Convert.ToInt64 Method (String, Int32)

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
public static long ToInt64 (
	String value, 
	int fromBase
public static function ToInt64 (
	value : String, 
	fromBase : int
) : long
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 signed 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 signed 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 signed number, is prefixed with a negative sign.


The return value is less than Int64.MinValue or larger 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. Rather than throwing an exception, the method displays the message, "0xFFFFFFFFFFFFFFFF converts to -1."

When performing binary operations or numeric conversions, it is always the responsibility of the developer to verify that a method uses 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. Then, throw an exception if the conversion back to an integer yields a value whose sign bit is on but whose original value was an unsigned type.

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

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