Null (computing)

In computing, null has different definitions in different contexts.

The general idea is "nonexistence".

Definition

• Null (SQL), a special marker and keyword in SQL indicating that something has no value.
• Null character, the zero-valued ASCII character, also designated by NUL, often used as a terminator, separator or filler. This symbol has no visual representation.
• Null device, a special computer file that discards all data written to it
• Null modem, a specially wired serial communications cable
• Null Object pattern, a software design pattern using an object with defined neutral behavior
• Null pointer (sometimes written NULL, nil, or None), used in computer programming for an uninitialized, undefined, empty, or meaningless value
• Null string, the unique string of length zero (in computer science and formal language theory)
• Null-terminated string, a character string of which the length is determined by the first null-character (in programming language C and related languages)
• Nullable type, a feature of some statically-typed programming languages which allows a data type to be set to the special value NULL

External links

• Null References: The Billion Dollar Mistake by Tony Hoare