This method uses the composite formatting feature of the .NET Framework to convert the value of an object to its text representation and embed that representation in the current System.Text.StringBuilder object.

The format parameter consists of zero or more runs of text intermixed with zero or more indexed placeholders, called format items. The index of the format items must be 0, to correspond to arg0, the single object in the parameter list of this method. The formatting process replaces each format item with the string representation of arg0.

The syntax of a format item is as follows:

{index[,length][:formatString]}

Elements in square brackets are optional. The following table describes each element.

arg0 represents the object to be formatted. Each format item in format is replaced with the string representation of arg0. If the format item includes formatString and arg0 implements the IFormattable interface, then arg0.Format(formatString, null) defines the formatting. Otherwise, arg0.ToString() defines the formatting.

If the string assigned to format is "Thank you for your donation of {0:####} cans of food to our charitable organization." and arg0 is an integer with the value 10, the return value will be "Thank you for your donation of 10 cans of food to our charitable organization."

using System;
using System.Text;

public class StringBuilderTest {
  public static void Main() { 
     
      StringBuilder sb = new StringBuilder("The high ");
      Console.WriteLine( sb.AppendFormat("temperature today was {0, 6}.", 88) ); 
  }
}
      

The output is

The high temperature today was     88.