Updated: May 2009
Represents a double-precision floating-point number.
Assembly: mscorlib (in mscorlib.dll)
The value type represents a double-precision 64-bit number with values ranging from negative 1.79769313486232e308 to positive 1.79769313486232e308, as well as positive or negative zero, PositiveInfinity, NegativeInfinity, and Not-a-Number (NaN).
complies with the IEC 60559:1989 (IEEE 754) standard for binary floating-point arithmetic.
provides methods to compare instances of this type, convert the value of an instance to its string representation, and convert the string representation of a number to an instance of this type. For information about how format specification codes control the string representation of value types, see Formatting Overview, Standard Numeric Format Strings, and Custom Numeric Format Strings.
Using Floating-Point Numbers
When performing binary operations, if one of the operands is a , then the other operand is required to be an integral type or a floating-point type ( or Single). Prior to performing the operation, if the other operand is not a , it is converted to , and the operation is performed using at least range and precision. If the operation produces a numeric result, the type of the result is .
The floating-point operators, including the assignment operators, do not throw exceptions. Instead, in exceptional situations the result of a floating-point operation is zero, infinity, or NaN, as described below:
If the result of a floating-point operation is too small for the destination format, the result of the operation is zero.
If the magnitude of the result of a floating-point operation is too large for the destination format, the result of the operation is PositiveInfinity or NegativeInfinity, as appropriate for the sign of the result.
If a floating-point operation is invalid, the result of the operation is NaN.
Floating-Point Values and Loss of Precision
Remember that a floating-point number can only approximate a decimal number, and that the precision of a floating-point number determines how accurately that number approximates a decimal number. By default, a value contains 15 decimal digits of precision, although a maximum of 17 digits is maintained internally. The precision of a floating-point number has several consequences:
Two floating-point numbers that appear equal for a particular precision might not compare equal because their least significant digits are different.
A mathematical or comparison operation that uses a floating-point number might not yield the same result if a decimal number is used because the floating-point number might not exactly approximate the decimal number.
A value might not roundtrip if a floating-point number is involved. A value is said to roundtrip if an operation converts an original floating-point number to another form, an inverse operation transforms the converted form back to a floating-point number, and the final floating-point number is equal to the original floating-point number. The roundtrip might fail because one or more least significant digits are lost or changed in a conversion.
In addition, the loss of precision that results from arithmetic, assignment, and parsing operations with values may differ by platform. For example, the result of assigning a literal value may differ in the 32-bit and 64-bit versions of the .NET Framework. The following example illustrates this difference when the literal value -4.42330604244772E-305 and a variable whose value is -4.42330604244772E-305 are assigned to a variable. Note that the result of the Parse(String) method in this case does not suffer from a loss of precision.
Such differences by processor architecture are most likely to occur for values that are less than Epsilon. The following example attempts to parse the string "4.9E-324", which is a value slightly less than Epsilon. As the output from the example shows, it is rounded up to Epsilon on 32-bit platforms and rounded down to 0.0 on 64-bit platforms.
If an application requires identical behavior across platforms, it should be compiled with the /platform:x86 switch so that it always runs on the 32-bit runtime regardless of processor architecture.
All members of this type are thread safe. Members that appear to modify instance state actually return a new instance initialized with the new value. As with any other type, reading and writing to a shared variable that contains an instance of this type must be protected by a lock to guarantee thread safety.
Assigning an instance of this type is not thread safe on all hardware platforms because the binary representation of that instance might be too large to assign in a single atomic operation.
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.