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String functions are used in computer programming languages to manipulate a string or query information about a string (some do both).. Most programming languages that have a string datatype will have some string functions although there may be other low-level ways within each language to handle strings directly.
The length of a string is the number of code units before the zero code unit. [1] The memory occupied by a string is always one more code unit than the length, as space is needed to store the zero terminator. Generally, the term string means a string where the code unit is of type char, which is exactly 8 bits on all modern machines.
Hence, this representation is commonly referred to as a C string. This representation of an n-character string takes n + 1 space (1 for the terminator), and is thus an implicit data structure. In terminated strings, the terminating code is not an allowable character in any string.
The std::string class is the standard representation for a text string since C++98. The class provides some typical string operations like comparison, concatenation, find and replace, and a function for obtaining substrings. An std::string can be constructed from a C-style string, and a C-style string can also be obtained from one. [7]
A string substitution or simply a substitution is a mapping f that maps characters in Σ to languages (possibly in a different alphabet). Thus, for example, given a character a ∈ Σ, one has f(a)=L a where L a ⊆ Δ * is some language whose alphabet is Δ. This mapping may be extended to strings as f(ε)=ε
String interning also reduces memory usage if there are many instances of the same string value; for instance, it is read from a network or from storage. Such strings may include magic numbers or network protocol information. For example, XML parsers may intern names of tags and attributes to save memory.
A single edit operation may be changing a single symbol of the string into another (cost W C), deleting a symbol (cost W D), or inserting a new symbol (cost W I). [2] If all edit operations have the same unit costs (W C = W D = W I = 1) the problem is the same as computing the Levenshtein distance of two strings.
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