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IFormattable.ToString Method

Updated: April 2009

Formats the value of the current instance using the specified format.

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

string ToString(
	string format,
	IFormatProvider formatProvider
)

Parameters

format
Type: System.String

The format to use.

-or-

A null reference (Nothing in Visual Basic) to use the default format defined for the type of the IFormattable implementation.

formatProvider
Type: System.IFormatProvider

The provider to use to format the value.

-or-

A null reference (Nothing in Visual Basic) to obtain the numeric format information from the current locale setting of the operating system.

Return Value

Type: System.String
The value of the current instance in the specified format.

The ToString method converts a value to a string representation that can be expressed in multiple ways. Its precise format depends on specific symbols or a specified order defined by specific cultures, professions, or industries. You can call the method directly. It is also called automatically by the Convert.ToString(Object) and Convert.ToString(Object, IFormatProvider) methods, and by methods that use the composite formatting feature in the .NET Framework, such as String.Format(String, Object[]), Console.WriteLine(String, Object[]), and StringBuilder.AppendFormat(String, Object[]).(For more information, see Composite Formatting.)

Composite formatting methods call the ToString method once for each format item in a format string. The parameters passed to the method depend on the specific formatting method that is called and on the content of the format item, as follows:

NoteNote:

An object's ToString implementation is called by composite formatting methods only if they are not passed an ICustomFormatter format provider, or if the Format method of the custom format provider returns null.

The .NET Framework includes three format providers, all of which implement the IFormatProvider interface:

  • NumberFormatInfo supplies numeric formatting information, such as the characters to use for decimal and group separators, and the spelling and placement of currency symbols in monetary values.

  • DateTimeFormatInfo supplies date-related and time-related formatting information, such as the position of the month, the day, and the year in a date pattern.

  • CultureInfo contains the default formatting information in a specific culture, including the numeric format information, and date-related and time-related formatting information.

In addition, you can define your own custom format provider.

Notes to Implementers:

The ToString method must support the "G" (general) format specifier. Besides the "G" specifier, the class can define the list of format specifiers that it supports. In addition, the class must be prepared to handle a format specifier that is null. For more information about formatting and formatting codes, see Formatting Overview

The following example demonstrates a Temperature class that implements the ToString method. This code example is part of a larger example provided for the IFormattable class.

using System;
using System.Globalization;

public class Temperature : IFormattable
{
   private decimal temp;

   public Temperature(decimal temperature)
   {
      if (temperature < -273.15m) 
        throw new ArgumentOutOfRangeException(String.Format("{0} is less than absolute zero.", 
                                              temperature));
      this.temp = temperature;
   }

   public decimal Celsius
   {
      get { return temp; }
   }

   public decimal Fahrenheit
   {
      get { return temp * 9 / 5 + 32; }
   }

   public decimal Kelvin
   {
      get { return temp + 273.15m; }
   }

   public override string ToString()
   {
      return this.ToString("G", CultureInfo.CurrentCulture);
   }

   public string ToString(string format)
   {
      return this.ToString(format, CultureInfo.CurrentCulture);
   }

   public string ToString(string format, IFormatProvider provider) 
   {
      if (String.IsNullOrEmpty(format)) format = "G";
      if (provider == null) provider = CultureInfo.CurrentCulture;

      switch (format.ToUpperInvariant())
      {
         case "G":
         case "C":
            return temp.ToString("F2", provider) + " °C"; 
         case "F":
            return Fahrenheit.ToString("F2", provider) + " °F";
         case "K":
            return Kelvin.ToString("F2", provider) + " K";
         default:
            throw new FormatException(String.Format("The {0} format string is not supported.", format));
      }
   }
}

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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

.NET Framework

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

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0

Date

History

Reason

April 2009

Revised and expanded the Remarks section.

Information enhancement.

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