Convert.ToUInt64 Method (String, Int32)
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Converts the string representation of a number in a specified base to an equivalent 64-bit unsigned integer.
Assembly: mscorlib (in mscorlib.dll)
'Declaration <CLSCompliantAttribute(False)> _ Public Shared Function ToUInt64 ( _ value As String, _ fromBase As Integer _ ) As ULong
Parameters
- value
- Type: System.String
A string containing a number.
- fromBase
- Type: System.Int32
The base of the number in value, which must be 2, 8, 10, or 16.
Return Value
Type: System.UInt64A 64-bit unsigned integer equivalent to the number in value.
-or-
Zero if value is Nothing.
| Exception | Condition |
|---|---|
| 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. |
| 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 non-base 10 unsigned number, is prefixed with a negative sign. -or- The return value is less than UInt64.MinValue or larger than UInt64.MaxValue. |
If fromBase is 16, you can prefix the number specified by the value parameter with "0x" or "0X".
Because the UInt64 data type supports unsigned values only, the ToUInt64(String, Int32) method assumes that value is expressed using unsigned binary representation. In other words, all 64 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 long integer value that is out of the range of the UInt64 data type is converted to a UInt64 value without the method throwing an exception. The following example converts MinValue to its hexadecimal string representation and then calls the ToUInt64(String, Int32) method. Rather than throwing an exception, the method displays the message, "0x8000000000000000 converts to 9223372036854775808."
' Create a hexadecimal value out of range of the UInt64 type. Dim value As String = Convert.ToString(Long.MinValue, 16) ' Convert it back to a number. Try Dim number As UInt64 = Convert.ToUInt64(value, 16) outputBlock.Text += String.Format("0x{0} converts to {1}.", value, number) & vbCrLf Catch e As OverflowException outputBlock.Text += String.Format("Unable to convert '0x{0}' to an unsigned long integer.", _ value) & vbCrLf End Try
When performing binary operations or numeric conversions, it is always the responsibility of the developer to verify that a method or operator uses the appropriate numeric representation to interpret a particular value. The following example illustrates one technique for ensuring that the method does not inappropriately use binary representation to interpret a value that uses two's complement representation when converting a hexadecimal string to a UInt64 value. It determines whether a value represents a signed or an unsigned integer at the same time that it converts that value to its string representation. When converting the value to a UInt64 value, the example checks whether the original value was a signed integer. If so, and its high-order bit is set (which indicates that the original value was negative), the method throws an exception.
' Create a negative hexadecimal value out of range of the UInt64 type. Dim sourceNumber As Long = Long.MinValue Dim isSigned As Boolean = Math.Sign(Long.MinValue) = -1 Dim value As String = Convert.ToString(sourceNumber, 16) Dim targetNumber As UInt64 Try targetNumber = Convert.ToUInt64(value, 16) If isSigned And ((targetNumber And &H8000000000000000UL) <> 0) Then Throw New OverflowException() Else outputBlock.Text += String.Format("0x{0} converts to {1}.", value, targetNumber) & vbCrLf End If Catch e As OverflowException outputBlock.Text += String.Format("Unable to convert '0x{0}' to an unsigned long integer.", _ value) & vbCrLf End Try ' Displays the following: ' Unable to convert '0x8000' to an unsigned long integer.