Convert.ToByte Method (String, Int32)
Converts the string representation of a number in a specified base to an equivalent 8bit unsigned integer.
Assembly: mscorlib (in mscorlib.dll)
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.ByteAn 8bit unsigned integer that is equivalent to the number in value, or 0 (zero) if value is null.
Exception  Condition 

ArgumentException  fromBase is not 2, 8, 10, or 16. or value, which represents a nonbase 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 highorder 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.
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1