31 Regular expressions library [re]

31.3 Requirements [re.req]

This subclause defines requirements on classes representing regular expression traits.
[Note
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The class template regex_­traits, defined in Clause [re.traits], satisfies these requirements.
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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 typedef-names and functions in the template parameter traits used by the basic_­regex class template.
This subclause defines the semantics of 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 129 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.
Table 129 — Regular expression traits class requirements
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
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 representing a particular character classification.
X​::​length(p)
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
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The value of I will only be 8, 10, or 16.
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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
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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].
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