# C++ named requirements: RegexTraits (since C++11)

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RegexTraits is a traits class that abstracts operations needed for a given character type when as template type parameters for std::basic_regex.

### Requirements

Given

- CharT, a character type
- X, a RegexTraits type for type CharT
- u, an object of type X
- v, an object of type const X
- p, a value of type const CharT*
- I1, I2, input iterators
- F1, F2, forward iterators
- c, a value of type const CharT
- s, an object of type X::string_type
- cs, an object of type const X::string_type
- b, a value of type bool
- I, a value of type int
- cl, an object of type X::char_class_type
- loc, an object of type X::locale_type

expression | return type | semantics
--- | --- | ---
X::char_type | CharT | Used to refer to the character type.
X::string_type | std::basic_string<CharT> |
X::locale_type |  | A CopyConstructible type that represents the locale used by the traits class.
X::char_class_type |  | A BitmaskType type that represents a particular character classification.
X::length(p) | std::size_t | Returns: 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 considered to be equivalent to c, then v.translate(c) == v.translate(d).
v.translate_nocase(c) | X::char_type | Returns: a character such that for any character C considered to be equivalent to c 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) without regard to case, then v.transform_primary(G1, G2) < v.transform_primary(H1, H2).
v.lookup_collatename(F1, F2) | X::string_type | Returns: An empty string if the character sequence is not a valid collating element A sequence of characters that represents the collating element consisting of the character sequence designated by the iterator range [F1, F2) otherwise
v.lookup_classname(F1, F2, b) | X::char_class_type | Converts the character sequence designated by the iterator range [F1, F2) into a value of a BitmaskType that can subsequently be passed to isctype Values returned from lookup_classname can be bitwise or'ed together; the resulting value represents membership in either of the corresponding character classes If b is true, the returned bitmask is suitable for matching characters without regard to their case. 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.isctype(c, cl) | bool | Returns: whether c is a member of one of the character classes designated by cl or not.
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 -1 otherwise
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 previous locale used by v if any.

### Standard library

RegexTraits is satisfied by the following standard library classes:

template<> class regex_traits<char>; template<> class regex_traits<wchar_t>; |  | (since C++11) (since C++11)

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