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String.Format Method (String, Object, Object)

Replaces the format items in a specified string with the string representation of two specified objects.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

public static string Format(
	string format,
	Object arg0,
	Object arg1
)

Parameters

format
Type: System.String
A composite format string (see Remarks).
arg0
Type: System.Object
The first object to format.
arg1
Type: System.Object
The second object to format.

Return Value

Type: System.String
A copy of format in which format items are replaced by the string representations of arg0 and arg1.

ExceptionCondition
ArgumentNullException

format is null.

FormatException

format is invalid.

-or-

The index of a format item is not zero or one.

This method uses the composite formatting feature of the .NET Framework to convert the value of an object to its string representation and to embed that representation in a string. The .NET Framework provides extensive formatting support, which is described in greater detail in the following formatting topics:

The format parameter consists of zero or more runs of text intermixed with zero or more indexed placeholders, called format items, that correspond to an object in the parameter list of this method. The formatting process replaces each format item with the string representation of the value of the corresponding object.

The syntax of a format item is as follows:

{index[,length][:formatString]}

Elements in square brackets are optional. The following table describes each element. For more information about the composite formatting feature, including the syntax of a format item, see Composite Formatting.

Element

Description

index

The zero-based position in the parameter list of the object to be formatted. If the object specified by index is null, the format item is replaced by String.Empty. Because this overload has two objects in its parameter list, the value of index must be 0 or 1. If there is no parameter in the index position, a FormatException is thrown.

,length

The minimum number of characters in the string representation of the parameter. If positive, the parameter is right-aligned; if negative, it is left-aligned.

:formatString

A standard or custom format string that is supported by the object to be formatted. Possible values for formatString are the same as the values supported by the object's ToString(format) method. If formatString is not specified and the object to be formatted implements the IFormattable interface, null is passed as the value of the format parameter that is used as the IFormattable.ToString format string.

NoteNote

For the standard and custom format strings used with date and time values, see Standard Date and Time Format Strings and Custom Date and Time Format Strings. For the standard and custom format strings used with numeric values, see Standard Numeric Format Strings and Custom Numeric Format Strings. For the standard format strings used with enumerations, see Enumeration Format Strings.

The leading and trailing brace characters, "{" and "}", are required. To specify a single literal brace character in format, specify two leading or trailing brace characters; that is, "{{" or "}}".

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."

The following example uses the Format(String, Object, Object) method to display time and temperature data stored in a generic Dictionary<TKey, TValue> object. Note that the format string has three format items, whereas there are only two objects to format. This is because the first object in the list (a date and time value) is used by two format items: The first format item displays the time in the date and time value, and the second displays the date in the date and time value.


using System;
using System.Collections.Generic;

public class Example
{
   public static void Main()
   {
      Dictionary<DateTime, Double> temperatureInfo = new Dictionary<DateTime, Double>(); 
      temperatureInfo.Add(new DateTime(2010, 6, 1, 14, 0, 0), 87.46);
      temperatureInfo.Add(new DateTime(2010, 12, 1, 10, 0, 0), 36.81);

      Console.WriteLine("Temperature Information:\n");
      string output;   
      foreach (var item in temperatureInfo)
      {
         output = String.Format("Temperature at {0,8:t} on {0,9:d}: {1,5:N1}°F", 
                                item.Key, item.Value);
         Console.WriteLine(output);
      }
   }
}
// The example displays the following output:
//       Temperature Information:
//       
//       Temperature at  2:00 PM on  6/1/2010:  87.5°F
//       Temperature at 10:00 AM on 12/1/2010:  36.8°F


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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