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In computer programming, null is a special value for a pointer (or other kind of reference) used to signify that the pointer's target is intentionally not a valid data element. Often, 0 (zero) is used as the null value, as most operating systems consider it an error to try to access such a low memory address. ("Null" also happens to be the German word for zero.)
However, null is used in many other computing disciplines (often interchangeably with nul or nil):
:/dev/null is a virtual device on UNIX systems that does nothing with its input and produces no output. The NUL device has similar functionality on DOS and Windows.The ASCII character code with code value 0 is called a null character, conventionally denoted as NUL. Also, Unicode character 0000 is Null, denoted, like ASCII convention, as NUL.
In some programming languages, such as LISP or Pascal, the designation is called nil. In C and similar languages it is called NULL.
In many disciplines, the concept of null allows a three-valued logic, with null indicating 'unknown'.
Note that this is not the same as the definition of nothingNothing is the lack or absence of anything. Nothing" and " zero" are closely related but not identical concepts. The term "nothing" is rarely used mathematically, though it could be said that a set contains nothing if and only if it is the empty set, in w because it is more related to computer science.
See also: null setIn measure theory, a null set is a set that it is negligible for the purposes of the measure in question. Which sets are null will depend on the measure considered. Thus one may speak of m-null sets for a given measure m. The term "null set" is sometimes, null resultGenerally, a null result is a result which is null (that is, nothing). In science, it can be an experimental outcome that does not show an effect which is otherwise expected. Statistics In statistics, specifically, a null result occurs when there are non-
In cryptography, especially classical cryptography, a null is a ciphertext symbol which has no actual meaning, but is intended to confuse the cryptanalyst. Typically, a null will be a character which decrypts to obvious nonsense at the end of an otherwise intelligible phrase. In a null cipherA null cipher is an ancient form of encryption where the plaintext is mixed with a large amount of non-cipher material. It would today be regarded as a simple form of steganography. Null ciphers can also be used to hide ciphertext, as part of a more compl, most of the characters may be nulls.
In radio electronics, a null is an area or vector at which the signal from two or more of the antenna element s in an antenna system cancels out almost entirely.
This can be an advantage, as nulls in the horizontal plane can be used to protect other transmitters from interference. If not carefully planned however, nulls can affect the receivability of a signal in any given place. Null fill in the vertical plane is used to prevent this.
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