Traits Class Requirements

There are two sets of requirements for the traits template argument to basic_regex: a minimal interface (which is part of the regex standardization proposal), and an optional Boost-specific enhanced interface.

Minimal requirements.

In the following table X denotes a traits class defining types and functions for the character container type charT; u is an object of type X; v is an object of type const X; p is a value of type const charT*; I1 and I2 are Input Iterators; c is a value of type const charT; s is an object of type X::string_type; cs is an object of type const X::string_type; b is a value of type bool; I is a value of type int; F1 and F2 are values of type const charT*; and loc is an object of type X::locale_type.

Expression	Return type	Assertion / Note Pre / Post condition
X::char_type	charT	The character container type used in the implementation of class template basic_regex.
X::size_type		An unsigned integer type, capable of holding the length of a null-terminated string of charT's.
X::string_type	std::basic_string<charT> or std::vector<charT>
X::locale_type	Implementation defined	A copy constructible type that represents the locale used by the traits class.
X::char_class_type	Implementation defined	A bitmask type representing a particular character classification. Multiple values of this type can be bitwise-or'ed together to obtain a new valid value.
X::length(p)	X::size_type	Yields the smallest i such that p[i] == 0. Complexity is linear in i.
v.translate(c)	X::char_type	Returns a character such that for any character d that is to be considered equivalent to c then v.translate(c) == v.translate(d).
v.translate_nocase(c)	X::char_type	For all characters C that are to be considered equivalent to c when comparisons are to be performed without regard to case, then v.translate_nocase(c) == v.translate_nocase(C).
v.transform(F1, F2)	X::string_type	Returns a sort key for the character sequence designated by the iterator range [F1, F2) such that if the character sequence [G1, G2) sorts before the character sequence [H1, H2) then v.transform(G1, G2) < v.transform(H1, H2).
v.transform_primary(F1, F2)	X::string_type	Returns a sort key for the character sequence designated by the iterator range [F1, F2) such that if the character sequence [G1, G2) sorts before the character sequence [H1, H2) when character case is not considered then v.transform_primary(G1, G2) < v.transform_primary(H1, H2).
v.lookup_classname(F1, F2)	X::char_class_type	Converts the character sequence designated by the iterator range [F1,F2) into a bitmask type that can subsequently be passed to isctype. Values returned from lookup_classname can be safely bitwise or'ed together. Returns 0 if the character sequence is not the name of a character class recognized by X. The value returned shall be independent of the case of the characters in the sequence.
v.lookup_collatename(F1, F2)	X::string_type	Returns a sequence of characters that represents the collating element consisting of the character sequence designated by the iterator range [F1, F2). Returns an empty string if the character sequence is not a valid collating element.
v.isctype(c, v.lookup_classname (F1, F2))	bool	Returns true if character c is a member of the character class designated by the iterator range [F1, F2), false otherwise.
v.value(c, I)	int	Returns the value represented by the digit c in base I if the character c is a valid digit in base I; otherwise returns -1. [Note: the value of I will only be 8, 10, or 16. -end note]
u.imbue(loc)	X::locale_type	Imbues u with the locale loc, returns the previous locale used by u if any.
v.getloc()	X::locale_type	Returns the current locale used by v if any.

Additional Optional Requirements

The following additional requirements are strictly optional, however in order for basic_regex to take advantage of these additional interfaces, all of the following requirements must be met; basic_regex will detect the presence or absence of the member boost_extensions_tag and configure itself appropriately.

Expression	Result	Assertion / Note Pre / Post condition
X::boost_extensions_tag	An unspecified type.	When present, all of the extensions listed in this table must be present.
v.syntax_type(c)	regex_constants::syntax_type	Returns a symbolic value of type regex_constants::syntax_type that signifies the meaning of character c within the regular expression grammar.
v.escape_syntax_type(c)	regex_constants::escape_syntax_type	Returns a symbolic value of type regex_constants::escape_syntax_type, that signifies the meaning of character c within the regular expression grammar, when c has been preceded by an escape character. Precondition: if b is the character preceding c in the expression being parsed then: `v.syntax_type(b) == syntax_escape`
v.translate(c, b)	X::char_type	Returns a character d such that: for any character d that is to be considered equivalent to c then `v.translate(c,false)==v.translate(d,false)`. Likewise for all characters C that are to be considered equivalent to c when comparisons are to be performed without regard to case, then `v.translate(c,true)==v.translate(C,true)`.
v.toi(I1, I2, i)	An integer type capable of holding either a charT or an int.	Behaves as follows: if `p == q` or if `p` is not a digit character then returns -1. Otherwise performs formatted numeric input on the sequence [p,q) and returns the result as an int. Postcondition: either p == q or p is a non-digit character.
v.error_string(I)	std::string	Returns a human readable error string for the error condition i, where i is one of the values enumerated by type regex_constants::error_type. If the value I is not recognized then returns the string "Unknown error" or a localized equivalent.
v.tolower(c)	X::char_type	Converts c to lower case, used for Perl-style \l and \L formatting operations.
v.toupper(c)	X::char_type	Converts c to upper case, used for Perl-style \u and \U formatting operations.