STD::REGEX_TRAITS(3cxx)

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version 14-20240412 · 23 versions
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🎀 NAME 🎀

okay bestie, welcome to the std::regex_traits< _Ch_type >(3cxx) page 💖 This is all about std::regex_traits< _Ch_type > — and the official vibe is: describes aspects of a regular expression. periodt ✨

✨ SYNOPSIS ✨

#include <regex>

🌸 Public Types 🌸

the type aliases are giving “small but iconic”:

typedef _RegexMask char_class_type
typedef _Ch_type char_type
typedef std::locale locale_type
typedef std::basic_string< char_type > string_type

💖 Public Member Functions 💖

  • regex_traits() — Constructs a default traits object. default-constructor slay 🫶
  • locale_type getloc () const — Gets a copy of the current locale in use by the regex_traits object.
  • locale_type imbue (locale_type __loc) — Imbues the regex_traits object with a copy of a new locale.
  • bool isctype (_Ch_type __c, char_class_type __f) const — Determines if c is a member of an identified class.
  • template<typename _Fwd_iter > char_class_type lookup_classname (_Fwd_iter __first, _Fwd_iter __last, bool __icase=false) const — Maps one or more characters to a named character classification.
  • template<typename _Fwd_iter > string_type lookup_collatename (_Fwd_iter __first, _Fwd_iter __last) const — Gets a collation element by name.
  • template<typename _Fwd_iter > string_type transform (_Fwd_iter __first, _Fwd_iter __last) const — Gets a sort key for a character sequence.
  • template<typename _Fwd_iter > string_type transform_primary (_Fwd_iter __first, _Fwd_iter __last) const — Gets a sort key for a character sequence, independent of case.
  • char_type translate (char_type __c) const — Performs the identity translation.
  • char_type translate_nocase (char_type __c) const — Translates a character into a case-insensitive equivalent.
  • int value (_Ch_type __ch, int __radix) const — Converts a digit to an int.

⭐ Static Public Member Functions ⭐

  • static std::size_t length (const char_type *__p) — Gives the length of a C-style string starting at __p.

🛡️ Protected Attributes 🛡️

  • locale_type _M_locale — yes bestie, that’s the protected attribute, no extra lore 💅

💫 Detailed Description 💫

the docs literally print the template line as template<typename _Ch_type> and then the class line as:

class std::regex_traits< _Ch_type >"Describes aspects of a regular expression.

(yes, there’s a stray quote in there — iconic, not me fixing it 💀)

so what is this class? it’s a regular expression traits class that satisfies the requirements of section [28.7] ✨

the class regex is parameterized around a set of related types and functions used to complete the definition of its semantics. this class satisfies the requirements of such a traits class. no cap 🫶

Since: C++11

🧸 Constructor & Destructor Documentation 🧸

🌸 regex_traits ()

template<typename _Ch_type > std::regex_traits< _Ch_type >::regex_traits ()
       [inline]

Constructs a default traits object. cute, simple, default 💖

💅 Member Function Documentation 💅

🦋 getloc ()

template<typename _Ch_type > locale_type std::regex_traits< _Ch_type
       >::getloc () const [inline]

Gets a copy of the current locale in use by the regex_traits object.

Referenced by std::regex_traits< _CharType >::isctype().

🎀 imbue (locale_type __loc)

template<typename _Ch_type > locale_type std::regex_traits< _Ch_type
       >::imbue (locale_type __loc) [inline]

Imbues the regex_traits object with a copy of a new locale.

Parameters

  • __loc — A locale.

Returns

  • a copy of the previous locale in use by the regex_traits object.

Note

Calling imbue with a different locale than the one currently in use invalidates all cached data held by *this. that’s the drama, bestie 😭

🔥 isctype (_Ch_type __c, char_class_type __f)

template<typename _Ch_type > bool std::regex_traits< _Ch_type >::isctype
       (_Ch_type __c, char_class_type __f) const

Determines if c is a member of an identified class.

Parameters

  • __c — a character.
  • __f — a class type (as returned from lookup_classname).

Returns

  • true if the character __c is a member of the classification represented by __f, false otherwise.

Exceptions

  • std::bad_cast if the current locale does not have a ctype facet.

🌈 length (const char_type * __p)

template<typename _Ch_type > static std::size_t std::regex_traits< _Ch_type
       >::length (const char_type * __p) [inline],  [static]

Gives the length of a C-style string starting at __p.

Parameters

  • __p — a pointer to the start of a character sequence.

Returns

  • the number of characters between *__p and the first default-initialized value of type char_type. In other words, uses the C-string algorithm for determining the length of a sequence of characters.

References std::basic_string< _CharT, _Traits, _Alloc >::length().

🌸 lookup_classname (_Fwd_iter __first, _Fwd_iter __last, bool __icase = false)

template<typename _Ch_type > template<typename _Fwd_iter > regex_traits<
       _Ch_type >::char_class_type std::regex_traits< _Ch_type
       >::lookup_classname (_Fwd_iter __first, _Fwd_iter __last, bool __icase =
       false) const

Maps one or more characters to a named character classification.

Parameters

  • __first — beginning of the character sequence.
  • __last — one-past-the-end of the character sequence.
  • __icase — ignores the case of the classification name.

Returns

  • an unspecified value that represents the character classification named by the character sequence designated by the iterator range [__first, __last). If icase is true, the returned mask identifies the classification regardless of the case of the characters to be matched (for example, [[:lower:]] is the same as [[:alpha:]]), otherwise a case-dependent classification is returned. The value returned shall be independent of the case of the characters in the character sequence. If the name is not recognized then returns a value that compares equal to 0.

At least the following names (or their wide-character equivalent) are supported.

  • d
  • w
  • s
  • alnum
  • alpha
  • blank
  • cntrl
  • digit
  • graph
  • lower
  • print
  • punct
  • space
  • upper
  • xdigit

🫶 lookup_collatename (_Fwd_iter __first, _Fwd_iter __last)

template<typename _Ch_type > template<typename _Fwd_iter > regex_traits<
       _Ch_type >::string_type std::regex_traits< _Ch_type
       >::lookup_collatename (_Fwd_iter __first, _Fwd_iter __last) const

Gets a collation element by name.

Parameters

  • __first — beginning of the collation element name.
  • __last — one-past-the-end of the collation element name.

Returns

  • a sequence of one or more characters that represents the collating element consisting of the character sequence designated by the iterator range [__first, __last). Returns an empty string if the character sequence is not a valid collating element.

💜 transform (_Fwd_iter __first, _Fwd_iter __last)

template<typename _Ch_type > template<typename _Fwd_iter > string_type
       std::regex_traits< _Ch_type >::transform (_Fwd_iter __first, _Fwd_iter
       __last) const [inline]

Gets a sort key for a character sequence.

Parameters

  • __first — beginning of the character sequence.
  • __last — one-past-the-end of the character sequence.

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).

what this really does is provide a more efficient way to compare a string to multiple other strings in locales with fancy collation rules and equivalence classes.

Returns

  • a locale-specific sort key equivalent to the input range.

Exceptions

  • std::bad_cast if the current locale does not have a collate facet.

References std::basic_string< _CharT, _Traits, _Alloc >::data(), and std::basic_string< _CharT, _Traits, _Alloc >::size().

Referenced by std::regex_traits< _Ch_type >::transform_primary().

🦋 transform_primary (_Fwd_iter __first, _Fwd_iter __last)

template<typename _Ch_type > template<typename _Fwd_iter > string_type
       std::regex_traits< _Ch_type >::transform_primary (_Fwd_iter __first,
       _Fwd_iter __last) const [inline]

Gets a sort key for a character sequence, independent of case.

Parameters

  • __first — beginning of the character sequence.
  • __last — one-past-the-end of the character sequence.

Effects: if typeid(use_facet<collate<_Ch_type> >) == typeid(collate_byname<_Ch_type>) and the form of the sort key returned by collate_byname<_Ch_type>::transform(__first, __last) is known and can be converted into a primary sort key then returns that key, otherwise returns an empty string.

Todo

Implement this function correctly. yes bestie, the docs said it, not me 😭

References std::regex_traits< _Ch_type >::transform().

🎀 translate (char_type __c)

template<typename _Ch_type > char_type std::regex_traits< _Ch_type
       >::translate (char_type __c) const [inline]

Performs the identity translation.

Parameters

  • __c — A character to the locale-specific character set.

Returns

  • __c.

🌈 translate_nocase (char_type __c)

template<typename _Ch_type > char_type std::regex_traits< _Ch_type
       >::translate_nocase (char_type __c) const [inline]

Translates a character into a case-insensitive equivalent.

Parameters

  • __c — A character to the locale-specific character set.

Returns

  • the locale-specific lower-case equivalent of __c.

Exceptions

  • std::bad_cast if the imbued locale does not support the ctype facet.

🔥 value (_Ch_type __ch, int __radix)

template<typename _Ch_type > int std::regex_traits< _Ch_type >::value
       (_Ch_type __ch, int __radix) const

Converts a digit to an int.

Parameters

  • __ch — a character representing a digit.
  • __radix — the radix if the numeric conversion (limited to 8, 10, or 16).

Returns

  • the value represented by the digit __ch in base radix if the character __ch is a valid digit in base radix; otherwise returns -1.

References std::basic_ios< _CharT, _Traits >::fail(), std::hex(), and std::oct().

👑 Author 👑

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