Reputation: 67928

The simplest and most efficient way is to perform this command:

data.Length--;

by doing this you move the pointer (i.e. last index) back one character but you don't change the mutability of the object. In fact, clearing a StringBuilder is best done with Length as well (but do actually use the Clear() method for clarity instead because that's what its implementation looks like):

data.Length = 0;

again, because it doesn't change the allocation table. Think of it like saying, I don't want to recognize these bytes anymore. Now, even when calling ToString(), it won't recognize anything past its Length, well, it can't. It's a mutable object that allocates more space than what you provide it, it's simply built this way.

Upvotes: 300

bastos.sergio

Reputation: 6764

I prefer manipulating the length of the stringbuilder:

data.Length = data.Length - 1;

Upvotes: 12

studert

Reputation: 137

The most simple way would be to use the Join() method:

public static void Trail()
{
    var list = new List<string> { "lala", "lulu", "lele" };
    var data = string.Join(",", list);
}

If you really need the StringBuilder, trim the end comma after the loop:

data.ToString().TrimEnd(',');

Upvotes: 3

MrB

Reputation: 424

Best way to remove the last character from a string built with stringbuilder

Answers (13)

Gotcha!!

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