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The empty string is a legitimate string, upon which most string operations should work. Some languages treat some or all of the following in similar ways: empty strings, null references, the integer 0, the floating point number 0, the Boolean value false , the ASCII character NUL , or other such values.
The ability to represent a null character does not always mean the resulting string will be correctly interpreted, as many programs will consider the null to be the end of the string. Thus the ability to type it (in case of unchecked user input ) creates a vulnerability known as null byte injection and can lead to security exploits.
The null sign (∅) is often used in mathematics for denoting the empty set. The same letter in linguistics represents zero , the lack of an element. It is commonly used in phonology , morphology , and syntax .
Null sign (∅), the empty set; Null (SQL) (ω), a special marker and keyword NULL in SQL; Empty string (λ, Λ, or ε), in formal language theory; See also.
In computer programming, a null-terminated string is a character string stored as an array containing the characters and terminated with a null character (a character with an internal value of zero, called "NUL" in this article, not same as the glyph zero).
String concatenation is an associative, but non-commutative operation. The empty string ε serves as the identity element; for any string s, εs = sε = s. Therefore, the set Σ * and the concatenation operation form a monoid, the free monoid generated by Σ.
These mistakes are usually the result of confusion between Null and either 0 (zero) or an empty string (a string value with a length of zero, represented in SQL as ''). Null is defined by the SQL standard as different from both an empty string and the numerical value 0, however. While Null indicates the absence of any value, the empty string ...
A → w, where A is a non-terminal in N and w is in a (possibly empty) string of terminals Σ * A → wB, where A and B are in N and w is in Σ *. Some authors call this type of grammar a right-regular grammar (or right-linear grammar) [1] and the type above a strictly right-regular grammar (or strictly right-linear grammar). [2]