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String.Format Method

Replaces each format item in a specified string with the text equivalent of a corresponding object's value.

This member is overloaded. For complete information about this member, including syntax, usage, and examples, click a name in the overload list.

  Name Description
Public method Static member Supported by Silverlight for Windows Phone Supported by Xbox 360 Format(String, Object) Replaces one or more format items in a specified string with the string representation of a specified object.
Public method Static member Supported by Silverlight for Windows Phone Supported by Xbox 360 Format(String, Object[]) Replaces the format item in a specified string with the string representation of a corresponding object in a specified array.
Public method Static member Supported by Silverlight for Windows Phone Supported by Xbox 360 Format(IFormatProvider, String, Object[]) Replaces the format item in a specified string with the text equivalent of the value of a corresponding object in a specified array. A specified parameter supplies culture-specific formatting information.
Public method Static member Supported by Silverlight for Windows Phone Supported by Xbox 360 Format(String, Object, Object) Replaces the format item in a specified string with the string representations of two specified objects.
Public method Static member Supported by Silverlight for Windows Phone Supported by Xbox 360 Format(String, Object, Object, Object) Replaces the format items in a specified string with the string representation of three specified objects.
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Each overload of the Format method uses the composite formatting feature to include zero-based indexed placeholders, called format items, in a composite format string. At run time, each format item is replaced with the string representation of the corresponding argument in a parameter list. If the value of the argument is null, it is replaced with String.Empty. For example, the following call to the Format method includes a format string with three format items, {0}, {1}, and {2}, and an argument list with three items.


DateTime dat = new DateTime(2012, 1, 17, 9, 30, 0); 
string city = "Chicago";
int temp = -16;
string output = String.Format("At {0} in {1}, the temperature was {2} degrees.",
                              dat, city, temp);
inputBlock.Text += output;
// The example displays the following output:
//    At 1/17/2012 9:30:00 AM in Chicago, the temperature was -16 degrees.   


A format item has the following syntax:

{ index[,alignment][ : formatString] }

Brackets denote optional elements. The opening and closing brackets are required. A format item has the following elements:

index

The zero-based index of the argument whose string representation is to be included at this position in the string.

alignment

A signed integer that indicates the total length of the field into which the argument is inserted and whether it is right-aligned (a positive integer) or left-aligned (a negative integer). If alignment is omitted, the string representation of the corresponding argument is inserted in a field with no leading or trailing spaces.

formatString

A format string that specifies the format of the corresponding argument's result string. If formatString is omitted, the corresponding argument's parameterless ToString method is called to produce its string representation. If formatString is present, the argument referenced by the format item must implement the IFormattable interface. Types that support format strings include the following:

The following example illustrates how to use optional elements in format items to produce formatted output.


using System;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      // Create array of 5-tuples with population data for three U.S. cities, 1940-1950.
      Tuple<string, DateTime, int, DateTime, int>[] cities = 
          { Tuple.Create("Los Angeles", new DateTime(1940, 1, 1), 1504277, 
                         new DateTime(1950, 1, 1), 1970358),
            Tuple.Create("New York", new DateTime(1940, 1, 1), 7454995, 
                         new DateTime(1950, 1, 1), 7891957),  
            Tuple.Create("Chicago", new DateTime(1940, 1, 1), 3396808, 
                         new DateTime(1950, 1, 1), 3620962),  
            Tuple.Create("Detroit", new DateTime(1940, 1, 1), 1623452, 
                         new DateTime(1950, 1, 1), 1849568) };

      // Display header
      string header = String.Format("{0,-12}{1,8}{2,12}{1,8}{2,12}{3,14}\n",
                                    "City", "Year", "Population", "Change (%)");
      outputBlock.Text += header + Environment.Newline;
      string output;      
      foreach (var city in cities) {
         output = String.Format("{0,-12}{1,8:yyyy}{2,12:N0}{3,8:yyyy}{4,12:N0}{5,14:P1}",
                                city.Item1, city.Item2, city.Item3, city.Item4, city.Item5,
                                (city.Item5 - city.Item3)/city.Item3 * 1.0);
         outputBlock.Text += output + Environment.Newline;
      }
   }
}
// The example displays the following output:
//    City            Year  Population    Year  Population    Change (%)
//    
//    Los Angeles     1940   1,504,277    1950   1,970,358        31.0 %
//    New York        1940   7,454,995    1950   7,891,957         5.9 %
//    Chicago         1940   3,396,808    1950   3,620,962         6.6 %
//    Detroit         1940   1,623,452    1950   1,849,568        13.9 %


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