System Namespace


.NET Framework Class Library
IConvertible Interface

Updated: March 2009

Defines methods that convert the value of the implementing reference or value type to a common language runtime type that has an equivalent value.

This API is not CLS-compliant. 

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)
Syntax
Visual Basic (Declaration) 
<ComVisibleAttribute(True)> _
<CLSCompliantAttribute(False)> _
Public Interface IConvertible
Visual Basic (Usage) 
Dim instance As IConvertible
C# 
[ComVisibleAttribute(true)]
[CLSCompliantAttribute(false)]
public interface IConvertible
Visual C++ 
[ComVisibleAttribute(true)]
[CLSCompliantAttribute(false)]
public interface class IConvertible
JScript 
public interface IConvertible
Remarks

This interface provides methods to convert the value of an instance of an implementing type to a common language runtime type that has an equivalent value. The common language runtime types are Boolean, SByte, Byte, Int16, UInt16, Int32, UInt32, Int64, UInt64, Single, Double, Decimal, DateTime, Char, and String.

If there is no meaningful conversion to a common language runtime type, then a particular interface method implementation throws InvalidCastException. For example, if this interface is implemented on a Boolean type, the implementation of the ToDateTime method throws an exception because there is no meaningful DateTime equivalent to a Boolean type.

The common language runtime typically exposes the IConvertible interface through the Convert class. The common language runtime also uses the IConvertible interface internally, in explicit interface implementations, to simplify the code used to support conversions in the Convert class and basic common language runtime types.

In addition to the IConvertible interface, the .NET Framework provides classes called type converters for converting user-defined data types to other data types. For more information, see the Generalized Type Conversion topic.

Notes to Implementers:

If you implement the IConvertible interface, your implementation will be called automatically by the Convert..::.ChangeType(Object, Type) method if the Object parameter is an instance of your implementing type and the Type parameter is a common language runtime type.

Most conversion methods have a parameter of type IFormatProvider. Most commonly, this parameter represents either the current culture (CultureInfo..::.CurrentCulture) or a specific culture. Generally, the IConvertible implementations of the base types ignore this parameter. However, you can choose whether to use it in your code.
Examples

The following code sample demonstrates an implementation of IConvertible for a Complex number class, allowing it to be cast first as a Double and then calling the static Convert members on that Double.

Visual Basic 
Imports System

Module Module1

    Public Class Complex
        Implements IConvertible
        Private x As Double
        Private y As Double


        Public Sub New(ByVal x As Double, ByVal y As Double)
            Me.x = x
            Me.y = y
        End Sub 'New


        Public Function GetTypeCode() As TypeCode Implements IConvertible.GetTypeCode
            Return TypeCode.Object
        End Function


        Function ToBoolean(ByVal provider As IFormatProvider) As Boolean Implements IConvertible.ToBoolean
            If x <> 0 Or y <> 0 Then
                Return True
            Else
                Return False
            End If
        End Function

        Function GetDoubleValue() As Double
            Return Math.Sqrt((x * x + y * y))
        End Function


        Function ToByte(ByVal provider As IFormatProvider) As Byte Implements IConvertible.ToByte
            Return Convert.ToByte(GetDoubleValue())
        End Function


        Function ToChar(ByVal provider As IFormatProvider) As Char Implements IConvertible.ToChar
            Return Convert.ToChar(GetDoubleValue())
        End Function


        Function ToDateTime(ByVal provider As IFormatProvider) As DateTime Implements IConvertible.ToDateTime
            Return Convert.ToDateTime(GetDoubleValue())
        End Function


        Function ToDecimal(ByVal provider As IFormatProvider) As Decimal Implements IConvertible.ToDecimal
            Return Convert.ToDecimal(GetDoubleValue())
        End Function


        Function ToDouble(ByVal provider As IFormatProvider) As Double Implements IConvertible.ToDouble
            Return GetDoubleValue()
        End Function


        Function ToInt16(ByVal provider As IFormatProvider) As Short Implements IConvertible.ToInt16
            Return Convert.ToInt16(GetDoubleValue())
        End Function


        Function ToInt32(ByVal provider As IFormatProvider) As Integer Implements IConvertible.ToInt32
            Return Convert.ToInt32(GetDoubleValue())
        End Function


        Function ToInt64(ByVal provider As IFormatProvider) As Long Implements IConvertible.ToInt64
            Return Convert.ToInt64(GetDoubleValue())
        End Function


        Function ToSByte(ByVal provider As IFormatProvider) As SByte Implements IConvertible.ToSByte
            Return Convert.ToSByte(GetDoubleValue())
        End Function


        Function ToSingle(ByVal provider As IFormatProvider) As Single Implements IConvertible.ToSingle
            Return Convert.ToSingle(GetDoubleValue())
        End Function


        Overloads Function ToString(ByVal provider As IFormatProvider) As String Implements IConvertible.ToString
            Return "( " + x.ToString() + " , " + y.ToString() + " )"
        End Function


        Function ToType(ByVal conversionType As Type, ByVal provider As IFormatProvider) As Object Implements IConvertible.ToType
            Return Convert.ChangeType(GetDoubleValue(), conversionType)
        End Function


        Function ToUInt16(ByVal provider As IFormatProvider) As UInt16 Implements IConvertible.ToUInt16
            Return Convert.ToUInt16(GetDoubleValue())
        End Function


        Function ToUInt32(ByVal provider As IFormatProvider) As UInt32 Implements IConvertible.ToUInt32
            Return Convert.ToUInt32(GetDoubleValue())
        End Function


        Function ToUInt64(ByVal provider As IFormatProvider) As UInt64 Implements IConvertible.ToUInt64
            Return Convert.ToUInt64(GetDoubleValue())
        End Function

    End Class


    Sub Main()
        Dim testComplex As New Complex(4, 7)

        WriteObjectInfo(testComplex)
        WriteObjectInfo(Convert.ToBoolean(testComplex))
        WriteObjectInfo(Convert.ToDecimal(testComplex))
        WriteObjectInfo(Convert.ToString(testComplex))

    End Sub

    Sub WriteObjectInfo(ByVal testObject As Object)
        Dim typeCode As TypeCode = Type.GetTypeCode(testObject.GetType())

        Select Case typeCode
            Case typeCode.Boolean
                Console.WriteLine("Boolean: {0}", testObject)

            Case typeCode.Double
                Console.WriteLine("Double: {0}", testObject)

            Case Else
                Console.WriteLine("{0}: {1}", typeCode.ToString(), testObject)
        End Select
    End Sub

End Module
C# 
using System;

namespace ConsoleApplication2
{

    /// Class that implements IConvertible
    class Complex : IConvertible
    {
        double    x;
        double    y;

        public Complex(double x, double y)
        {
            this.x = x;
            this.y = y;
        }

        public TypeCode GetTypeCode()
        {
            return TypeCode.Object;
        }

        bool IConvertible.ToBoolean(IFormatProvider provider)
        {
            if(    (x != 0.0) || (y != 0.0) )
                return true;
            else
                return false;
        }

        double GetDoubleValue()
        {
            return Math.Sqrt(x*x + y*y);
        }

        byte IConvertible.ToByte(IFormatProvider provider)
        {
            return Convert.ToByte(GetDoubleValue());
        }

        char IConvertible.ToChar(IFormatProvider provider)
        {
            return Convert.ToChar(GetDoubleValue());
        }

        DateTime IConvertible.ToDateTime(IFormatProvider provider)
        {
            return Convert.ToDateTime(GetDoubleValue());
        }

        decimal IConvertible.ToDecimal(IFormatProvider provider)
        {
            return Convert.ToDecimal(GetDoubleValue());
        }

        double IConvertible.ToDouble(IFormatProvider provider)
        {
            return GetDoubleValue();
        }

        short IConvertible.ToInt16(IFormatProvider provider)
        {
            return Convert.ToInt16(GetDoubleValue());
        }

        int IConvertible.ToInt32(IFormatProvider provider)
        {
            return Convert.ToInt32(GetDoubleValue());
        }

        long IConvertible.ToInt64(IFormatProvider provider)
        {
            return Convert.ToInt64(GetDoubleValue());
        }

        sbyte IConvertible.ToSByte(IFormatProvider provider)
        {
            return Convert.ToSByte(GetDoubleValue());
        }

        float IConvertible.ToSingle(IFormatProvider provider)
        {
            return Convert.ToSingle(GetDoubleValue());
        }

        string IConvertible.ToString(IFormatProvider provider)
        {
            return "( " + x.ToString() + " , " + y.ToString() + " )";
        }

        object IConvertible.ToType(Type conversionType, IFormatProvider provider)
        {
            return Convert.ChangeType(GetDoubleValue(),conversionType);
        }

        ushort IConvertible.ToUInt16(IFormatProvider provider)
        {
            return Convert.ToUInt16(GetDoubleValue());
        }

        uint IConvertible.ToUInt32(IFormatProvider provider)
        {
            return Convert.ToUInt32(GetDoubleValue());
        }

        ulong IConvertible.ToUInt64(IFormatProvider provider)
        {
            return Convert.ToUInt64(GetDoubleValue());
        }

    }

    /// <summary>
    /// Summary description for Class1.
    /// </summary>
    class Class1
    {
        static void Main(string[] args)
        {

            Complex        testComplex = new Complex(4,7);

            WriteObjectInfo(testComplex);
            WriteObjectInfo(Convert.ToBoolean(testComplex));
            WriteObjectInfo(Convert.ToDecimal(testComplex));
            WriteObjectInfo(Convert.ToString(testComplex));

        }

        static void WriteObjectInfo(object testObject)
        {
            TypeCode    typeCode = Type.GetTypeCode( testObject.GetType() );

            switch( typeCode )
            {
                case TypeCode.Boolean:
                    Console.WriteLine("Boolean: {0}", testObject);
                    break;

                case TypeCode.Double:
                    Console.WriteLine("Double: {0}", testObject);
                    break;
                                
                default:
                    Console.WriteLine("{0}: {1}", typeCode.ToString(), testObject);
                    break;
            }
        }
    }
}
Visual C++ 
#using <System.dll>

using namespace System;

/// Class that implements IConvertible
ref class Complex: public IConvertible
{
private:
   double x;
   double y;

public:
   Complex( double x, double y )
   {
      this->x = x;
      this->y = y;
   }

   virtual TypeCode GetTypeCode()
   {
      return TypeCode::Object;
   }

   virtual bool ToBoolean( IFormatProvider^ /*provider*/ ) = IConvertible::ToBoolean
   {
      if ( (x != 0.0) || (y != 0.0) )
            return true;
      else
            return false;
   }

   double GetDoubleValue()
   {
      return Math::Sqrt( x * x + y * y );
   }

   virtual Byte ToByte( IFormatProvider^ /*provider*/ ) = IConvertible::ToByte
   {
      return Convert::ToByte( GetDoubleValue() );
   }

   virtual Char ToChar( IFormatProvider^ /*provider*/ ) = IConvertible::ToChar
   {
      return Convert::ToChar( GetDoubleValue() );
   }

   virtual DateTime ToDateTime( IFormatProvider^ /*provider*/ ) = IConvertible::ToDateTime
   {
      return Convert::ToDateTime( GetDoubleValue() );
   }

   virtual Decimal ToDecimal( IFormatProvider^ /*provider*/ ) = IConvertible::ToDecimal
   {
      return Convert::ToDecimal( GetDoubleValue() );
   }

   virtual double ToDouble( IFormatProvider^ /*provider*/ ) = IConvertible::ToDouble
   {
      return GetDoubleValue();
   }

   virtual short ToInt16( IFormatProvider^ /*provider*/ ) = IConvertible::ToInt16
   {
      return Convert::ToInt16( GetDoubleValue() );
   }

   virtual int ToInt32( IFormatProvider^ /*provider*/ ) = IConvertible::ToInt32
   {
      return Convert::ToInt32( GetDoubleValue() );
   }

   virtual Int64 ToInt64( IFormatProvider^ /*provider*/ ) = IConvertible::ToInt64
   {
      return Convert::ToInt64( GetDoubleValue() );
   }

   virtual signed char ToSByte( IFormatProvider^ /*provider*/ ) = IConvertible::ToSByte
   {
      return Convert::ToSByte( GetDoubleValue() );
   }

   virtual float ToSingle( IFormatProvider^ /*provider*/ ) = IConvertible::ToSingle
   {
      return Convert::ToSingle( GetDoubleValue() );
   }

   virtual String^ ToString( IFormatProvider^ /*provider*/ ) = IConvertible::ToString
   {
      return String::Format( "( {0} , {1} )", x, y );
   }

   virtual Object^ ToType( Type^ conversionType, IFormatProvider^ /*provider*/ ) = IConvertible::ToType
   {
      return Convert::ChangeType( GetDoubleValue(), conversionType );
   }

   virtual UInt16 ToUInt16( IFormatProvider^ /*provider*/ ) = IConvertible::ToUInt16
   {
      return Convert::ToUInt16( GetDoubleValue() );
   }

   virtual UInt32 ToUInt32( IFormatProvider^ /*provider*/ ) = IConvertible::ToUInt32
   {
      return Convert::ToUInt32( GetDoubleValue() );
   }

   virtual UInt64 ToUInt64( IFormatProvider^ /*provider*/ ) = IConvertible::ToUInt64
   {
      return Convert::ToUInt64( GetDoubleValue() );
   }

};

void WriteObjectInfo( Object^ testObject )
{
   TypeCode typeCode = Type::GetTypeCode( testObject->GetType() );
   switch ( typeCode )
   {
      case TypeCode::Boolean:
         Console::WriteLine( "Boolean: {0}", testObject );
         break;

      case TypeCode::Double:
         Console::WriteLine( "Double: {0}", testObject );
         break;

      default:
         Console::WriteLine( "{0}: {1}", typeCode, testObject );
         break;
   }
}

int main()
{
   Complex^ testComplex = gcnew Complex( 4,7 );
   WriteObjectInfo( testComplex );
   WriteObjectInfo( Convert::ToBoolean( testComplex ) );
   WriteObjectInfo( Convert::ToDecimal( testComplex ) );
   WriteObjectInfo( Convert::ToString( testComplex ) );
}
Platforms

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.
Version Information

.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
See Also

Reference

IConvertible Members
System Namespace
Change History

Date

History

Reason

March 2009

Added the Notes for Implementors section.

Information enhancement.

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