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Convert.ToByte Method (String, Int32)

Converts the string representation of a number in a specified base to an equivalent 8-bit unsigned integer.

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

'Declaration
Public Shared Function ToByte ( _
	value As String, _
	fromBase As Integer _
) As Byte

Parameters

value
Type: System.String

A string that contains the number to convert.

fromBase
Type: System.Int32

The base of the number in value, which must be 2, 8, 10, or 16.

Return Value

Type: System.Byte
An 8-bit unsigned integer that is equivalent to the number in value, or 0 (zero) if value is Nothing.

ExceptionCondition
ArgumentException

fromBase is not 2, 8, 10, or 16.

-or-

value, which represents a non-base 10 unsigned number, is prefixed with a negative sign.

ArgumentOutOfRangeException

value is String.Empty.

FormatException

value contains a character that is not a valid digit in the base specified by fromBase. The exception message indicates that there are no digits to convert if the first character in value is invalid; otherwise, the message indicates that value contains invalid trailing characters.

OverflowException

value, which represents a base 10 unsigned number, is prefixed with a negative sign.

-or-

value represents a number that is less than Byte.MinValue or greater than Byte.MaxValue.

If fromBase is 16, you can prefix the number specified by the value parameter with "0x" or "0X".

Because the Byte data type supports unsigned values only, the ToByte(String, Int32) method assumes that value is expressed using unsigned binary representation. In other words, all eight bits are used to represent the numeric value, and a sign bit is absent. As a result, it is possible to write code in which a signed byte value that is out of the range of the Byte data type is converted to a Byte value without the method throwing an exception. The following example converts MinValue to its hexadecimal string representation, and then calls the ToByte(String, Int32) method. Instead of throwing an exception, the method displays the message, "0x80 converts to 128."

' Create a hexadecimal value out of range of the Byte type. 
Dim value As String = SByte.MinValue.ToString("X")
' Convert it back to a number. 
Try 
   Dim number As Byte = Convert.ToByte(value, 16)
   Console.WriteLine("0x{0} converts to {1}.", value, number)
Catch e As OverflowException
   Console.WriteLine("Unable to convert '0x{0}' to a byte.", value)
End Try   

When performing binary operations or numeric conversions, it is always the responsibility of the developer to verify that a method or operator is using the appropriate numeric representation to interpret a particular value. The following example illustrates one technique for ensuring that the method does not inappropriately use unsigned binary representation when it converts a hexadecimal string representation to a Byte value. The example determines whether a value represents a signed or an unsigned integer while it is converting that value to its string representation. When the example converts the value back to a Byte value, it checks whether the original value was a signed integer. If so, and if its high-order bit is set (which indicates that the value is negative and that it uses two's complement instead of unsigned binary representation), the method throws an exception.

' Create a negative hexadecimal value out of range of the Byte type. 
Dim sourceNumber As SByte = SByte.MinValue
Dim isSigned As Boolean = Math.Sign(sourceNumber.MinValue) = -1
Dim value As String = sourceNumber.ToString("X")
Dim targetNumber As Byte 
Try
   targetNumber = Convert.ToByte(value, 16)
   If isSigned And ((targetNumber And &H80) <> 0) Then 
      Throw New OverflowException()
   Else 
      Console.WriteLine("0x{0} converts to {1}.", value, targetNumber)
   End If     
Catch e As OverflowException
   Console.WriteLine("Unable to convert '0x{0}' to an unsigned byte.", value)
End Try  
' Displays the following to the console: 
'    Unable to convert '0x80' to an unsigned byte.     

The following example alternately attempts to interpret an array of strings as the representation of binary, octal, decimal, and hexadecimal values.

Module Example
   Public Sub Main()
      Dim bases() As Integer = { 2, 8, 10, 16 }
      Dim values() As String = { "-1", "1", "08", "0F", "11" , "12", "30", _                
                                  "101", "255", "FF", "10000000", "80" }
      Dim number As Byte 
      For Each base As Integer In bases
         Console.WriteLine("Base {0}:", base)
         For Each value As String In values
            Try
               number = Convert.ToByte(value, base)
               Console.WriteLine("   Converted '{0}' to {1}.", value, number)
            Catch e As FormatException
               Console.WriteLine("   '{0}' is not in the correct format for a base {1} conversion.", _
                                 value, base)
            Catch e As OverflowException
               Console.WriteLine("   '{0}' is outside the range of the Byte type.", value)
            Catch e As ArgumentException
               Console.WriteLine("   '{0}' is invalid in base {1}.", value, base)
            End Try    
         Next                                  
      Next  
   End Sub 
End Module 
' The example displays the following output: 
'    Base 2: 
'       '-1' is invalid in base 2. 
'       Converted '1' to 1. 
'       '08' is not in the correct format for a base 2 conversion. 
'       '0F' is not in the correct format for a base 2 conversion. 
'       Converted '11' to 3. 
'       '12' is not in the correct format for a base 2 conversion. 
'       '30' is not in the correct format for a base 2 conversion. 
'       Converted '101' to 5. 
'       '255' is not in the correct format for a base 2 conversion. 
'       'FF' is not in the correct format for a base 2 conversion. 
'       Converted '10000000' to 128. 
'       '80' is not in the correct format for a base 2 conversion. 
'    Base 8: 
'       '-1' is invalid in base 8. 
'       Converted '1' to 1. 
'       '08' is not in the correct format for a base 8 conversion. 
'       '0F' is not in the correct format for a base 8 conversion. 
'       Converted '11' to 9. 
'       Converted '12' to 10. 
'       Converted '30' to 24. 
'       Converted '101' to 65. 
'       Converted '255' to 173. 
'       'FF' is not in the correct format for a base 8 conversion. 
'       '10000000' is outside the range of the Byte type. 
'       '80' is not in the correct format for a base 8 conversion. 
'    Base 10: 
'       '-1' is outside the range of the Byte type. 
'       Converted '1' to 1. 
'       Converted '08' to 8. 
'       '0F' is not in the correct format for a base 10 conversion. 
'       Converted '11' to 11. 
'       Converted '12' to 12. 
'       Converted '30' to 30. 
'       Converted '101' to 101. 
'       Converted '255' to 255. 
'       'FF' is not in the correct format for a base 10 conversion. 
'       '10000000' is outside the range of the Byte type. 
'       Converted '80' to 80. 
'    Base 16: 
'       '-1' is invalid in base 16. 
'       Converted '1' to 1. 
'       Converted '08' to 8. 
'       Converted '0F' to 15. 
'       Converted '11' to 17. 
'       Converted '12' to 18. 
'       Converted '30' to 48. 
'       '101' is outside the range of the Byte type. 
'       '255' is outside the range of the Byte type. 
'       Converted 'FF' to 255. 
'       '10000000' is outside the range of the Byte type. 
'       Converted '80' to 128.

.NET Framework

Supported in: 4.6, 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

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

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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