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In object-oriented computer programming, a null object is an object with no referenced value or with defined neutral (null) behavior.The null object design pattern, which describes the uses of such objects and their behavior (or lack thereof), was first published as "Void Value" [1] and later in the Pattern Languages of Program Design book series as "Null Object".
In computing, a null pointer or null reference is a value saved for indicating that the pointer or reference does not refer to a valid object. Programs routinely use null pointers to represent conditions such as the end of a list of unknown length or the failure to perform some action; this use of null pointers can be compared to nullable types ...
In long mode, XCHG RAX,RAX requires two bytes, as it would begin with an REX.W prefix, making the encoding 0x48 0x90. However, 0x90 is interpreted as a NOP in long mode regardless of whether it is preceded by 0x48. [2] multi-byte NOP: 2–9 for Pentium Pro and later Intel processors, and all AMD AMD64 processors 0x66 0x90. 0x0F 0x1F 0x00. 0x0F ...
The dual notion is that of a terminal object (also called terminal element): T is terminal if for every object X in C there exists exactly one morphism X → T. Initial objects are also called coterminal or universal, and terminal objects are also called final. If an object is both initial and terminal, it is called a zero object or null object.
A null pointer has a value reserved for indicating that the pointer does not refer to a valid object. Null pointers are routinely used to represent conditions such as the end of a list of unknown length or the failure to perform some action; this use of null pointers can be compared to nullable types and to the Nothing value in an option type.
It is often abbreviated as NUL (or NULL, though in some contexts that term is used for the null pointer). In 8-bit codes, it is known as a null byte . The original meaning of this character was like NOP —when sent to a printer or a terminal , it has no effect (some terminals, however, incorrectly display it as space ).
In computer science, a null function (or null operator) is a subroutine that leaves the program state unchanged. When it is part of the instruction set of a processor, it is called a NOP or NOOP (No OPeration). Mathematically, a (computer) function is null if and only if its execution leaves the program state unchanged.
0x00 (null, NUL, \0, ^@), originally intended to be an ignored character, but now used by many programming languages including C to mark the end of a string. 0x07 (bell, BEL, \a, ^G), which may cause the device to emit a warning such as a bell or beep sound or the screen flashing. 0x08 (backspace, BS, \b, ^H), may overprint the previous character.