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Convert.ToUInt64 Method (String, Int32)

Converts the string representation of a number in a specified base to an equivalent 64-bit unsigned integer.

This method is not CLS-compliant.  

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

public static ulong ToUInt64 (
	string value,
	int fromBase
/** @attribute CLSCompliantAttribute(false) */ 
public static UInt64 ToUInt64 (
	String value, 
	int fromBase
public static function ToUInt64 (
	value : String, 
	fromBase : int
) : ulong
Not applicable.



A string containing a number.


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

Return Value

A 64-bit unsigned integer equivalent to the number in value. -or- Zero if value is a null reference (Nothing in Visual Basic).

Exception typeCondition


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


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


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.


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


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.”

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.

Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0