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PHP has hundreds of base functions and thousands more from extensions. Prior to PHP version 5.3.0, functions are not first-class functions and can only be referenced by their name, whereas PHP 5.3.0 introduces closures. [35] User-defined functions can be created at any time and without being prototyped. [35]
In functional and list-based languages a string is represented as a list (of character codes), therefore all list-manipulation procedures could be considered string functions. However such languages may implement a subset of explicit string-specific functions as well.
Visual Basic and Visual Basic .NET can also use the "+" sign but at the risk of ambiguity if a string representing a number and a number are together. Microsoft Excel allows both "&" and the function "=CONCATENATE(X,Y)". Rust has the concat! macro and the format! macro, of which the latter is the most prevalent throughout the documentation and ...
Many trim functions have an optional parameter to specify a list of characters to trim, instead of the default whitespace characters. For example, PHP and Python allow this optional parameter, while Pascal and Java do not. With Common Lisp's string-trim function, the parameter (called character-bag) is required.
Perhaps the most well-known is Hungarian notation, which encodes either the purpose ("Apps Hungarian") or the type ("Systems Hungarian") of a variable in its name. [17] For example, the prefix "sz" for the variable szName indicates that the variable is a null-terminated string.
Both character termination and length codes limit strings: For example, C character arrays that contain null (NUL) characters cannot be handled directly by C string library functions: Strings using a length code are limited to the maximum value of the length code. Both of these limitations can be overcome by clever programming.
In lieu of function pointers, functions in PHP can be referenced by a string containing their name. In this manner, normal PHP functions can be used, for example, as callbacks or within function tables. [225] User-defined functions may be created at any time without being prototyped.
Simple single-letter substitution ciphers are examples of (ε-free) string homomorphisms. An example string homomorphism g uc can also be obtained by defining similar to the above substitution: g uc (‹a›) = ‹A›, ..., g uc (‹0›) = ε, but letting g uc be undefined on punctuation chars. Examples for inverse homomorphic images are