IFormattable.ToString(String, IFormatProvider) Method

public:
 System::String ^ ToString(System::String ^ format, IFormatProvider ^ formatProvider);

public string ToString(string format, IFormatProvider formatProvider);

public string ToString(string? format, IFormatProvider? formatProvider);

abstract member ToString : string * IFormatProvider -> string

Public Function ToString (format As String, formatProvider As IFormatProvider) As String

Parameters

Returns

The value of the current instance in the specified format.

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));
 }
 }
}

open System
open System.Globalization

type Temperature(temperature: decimal) =
 do 
 if temperature < -273.15M then
 raise (ArgumentOutOfRangeException $"{temperature} is less than absolute zero.")

 member _.Celsius =
 temperature

 member _.Fahrenheit =
 temperature * 9M / 5M + 32M

 member _.Kelvin =
 temperature + 273.15m

 override this.ToString() =
 this.ToString("G", CultureInfo.CurrentCulture)

 member this.ToString(format) =
 this.ToString(format, CultureInfo.CurrentCulture)

 member this.ToString(format, provider: IFormatProvider) =
 let format =
 if String.IsNullOrEmpty format then "G"
 else format

 let provider =
 if isNull provider then 
 CultureInfo.CurrentCulture :> IFormatProvider
 else provider

 match format.ToUpperInvariant() with
 | "G" | "C" ->
 temperature.ToString("F2", provider) + " °C"
 | "F" ->
 this.Fahrenheit.ToString("F2", provider) + " °F"
 | "K" ->
 this.Kelvin.ToString("F2", provider) + " K"
 | _ ->
 raise (FormatException $"The {format} format string is not supported.")

 interface IFormattable with
 member this.ToString(format, provider) = this.ToString(format, provider)

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

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 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:

• 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 System.String parameter.

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

• If the original method call does not include an System.IFormatProvider parameter, CultureInfo.CurrentCulture is passed as the value of the System.IFormatProvider parameter.

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

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(String, IFormatProvider) 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.

See also

• String
• IFormatProvider
• NumberFormatInfo
• DateTimeFormatInfo
• CultureInfo