AppendFormat

This C# method is available on StringBuilder. It handles formatting strings. With it we append different kinds of data—including string literals—to an underlying string buffer.

With AppendFormat, we can write code that is clearer to read and modify. Fewer method calls are needed—more complex formatting can be done in single invocation.

This first example uses a string literal to generate sentences in a StringBuilder. We can put characters (like parentheses) around values.

using System;
using System.Text;

StringBuilder builder = new StringBuilder();
string value = "ABC";
int number = 1;
// Combine the 2 values with AppendFormat.
builder.AppendFormat("R: {0} ({1}).", value, number);
Console.WriteLine(builder);
R: ABC (1).

Int example

To continue, we can format integers with AppendFormat using standard format strings. Here we control the number of places after the decimal.

using System;
using System.Text;

class Program
{
    static int[] _v = new int[]
    {
        1,
        4,
        6
    };

    static void Main()
    {
        StringBuilder b = new StringBuilder();
        foreach (int v in _v)
        {
            b.AppendFormat("int: {0:0.0}{1}", v, Environment.NewLine);
        }
        Console.WriteLine(b.ToString());
    }
}
int: 1.0
int: 4.0
int: 6.0

The StringBuilder AppendFormat method is useful for generating text based on a pattern. The method receives a variable number of arguments.

Final note

For optimal code clarity, the AppendFormat method is ideal. Usually it is not ideal for performance, but this performance often is not the primary issue.