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Information about Null (computer)

Null has several meanings in computer programming.

Null pointer or null reference
  • Null is a special pointer value (or other kind of object reference) used to signify that a pointer intentionally does not point to (or refer to) an object. Such a pointer is called a null pointer. Many implementations use a value of 0 (all bits zero) to represent the null pointer, as this is at the bottom of the address space of most CPUs (e.g., the INMOS Transputer has a signed address space and uses the most negative value). Many operating systems generate an exception when an attempt is made to access this memory address. Some languages use other nomenclature for such a pointer, e.g., Pascal uses nil.
Null value
  • In many disciplines, the concept of null allows a three-valued logic, with null indicating "unknown value". The SQL database query language uses Null in this way, as do Visual Basic and its derivatives. In this model, an expression that depends on the value of a Null operand will evaluate to Null (VB) or "unknown" (SQL). So, for any A, the expressions "A = Null" and "A <> Null" are neither true nor false. However, the boolean operation "A and False" produces false, and similarly "A or True" is true, even when A is Null, because these expressions do not depend on the value of A. (Some SQL implementations may consider A = Null to be "true" if A is Null; see Null (SQL)).
Null device
  • In UNIX systems, (also referred to as the black hole or bit bucket) is a special file that delivers no input when read from and discards all output when written to. The NUL device has similar functionality in DOS and Windows.
  • In Windows XP, null device is a file in system32/drivers, named Null.sys, the size is 2944 bytes. It can be seen in device manager, non-plug-and-play group.
Null character
  • In the C0 control code set defined in the ISO 646, ASCII, and Unicode character set standards, code value 0 is the null character (NUL). Most programming languages provide syntax for representing this character as a literal value (e.g., Pascal uses chr(0) or #0, C and its many derivatives use '\0').
  • In some programming languages, the null character denotes the end of a character string. Such strings that are encoded with the ASCII character set are sometimes referred to as ASCIIZ or ASCIZ strings — the "Z" indicating that the string ends with a "Zero", or null character.
Null variant
  • Some programming languages (such as LISP; Ruby; and Pascal, Delphi, and other languages based on Pascal) use nil for the null variant, which can sometimes lead to confusing errors if null is accidentally used instead of nil.
Null script




Null Account
  • On Certain forums and other internet sites user accounts may suddenly show up as "null" and reset all the users settings. Generally it will destroy the users ability to add new content to the site and is usually fixed within a short period of time. A person who's account goes to "null" is commonly said to have been attacked by the "null monster" a fictional character used to describe the "null" phenomenon.
Null is an English word meaning 'nothing' or without value or consequence. It is derived from the Latin word nullus meaning 'none'.

Null may refer to:

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Computer programming (often shortened to programming or coding) is the process of writing, testing, and maintaining the source code of computer programs. The source code is written in a programming language.
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pointer is a programming language data type whose value refers directly to (or “points to”) another value stored elsewhere in the computer memory using its address. Obtaining the value to which a pointer refers is called dereferencing the pointer.
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reference is an object containing information which refers to data stored elsewhere, as opposed to containing the data itself. Accessing the value referred to by a reference is called dereferencing it.
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central processing unit (CPU), or sometimes simply processor, is the component in a digital computer capable of executing a program.(Knott 1974) It interprets computer program instructions and processes data.
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The INMOS transputer (the all-lowercase "transputer" was the official written form) was a pioneering concurrent computing microprocessor design of the 1980s from INMOS, a British semiconductor company based in Bristol.
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An operating system (OS) is the software that manages the sharing of the resources of a computer. An operating system processes system data and user input, and responds by allocating and managing tasks and internal system resources as a service to users and programs of the
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Pascal is a structured imperative computer programming language, developed in 1970 by Niklaus Wirth as a language particularly suitable for structured programming. A derivative known as Object Pascal was designed for object oriented programming.
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Null is an English word meaning 'nothing' or without value or consequence. It is derived from the Latin word nullus meaning 'none'.

Null may refer to:

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Multi-valued logics are logical calculi in which there are more than two truth values. Traditionally, logical calculi are two-valued—that is, there are only two possible truth values (i.e. truth and falsehood) for any proposition to take.
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SQL
Paradigm: multi-paradigm
Appeared in: 1974
Designed by: Donald D. Chamberlin and Raymond F. Boyce
Developer: IBM
Latest release: SQL:2003/ 2003
Typing discipline: static, strong
Major implementations: Many
SQL
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Visual Basic

Paradigm: Event-driven
Developer: Microsoft
Typing discipline: Static, strong
Influenced by: QuickBASIC
Influenced: Visual Basic .NET
OS: Microsoft Windows

Visual Basic (VB
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Null is a special marker used to indicate that a data value is unknown in the Structured Query Language (SQL). Introduced by the creator of the relational database model, Dr. E.F.
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Unix (officially trademarked as UNIX®) is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie and Douglas McIlroy.
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black hole is a region of space in which the gravitational field is so powerful that nothing can escape after having fallen past the event horizon. The name comes from the fact that even electromagnetic radiation (e.g. light) is unable to escape, rendering the interior invisible.
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The bit bucket is jargon for where lost computerized data has gone, by any means; any data which does not end up where it is supposed to, being lost in transmission, a computer crash, or the like is said to have gone to the bit bucket — that mysterious place on a computer
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A device file or special file is an interface for a device driver that appears in a file system as if it were an ordinary file. This allows software to interact with the device driver using standard input/output system calls, which simplifies many tasks.
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The C0 and C1 control code sets define control codes for use in text. C0, originally defined in ISO 646, defines codes in the range 00HEX–1FHEX. C1, originally defined in ISO 6429, defines codes in the range 80HEX–9FHEX.
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ISO 646 is an ISO standard that since 1972 has specified a 7-bit character code from which several national standards are derived. Since the portion of ISO 646 shared by all countries specified only those letters used in the English alphabet, other countries using the Latin
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American Standard Code for Information Interchange (ASCII), generally pronounced ask-ee IPA: /ˈæski/ ( [1] ), is a character encoding based on the English alphabet.
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Unicode is an industry standard allowing computers to consistently represent and manipulate text expressed in any of the world's writing systems. Developed in tandem with the Universal Character Set standard and published in book form as The Unicode Standard
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The null character (also null terminator) is a character with the value zero, present in the ASCII and Unicode character sets, and available in nearly all mainstream programming languages.
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A programming language is an artificial language that can be used to control the behavior of a machine, particularly a computer. Programming languages, like natural languagess, are defined by syntactic and semantic rules which describe their structure and meaning respectively.
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Pascal is a structured imperative computer programming language, developed in 1970 by Niklaus Wirth as a language particularly suitable for structured programming. A derivative known as Object Pascal was designed for object oriented programming.
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C

The C Programming Language, Brian Kernighan and Dennis Ritchie, the original edition that served for many years as an informal specification of the language.
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A programming language is an artificial language that can be used to control the behavior of a machine, particularly a computer. Programming languages, like natural languagess, are defined by syntactic and semantic rules which describe their structure and meaning respectively.
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string is an ordered sequence of symbols. These symbols are chosen from a predetermined set.

In programming, when stored in memory each symbol is represented using a numeric value.
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American Standard Code for Information Interchange (ASCII), generally pronounced ask-ee IPA: /ˈæski/ ( [1] ), is a character encoding based on the English alphabet.
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C string.


In computing, a C string is a character sequence stored as a one-dimensional character array and terminated with a null character ('\0', called NUL in ASCII).
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Lisp
Paradigm: multi-paradigm: functional, procedural, reflective
Appeared in: 1958
Designed by: John McCarthy
Developer: Steve Russell, Timothy P. Hart, and Mike Levin
Typing discipline: dynamic, strong
Dialects: Common Lisp, Scheme, Emacs Lisp
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