IFormattable Interface

Provides functionality to format the value of an object into a string representation.

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

[ComVisibleAttribute(true)]
public interface class IFormattable

The IFormattable type exposes the following members.

  NameDescription
Public methodSupported by the XNA FrameworkSupported by Portable Class LibrarySupported in .NET for Windows Store appsToStringFormats the value of the current instance using the specified format.
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The IFormattable interface converts an object to its string representation based on a format string and a format provider.

A format string typically defines the general appearance of an object. For example, the .NET Framework supports the following:

You can also define your own format strings to support formatting of your application-defined types.

A format provider returns a formatting object that typically defines the symbols used in converting an object to its string representation. For example, when you convert a number to a currency value, a format provider defines the currency symbol that appears in the result string. The .NET Framework defines three format providers:

In addition, you can define your own custom format providers to supply culture-specific, profession-specific, or industry-specific information used in formatting. For more information about implementing custom formatting by using a custom format provider, see ICustomFormatter.

The IFormattable interface defines a single method, ToString, that supplies formatting services for the implementing type. The ToString method can be called directly. In addition, it is 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 methods include Console::WriteLine(String, Object), String::Format, and StringBuilder::AppendFormat(String, Object), among others. The ToString method is called for each format item in the method's format string.

The IFormattable interface is implemented by the base data types.

Notes to Implementers

Classes that require more control over the formatting of strings than Object::ToString provides should implement IFormattable.

A class that implements IFormattable 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 nullptr. For more information about formatting and formatting codes, see Formatting Types

The following example defines a Temperature class that implements the IFormattable interface. The class supports four format specifiers: "G" and "C", which indicate that the temperature is to be displayed in Celsius; "F", which indicates that the temperature is to be displayed in Fahrenheit; and "K", which indicates that the temperature is to be displayed in Kelvin. In addition, the IFormattable::ToString implementation also can handle a format string that is nullptr or empty. The other two ToString methods defined by the Temperature class simply wrap a call to the IFormattable::ToString implementation.

No code example is currently available or this language may not be supported.

The following example then calls the IFormattable::ToString implementation either directly or by using a composite format string.

No code example is currently available or this language may not be supported.

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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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