IFormattableToString Method
 

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

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

Syntax
string ToString(
	string format,
	IFormatProvider formatProvider
)
String^ ToString(
	String^ format,
	IFormatProvider^ formatProvider
)
abstract ToString : 
        format:string *
        formatProvider:IFormatProvider -> string
Function ToString (
	format As String,
	formatProvider As IFormatProvider
) As String

Parameters

format
Type:

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:

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:

The value of the current instance in the specified format.

Remarks

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 ConvertToString and ConvertToString methods, and by methods that use the composite formatting feature in the .NET Framework, such as StringFormat, ConsoleWriteLine, and StringBuilderAppendFormat. (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:

  • If the format item does not include a format string (for example, if the format item is simply {0}), it is passed null as the value of the SystemString parameter.

  • If the format item includes a format string (for example, {0:G}), that format string is passed as the value of the SystemString parameter.

  • If the original method call does not include an SystemIFormatProvider parameter, is passed as the value of the SystemIFormatProvider parameter.

  • If the original method call includes an SystemIFormatProvider parameter, the provider that is supplied in the method call is passed as the value of the SystemIFormatProvider parameter.

System_CAPS_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 Types in the .NET Framework.

Examples

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));
      }
   }
}
Imports System.Globalization

Public Class Temperature : Implements IFormattable
   Private temp As Decimal

   Public Sub New(temperature As Decimal)
      If temperature < -273.15 Then _ 
        Throw New ArgumentOutOfRangeException(String.Format("{0} is less than absolute zero.", _
                                              temperature))
      Me.temp = temperature
   End Sub

   Public ReadOnly Property Celsius As Decimal
      Get
         Return temp
      End Get
   End Property

   Public ReadOnly Property Fahrenheit As Decimal
      Get
         Return temp * 9 / 5 + 32
      End Get
   End Property

   Public ReadOnly Property Kelvin As Decimal
      Get
         Return temp + 273.15d
      End Get
   End Property

   Public Overrides Function ToString() As String
      Return Me.ToString("G", CultureInfo.CurrentCulture)
   End Function

   Public Overloads Function ToString(fmt As String) As String
      Return Me.ToString(fmt, CultureInfo.CurrentCulture)
   End Function

   Public Overloads Function ToString(fmt As String, provider As IFormatProvider) _
                   As String _
                   Implements IFormattable.ToString
      If String.IsNullOrEmpty(fmt) Then fmt = "G"
      If provider Is Nothing Then provider = CultureInfo.CurrentCulture

      Select Case fmt.ToUpperInvariant()
         Case "G", "C"
            Return temp.ToString("F2", provider) + " °C" 
         Case "F"
            Return Fahrenheit.ToString("F2", provider) + " °F"
         Case "K"
            Return Kelvin.ToString("F2", provider) + " K"
         Case Else
            Throw New FormatException(String.Format("The {0} format string is not supported.", fmt))
      End Select
   End Function
End Class
Version Information
Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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