Convert.ToInt64 Method (String, Int32)


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

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

public static long ToInt64(
	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.Int64

A 64-bit signed 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 signed 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 signed number, is prefixed with a negative sign.


value represents a number that is less than Int64.MinValue or greater than Int64.MaxValue.

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

Because the negative sign is not supported for non-base 10 numeric representations, the ToInt64(String, Int32) method assumes that negative numbers use two’s complement representation. In other words, the method always interprets the highest-order binary bit of a long integer (bit 63) as its sign bit. As a result, it is possible to write code in which a non-base 10 number that is out of the range of the Int64 data type is converted to an Int64 value without the method throwing an exception. The following example converts MaxValue to its hexadecimal string representation, and then calls the ToInt64(String, Int32) method. Instead of throwing an exception, the method displays the message, "0xFFFFFFFFFFFFFFFF converts to -1."

// Create a hexadecimal value out of range of the long type.
string value = ulong.MaxValue.ToString("X");
// Use Convert.ToInt64 to convert it back to a number.
   long number = Convert.ToInt64(value, 16);
   Console.WriteLine("0x{0} converts to {1}.", value, number);
catch (OverflowException)
   Console.WriteLine("Unable to convert '0x{0}' to a long integer.", value);

When performing binary operations or numeric conversions, it is always the responsibility of the developer to verify that a method is using the appropriate numeric representation to interpret a particular value. As the following example illustrates, you can ensure that the method handles overflows appropriately by first determining whether a value represents an unsigned or a signed type when converting it to its hexadecimal string representation. Throw an exception if the original value was an unsigned type but the conversion back to an integer yields a value whose sign bit is on.

// Create a negative hexadecimal value out of range of the Byte type.
ulong sourceNumber = ulong.MaxValue;
bool isSigned = Math.Sign(Convert.ToDouble(sourceNumber.GetType().GetField("MinValue").GetValue(null))) == -1;
string value = sourceNumber.ToString("X");
long targetNumber;
   targetNumber = Convert.ToInt64(value, 16);
   if (! isSigned && ((targetNumber & 0x80000000) != 0))
      throw new OverflowException();
      Console.WriteLine("0x{0} converts to {1}.", value, targetNumber);
catch (OverflowException)
   Console.WriteLine("Unable to convert '0x{0}' to a long integer.", value);
// Displays the following to the console:
//    Unable to convert '0xFFFFFFFFFFFFFFFF' to a long integer.     

The following example attempts to interpret each element in a string array as a hexadecimal string and convert it to a long integer.

using System;

public class Example
   public static void Main()
      string[] hexStrings = { "8000000000000000", "0FFFFFFFFFFFFFFF", 
                              "f0000000000001000", "00A30", "D", "-13", "GAD" };
      foreach (string hexString in hexStrings)
         try {
            long number = Convert.ToInt64(hexString, 16);
            Console.WriteLine("Converted '{0}' to {1:N0}.", hexString, number);
         catch (FormatException) {
            Console.WriteLine("'{0}' is not in the correct format for a hexadecimal number.",
         catch (OverflowException) {
            Console.WriteLine("'{0}' is outside the range of an Int64.", hexString);
         catch (ArgumentException) {
            Console.WriteLine("'{0}' is invalid in base 16.", hexString);
// The example displays the following output:
//       Converted '8000000000000000' to -9,223,372,036,854,775,808.
//       Converted '0FFFFFFFFFFFFFFF' to 1,152,921,504,606,846,975.
//       'f0000000000001000' is outside the range of an Int64.
//       Converted '00A30' to 2,608.
//       Converted 'D' to 13.
//       '-13' is invalid in base 16.
//       'GAD' is not in the correct format for a hexadecimal number.

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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