Convert.ToUInt64 Method (String, Int32)


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

This API is not CLS-compliant.

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

public static ulong ToUInt64(
	string value,
	int fromBase


Type: System.String

A string that contains the number to convert.

Type: System.Int32

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

Return Value

Type: System.UInt64

A 64-bit unsigned integer that is equivalent to the number in value, or 0 (zero) if value is null.

Exception Condition

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


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


value is String.Empty.


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.


value represents a number that is less than UInt64.MinValue or greater 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. Instead of throwing an exception, the method displays the message, "0x8000000000000000 converts to 9223372036854775808."

// Create a hexadecimal value out of range of the UInt64 type.
string value = Convert.ToString(Int64.MinValue, 16);
// Convert it back to a number.
   UInt64 number = Convert.ToUInt64(value, 16);
   Console.WriteLine("0x{0} converts to {1}.", value, number);
catch (OverflowException)
   Console.WriteLine("Unable to convert '0x{0}' to an unsigned long integer.", 

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 binary representation to interpret a value that uses two's complement representation when converting a hexadecimal string to a UInt64 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 to a UInt64 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 original value was negative), the method throws an exception.

// Create a negative hexadecimal value out of range of the UInt64 type.
long sourceNumber = Int64.MinValue;
bool isSigned = Math.Sign((long)sourceNumber.GetType().GetField("MinValue").GetValue(null)) == -1;
string value = Convert.ToString(sourceNumber, 16);
UInt64 targetNumber;
   targetNumber = Convert.ToUInt64(value, 16);
   if (isSigned && ((targetNumber & 0x8000000000000000) != 0))
      throw new OverflowException();
      Console.WriteLine("0x{0} converts to {1}.", value, targetNumber);
catch (OverflowException)
   Console.WriteLine("Unable to convert '0x{0}' to an unsigned long integer.", 
// Displays the following to the console:
//    Unable to convert '0x8000000000000000' to an unsigned long integer.     

The following example attempts to interpret each element in an array of numeric strings as a hexadecimal value and to convert it to an unsigned long integer.

using System;

public class Example
   public static void Main()
      string[] hexStrings = { "8000000000000000", "0FFFFFFFFFFFFFFF",
                              "F000000000000000", "00A3000000000000",
                              "D", "-13", "9AC61", "GAD",
                              "FFFFFFFFFFFFFFFFF" };

      foreach (string hexString in hexStrings)
         Console.Write("{0,-18}  -->  ", hexString);
         try {
            ulong number = Convert.ToUInt64(hexString, 16);
            Console.WriteLine("{0,26:N0}", number);
         catch (FormatException) {
            Console.WriteLine("{0,26}", "Bad Format");
         catch (OverflowException) {
            Console.WriteLine("{0,26}", "Numeric Overflow");
         catch (ArgumentException) {
            Console.WriteLine("{0,26}", "Invalid in Base 16");
// The example displays the following output:
//    8000000000000000    -->   9,223,372,036,854,775,808
//    0FFFFFFFFFFFFFFF    -->   1,152,921,504,606,846,975
//    F000000000000000    -->  17,293,822,569,102,704,640
//    00A3000000000000    -->      45,880,421,203,836,928
//    D                   -->                          13
//    -13                 -->          Invalid in Base 16
//    9AC61               -->                     633,953
//    GAD                 -->                  Bad Format
//    FFFFFFFFFFFFFFFFF   -->            Numeric Overflow

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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