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IFormatProvider Interface

Provides a mechanism for retrieving an object to control formatting.

For a list of all members of this type, see IFormatProvider Members.

[Visual Basic]
Public Interface IFormatProvider
[C#]
public interface IFormatProvider
[C++]
public __gc __interface IFormatProvider
[JScript]
public interface IFormatProvider

Classes that Implement IFormatProvider

Class Description
CultureInfo Represents information about a specific culture including the names of the culture, the writing system, and the calendar used, as well as access to culture-specific objects that provide information for common operations, such as formatting dates and sorting strings.
DateTimeFormatInfo Defines how DateTime values are formatted and displayed, depending on the culture.
NumberFormatInfo Defines how numeric values are formatted and displayed, depending on the culture.

Remarks

Some methods in the common language runtime convert a value to or from a string representation and take a string parameter that contains one or more characters, called format specifiers, which indicate how the value is to be converted. If the meaning of the format specifier varies by culture, a formatting object supplies the actual characters used in the string representation.

A class or value type implements the GetFormat method of this interface to obtain an object that provides format information or processing for the implementing type.

For example, IFormatProvider is implemented by NumberFormatInfo and DateTimeFormatInfo. NumberFormatInfo provides culture-specific information used to format numbers in the base data types, and DateTimeFormatInfo provides culture-specific information used to format date and time values.

Example

[Visual Basic, C#, C++] The following code example illustrates the use of a class that implements the IFormatProvider interface and the GetFormat method. The AnyRadix class supports the "Ra" formatting code and converts an Int64 value to a string of any specified radix between 2 and 36. GetFormat returns a reference to itself if the Type parameter refers to a class that implements ICustomFormatter; otherwise, GetFormat returns a null reference (Nothing in Visual Basic).

[Visual Basic] 
' Sample for the IFormatProvider interface and
' the IFormatProvider.GetFormat( Type ) method.
Imports System
Imports Microsoft.VisualBasic

' This class implements the "Ra" formatting code. An instance of this 
' class should be passed to methods requiring an IFormatProvider.
Public Class AnyRadix
    Implements ICustomFormatter 
    Implements IFormatProvider

    ' The value to be formatted is returned as a signed string 
    ' of digits from the rDigits array. 
    Const radixCode As String = "Ra"
    Private Shared rDigits As Char( ) = { _
        "0"c, "1"c, "2"c, "3"c, "4"c, "5"c, "6"c, "7"c, "8"c, _
        "9"c, "A"c, "B"c, "C"c, "D"c, "E"c, "F"c, "G"c, "H"c, _
        "I"c, "J"c, "K"c, "L"c, "M"c, "N"c, "O"c, "P"c, "Q"c, _
        "R"c, "S"c, "T"c, "U"c, "V"c, "W"c, "X"c, "Y"c, "Z"c }
        
    ' This method returns an object that implements ICustomFormatter 
    ' to do the formatting. 
    Public Function GetFormat( argType As Type ) As Object _
        Implements IFormatProvider.GetFormat

        ' Here, the same object (Me) is returned, but it would be 
        ' possible to return an object of a different type.
        If argType Is GetType( ICustomFormatter ) Then
            Return Me
        Else
            Return Nothing
        End If
    End Function 
        
    ' This method does the formatting only if it recognizes the 
    ' format codes. 
    Public Function Format( formatString As String, _
        argToBeFormatted As Object, _
        provider As IFormatProvider ) As String _
        Implements ICustomFormatter.Format
            
        ' If no format string is provided or the format string cannot 
        ' be handled, use IFormattable or standard string processing.
        If formatString Is Nothing OrElse _
            Not formatString.Trim( ).StartsWith( radixCode ) Then

            If TypeOf argToBeFormatted Is IFormattable Then
                Return CType( argToBeFormatted, IFormattable ). _
                    ToString( formatString, provider )
            Else
                Return argToBeFormatted.ToString( )
            End If
        End If 

        ' The formatting is handled here.
        Dim digitIndex          As Integer = 0
        Dim radix               As Long 
        Dim longToBeFormatted   As Long 
        Dim longPositive        As Long
        Dim outDigits( 63 )     As Char
            
        ' Extract the radix from the format string.
        formatString = formatString.Replace( radixCode, "" )
        Try
            radix = Convert.ToInt64( formatString )
        Catch ex As Exception
            Throw New ArgumentException( String.Format( _
                "The radix ""{0}"" is invalid.", _
                formatString ), ex )
        End Try

        ' Verify that the radix is in the proper range.
        If radix < 2 OrElse radix > 36 Then
            Throw New ArgumentException( String.Format( _
                "The radix ""{0}"" is not in the range 2..36.", _
                formatString ) )
        End If
            
        ' Verify that the argument can be converted to a long integer.
        Try
            longToBeFormatted = CType( argToBeFormatted, Long )
        Catch ex As Exception
            Throw New ArgumentException( String.Format( _
                "The argument ""{0}"" cannot be " & _
                "converted to an integer value.", _
                argToBeFormatted ), ex )
        End Try
            
        ' Extract the magnitude for conversion.
        longPositive = Math.Abs( longToBeFormatted )

        ' Convert the magnitude to a digit string.
        For digitIndex = 0 To 64
            If longPositive = 0 Then Exit For

            outDigits( outDigits.Length - digitIndex - 1 ) = _
                rDigits( longPositive Mod radix )
            longPositive \= radix
        Next digitIndex
            
        ' Add a minus sign if the argument is negative.
        If longToBeFormatted < 0 Then
            outDigits( outDigits.Length - digitIndex - 1 ) = "-"c 
            digitIndex += 1
        End If 

        Return New String( outDigits, _
            outDigits.Length - digitIndex, digitIndex )
    End Function 
End Class

Module IFormatProviderDemo
    
    Sub ConvertToAnyRadix( argToConvert As Object, _
        formatStr As String )

        Dim provider As New AnyRadix( )
        Dim messageStr As String = _
            String.Format( "{{0:{0}}}", formatStr )

        ' Write the first part of the output line.
        Console.Write( "{0,18}  {1,-6}", _ 
            argToConvert, formatStr )

        ' Convert the specified argument using the specified format.
        Try
            Console.WriteLine( String.Format( _
                provider, messageStr, argToConvert ) )
        Catch ex As Exception
            Dim lineEnd As Integer = _
                ex.ToString( ).IndexOf( vbLf )
            Console.WriteLine( _
                ex.ToString( ).Substring( 0, lineEnd ) )
            Console.WriteLine( )
        End Try
    End Sub 
        
    Sub Main( )
        Dim TwoToThe32      As Long = 4294967296
        Dim fifteenNines    As Long = 999999999999999
            
        Console.WriteLine( _
            "This example of the IFormatProvider interface " & _
            vbCrLf & "and the IFormatProvider." & _
            "GetFormat( Type ) method " & vbCrLf & _
            "generates the following output." & vbCrLf )
        Console.WriteLine( "{0,18} Format Result", "Number" )
        Console.WriteLine( "{0,18} ------ ------", "------" )
            
        ' These are valid conversions.
        ConvertToAnyRadix( TwoToThe32, "Ra2" )
        ConvertToAnyRadix( TwoToThe32, "Ra5" )
        ConvertToAnyRadix( TwoToThe32, "Ra16" )
        ConvertToAnyRadix( TwoToThe32, "Ra23" )
        ConvertToAnyRadix( TwoToThe32, "Ra36" )
        ConvertToAnyRadix( fifteenNines, "Ra2" )
        ConvertToAnyRadix( fifteenNines, "Ra3" )
        ConvertToAnyRadix( fifteenNines, "Ra8" )
        ConvertToAnyRadix( fifteenNines, "Ra11" )
        ConvertToAnyRadix( fifteenNines, "Ra16" )
        ConvertToAnyRadix( fifteenNines, "Ra23" )
        ConvertToAnyRadix( fifteenNines, "Ra36" )
        ConvertToAnyRadix( fifteenNines, "E16" )
        ConvertToAnyRadix( fifteenNines, "" )
            
        ' These are error conditions.
        ConvertToAnyRadix( fifteenNines, "Ra37" )
        ConvertToAnyRadix( "ABCDEFGHIJKLM", "Ra16" )
    End Sub 
End Module 

' This example of the IFormatProvider interface
' and the IFormatProvider.GetFormat( Type ) method
' generates the following output.
' 
'             Number Format Result
'             ------ ------ ------
'         4294967296  Ra2   100000000000000000000000000000000
'         4294967296  Ra5   32244002423141
'         4294967296  Ra16  100000000
'         4294967296  Ra23  1606K7IC
'         4294967296  Ra36  1Z141Z4
'    999999999999999  Ra2   11100011010111111010100100110001100111111111111111
'    999999999999999  Ra3   11212010201001210101011021212000
'    999999999999999  Ra8   34327724461477777
'    999999999999999  Ra11  26A6A3689065639
'    999999999999999  Ra16  38D7EA4C67FFF
'    999999999999999  Ra23  1134DIFHLMM4
'    999999999999999  Ra36  9UGXNORJLR
'    999999999999999  E16   9.9999999999999900E+014
'    999999999999999        999999999999999
'    999999999999999  Ra37  System.ArgumentException: The radix "37" is not in
' the range 2..36.
' 
'      ABCDEFGHIJKLM  Ra16  System.ArgumentException: The argument "ABCDEFGHIJK
' LM" cannot be converted to an integer value. ---> System.InvalidCastException
' : Cast from string "ABCDEFGHIJKLM" to type 'Long' is not valid. ---> System.F
' ormatException: Input string was not in a correct format.

[C#] 
// Sample for the IFormatProvider interface and
// the IFormatProvider.GetFormat( Type ) method.
using System;

// This class implements the "Ra" formatting code. An instance of this 
// class should be passed to methods requiring an IFormatProvider.
public class AnyRadix : ICustomFormatter, IFormatProvider
{
    // The value to be formatted is returned as a signed string 
    // of digits from the rDigits array. 
    const string radixCode = "Ra";
    private static char[] rDigits = {
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 
        'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 
        'U', 'V', 'W', 'X', 'Y', 'Z' };
        
    // This method returns an object that implements ICustomFormatter 
    // to do the formatting. 
    public object GetFormat( Type argType )
    {
        // Here, the same object (this) is returned, but it would 
        // be possible to return an object of a different type.
        if ( argType == typeof( ICustomFormatter ) )
            return this;
        else
            return null;
    } 
        
    // This method does the formatting only if it recognizes the 
    // format codes. 
    public string Format( string formatString, 
        object argToBeFormatted, IFormatProvider provider )
    {
        // If no format string is provided or the format string cannot 
        // be handled, use IFormattable or standard string processing.
        if( formatString == null || 
            ! formatString.Trim( ).StartsWith( radixCode ) )
        {
            if( argToBeFormatted is IFormattable )
                return ( (IFormattable)argToBeFormatted ).
                    ToString( formatString, provider );
            else
                return argToBeFormatted.ToString( );
        }

        // The formatting is handled here.
        int     digitIndex = 0;
        long    radix;
        long    longToBeFormatted;
        long    longPositive;
        char[ ] outDigits = new char[ 63 ];
            
        // Extract the radix from the format string.
        formatString = formatString.Replace( radixCode, "" );
        try
        {
            radix = Convert.ToInt64( formatString );
        }
        catch( Exception ex )
        {
            throw new ArgumentException( String.Format( 
                "The radix \"{0}\" is invalid.", 
                formatString ), ex );
        }

        // Verify that the radix is in the proper range.
        if( radix <2 || radix > 36 )
            throw new ArgumentException( String.Format( 
                "The radix \"{0}\" is not in the range 2..36.", 
                formatString ) );
            
        // Verify that the argument can be converted to a long integer.
        try
        {
            longToBeFormatted = (long)argToBeFormatted;
        }
        catch( Exception ex )
        {
            throw new ArgumentException( String.Format(
                "The argument \"{0}\" cannot be " +
                "converted to an integer value.", 
                argToBeFormatted ), ex );
        }
            
        // Extract the magnitude for conversion.
        longPositive = Math.Abs( longToBeFormatted );

        // Convert the magnitude to a digit string.
        for( digitIndex = 0; digitIndex <= 64; digitIndex++ )
        {
            if( longPositive == 0 ) break;

            outDigits[ outDigits.Length - digitIndex - 1 ] = 
                rDigits[ longPositive % radix ];
            longPositive /= radix;
        }
            
        // Add a minus sign if the argument is negative.
        if( longToBeFormatted < 0 )
            outDigits[ outDigits.Length - digitIndex++ - 1 ] = 
                '-';

        return new string( outDigits, 
            outDigits.Length - digitIndex, digitIndex );
    } 
} 

class IFormatProviderDemo
{
    static void ConvertToAnyRadix( object argToConvert, 
        string formatStr )
    {
        AnyRadix    provider = new AnyRadix( );
        string      messageStr = 
            String.Format( "{{0:{0}}}", formatStr );

        // Write the first part of the output line.
        Console.Write( "{0,18}  {1,-6}", argToConvert, formatStr );

        // Convert the specified argument using the specified format.
        try
        {
            Console.WriteLine( String.Format( 
                provider, messageStr, argToConvert ) );
        }
        catch( Exception ex )
        {
            // Display the exception without the stack trace.
            int lineEnd = ex.ToString( ).IndexOf( '\n' );
            Console.WriteLine( "{0}\n",
                ex.ToString( ).Substring( 0, lineEnd ) );
        }
    } 
        
    static void Main( )
    {
        long twoToThe32 = 4294967296;
        long fifteenNines = 999999999999999;
            
        Console.WriteLine(
            "This example of the IFormatProvider interface \n" +
            "and the IFormatProvider.GetFormat( Type ) method " +
            "\ngenerates the following output.\n" );
        Console.WriteLine( "{0,18} Format Result", "Number" );
        Console.WriteLine( "{0,18} ------ ------", "------" );
            
        // These are valid conversions.
        ConvertToAnyRadix( twoToThe32, "Ra2" );
        ConvertToAnyRadix( twoToThe32, "Ra5" );
        ConvertToAnyRadix( twoToThe32, "Ra16" );
        ConvertToAnyRadix( twoToThe32, "Ra23" );
        ConvertToAnyRadix( twoToThe32, "Ra36" );
        ConvertToAnyRadix( fifteenNines, "Ra2" );
        ConvertToAnyRadix( fifteenNines, "Ra3" );
        ConvertToAnyRadix( fifteenNines, "Ra8" );
        ConvertToAnyRadix( fifteenNines, "Ra11" );
        ConvertToAnyRadix( fifteenNines, "Ra16" );
        ConvertToAnyRadix( fifteenNines, "Ra23" );
        ConvertToAnyRadix( fifteenNines, "Ra36" );
        ConvertToAnyRadix( fifteenNines, "E16" );
        ConvertToAnyRadix( fifteenNines, "" );
            
        // These are error conditions.
        ConvertToAnyRadix( fifteenNines, "Ra37" );
        ConvertToAnyRadix( "ABCDEFGHIJKLM", "Ra16" );
    } 
} 

/*
This example of the IFormatProvider interface
and the IFormatProvider.GetFormat( Type ) method
generates the following output.

            Number Format Result
            ------ ------ ------
        4294967296  Ra2   100000000000000000000000000000000
        4294967296  Ra5   32244002423141
        4294967296  Ra16  100000000
        4294967296  Ra23  1606K7IC
        4294967296  Ra36  1Z141Z4
   999999999999999  Ra2   11100011010111111010100100110001100111111111111111
   999999999999999  Ra3   11212010201001210101011021212000
   999999999999999  Ra8   34327724461477777
   999999999999999  Ra11  26A6A3689065639
   999999999999999  Ra16  38D7EA4C67FFF
   999999999999999  Ra23  1134DIFHLMM4
   999999999999999  Ra36  9UGXNORJLR
   999999999999999  E16   9.9999999999999900E+014
   999999999999999        999999999999999
   999999999999999  Ra37  System.ArgumentException: The radix "37" is not in th
e range 2..36.

     ABCDEFGHIJKLM  Ra16  System.ArgumentException: The argument "ABCDEFGHIJKLM
" cannot be converted to an integer value. ---> System.InvalidCastException: Sp
ecified cast is not valid.
*/

[C++] 
// Sample for the IFormatProvider interface and
// the IFormatProvider::GetFormat( Type* ) method.
#using <mscorlib.dll>
using namespace System;

// This class implements the "Ra" formatting code. An instance of this 
// class should be passed to methods requiring an IFormatProvider.
__gc class AnyRadix : public IFormatProvider, public ICustomFormatter
{
    static Object* null = 0;

    // The value to be formatted is returned as a signed string 
    // of digits from the rDigits array. 
    static String* radixCode = S"Ra";
    static Char rDigits[ ] = {
        '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 
        'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 
        'U', 'V', 'W', 'X', 'Y', 'Z' };
        
    // This method returns an object that implements ICustomFormatter 
    // to do the formatting. 
    public: Object* GetFormat( Type* argType )
    {
        // Here, the same object (this) is returned, but it would 
        // be possible to return an object of a different type.
        if( argType == __typeof( ICustomFormatter ) ) 
            return this;
        else
            return null;
    } 
        
    // This method does the formatting only if it recognizes the 
    // format codes. 
    public: String* Format( String* formatString, 
        Object* argToBeFormatted, IFormatProvider* provider )
    {
        // If no format string is provided or the format string cannot 
        // be handled, use IFormattable or standard string processing.
        if( formatString == null || 
            ! formatString->Trim( )->StartsWith( radixCode ) )
        {
            if( dynamic_cast<IFormattable*>( argToBeFormatted ) != 0 )
                return static_cast<IFormattable*>( argToBeFormatted )->
                    ToString( formatString, provider );
            else
                return argToBeFormatted->ToString(); 
        }

        // The formatting is handled here.
        int         digitIndex = 0;
        __int64     radix;
        __int64     longToBeFormatted;
        __int64     longPositive;
        Char        outDigits[] = __gc new Char[ 64 ];
            
        // Extract the radix from the format string.
        formatString = formatString->Replace( radixCode, "" );
        try
        {
            radix = Convert::ToInt64( formatString );
        }
        catch( Exception* ex )
        {
            throw new ArgumentException( String::Format( 
                S"The radix \"{0}\" is invalid.\n", 
                    formatString ), ex );
        }

        // Verify that the radix is in the proper range.
        if( radix <2 || radix > 36 )
            throw new ArgumentException( String::Format(
                S"The radix \"{0}\" is not in the range 2..36.", 
                formatString ) );
            
        // Verify that the argument can be converted to a long integer.
        try
        {
            longToBeFormatted = 
                * static_cast<__box __int64 *>( argToBeFormatted );
        }
        catch( Exception* ex )
        {
            throw new ArgumentException( String::Format(
                S"The argument \"{0}\" cannot be " 
                S"converted to an integer value.", 
                argToBeFormatted ), ex );
        }
            
        // Extract the magnitude for conversion.
        longPositive = Math::Abs( longToBeFormatted );

        // Convert the magnitude to a digit string.
        for( digitIndex = 0; longPositive != 0 && digitIndex <= 64; 
            digitIndex++ )
        {
            outDigits[ outDigits->Length - digitIndex - 1 ] = 
                rDigits[ longPositive % radix ];
            longPositive /= radix;
        }
            
        // Add a minus sign if the argument is negative.
        if( longToBeFormatted < 0 )
            outDigits[ outDigits->Length - digitIndex++ - 1 ] = '-';

        return new String( outDigits, 
            outDigits->Length - digitIndex, digitIndex );
    } 
}; 

void ConvertToAnyRadix( Object* argToConvert, String* formatStr )
{
    AnyRadix*    provider = new AnyRadix( );
    String*      messageStr = 
        String::Format( S"{{0:{0}}}", formatStr );

    // Write the first part of the output line.
    Console::Write( S"{0,18}  {1,-6}", argToConvert, formatStr );

    // Convert the specified argument using the specified format.
    try
    {
        Object*     argArray __gc [] = { argToConvert };
        Console::WriteLine( String::Format( 
            provider, messageStr, argArray ) );
    }
    catch( Exception* ex )
    {
        // Display the exception without the stack trace.
        int     lineEnd = ex->ToString( )->IndexOf( '\n' );
        Console::WriteLine( S"{0}\n",
            ex->ToString( )->Substring( 0, lineEnd ) );
    }
} 
    
void main( )
{
    __int64     twoToThe32 = 4294967296;
    __int64     fifteenNines = 999999999999999;
        
    Console::WriteLine(
        S"This example of the IFormatProvider interface \n" 
        S"and the IFormatProvider::GetFormat( Type* ) method " 
        S"\ngenerates the following output.\n" );
    Console::WriteLine( S"{0,18} Format Result", S"Number" );
    Console::WriteLine( S"{0,18} ------ ------", S"------" );
        
    // These are valid conversions.
    ConvertToAnyRadix( __box( twoToThe32 ), S"Ra2" );
    ConvertToAnyRadix( __box( twoToThe32 ), S"Ra5" );
    ConvertToAnyRadix( __box( twoToThe32 ), S"Ra16" );
    ConvertToAnyRadix( __box( twoToThe32 ), S"Ra23" );
    ConvertToAnyRadix( __box( twoToThe32 ), S"Ra36" );
    ConvertToAnyRadix( __box( fifteenNines ), S"Ra2" );
    ConvertToAnyRadix( __box( fifteenNines ), S"Ra3" );
    ConvertToAnyRadix( __box( fifteenNines ), S"Ra8" );
    ConvertToAnyRadix( __box( fifteenNines ), S"Ra11" );
    ConvertToAnyRadix( __box( fifteenNines ), S"Ra16" );
    ConvertToAnyRadix( __box( fifteenNines ), S"Ra23" );
    ConvertToAnyRadix( __box( fifteenNines ), S"Ra36" );
    ConvertToAnyRadix( __box( fifteenNines ), S"E16" );
    ConvertToAnyRadix( __box( fifteenNines ), S"" );
        
    // These are error conditions.
    ConvertToAnyRadix( __box( fifteenNines ), S"Ra37" );
    ConvertToAnyRadix( S"ABCDEFGHIJKLM", S"Ra16" );
} 

/*
This example of the IFormatProvider interface
and the IFormatProvider::GetFormat( Type* ) method
generates the following output.

            Number Format Result
            ------ ------ ------
        4294967296  Ra2   100000000000000000000000000000000
        4294967296  Ra5   32244002423141
        4294967296  Ra16  100000000
        4294967296  Ra23  1606K7IC
        4294967296  Ra36  1Z141Z4
   999999999999999  Ra2   11100011010111111010100100110001100111111111111111
   999999999999999  Ra3   11212010201001210101011021212000
   999999999999999  Ra8   34327724461477777
   999999999999999  Ra11  26A6A3689065639
   999999999999999  Ra16  38D7EA4C67FFF
   999999999999999  Ra23  1134DIFHLMM4
   999999999999999  Ra36  9UGXNORJLR
   999999999999999  E16   9.9999999999999900E+014
   999999999999999        999999999999999
   999999999999999  Ra37  System.ArgumentException: The radix "37" is not in th
e range 2..36.

     ABCDEFGHIJKLM  Ra16  System.ArgumentException: The argument "ABCDEFGHIJKLM
" cannot be converted to an integer value. ---> System.InvalidCastException: Sp
ecified cast is not valid.
*/

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Namespace: System

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework

Assembly: Mscorlib (in Mscorlib.dll)

See Also

IFormatProvider Members | System Namespace | ICustomFormatter | IFormattable

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