This subclause defines requirements on classes representing regular expression traits. [ Note: The class template regex_traits, defined in Clause [re.traits], satisfies these requirements. — end note ]
The class template basic_regex, defined in Clause [re.regex], needs a set of related types and functions to complete the definition of its semantics. These types and functions are provided as a set of member typedefs and functions in the template parameter traits used by the basic_regex class template. This subclause defines the semantics guaranteed by these members.
To specialize class template basic_regex for a character container CharT and its related regular expression traits class Traits, use basic_regex<CharT, Traits>.
In Table [tab:re:RegexpTraits] 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; F1 and F2 are forward 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; cl is an object of type X::char_class_type, 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::string_type | std::basic_string<charT> | |
| X::locale_type | A copy constructible type | A type that represents the locale used by the traits class. |
| X::char_class_type | A bitmask type ([bitmask.types]). | A bitmask type representing a particular character classification. |
| X::length(p) | std::size_t | 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_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.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 bitmask type 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 true if character c is a member of one of the character classes designated by cl, 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 and returns the previous locale used by u if any. |
| v.getloc() | X::locale_type | Returns the current locale used by v, if any. |
[ Note: Class template regex_traits satisfies the requirements for a regular expression traits class when it is specialized for char or wchar_t. This Class template is described in the header <regex>, and is described in Clause [re.traits]. — end note ]