28 Text processing library [text] (original) (raw)

28.6 Regular expressions library [re]

28.6.1 General [re.general]

Subclause [re] describes components that C++ programs may use to perform operations involving regular expression matching and searching.

The following subclauses describe a basic regular expression class template and its traits that can handle char-like ([strings.general]) template arguments, two specializations of this class template that handle sequences of char and wchar_t, a class template that holds the result of a regular expression match, a series of algorithms that allow a character sequence to be operated upon by a regular expression, and two iterator types for enumerating regular expression matches, as summarized in Table 115.

Table 115 — Regular expressions library summary [tab:re.summary]

🔗 Subclause Header
🔗[re.req] Requirements
🔗[re.const] Constants <regex>
🔗[re.badexp] Exception type
🔗[re.traits] Traits
🔗[re.regex] Regular expression template
🔗[re.submatch] Submatches
🔗[re.results] Match results
🔗[re.alg] Algorithms
🔗[re.iter] Iterators
🔗[re.grammar] Grammar

The ECMAScript Language Specification described in Standard Ecma-262 is called ECMA-262 in this Clause.

28.6.2 Requirements [re.req]

This subclause defines requirements on classes representing regular expression traits.

[Note 1:

The class templateregex_traits, defined in [re.traits], meets these requirements.

— _end note_]

The class template basic_regex, defined in[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 the following requirements,

A traits class X meets the regular expression traits requirements if the following types and expressions are well-formed and have the specified semantics.

Result: charT, the character container type used in the implementation of class template basic_regex.

Result: basic_string<charT>

Result: A copy constructible type that represents the locale used by the traits class.

typename X::char_class_type

Result: A bitmask type ([bitmask.types]) representing a particular character classification.

Returns: The smallest i such that p[i] == 0.

Returns: A character such that for any character dthat is to be considered equivalent to cthen v.translate(c) == v.translate(d).

Returns: For all characters C that are to be considered equivalent to cwhen comparisons are to be performed without regard to case, then v.translate_nocase(c) == v.translate_nocase(C).

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)

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)

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)

Result: X​::​char_class_type

Returns: 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 0if 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.

Returns: Returns true if character c is a member of one of the character classes designated by cl,false otherwise.

Returns: 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 2:

The value of I will only be 8, 10, or 16.

— _end note_]

Effects: Imbues u with the locale loc and returns the previous locale used by u if any.

Returns: Returns the current locale used by v, if any.

[Note 3:

Class template regex_traits meets the requirements for a regular expression traits class when it is specialized forchar or wchar_t.

This class template is described in the header , and is described in [re.traits].

— _end note_]

28.6.4 Namespace std​::​regex_constants [re.const]

28.6.4.1 General [re.const.general]

The namespace std​::​regex_constants holds symbolic constants used by the regular expression library.

This namespace provides three types, syntax_option_type,match_flag_type, and error_type, along with several constants of these types.

28.6.4.2 Bitmask type syntax_option_type [re.synopt]

namespace std::regex_constants { using syntax_option_type = T1;inline constexpr syntax_option_type icase = unspecified;inline constexpr syntax_option_type nosubs = unspecified;inline constexpr syntax_option_type optimize = unspecified;inline constexpr syntax_option_type collate = unspecified;inline constexpr syntax_option_type ECMAScript = unspecified;inline constexpr syntax_option_type basic = unspecified;inline constexpr syntax_option_type extended = unspecified;inline constexpr syntax_option_type awk = unspecified;inline constexpr syntax_option_type grep = unspecified;inline constexpr syntax_option_type egrep = unspecified;inline constexpr syntax_option_type multiline = unspecified;}

The type syntax_option_type is an implementation-defined bitmask type ([bitmask.types]).

Setting its elements has the effects listed in Table 116.

A valid value of typesyntax_option_type shall have at most one of the grammar elementsECMAScript, basic, extended, awk, grep, egrep, set.

If no grammar element is set, the default grammar is ECMAScript.

Table 116 — syntax_option_type effects [tab:re.synopt]

🔗Element Effect(s) if set
🔗icase Specifies that matching of regular expressions against a character container sequence shall be performed without regard to case.
🔗nosubs Specifies that no sub-expressions shall be considered to be marked, so that when a regular expression is matched against a character container sequence, no sub-expression matches shall be stored in the supplied match_results object.
🔗optimize Specifies that the regular expression engine should pay more attention to the speed with which regular expressions are matched, and less to the speed with which regular expression objects are constructed. Otherwise it has no detectable effect on the program output.
🔗collate Specifies that character ranges of the form "[a-b]" shall be locale sensitive.
🔗ECMAScript Specifies that the grammar recognized by the regular expression engine shall be that used by ECMAScript in ECMA-262, as modified in [re.grammar]. See also: ECMA-262 15.10
🔗basic Specifies that the grammar recognized by the regular expression engine shall be that used by basic regular expressions in POSIX.See also: POSIX, Base Definitions and Headers, Section 9.3
🔗extended Specifies that the grammar recognized by the regular expression engine shall be that used by extended regular expressions in POSIX.See also: POSIX, Base Definitions and Headers, Section 9.4
🔗awk Specifies that the grammar recognized by the regular expression engine shall be that used by the utility awk in POSIX.
🔗grep Specifies that the grammar recognized by the regular expression engine shall be that used by the utility grep in POSIX.
🔗egrep Specifies that the grammar recognized by the regular expression engine shall be that used by the utility grep when given the -E option in POSIX.
🔗multiline Specifies that ^ shall match the beginning of a line and$ shall match the end of a line, if the ECMAScript engine is selected.

28.6.4.3 Bitmask type match_flag_type [re.matchflag]

namespace std::regex_constants { using match_flag_type = T2;inline constexpr match_flag_type match_default = {};inline constexpr match_flag_type match_not_bol = unspecified;inline constexpr match_flag_type match_not_eol = unspecified;inline constexpr match_flag_type match_not_bow = unspecified;inline constexpr match_flag_type match_not_eow = unspecified;inline constexpr match_flag_type match_any = unspecified;inline constexpr match_flag_type match_not_null = unspecified;inline constexpr match_flag_type match_continuous = unspecified;inline constexpr match_flag_type match_prev_avail = unspecified;inline constexpr match_flag_type format_default = {};inline constexpr match_flag_type format_sed = unspecified;inline constexpr match_flag_type format_no_copy = unspecified;inline constexpr match_flag_type format_first_only = unspecified;}

The type match_flag_type is animplementation-defined bitmask type ([bitmask.types]).

The constants of that type, except for match_default andformat_default, are bitmask elements.

The match_default andformat_default constants are empty bitmasks.

Matching a regular expression against a sequence of characters [first, last) proceeds according to the rules of the grammar specified for the regular expression object, modified according to the effects listed in Table 117 for any bitmask elements set.

Table 117 — regex_constants​::​match_flag_type effects [tab:re.matchflag]

🔗Element Effect(s) if set
🔗match_not_bol The first character in the sequence [first, last) shall be treated as though it is not at the beginning of a line, so the character^ in the regular expression shall not match [first, first).
🔗match_not_eol The last character in the sequence [first, last) shall be treated as though it is not at the end of a line, so the character"$" in the regular expression shall not match [last, last).
🔗match_not_bow The expression "\\b" shall not match the sub-sequence [first, first).
🔗match_not_eow The expression "\\b" shall not match the sub-sequence [last, last).
🔗match_any If more than one match is possible then any match is an acceptable result.
🔗match_not_null The expression shall not match an empty sequence.
🔗match_continuous The expression shall only match a sub-sequence that begins atfirst.
🔗match_prev_avail --first is a valid iterator position. When this flag is set the flags match_not_bol and match_not_bow shall be ignored by the regular expression algorithms ([re.alg]) and iterators ([re.iter]).
🔗format_default When a regular expression match is to be replaced by a new string, the new string shall be constructed using the rules used by the ECMAScript replace function in ECMA-262, part 15.5.4.11 String.prototype.replace. In addition, during search and replace operations all non-overlapping occurrences of the regular expression shall be located and replaced, and sections of the input that did not match the expression shall be copied unchanged to the output string.
🔗format_sed When a regular expression match is to be replaced by a new string, the new string shall be constructed using the rules used by the sed utility in POSIX.
🔗format_no_copy During a search and replace operation, sections of the character container sequence being searched that do not match the regular expression shall not be copied to the output string.
🔗format_first_only When specified during a search and replace operation, only the first occurrence of the regular expression shall be replaced.

28.6.4.4 Implementation-defined error_type [re.err]

namespace std::regex_constants { using error_type = T3;inline constexpr error_type error_collate = unspecified;inline constexpr error_type error_ctype = unspecified;inline constexpr error_type error_escape = unspecified;inline constexpr error_type error_backref = unspecified;inline constexpr error_type error_brack = unspecified;inline constexpr error_type error_paren = unspecified;inline constexpr error_type error_brace = unspecified;inline constexpr error_type error_badbrace = unspecified;inline constexpr error_type error_range = unspecified;inline constexpr error_type error_space = unspecified;inline constexpr error_type error_badrepeat = unspecified;inline constexpr error_type error_complexity = unspecified;inline constexpr error_type error_stack = unspecified;}

The type error_type is an implementation-defined enumerated type ([enumerated.types]).

Values of type error_type represent the error conditions described in Table 118:

Table 118 — error_type values in the C locale [tab:re.err]

🔗Value Error condition
🔗error_collate The expression contains an invalid collating element name.
🔗error_ctype The expression contains an invalid character class name.
🔗error_escape The expression contains an invalid escaped character, or a trailing escape.
🔗error_backref The expression contains an invalid back reference.
🔗error_brack The expression contains mismatched [ and ].
🔗error_paren The expression contains mismatched ( and ).
🔗error_brace The expression contains mismatched { and }.
🔗error_badbrace The expression contains an invalid range in a {} expression.
🔗error_range The expression contains an invalid character range, such as[b-a] in most encodings.
🔗error_space There is insufficient memory to convert the expression into a finite state machine.
🔗error_badrepeat One of *?+{ is not preceded by a valid regular expression.
🔗error_complexity The complexity of an attempted match against a regular expression exceeds a pre-set level.
🔗error_stack There is insufficient memory to determine whether the regular expression matches the specified character sequence.

28.6.5 Class regex_error [re.badexp]

namespace std { class regex_error : public runtime_error { public: explicit regex_error(regex_constants::error_type ecode); regex_constants::error_type code() const;};}

The class regex_error defines the type of objects thrown as exceptions to report errors from the regular expression library.

regex_error(regex_constants::error_type ecode);

Postconditions: ecode == code().

regex_constants::error_type code() const;

Returns: The error code that was passed to the constructor.

28.6.6 Class template regex_traits [re.traits]

namespace std { template<class charT> struct regex_traits { using char_type = charT;using string_type = basic_string<char_type>;using locale_type = locale;using char_class_type = bitmask_type; regex_traits();static size_t length(const char_type* p); charT translate(charT c) const; charT translate_nocase(charT c) const;template<class ForwardIterator> string_type transform(ForwardIterator first, ForwardIterator last) const;template<class ForwardIterator> string_type transform_primary( ForwardIterator first, ForwardIterator last) const;template<class ForwardIterator> string_type lookup_collatename( ForwardIterator first, ForwardIterator last) const;template<class ForwardIterator> char_class_type lookup_classname( ForwardIterator first, ForwardIterator last, bool icase = false) const;bool isctype(charT c, char_class_type f) const;int value(charT ch, int radix) const; locale_type imbue(locale_type l); locale_type getloc() const;};}

The specializations regex_traits<char> andregex_traits<wchar_t> meet the requirements for a regular expression traits class ([re.req]).

using char_class_type = _bitmasktype_;

The type char_class_type is used to represent a character classification and is capable of holding an implementation specific set returned by lookup_classname.

static size_t length(const char_type* p);

Returns: char_traits<charT>​::​length(p).

charT translate(charT c) const;

charT translate_nocase(charT c) const;

Returns: use_facet<ctype<charT>>(getloc()).tolower(c).

template<class ForwardIterator> string_type transform(ForwardIterator first, ForwardIterator last) const;

Effects: As if by:string_type str(first, last);return use_facet<collate<charT>>( getloc()).transform(str.data(), str.data() + str.length());

template<class ForwardIterator> string_type transform_primary(ForwardIterator first, ForwardIterator last) const;

Effects: Iftypeid(use_facet<collate<charT>>(getloc())) == typeid(collate_byname<charT>) and the form of the sort key returned by collate_byname<charT>​::​transform(first, last) is known and can be converted into a primary sort key then returns that key, otherwise returns an empty string.

template<class ForwardIterator> string_type lookup_collatename(ForwardIterator first, ForwardIterator last) const;

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.

template<class ForwardIterator> char_class_type lookup_classname( ForwardIterator first, ForwardIterator last, bool icase = false) const;

Returns: An unspecified value that represents the character classification named by the character sequence designated by the iterator range [first, last).

If the parameter icase is true then the returned mask identifies the character classification without regard to the case of the characters being matched, otherwise it does honor the case of the characters being matched.239

The value returned shall be independent of the case of the characters in the character sequence.

If the name is not recognized then returns char_class_type().

Remarks: For regex_traits<char>, at least the narrow character names in Table 119 shall be recognized.

For regex_traits<wchar_t>, at least the wide character names in Table 119 shall be recognized.

bool isctype(charT c, char_class_type f) const;

Effects: Determines if the character c is a member of the character classification represented by f.

Returns: Given the following function declaration: template<class C> ctype_base::mask convert(typename regex_traits<C>::char_class_type f);that returns a value in which each ctype_base​::​mask value corresponding to a value in f named in Table 119 is set, then the result is determined as if by:ctype_base::mask m = convert<charT>(f);const ctype<charT>& ct = use_facet<ctype<charT>>(getloc());if (ct.is(m, c)) { return true;} else if (c == ct.widen('_')) { charT w[1] = { ct.widen('w') }; char_class_type x = lookup_classname(w, w+1);return (f&x) == x;} else { return false;}

[Example 1: regex_traits<char> t; string d("d"); string u("upper"); regex_traits<char>::char_class_type f; f = t.lookup_classname(d.begin(), d.end()); f |= t.lookup_classname(u.begin(), u.end()); ctype_base::mask m = convert<char>(f); — _end example_]

[Example 2: regex_traits<char> t; string w("w"); regex_traits<char>::char_class_type f; f = t.lookup_classname(w.begin(), w.end()); t.isctype('A', f); t.isctype('_', f); t.isctype(' ', f); — _end example_]

int value(charT ch, int radix) const;

Preconditions: The value of radix is 8, 10, or 16.

Returns: The value represented by the digit ch in baseradix if the character ch is a valid digit in baseradix; otherwise returns -1.

locale_type imbue(locale_type loc);

Effects: Imbues *this with a copy of the locale loc.

[Note 1:

Calling imbue with a different locale than the one currently in use invalidates all cached data held by *this.

— _end note_]

Postconditions: getloc() == loc.

Returns: If no locale has been previously imbued then a copy of the global locale in effect at the time of construction of *this, otherwise a copy of the last argument passed to imbue.

locale_type getloc() const;

Returns: If no locale has been imbued then a copy of the global locale in effect at the time of construction of *this, otherwise a copy of the last argument passed to imbue.

Table 119 — Character class names and corresponding ctype masks [tab:re.traits.classnames]

🔗Narrow character name Wide character name Corresponding ctype_base​::​mask value
🔗"alnum" L"alnum" ctype_base​::​alnum
🔗"alpha" L"alpha" ctype_base​::​alpha
🔗"blank" L"blank" ctype_base​::​blank
🔗"cntrl" L"cntrl" ctype_base​::​cntrl
🔗"digit" L"digit" ctype_base​::​digit
🔗"d" L"d" ctype_base​::​digit
🔗"graph" L"graph" ctype_base​::​graph
🔗"lower" L"lower" ctype_base​::​lower
🔗"print" L"print" ctype_base​::​print
🔗"punct" L"punct" ctype_base​::​punct
🔗"space" L"space" ctype_base​::​space
🔗"s" L"s" ctype_base​::​space
🔗"upper" L"upper" ctype_base​::​upper
🔗"w" L"w" ctype_base​::​alnum
🔗"xdigit" L"xdigit" ctype_base​::​xdigit

28.6.7 Class template basic_regex [re.regex]

28.6.7.1 General [re.regex.general]

For a char-like type charT, specializations of class template basic_regex represent regular expressions constructed from character sequences of charT characters.

In the rest of [re.regex], charT denotes a given char-like type.

Storage for a regular expression is allocated and freed as necessary by the member functions of class basic_regex.

Objects of type specialization of basic_regex are responsible for converting the sequence of charT objects to an internal representation.

It is not specified what form this representation takes, nor how it is accessed by algorithms that operate on regular expressions.

[Note 1:

Implementations will typically declare some function templates as friends of basic_regex to achieve this.

— _end note_]

The functions described in [re.regex] report errors by throwing exceptions of type regex_error.

namespace std { template<class charT, class traits = regex_traits<charT>> class basic_regex { public: using value_type = charT;using traits_type = traits;using string_type = typename traits::string_type;using flag_type = regex_constants::syntax_option_type;using locale_type = typename traits::locale_type;static constexpr flag_type icase = regex_constants::icase;static constexpr flag_type nosubs = regex_constants::nosubs;static constexpr flag_type optimize = regex_constants::optimize;static constexpr flag_type collate = regex_constants::collate;static constexpr flag_type ECMAScript = regex_constants::ECMAScript;static constexpr flag_type basic = regex_constants::basic;static constexpr flag_type extended = regex_constants::extended;static constexpr flag_type awk = regex_constants::awk;static constexpr flag_type grep = regex_constants::grep;static constexpr flag_type egrep = regex_constants::egrep;static constexpr flag_type multiline = regex_constants::multiline; basic_regex();explicit basic_regex(const charT* p, flag_type f = regex_constants::ECMAScript); basic_regex(const charT* p, size_t len, flag_type f = regex_constants::ECMAScript); basic_regex(const basic_regex&); basic_regex(basic_regex&&) noexcept;template<class ST, class SA> explicit basic_regex(const basic_string<charT, ST, SA>& s, flag_type f = regex_constants::ECMAScript);template<class ForwardIterator> basic_regex(ForwardIterator first, ForwardIterator last, flag_type f = regex_constants::ECMAScript); basic_regex(initializer_list<charT> il, flag_type f = regex_constants::ECMAScript);~basic_regex(); basic_regex& operator=(const basic_regex& e); basic_regex& operator=(basic_regex&& e) noexcept; basic_regex& operator=(const charT* p); basic_regex& operator=(initializer_list<charT> il);template<class ST, class SA> basic_regex& operator=(const basic_string<charT, ST, SA>& s); basic_regex& assign(const basic_regex& e); basic_regex& assign(basic_regex&& e) noexcept; basic_regex& assign(const charT* p, flag_type f = regex_constants::ECMAScript); basic_regex& assign(const charT* p, size_t len, flag_type f = regex_constants::ECMAScript);template<class ST, class SA> basic_regex& assign(const basic_string<charT, ST, SA>& s, flag_type f = regex_constants::ECMAScript);template<class InputIterator> basic_regex& assign(InputIterator first, InputIterator last, flag_type f = regex_constants::ECMAScript); basic_regex& assign(initializer_list<charT>, flag_type f = regex_constants::ECMAScript);unsigned mark_count() const; flag_type flags() const; locale_type imbue(locale_type loc); locale_type getloc() const;void swap(basic_regex&);};template<class ForwardIterator> basic_regex(ForwardIterator, ForwardIterator, regex_constants::syntax_option_type = regex_constants::ECMAScript) -> basic_regex<typename iterator_traits<ForwardIterator>::value_type>;}

28.6.7.2 Constructors [re.regex.construct]

Postconditions: *this does not match any character sequence.

explicit basic_regex(const charT* p, flag_type f = regex_constants::ECMAScript);

Preconditions: [p, p + char_traits<charT>​::​length(p)) is a valid range.

Effects: The object's internal finite state machine is constructed from the regular expression contained in the sequence of characters [p, p + char_traits<charT>​::​​length(p)), and interpreted according to the flags f.

Postconditions: flags() returns f.

mark_count() returns the number of marked sub-expressions within the expression.

Throws: regex_error if [p, p + char_traits<charT>​::​length(p)) is not a valid regular expression.

basic_regex(const charT* p, size_t len, flag_type f = regex_constants::ECMAScript);

Preconditions: [p, p + len) is a valid range.

Effects: The object's internal finite state machine is constructed from the regular expression contained in the sequence of characters [p, p + len), and interpreted according the flags specified in f.

Postconditions: flags() returns f.

mark_count() returns the number of marked sub-expressions within the expression.

Throws: regex_error if [p, p + len) is not a valid regular expression.

basic_regex(const basic_regex& e);

Postconditions: flags() and mark_count() returne.flags() and e.mark_count(), respectively.

basic_regex(basic_regex&& e) noexcept;

Postconditions: flags() and mark_count() return the values thate.flags() and e.mark_count(), respectively, had before construction.

template<class ST, class SA> explicit basic_regex(const basic_string<charT, ST, SA>& s, flag_type f = regex_constants::ECMAScript);

Effects: The object's internal finite state machine is constructed from the regular expression contained in the string s, and interpreted according to the flags specified in f.

Postconditions: flags() returns f.

mark_count() returns the number of marked sub-expressions within the expression.

Throws: regex_error if s is not a valid regular expression.

template<class ForwardIterator> basic_regex(ForwardIterator first, ForwardIterator last, flag_type f = regex_constants::ECMAScript);

Effects: The object's internal finite state machine is constructed from the regular expression contained in the sequence of characters [first, last), and interpreted according to the flags specified in f.

Postconditions: flags() returns f.

mark_count() returns the number of marked sub-expressions within the expression.

Throws: regex_error if the sequence [first, last) is not a valid regular expression.

basic_regex(initializer_list<charT> il, flag_type f = regex_constants::ECMAScript);

Effects: Same as basic_regex(il.begin(), il.end(), f).

28.6.7.3 Assignment [re.regex.assign]

basic_regex& operator=(const basic_regex& e);

Postconditions: flags() and mark_count() returne.flags() and e.mark_count(), respectively.

basic_regex& operator=(basic_regex&& e) noexcept;

Postconditions: flags() and mark_count() return the values thate.flags() and e.mark_count(), respectively, had before assignment.

e is in a valid state with unspecified value.

basic_regex& operator=(const charT* p);

Effects: Equivalent to: return assign(p);

basic_regex& operator=(initializer_list<charT> il);

Effects: Equivalent to: return assign(il.begin(), il.end());

template<class ST, class SA> basic_regex& operator=(const basic_string<charT, ST, SA>& s);

Effects: Equivalent to: return assign(s);

basic_regex& assign(const basic_regex& e);

Effects: Equivalent to: return *this = e;

basic_regex& assign(basic_regex&& e) noexcept;

Effects: Equivalent to: return *this = std​::​move(e);

basic_regex& assign(const charT* p, flag_type f = regex_constants::ECMAScript);

Effects: Equivalent to: return assign(string_type(p), f);

basic_regex& assign(const charT* p, size_t len, flag_type f = regex_constants::ECMAScript);

Effects: Equivalent to: return assign(string_type(p, len), f);

template<class ST, class SA> basic_regex& assign(const basic_string<charT, ST, SA>& s, flag_type f = regex_constants::ECMAScript);

Effects: Assigns the regular expression contained in the strings, interpreted according the flags specified in f.

If an exception is thrown, *this is unchanged.

Postconditions: If no exception is thrown,flags() returns f and mark_count()returns the number of marked sub-expressions within the expression.

Throws: regex_error if s is not a valid regular expression.

template<class InputIterator> basic_regex& assign(InputIterator first, InputIterator last, flag_type f = regex_constants::ECMAScript);

Effects: Equivalent to: return assign(string_type(first, last), f);

basic_regex& assign(initializer_list<charT> il, flag_type f = regex_constants::ECMAScript);

Effects: Equivalent to: return assign(il.begin(), il.end(), f);

28.6.7.4 Constant operations [re.regex.operations]

unsigned mark_count() const;

Effects: Returns the number of marked sub-expressions within the regular expression.

Effects: Returns a copy of the regular expression syntax flags that were passed to the object's constructor or to the last call to assign.

28.6.7.5 Locale [re.regex.locale]

locale_type imbue(locale_type loc);

Effects: Returns the result of traits_inst.imbue(loc) wheretraits_inst is a (default-initialized) instance of the template type argument traits stored within the object.

After a call to imbue the basic_regex object does not match any character sequence.

locale_type getloc() const;

Effects: Returns the result of traits_inst.getloc() wheretraits_inst is a (default-initialized) instance of the template parameter traits stored within the object.

28.6.7.6 Swap [re.regex.swap]

void swap(basic_regex& e);

Effects: Swaps the contents of the two regular expressions.

Postconditions: *this contains the regular expression that was in e, e contains the regular expression that was in *this.

Complexity: Constant time.

28.6.7.7 Non-member functions [re.regex.nonmemb]

template<class charT, class traits> void swap(basic_regex<charT, traits>& lhs, basic_regex<charT, traits>& rhs);

Effects: Calls lhs.swap(rhs).

28.6.8 Class template sub_match [re.submatch]

28.6.8.1 General [re.submatch.general]

Class template sub_match denotes the sequence of characters matched by a particular marked sub-expression.

namespace std { template<class BidirectionalIterator> class sub_match : public pair<BidirectionalIterator, BidirectionalIterator> { public: using value_type = typename iterator_traits<BidirectionalIterator>::value_type;using difference_type = typename iterator_traits<BidirectionalIterator>::difference_type;using iterator = BidirectionalIterator;using string_type = basic_string<value_type>;bool matched;constexpr sub_match(); difference_type length() const;operator string_type() const; string_type str() const;int compare(const sub_match& s) const;int compare(const string_type& s) const;int compare(const value_type* s) const;void swap(sub_match& s) noexcept(see below);};}

28.6.8.2 Members [re.submatch.members]

Effects: Value-initializes the pair base class subobject and the membermatched.

difference_type length() const;

Returns: matched ? distance(first, second) : 0.

operator string_type() const;

Returns: matched ? string_type(first, second) : string_type().

Returns: matched ? string_type(first, second) : string_type().

int compare(const sub_match& s) const;

Returns: str().compare(s.str()).

int compare(const string_type& s) const;

Returns: str().compare(s).

int compare(const value_type* s) const;

Returns: str().compare(s).

void swap(sub_match& s) noexcept(_see below_);

Effects: Equivalent to:this->pair<BidirectionalIterator, BidirectionalIterator>::swap(s); std::swap(matched, s.matched);

Remarks: The exception specification is equivalent tois_nothrow_swappable_v<BidirectionalIterator>.

28.6.8.3 Non-member operators [re.submatch.op]

Let SM-CAT(I) becompare_three_way_result_t<basic_string<typename iterator_traits<I>::value_type>>

template<class BiIter> bool operator==(const sub_match<BiIter>& lhs, const sub_match<BiIter>& rhs);

Returns: lhs.compare(rhs) == 0.

template<class BiIter> auto operator<=>(const sub_match<BiIter>& lhs, const sub_match<BiIter>& rhs);

Returns: static_cast<_SM-CAT_(BiIter)>(lhs.compare(rhs) <=> 0).

template<class BiIter, class ST, class SA> bool operator==( const sub_match<BiIter>& lhs,const basic_string<typename iterator_traits<BiIter>::value_type, ST, SA>& rhs);

Returns: lhs.compare(typename sub_match<BiIter>::string_type(rhs.data(), rhs.size())) == 0

template<class BiIter, class ST, class SA> auto operator<=>( const sub_match<BiIter>& lhs,const basic_string<typename iterator_traits<BiIter>::value_type, ST, SA>& rhs);

Returns: static_cast<_SM-CAT_(BiIter)>(lhs.compare( typename sub_match<BiIter>::string_type(rhs.data(), rhs.size())) <=> 0 )

template<class BiIter> bool operator==(const sub_match<BiIter>& lhs,const typename iterator_traits<BiIter>::value_type* rhs);

Returns: lhs.compare(rhs) == 0.

template<class BiIter> auto operator<=>(const sub_match<BiIter>& lhs,const typename iterator_traits<BiIter>::value_type* rhs);

Returns: static_cast<_SM-CAT_(BiIter)>(lhs.compare(rhs) <=> 0).

template<class BiIter> bool operator==(const sub_match<BiIter>& lhs,const typename iterator_traits<BiIter>::value_type& rhs);

Returns: lhs.compare(typename sub_match<BiIter>​::​string_type(1, rhs)) == 0.

template<class BiIter> auto operator<=>(const sub_match<BiIter>& lhs,const typename iterator_traits<BiIter>::value_type& rhs);

Returns: static_cast<_SM-CAT_(BiIter)>(lhs.compare( typename sub_match<BiIter>::string_type(1, rhs)) <=> 0 )

template<class charT, class ST, class BiIter> basic_ostream<charT, ST>& operator<<(basic_ostream<charT, ST>& os, const sub_match<BiIter>& m);

28.6.9 Class template match_results [re.results]

28.6.9.1 General [re.results.general]

Class template match_results denotes a collection of character sequences representing the result of a regular expression match.

Storage for the collection is allocated and freed as necessary by the member functions of class template match_results.

The class template match_results meets the requirements of an allocator-aware container ([container.alloc.reqmts]) and of a sequence container ([container.requirements.general], [sequence.reqmts]) except that only copy assignment, move assignment, and operations defined for const-qualified sequence containers are supported and that the semantics of the comparison operator functions are different from those required for a container.

A default-constructed match_results object has no fully established result state.

A match result is ready when, as a consequence of a completed regular expression match modifying such an object, its result state becomes fully established.

The effects of calling most member functions from a match_results object that is not ready are undefined.

The sub_match object stored at index 0 represents sub-expression 0, i.e., the whole match.

In this case the sub_match membermatched is always true.

The sub_matchobject stored at index n denotes what matched the marked sub-expression n within the matched expression.

If the sub-expression n participated in a regular expression match then the sub_match member matched evaluates to true, and members first and second denote the range of characters [first, second) which formed that match.

Otherwise matched is false, and members firstand second point to the end of the sequence that was searched.

[Note 1:

The sub_match objects representing different sub-expressions that did not participate in a regular expression match need not be distinct.

— _end note_]

namespace std { template<class BidirectionalIterator,class Allocator = allocator<sub_match<BidirectionalIterator>>> class match_results { public: using value_type = sub_match<BidirectionalIterator>;using const_reference = const value_type&;using reference = value_type&;using const_iterator = implementation-defined;using iterator = const_iterator;using difference_type = typename iterator_traits<BidirectionalIterator>::difference_type;using size_type = typename allocator_traits<Allocator>::size_type;using allocator_type = Allocator;using char_type = typename iterator_traits<BidirectionalIterator>::value_type;using string_type = basic_string<char_type>; match_results() : match_results(Allocator()) {} explicit match_results(const Allocator& a); match_results(const match_results& m); match_results(const match_results& m, const Allocator& a); match_results(match_results&& m) noexcept; match_results(match_results&& m, const Allocator& a); match_results& operator=(const match_results& m); match_results& operator=(match_results&& m);~match_results();bool ready() const; size_type size() const; size_type max_size() const;bool empty() const; difference_type length(size_type sub = 0) const; difference_type position(size_type sub = 0) const; string_type str(size_type sub = 0) const; const_reference operator[](size_type n) const; const_reference prefix() const; const_reference suffix() const; const_iterator begin() const; const_iterator end() const; const_iterator cbegin() const; const_iterator cend() const;template<class OutputIter> OutputIter format(OutputIter out,const char_type* fmt_first, const char_type* fmt_last, regex_constants::match_flag_type flags = regex_constants::format_default) const;template<class OutputIter, class ST, class SA> OutputIter format(OutputIter out,const basic_string<char_type, ST, SA>& fmt, regex_constants::match_flag_type flags = regex_constants::format_default) const;template<class ST, class SA> basic_string<char_type, ST, SA> format(const basic_string<char_type, ST, SA>& fmt, regex_constants::match_flag_type flags = regex_constants::format_default) const; string_type format(const char_type* fmt, regex_constants::match_flag_type flags = regex_constants::format_default) const; allocator_type get_allocator() const;void swap(match_results& that);};}

28.6.9.2 Constructors [re.results.const]

Table 120 lists the postconditions ofmatch_results copy/move constructors and copy/move assignment operators.

For move operations, the results of the expressions depending on the parameter m denote the values they had before the respective function calls.

explicit match_results(const Allocator& a);

Effects: The stored Allocator value is constructed from a.

Postconditions: ready() returns false.

size() returns 0.

match_results(const match_results& m); match_results(const match_results& m, const Allocator& a);

Effects: For the first form, the stored Allocator value is obtained as specified in [container.reqmts].

For the second form, the stored Allocator value is constructed from a.

Postconditions: As specified in Table 120.

match_results(match_results&& m) noexcept; match_results(match_results&& m, const Allocator& a);

Effects: For the first form, the stored Allocator value is move constructed from m.get_allocator().

For the second form, the stored Allocator value is constructed from a.

Postconditions: As specified in Table 120.

Throws: The second form throws nothing ifa == m.get_allocator() is true.

match_results& operator=(const match_results& m);

Postconditions: As specified in Table 120.

match_results& operator=(match_results&& m);

Postconditions: As specified in Table 120.

Table 120 — match_results copy/move operation postconditions [tab:re.results.const]

🔗Element Value
🔗ready() m.ready()
🔗size() m.size()
🔗str(n) m.str(n) for all non-negative integers n < m.size()
🔗prefix() m.prefix()
🔗suffix() m.suffix()
🔗(*this)[n] m[n] for all non-negative integers n < m.size()
🔗length(n) m.length(n) for all non-negative integers n < m.size()
🔗position(n) m.position(n) for all non-negative integers n < m.size()

28.6.9.3 State [re.results.state]

Returns: true if *this has a fully established result state, otherwisefalse.

28.6.9.4 Size [re.results.size]

Returns: One plus the number of marked sub-expressions in the regular expression that was matched if *this represents the result of a successful match.

Otherwise returns 0.

[Note 1:

The state of a match_results object can be modified only by passing that object to regex_match or regex_search.

Subclauses [re.alg.match] and [re.alg.search] specify the effects of those algorithms on their match_results arguments.

— _end note_]

size_type max_size() const;

Returns: The maximum number of sub_match elements that can be stored in *this.

28.6.9.5 Element access [re.results.acc]

difference_type length(size_type sub = 0) const;

Preconditions: ready() == true.

Returns: (*this)[sub].length().

difference_type position(size_type sub = 0) const;

Preconditions: ready() == true.

Returns: The distance from the start of the target sequence to (*this)[sub].first.

string_type str(size_type sub = 0) const;

Preconditions: ready() == true.

Returns: string_type((*this)[sub]).

const_reference operator[](size_type n) const;

Preconditions: ready() == true.

Returns: A reference to the sub_match object representing the character sequence that matched marked sub-expression n.

If n == 0then returns a reference to a sub_match object representing the character sequence that matched the whole regular expression.

Ifn >= size() then returns a sub_match object representing an unmatched sub-expression.

const_reference prefix() const;

Preconditions: ready() == true.

Returns: A reference to the sub_match object representing the character sequence from the start of the string being matched/searched to the start of the match found.

const_reference suffix() const;

Preconditions: ready() == true.

Returns: A reference to the sub_match object representing the character sequence from the end of the match found to the end of the string being matched/searched.

const_iterator begin() const; const_iterator cbegin() const;

Returns: A starting iterator that enumerates over all the sub-expressions stored in *this.

const_iterator end() const; const_iterator cend() const;

Returns: A terminating iterator that enumerates over all the sub-expressions stored in *this.

28.6.9.6 Formatting [re.results.form]

template<class OutputIter> OutputIter format( OutputIter out,const char_type* fmt_first, const char_type* fmt_last, regex_constants::match_flag_type flags = regex_constants::format_default) const;

Preconditions: ready() == true and OutputIter meets the requirements for a_Cpp17OutputIterator_ ([output.iterators]).

Effects: Copies the character sequence [fmt_first, fmt_last) to OutputIter out.

Replaces each format specifier or escape sequence in the copied range with either the character(s) it represents or the sequence of characters within *this to which it refers.

The bitmasks specified in flags determine which format specifiers and escape sequences are recognized.

template<class OutputIter, class ST, class SA> OutputIter format( OutputIter out,const basic_string<char_type, ST, SA>& fmt, regex_constants::match_flag_type flags = regex_constants::format_default) const;

Effects: Equivalent to:return format(out, fmt.data(), fmt.data() + fmt.size(), flags);

template<class ST, class SA> basic_string<char_type, ST, SA> format( const basic_string<char_type, ST, SA>& fmt, regex_constants::match_flag_type flags = regex_constants::format_default) const;

Preconditions: ready() == true.

Effects: Constructs an empty string result of type basic_string<char_type, ST, SA> and calls:format(back_inserter(result), fmt, flags);

string_type format( const char_type* fmt, regex_constants::match_flag_type flags = regex_constants::format_default) const;

Preconditions: ready() == true.

Effects: Constructs an empty string result of type string_type and calls:format(back_inserter(result), fmt, fmt + char_traits<char_type>::length(fmt), flags);

28.6.9.7 Allocator [re.results.all]

allocator_type get_allocator() const;

Returns: A copy of the Allocator that was passed to the object's constructor or, if that allocator has been replaced, a copy of the most recent replacement.

28.6.9.8 Swap [re.results.swap]

void swap(match_results& that);

Effects: Swaps the contents of the two sequences.

Postconditions: *this contains the sequence of matched sub-expressions that were in that, that contains the sequence of matched sub-expressions that were in *this.

Complexity: Constant time.

template<class BidirectionalIterator, class Allocator> void swap(match_results<BidirectionalIterator, Allocator>& m1, match_results<BidirectionalIterator, Allocator>& m2);

Effects: As if by m1.swap(m2).

28.6.9.9 Non-member functions [re.results.nonmember]

template<class BidirectionalIterator, class Allocator> bool operator==(const match_results<BidirectionalIterator, Allocator>& m1,const match_results<BidirectionalIterator, Allocator>& m2);

Returns: true if neither match result is ready, false if one match result is ready and the other is not.

If both match results are ready, returns true only if

28.6.10 Regular expression algorithms [re.alg]

28.6.10.1 Exceptions [re.except]

The algorithms described in subclause [re.alg] may throw an exception of type regex_error.

If such an exception e is thrown,e.code() shall return either regex_constants​::​error_complexityor regex_constants​::​error_stack.

28.6.10.2 regex_match [re.alg.match]

template<class BidirectionalIterator, class Allocator, class charT, class traits> bool regex_match(BidirectionalIterator first, BidirectionalIterator last, match_results<BidirectionalIterator, Allocator>& m,const basic_regex<charT, traits>& e, regex_constants::match_flag_type flags = regex_constants::match_default);

Effects: Determines whether there is a match between the regular expression e, and all of the character sequence [first, last).

The parameter flags is used to control how the expression is matched against the character sequence.

When determining if there is a match, only potential matches that match the entire character sequence are considered.

Returns true if such a match exists, falseotherwise.

[Example 1: std::regex re("Get|GetValue"); std::cmatch m; regex_search("GetValue", m, re); regex_match ("GetValue", m, re); regex_search("GetValues", m, re); regex_match ("GetValues", m, re); — _end example_]

Postconditions: m.ready() == true in all cases.

If the function returns false, then the effect on parameter m is unspecified except that m.size()returns 0 and m.empty() returns true.

Otherwise the effects on parameter m are given in Table 121.

Table 121 — Effects of regex_match algorithm [tab:re.alg.match]

🔗Element Value
🔗m.size() 1 + e.mark_count()
🔗m.empty() false
🔗m.prefix().first first
🔗m.prefix().second first
🔗m.prefix().matched false
🔗m.suffix().first last
🔗m.suffix().second last
🔗m.suffix().matched false
🔗m[0].first first
🔗m[0].second last
🔗m[0].matched true
🔗m[n].first For all integers 0 < n < m.size(), the start of the sequence that matched sub-expression n. Alternatively, if sub-expression n did not participate in the match, then last.
🔗m[n].second For all integers 0 < n < m.size(), the end of the sequence that matched sub-expression n. Alternatively, if sub-expression n did not participate in the match, then last.
🔗m[n].matched For all integers 0 < n < m.size(), true if sub-expression n participated in the match, false otherwise.

template<class BidirectionalIterator, class charT, class traits> bool regex_match(BidirectionalIterator first, BidirectionalIterator last,const basic_regex<charT, traits>& e, regex_constants::match_flag_type flags = regex_constants::match_default);

Effects: Behaves “as if” by constructing an instance ofmatch_results<BidirectionalIterator> what, and then returning the result ofregex_match(first, last, what, e, flags).

template<class charT, class Allocator, class traits> bool regex_match(const charT* str, match_results<const charT*, Allocator>& m,const basic_regex<charT, traits>& e, regex_constants::match_flag_type flags = regex_constants::match_default);

Returns: regex_match(str, str + char_traits<charT>​::​length(str), m, e, flags).

template<class ST, class SA, class Allocator, class charT, class traits> bool regex_match(const basic_string<charT, ST, SA>& s, match_results<typename basic_string<charT, ST, SA>::const_iterator, Allocator>& m,const basic_regex<charT, traits>& e, regex_constants::match_flag_type flags = regex_constants::match_default);

Returns: regex_match(s.begin(), s.end(), m, e, flags).

template<class charT, class traits> bool regex_match(const charT* str,const basic_regex<charT, traits>& e, regex_constants::match_flag_type flags = regex_constants::match_default);

Returns: regex_match(str, str + char_traits<charT>​::​length(str), e, flags).

template<class ST, class SA, class charT, class traits> bool regex_match(const basic_string<charT, ST, SA>& s,const basic_regex<charT, traits>& e, regex_constants::match_flag_type flags = regex_constants::match_default);

Returns: regex_match(s.begin(), s.end(), e, flags).

28.6.10.3 regex_search [re.alg.search]

template<class BidirectionalIterator, class Allocator, class charT, class traits> bool regex_search(BidirectionalIterator first, BidirectionalIterator last, match_results<BidirectionalIterator, Allocator>& m,const basic_regex<charT, traits>& e, regex_constants::match_flag_type flags = regex_constants::match_default);

Effects: Determines whether there is some sub-sequence within [first, last) that matches the regular expression e.

The parameter flags is used to control how the expression is matched against the character sequence.

Returns true if such a sequence exists, false otherwise.

Postconditions: m.ready() == true in all cases.

If the function returns false, then the effect on parameter m is unspecified except that m.size()returns 0 and m.empty() returns true.

Otherwise the effects on parameter m are given in Table 122.

Table 122 — Effects of regex_search algorithm [tab:re.alg.search]

🔗Element Value
🔗m.size() 1 + e.mark_count()
🔗m.empty() false
🔗m.prefix().first first
🔗m.prefix().second m[0].first
🔗m.prefix().matched m.prefix().first != m.prefix().second
🔗m.suffix().first m[0].second
🔗m.suffix().second last
🔗m.suffix().matched m.suffix().first != m.suffix().second
🔗m[0].first The start of the sequence of characters that matched the regular expression
🔗m[0].second The end of the sequence of characters that matched the regular expression
🔗m[0].matched true
🔗m[n].first For all integers 0 < n < m.size(), the start of the sequence that matched sub-expression n. Alternatively, if sub-expression ndid not participate in the match, then last.
🔗m[n].second For all integers 0 < n < m.size(), the end of the sequence that matched sub-expression n. Alternatively, if sub-expression n did not participate in the match, then last.
🔗m[n].matched For all integers 0 < n < m.size(), true if sub-expression nparticipated in the match, false otherwise.

template<class charT, class Allocator, class traits> bool regex_search(const charT* str, match_results<const charT*, Allocator>& m,const basic_regex<charT, traits>& e, regex_constants::match_flag_type flags = regex_constants::match_default);

Returns: regex_search(str, str + char_traits<charT>​::​length(str), m, e, flags).

template<class ST, class SA, class Allocator, class charT, class traits> bool regex_search(const basic_string<charT, ST, SA>& s, match_results<typename basic_string<charT, ST, SA>::const_iterator, Allocator>& m,const basic_regex<charT, traits>& e, regex_constants::match_flag_type flags = regex_constants::match_default);

Returns: regex_search(s.begin(), s.end(), m, e, flags).

template<class BidirectionalIterator, class charT, class traits> bool regex_search(BidirectionalIterator first, BidirectionalIterator last,const basic_regex<charT, traits>& e, regex_constants::match_flag_type flags = regex_constants::match_default);

Effects: Behaves “as if” by constructing an object whatof type match_results<BidirectionalIterator> and returningregex_search(first, last, what, e, flags).

template<class charT, class traits> bool regex_search(const charT* str,const basic_regex<charT, traits>& e, regex_constants::match_flag_type flags = regex_constants::match_default);

Returns: regex_search(str, str + char_traits<charT>​::​length(str), e, flags).

template<class ST, class SA, class charT, class traits> bool regex_search(const basic_string<charT, ST, SA>& s,const basic_regex<charT, traits>& e, regex_constants::match_flag_type flags = regex_constants::match_default);

Returns: regex_search(s.begin(), s.end(), e, flags).

28.6.10.4 regex_replace [re.alg.replace]

template<class OutputIterator, class BidirectionalIterator,class traits, class charT, class ST, class SA> OutputIterator regex_replace(OutputIterator out, BidirectionalIterator first, BidirectionalIterator last,const basic_regex<charT, traits>& e,const basic_string<charT, ST, SA>& fmt, regex_constants::match_flag_type flags = regex_constants::match_default);template<class OutputIterator, class BidirectionalIterator, class traits, class charT> OutputIterator regex_replace(OutputIterator out, BidirectionalIterator first, BidirectionalIterator last,const basic_regex<charT, traits>& e,const charT* fmt, regex_constants::match_flag_type flags = regex_constants::match_default);

Effects: Constructs a regex_iterator object ias if byregex_iterator<BidirectionalIterator, charT, traits> i(first, last, e, flags) and uses i to enumerate through all of the matches m of type match_results<BidirectionalIterator>that occur within the sequence [first, last).

If no such matches are found and!(flags & regex_constants​::​format_no_copy), then callsout = copy(first, last, out)

If any matches are found then, for each such match:

Finally, if such a match is found and !(flags & regex_constants​::​format_no_copy), callsout = copy(last_m.suffix().first, last_m.suffix().second, out) where last_m is a copy of the last match found.

If flags & regex_constants​::​format_first_onlyis nonzero, then only the first match found is replaced.

template<class traits, class charT, class ST, class SA, class FST, class FSA> basic_string<charT, ST, SA> regex_replace(const basic_string<charT, ST, SA>& s,const basic_regex<charT, traits>& e,const basic_string<charT, FST, FSA>& fmt, regex_constants::match_flag_type flags = regex_constants::match_default);template<class traits, class charT, class ST, class SA> basic_string<charT, ST, SA> regex_replace(const basic_string<charT, ST, SA>& s,const basic_regex<charT, traits>& e,const charT* fmt, regex_constants::match_flag_type flags = regex_constants::match_default);

Effects: Constructs an empty string result of type basic_string<charT, ST, SA> and calls:regex_replace(back_inserter(result), s.begin(), s.end(), e, fmt, flags);

template<class traits, class charT, class ST, class SA> basic_string<charT> regex_replace(const charT* s,const basic_regex<charT, traits>& e,const basic_string<charT, ST, SA>& fmt, regex_constants::match_flag_type flags = regex_constants::match_default);template<class traits, class charT> basic_string<charT> regex_replace(const charT* s,const basic_regex<charT, traits>& e,const charT* fmt, regex_constants::match_flag_type flags = regex_constants::match_default);

Effects: Constructs an empty string result of type basic_string<charT> and calls:regex_replace(back_inserter(result), s, s + char_traits<charT>::length(s), e, fmt, flags);

28.6.11 Regular expression iterators [re.iter]

28.6.11.1 Class template regex_iterator [re.regiter]

28.6.11.1.1 General [re.regiter.general]

The class template regex_iterator is an iterator adaptor.

It represents a new view of an existing iterator sequence, by enumerating all the occurrences of a regular expression within that sequence.

A regex_iterator uses regex_search to find successive regular expression matches within the sequence from which it was constructed.

After the iterator is constructed, and every time operator++ is used, the iterator finds and stores a value ofmatch_results<BidirectionalIterator>.

If the end of the sequence is reached (regex_search returns false), the iterator becomes equal to the end-of-sequence iterator value.

The default constructor constructs an end-of-sequence iterator object, which is the only legitimate iterator to be used for the end condition.

The result of operator* on an end-of-sequence iterator is not defined.

For any other iterator value a constmatch_results<BidirectionalIterator>& is returned.

The result ofoperator-> on an end-of-sequence iterator is not defined.

For any other iterator value a const match_results<BidirectionalIterator>* is returned.

It is impossible to store things into regex_iterators.

Two end-of-sequence iterators are always equal.

An end-of-sequence iterator is not equal to a non-end-of-sequence iterator.

Two non-end-of-sequence iterators are equal when they are constructed from the same arguments.

namespace std { template<class BidirectionalIterator,class charT = typename iterator_traits<BidirectionalIterator>::value_type,class traits = regex_traits<charT>> class regex_iterator { public: using regex_type = basic_regex<charT, traits>;using iterator_category = forward_iterator_tag;using iterator_concept = input_iterator_tag;using value_type = match_results<BidirectionalIterator>;using difference_type = ptrdiff_t;using pointer = const value_type*;using reference = const value_type&; regex_iterator(); regex_iterator(BidirectionalIterator a, BidirectionalIterator b,const regex_type& re, regex_constants::match_flag_type m = regex_constants::match_default); regex_iterator(BidirectionalIterator, BidirectionalIterator,const regex_type&&, regex_constants::match_flag_type = regex_constants::match_default) = delete; regex_iterator(const regex_iterator&); regex_iterator& operator=(const regex_iterator&);bool operator==(const regex_iterator&) const;bool operator==(default_sentinel_t) const { return *this == regex_iterator(); } const value_type& operator*() const;const value_type* operator->() const; regex_iterator& operator++(); regex_iterator operator++(int);private: BidirectionalIterator begin; BidirectionalIterator end; const regex_type* pregex; regex_constants::match_flag_type flags; match_results<BidirectionalIterator> match; };}

An object of type regex_iterator that is not an end-of-sequence iterator holds a zero-length match if match[0].matched == true andmatch[0].first == match[0].second.

[Note 1:

For example, this can occur when the part of the regular expression that matched consists only of an assertion (such as '^', '$','\b', '\B').

— _end note_]

28.6.11.1.2 Constructors [re.regiter.cnstr]

Effects: Constructs an end-of-sequence iterator.

regex_iterator(BidirectionalIterator a, BidirectionalIterator b,const regex_type& re, regex_constants::match_flag_type m = regex_constants::match_default);

Effects: Initializes begin and end toa and b, respectively, setspregex to addressof(re), sets flags tom, then calls regex_search(begin, end, match, *pregex, flags).

If this call returns false the constructor sets *this to the end-of-sequence iterator.

28.6.11.1.3 Comparisons [re.regiter.comp]

bool operator==(const regex_iterator& right) const;

Returns: true if *this and right are both end-of-sequence iterators or if the following conditions all hold:

otherwise false.

28.6.11.1.4 Indirection [re.regiter.deref]

const value_type& operator*() const;

const value_type* operator->() const;

Returns: addressof(match).

28.6.11.1.5 Increment [re.regiter.incr]

regex_iterator& operator++();

Effects: Constructs a local variable start of type BidirectionalIterator and initializes it with the value of match[0].second.

If the iterator holds a zero-length match and start == end the operator sets *this to the end-of-sequence iterator and returns *this.

Otherwise, if the iterator holds a zero-length match, the operator calls:regex_search(start, end, match, *pregex, flags | regex_constants::match_not_null | regex_constants::match_continuous)

If the call returns true the operator returns *this.

Otherwise the operator increments start and continues as if the most recent match was not a zero-length match.

If the most recent match was not a zero-length match, the operator setsflags to flags | regex_constants​::​match_prev_avail and calls regex_search(start, end, match, *pregex, flags).

If the call returnsfalse the iterator sets *this to the end-of-sequence iterator.

The iterator then returns *this.

In all cases in which the call to regex_search returns true,match.prefix().first shall be equal to the previous value ofmatch[0].second, and for each index i in the half-open range [0, match.size()) for which match[i].matched is true,match.position(i)shall return distance(begin, match[i].​first).

[Note 1:

This means that match.position(i) gives the offset from the beginning of the target sequence, which is often not the same as the offset from the sequence passed in the call to regex_search.

— _end note_]

It is unspecified how the implementation makes these adjustments.

[Note 2:

This means that an implementation can call an implementation-specific search function, in which case a program-defined specialization of regex_search will not be called.

— _end note_]

regex_iterator operator++(int);

Effects: As if by:regex_iterator tmp = *this;++(*this);return tmp;

28.6.11.2 Class template regex_token_iterator [re.tokiter]

28.6.11.2.1 General [re.tokiter.general]

The class template regex_token_iterator is an iterator adaptor; that is to say it represents a new view of an existing iterator sequence, by enumerating all the occurrences of a regular expression within that sequence, and presenting one or more sub-expressions for each match found.

Each position enumerated by the iterator is a sub_match class template instance that represents what matched a particular sub-expression within the regular expression.

When class regex_token_iterator is used to enumerate a single sub-expression with index the iterator performs field splitting: that is to say it enumerates one sub-expression for each section of the character container sequence that does not match the regular expression specified.

After it is constructed, the iterator finds and stores a valueregex_iterator<BidirectionalIterator> positionand sets the internal count N to zero.

It also maintains a sequencesubs which contains a list of the sub-expressions which will be enumerated.

Every time operator++ is used the count N is incremented; if N exceeds or equals subs.size(), then the iterator increments member positionand sets count N to zero.

If the end of sequence is reached (position is equal to the end of sequence iterator), the iterator becomes equal to the end-of-sequence iterator value, unless the sub-expression being enumerated has index , in which case the iterator enumerates one last sub-expression that contains all the characters from the end of the last regular expression match to the end of the input sequence being enumerated, provided that this would not be an empty sub-expression.

The default constructor constructs an end-of-sequence iterator object, which is the only legitimate iterator to be used for the end condition.

The result of operator* on an end-of-sequence iterator is not defined.

For any other iterator value aconst sub_match<BidirectionalIterator>& is returned.

The result of operator-> on an end-of-sequence iterator is not defined.

For any other iterator value a constsub_match<BidirectionalIterator>* is returned.

It is impossible to store things into regex_token_iterators.

Two end-of-sequence iterators are always equal.

An end-of-sequence iterator is not equal to a non-end-of-sequence iterator.

Two non-end-of-sequence iterators are equal when they are constructed from the same arguments.

namespace std { template<class BidirectionalIterator,class charT = typename iterator_traits<BidirectionalIterator>::value_type,class traits = regex_traits<charT>> class regex_token_iterator { public: using regex_type = basic_regex<charT, traits>;using iterator_category = forward_iterator_tag;using iterator_concept = input_iterator_tag;using value_type = sub_match<BidirectionalIterator>;using difference_type = ptrdiff_t;using pointer = const value_type*;using reference = const value_type&; regex_token_iterator(); regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,const regex_type& re,int submatch = 0, regex_constants::match_flag_type m = regex_constants::match_default); regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,const regex_type& re,const vector<int>& submatches, regex_constants::match_flag_type m = regex_constants::match_default); regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,const regex_type& re, initializer_list<int> submatches, regex_constants::match_flag_type m = regex_constants::match_default);template<size_t N> regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,const regex_type& re,const int (&submatches)[N], regex_constants::match_flag_type m = regex_constants::match_default); regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,const regex_type&& re,int submatch = 0, regex_constants::match_flag_type m = regex_constants::match_default) = delete; regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,const regex_type&& re,const vector<int>& submatches, regex_constants::match_flag_type m = regex_constants::match_default) = delete; regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,const regex_type&& re, initializer_list<int> submatches, regex_constants::match_flag_type m = regex_constants::match_default) = delete;template<size_t N> regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,const regex_type&& re,const int (&submatches)[N], regex_constants::match_flag_type m = regex_constants::match_default) = delete; regex_token_iterator(const regex_token_iterator&); regex_token_iterator& operator=(const regex_token_iterator&);bool operator==(const regex_token_iterator&) const;bool operator==(default_sentinel_t) const { return *this == regex_token_iterator(); } const value_type& operator*() const;const value_type* operator->() const; regex_token_iterator& operator++(); regex_token_iterator operator++(int);private: using position_iterator = regex_iterator<BidirectionalIterator, charT, traits>; position_iterator position; const value_type* result; value_type suffix; size_t N; vector<int> subs; };}

A suffix iterator is a regex_token_iterator object that points to a final sequence of characters at the end of the target sequence.

In a suffix iterator the member result holds a pointer to the data member suffix, the value of the member suffix.matchis true, suffix.first points to the beginning of the final sequence, and suffix.second points to the end of the final sequence.

[Note 1:

For a suffix iterator, data member suffix.first is the same as the end of the last match found, and suffix​.second is the same as the end of the target sequence.

— _end note_]

The current match is (*position).prefix() if subs[N] == -1, or(*position)[subs[N]] for any other value of subs[N].

28.6.11.2.2 Constructors [re.tokiter.cnstr]

Effects: Constructs the end-of-sequence iterator.

regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,const regex_type& re,int submatch = 0, regex_constants::match_flag_type m = regex_constants::match_default); regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,const regex_type& re,const vector<int>& submatches, regex_constants::match_flag_type m = regex_constants::match_default); regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,const regex_type& re, initializer_list<int> submatches, regex_constants::match_flag_type m = regex_constants::match_default);template<size_t N> regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,const regex_type& re,const int (&submatches)[N], regex_constants::match_flag_type m = regex_constants::match_default);

Preconditions: Each of the initialization values of submatches is >= -1.

Effects: The first constructor initializes the member subs to hold the single value submatch.

The second, third, and fourth constructors initialize the member subs to hold a copy of the sequence of integer values pointed to by the iterator range [begin(submatches), end(submatches)).

Each constructor then sets N to 0, and position toposition_iterator(a, b, re, m).

If position is not an end-of-sequence iterator the constructor sets result to the address of the current match.

Otherwise if any of the values stored in subs is equal to the constructor sets *this to a suffix iterator that points to the range [a, b), otherwise the constructor sets *this to an end-of-sequence iterator.

28.6.11.2.3 Comparisons [re.tokiter.comp]

bool operator==(const regex_token_iterator& right) const;

Returns: true if *this and right are both end-of-sequence iterators, or if *this and right are both suffix iterators and suffix == right.suffix; otherwise returns false if *this or right is an end-of-sequence iterator or a suffix iterator.

Otherwise returns true if position == right.position,N == right.N, and subs == right.subs.

Otherwise returns false.

28.6.11.2.4 Indirection [re.tokiter.deref]

const value_type& operator*() const;

const value_type* operator->() const;

28.6.11.2.5 Increment [re.tokiter.incr]

regex_token_iterator& operator++();

Effects: Constructs a local variable prev of type position_iterator, initialized with the value of position.

If *this is a suffix iterator, sets *this to an end-of-sequence iterator.

Otherwise, if N + 1 < subs.size(), increments N and sets result to the address of the current match.

Otherwise, sets N to 0 and increments position.

If position is not an end-of-sequence iterator the operator sets result to the address of the current match.

Otherwise, if any of the values stored in subs is equal to andprev->suffix().length() is not 0 the operator sets *this to a suffix iterator that points to the range [prev->suffix().first, prev->suffix().second).

Otherwise, sets *this to an end-of-sequence iterator.

regex_token_iterator& operator++(int);

Effects: Constructs a copy tmp of *this, then calls ++(*this).

28.6.12 Modified ECMAScript regular expression grammar [re.grammar]

The regular expression grammar recognized bybasic_regex objects constructed with the ECMAScript flag is that specified by ECMA-262, except as specified below.

Objects of type specialization of basic_regex store within themselves a default-constructed instance of their traits template parameter, henceforth referred to as traits_inst.

This traits_inst object is used to support localization of the regular expression; basic_regex member functions shall not call any locale dependent C or C++ API, including the formatted string input functions.

Instead they shall call the appropriate traits member function to achieve the required effect.

The following productions within the ECMAScript grammar are modified as follows:

ClassAtom ::
-
ClassAtomNoDash
ClassAtomExClass
ClassAtomCollatingElement
ClassAtomEquivalence

IdentityEscape ::
SourceCharacter but not c

The following new productions are then added:

ClassAtomExClass ::
[: ClassName :]

ClassAtomCollatingElement ::
[. ClassName .]

ClassAtomEquivalence ::
[= ClassName =]

ClassName ::
ClassNameCharacter
ClassNameCharacter ClassName

ClassNameCharacter ::
SourceCharacter but not one of . or = or :

The productions ClassAtomExClass, _ClassAtomCollatingElement_and ClassAtomEquivalence provide functionality equivalent to that of the same features in regular expressions in POSIX.

The regular expression grammar may be modified by any regex_constants​::​syntax_option_type flags specified when constructing an object of type specialization of basic_regexaccording to the rules in Table 116.

A ClassName production, when used in ClassAtomExClass, is not valid if traits_inst.lookup_classname returns zero for that name.

The names recognized as valid ClassName s are determined by the type of the traits class, but at least the following names shall be recognized:alnum, alpha, blank, cntrl, digit,graph, lower, print, punct, space,upper, xdigit, d, s, w.

In addition the following expressions shall be equivalent:

\d and [[:digit:]]\D and [^[:digit:]]\s and [[:space:]]\S and [^[:space:]]\w and [_[:alnum:]]\W and [^_[:alnum:]]

A ClassName production when used in a ClassAtomCollatingElement production is not valid if the value returned by traits_inst.lookup_collatename for that name is an empty string.

The results from multiple calls to traits_inst.lookup_classname can be bitwise or'ed together and subsequently passed to traits_inst.isctype.

A ClassName production when used in a ClassAtomEquivalence production is not valid if the value returned by traits_inst.lookup_collatename for that name is an empty string or if the value returned by traits_inst​.transform_primaryfor the result of the call to traits_inst.lookup_collatenameis an empty string.

When the sequence of characters being transformed to a finite state machine contains an invalid class name the translator shall throw an exception object of type regex_error.

If the CV of a UnicodeEscapeSequence is greater than the largest value that can be held in an object of type charT the translator shall throw an exception object of type regex_error.

[Note 1:

This means that values of the form "\uxxxx" that do not fit in a character are invalid.

— _end note_]

Where the regular expression grammar requires the conversion of a sequence of characters to an integral value, this is accomplished by calling traits_inst.value.

The behavior of the internal finite state machine representation when used to match a sequence of characters is as described in ECMA-262.

The behavior is modified according to any match_flag_type flags ([re.matchflag]) specified when using the regular expression object in one of the regular expression algorithms ([re.alg]).

The behavior is also localized by interaction with the traits class template parameter as follows:

See also: ECMA-262 15.10