std::regex_constants(3)

💖 std::regex_constants(3) 💖

okay bestie, welcome to the Library Functions Manual entry for std::regex_constants and honestly? it's giving "the settings menu nobody told you about" 😭✨ this namespace is where every option and flag that std::regex ever wanted lives, and we're about to go through all of it. no skimming, no skipping. we're doing this properly 💅

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🌸 NAME 🌸

std::regex_constants — the ISO C++ 2011 namespace for options and flags used with std::regex. it's the whole control room, fr fr 🎛️

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✨ SYNOPSIS ✨

🎀 5.1 Regular Expression Syntax Options 🎀

so first up, the big enum. this is a bitmask type that tells everyone how to interpret the regex 👑

enum syntax_option_type : unsigned int { _S_icase, _S_nosubs,
    _S_optimize, _S_collate, _S_ECMAScript, _S_basic, _S_extended,
    _S_awk, _S_grep, _S_egrep, _S_polynomial, _S_multiline }

and then, the constants you actually get to touch. all constexpr, all syntax_option_type, all iconic:

constexpr syntax_option_type icase
constexpr syntax_option_type nosubs
constexpr syntax_option_type optimize
constexpr syntax_option_type collate
constexpr syntax_option_type ECMAScript
constexpr syntax_option_type basic
constexpr syntax_option_type extended
constexpr syntax_option_type awk
constexpr syntax_option_type grep
constexpr syntax_option_type egrep
constexpr syntax_option_type multiline

• __multiline — bestie this one is an extension, and it's literally equivalent to regex_constants::multiline for C++11 and C++14. that's the whole thing. ✨

constexpr syntax_option_type __multiline
constexpr syntax_option_type __polynomial

and the operators, because bitmasks gotta bitmask 💅 — every single one of these is noexcept, and every single one is about combining flags on a bitmask type that says how to interpret the regex:

• operator& — constexpr syntax_option_type operator& (syntax_option_type __a, syntax_option_type __b) noexcept
• operator| — constexpr syntax_option_type operator| (syntax_option_type __a, syntax_option_type __b) noexcept
• operator^ — constexpr syntax_option_type operator^ (syntax_option_type __a, syntax_option_type __b) noexcept
• operator~ — constexpr syntax_option_type operator~ (syntax_option_type __a) noexcept
• operator&= — constexpr syntax_option_type & operator&= (syntax_option_type &__a, syntax_option_type __b) noexcept
• operator|= — constexpr syntax_option_type & operator|= (syntax_option_type &__a, syntax_option_type __b) noexcept
• operator^= — constexpr syntax_option_type & operator^= (syntax_option_type &__a, syntax_option_type __b) noexcept

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🌈 5.2 Matching Rules 🌈

here's the tea, and it's an actual rule so listen up 🫶:

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 below for any bitmask elements set.

translation: the grammar you picked runs the show, and then every bitmask bit you set gets to ✨modify✨ the outcome. no cap.

enum match_flag_type : unsigned int { _S_default, _S_not_bol,
    _S_not_eol, _S_not_bow, _S_not_eow, _S_any, _S_not_null,
    _S_continuous, _S_prev_avail, _S_sed, _S_no_copy, _S_first_only,
    _S_match_flag_last }

this is a bitmask type that spells out the regex matching rules, and here's every constant it hands you:

constexpr match_flag_type match_default
constexpr match_flag_type match_not_bol
constexpr match_flag_type match_not_eol
constexpr match_flag_type match_not_bow
constexpr match_flag_type match_not_eow
constexpr match_flag_type match_any
constexpr match_flag_type match_not_null
constexpr match_flag_type match_continuous
constexpr match_flag_type match_prev_avail
constexpr match_flag_type format_default
constexpr match_flag_type format_sed
constexpr match_flag_type format_no_copy
constexpr match_flag_type format_first_only

and yes, the operators are here too, all noexcept, all about a bitmask type indicating regex matching rules:

• operator& — constexpr match_flag_type operator& (match_flag_type __a, match_flag_type __b) noexcept
• operator| — constexpr match_flag_type operator| (match_flag_type __a, match_flag_type __b) noexcept
• operator^ — constexpr match_flag_type operator^ (match_flag_type __a, match_flag_type __b) noexcept
• operator~ — constexpr match_flag_type operator~ (match_flag_type __a) noexcept
• operator&= — constexpr match_flag_type & operator&= (match_flag_type &__a, match_flag_type __b) noexcept
• operator|= — constexpr match_flag_type & operator|= (match_flag_type &__a, match_flag_type __b) noexcept
• operator^= — constexpr match_flag_type & operator^= (match_flag_type &__a, match_flag_type __b) noexcept

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🦋 5.3 Error Types 🦋

the "something went wrong bestie" section. we love her even though she only shows up when things break 😭

enum error_type { _S_error_collate, _S_error_ctype, _S_error_escape,
    _S_error_backref, _S_error_brack, _S_error_paren, _S_error_brace,
    _S_error_badbrace, _S_error_range, _S_error_space,
    _S_error_badrepeat, _S_error_complexity, _S_error_stack, _S_null,
    _S_grammar }

and the constexpr values, each one paired with the underlying enumerator it wraps — keeping the receipts 💅:

constexpr error_type error_collate (_S_error_collate)
constexpr error_type error_ctype (_S_error_ctype)
constexpr error_type error_escape (_S_error_escape)
constexpr error_type error_backref (_S_error_backref)
constexpr error_type error_brack (_S_error_brack)
constexpr error_type error_paren (_S_error_paren)
constexpr error_type error_brace (_S_error_brace)
constexpr error_type error_badbrace (_S_error_badbrace)
constexpr error_type error_range (_S_error_range)
constexpr error_type error_space (_S_error_space)
constexpr error_type error_badrepeat (_S_error_badrepeat)
constexpr error_type error_complexity (_S_error_complexity)
constexpr error_type error_stack (_S_error_stack)

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💜 Detailed Description 💜

ISO C++ 2011 namespace for options and flags used with std::regex. that's it, that's the description, and it's lowkey the most honest one in the whole manual 🎀

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🌟 Enumeration Type Documentation 🌟

⭐ enum std::regex_constants::error_type

The expression contained an invalid collating element name. yep — that's the description, and it's very much pointing at exactly one specific crime 😭

⭐ enum std::regex_constants::match_flag_type : unsigned int

This is a bitmask type indicating regex matching rules. The match_flag_type is implementation defined — but it is valid to perform bitwise operations on these values and expect the right thing to happen. so go ahead and | away, bestie, the vibes are guaranteed ✨

⭐ enum std::regex_constants::syntax_option_type : unsigned int

This is a bitmask type indicating how to interpret the regex. The syntax_option_type is implementation defined — but again, it is valid to perform bitwise operations on these values and expect the right thing to happen. 🫶

A valid value of type syntax_option_type shall have exactly one of the elements ECMAScript, basic, extended, awk, grep, egrep set.

like. exactly one. not two. not zero. one. pick your grammar and commit to it, this is main character energy only 👑

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okay that's part 1 wrapped and honestly the rest is coming so stay tuned 💖

✨ FUNCTION DOCUMENTATION ✨

Okay bestie, we're in the function zone now. It's giving overload city, but every single one is here, no cap. 🫶

First up, the error_type constants. These are all [inline], [constexpr], and they're basically the regex error mood ring. 😭

• error_type std::regex_constants::error_backref (_S_error_backref ) [inline], [constexpr] — The expression contained an invalid back reference.
• error_type std::regex_constants::error_badbrace (_S_error_badbrace ) [inline], [constexpr] — The expression contained an invalid range in a {} expression.
• error_type std::regex_constants::error_badrepeat (_S_error_badrepeat ) [inline], [constexpr] — One of *?+{ was not preceded by a valid regular expression.
• error_type std::regex_constants::error_brace (_S_error_brace ) [inline], [constexpr] — The expression contained mismatched { and }
• error_type std::regex_constants::error_brack (_S_error_brack ) [inline], [constexpr] — The expression contained mismatched [ and ].
• error_type std::regex_constants::error_collate (_S_error_collate ) [inline], [constexpr] — The expression contained an invalid collating element name.
• error_type std::regex_constants::error_complexity (_S_error_complexity ) [inline], [constexpr] — The complexity of an attempted match against a regular expression exceeded a pre-set level.
• error_type std::regex_constants::error_ctype (_S_error_ctype ) [inline], [constexpr] — The expression contained an invalid character class name.
• error_type std::regex_constants::error_escape (_S_error_escape ) [inline], [constexpr] — The expression contained an invalid escaped character, or a trailing escape.
• error_type std::regex_constants::error_paren (_S_error_paren ) [inline], [constexpr] — The expression contained mismatched ( and ).
• error_type std::regex_constants::error_range (_S_error_range ) [inline], [constexpr] — The expression contained an invalid character range, such as [b-a] in most encodings.
• error_type std::regex_constants::error_space (_S_error_space ) [inline], [constexpr] — There was insufficient memory to convert the expression into a finite state machine.
• error_type std::regex_constants::error_stack (_S_error_stack ) [inline], [constexpr] — There was insufficient memory to determine whether the regular expression could match the specified character sequence.

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Now the operator overloads, and yes, they're all bitmask-y. 💅

• match_flag_type std::regex_constants::operator& (match_flag_type __a, match_flag_type __b) [constexpr], [noexcept] — This is a bitmask type indicating regex matching rules. The match_flag_type is implementation defined, but it is valid to perform bitwise operations on these values and expect the right thing to happen.
• syntax_option_type std::regex_constants::operator& (syntax_option_type __a, syntax_option_type __b) [constexpr], [noexcept] — This is a bitmask type indicating how to interpret the regex. The syntax_option_type is implementation defined, but it is valid to perform bitwise operations on these values and expect the right thing to happen.

A valid value of type syntax_option_type shall have exactly one of the elements ECMAScript, basic, extended, awk, grep, egrep set.

• match_flag_type & std::regex_constants::operator&= (match_flag_type & __a, match_flag_type __b) [inline], [constexpr], [noexcept] — This is a bitmask type indicating regex matching rules. The match_flag_type is implementation defined, but it is valid to perform bitwise operations on these values and expect the right thing to happen.
• syntax_option_type & std::regex_constants::operator&= (syntax_option_type & __a, syntax_option_type __b) [inline], [constexpr], [noexcept] — This is a bitmask type indicating how to interpret the regex. The syntax_option_type is implementation defined, but it is valid to perform bitwise operations on these values and expect the right thing to happen.

A valid value of type syntax_option_type shall have exactly one of the elements ECMAScript, basic, extended, awk, grep, egrep set.

• match_flag_type std::regex_constants::operator^ (match_flag_type __a, match_flag_type __b) [constexpr], [noexcept] — This is a bitmask type indicating regex matching rules. The match_flag_type is implementation defined, but it is valid to perform bitwise operations on these values and expect the right thing to happen.
• syntax_option_type std::regex_constants::operator^ (syntax_option_type __a, syntax_option_type __b) [constexpr], [noexcept] — This is a bitmask type indicating how to interpret the regex. The syntax_option_type is implementation defined, but it is valid to perform bitwise operations on these values and expect the right thing to happen.

A valid value of type syntax_option_type shall have exactly one of the elements ECMAScript, basic, extended, awk, grep, egrep set.

• match_flag_type & std::regex_constants::operator^= (match_flag_type & __a, match_flag_type __b) [inline], [constexpr], [noexcept] — This is a bitmask type indicating regex matching rules. The match_flag_type is implementation defined, but it is valid to perform bitwise operations on these values and expect the right thing to happen.
• syntax_option_type & std::regex_constants::operator^= (syntax_option_type & __a, syntax_option_type __b) [inline], [constexpr], [noexcept] — This is a bitmask type indicating how to interpret the regex. The syntax_option_type is implementation defined, but it is valid to perform bitwise operations on these values and expect the right thing to happen.

A valid value of type syntax_option_type shall have exactly one of the elements ECMAScript, basic, extended, awk, grep, egrep set.

• match_flag_type std::regex_constants::operator| (match_flag_type __a, match_flag_type __b) [constexpr], [noexcept] — This is a bitmask type indicating regex matching rules. The match_flag_type is implementation defined, but it is valid to perform bitwise operations on these values and expect the right thing to happen.
• syntax_option_type std::regex_constants::operator| (syntax_option_type __a, syntax_option_type __b) [constexpr], [noexcept] — This is a bitmask type indicating how to interpret the regex. The syntax_option_type is implementation defined, but it is valid to perform bitwise operations on these values and expect the right thing to happen.

A valid value of type syntax_option_type shall have exactly one of the elements ECMAScript, basic, extended, awk, grep, egrep set.

• match_flag_type & std::regex_constants::operator|= (match_flag_type & __a, match_flag_type __b) [inline], [constexpr], [noexcept] — This is a bitmask type indicating regex matching rules. The match_flag_type is implementation defined, but it is valid to perform bitwise operations on these values and expect the right thing to happen.
• syntax_option_type & std::regex_constants::operator|= (syntax_option_type & __a, syntax_option_type __b) [inline], [constexpr], [noexcept] — This is a bitmask type indicating how to interpret the regex. The syntax_option_type is implementation defined, but it is valid to perform bitwise operations on these values and expect the right thing to happen.

A valid value of type syntax_option_type shall have exactly one of the elements ECMAScript, basic, extended, awk, grep, egrep set.

• match_flag_type std::regex_constants::operator~ (match_flag_type __a) [constexpr], [noexcept] — This is a bitmask type indicating regex matching rules. The match_flag_type is implementation defined, but it is valid to perform bitwise operations on these values and expect the right thing to happen.
• syntax_option_type std::regex_constants::operator~ (syntax_option_type __a) [constexpr], [noexcept] — This is a bitmask type indicating how to interpret the regex. The syntax_option_type is implementation defined, but it is valid to perform bitwise operations on these values and expect the right thing to happen.

A valid value of type syntax_option_type shall have exactly one of the elements ECMAScript, basic, extended, awk, grep, egrep set.

✨ VARIABLE DOCUMENTATION ✨

Okay bestie, this is the final part: all the variables. Every single one is inline and constexpr, so they're compile-time constants, and we're gonna go through them like a group chat recap. No skipping, no summarizing. Periodt. 💅

💖 syntax_option_type std::regex_constants::__multiline [inline], [constexpr]

Extension: equivalent to regex_constants::multiline for C++11 and C++14. It's the little stand-in for the C++11/C++14 girlies. ✨

💖 syntax_option_type std::regex_constants::__polynomial [inline], [constexpr]

Extension: makes sure both the space complexity of the compiled regex and the time complexity of execution are not exponential. If you specify it in a regex with back-references, the exception regex_constants::error_complexity will be thrown. So like, polynomial vibes only, but backrefs? She throws. 💀

💖 syntax_option_type std::regex_constants::awk [inline], [constexpr]

Specifies that the grammar recognized by the regular expression engine is the one used by POSIX utility awk in IEEE Std 1003.1-2001. This option is identical to syntax_option_type extended, except that C-style escape sequences are supported. These sequences are: \\, \a, \b, \f, \n, \r, \t, \v, \&apos,, &apos,, and \ddd (where ddd is one, two, or three octal digits).

💖 syntax_option_type std::regex_constants::basic [inline], [constexpr]

Specifies that the grammar recognized by the regular expression engine is the one used by POSIX basic regular expressions in IEEE Std 1003.1-2001, Portable Operating System Interface (POSIX), Base Definitions and Headers, Section 9, Regular Expressions [IEEE, Information Technology -- Portable Operating System Interface (POSIX), IEEE Standard 1003.1-2001].

💖 syntax_option_type std::regex_constants::collate [inline], [constexpr]

Specifies that character ranges of the form [a-b] should be locale sensitive. It's giving "respect the locale, bestie." 🌍

💖 syntax_option_type std::regex_constants::ECMAScript [inline], [constexpr]

Specifies that the grammar recognized by the regular expression engine is the one used by ECMAScript in ECMA-262 [Ecma International, ECMAScript Language Specification, Standard Ecma-262, third edition, 1999], as modified in section [28.13]. This grammar is similar to the one defined in the PERL scripting language but extended with elements found in the POSIX regular expression grammar.

💖 syntax_option_type std::regex_constants::egrep [inline], [constexpr]

Specifies that the grammar recognized by the regular expression engine is the one used by POSIX utility grep when given the -E option in IEEE Std 1003.1-2001. This option is identical to syntax_option_type extended, except that newlines are treated as whitespace.

💖 syntax_option_type std::regex_constants::extended [inline], [constexpr]

Specifies that the grammar recognized by the regular expression engine is the one used by POSIX extended regular expressions in IEEE Std 1003.1-2001, Portable Operating System Interface (POSIX), Base Definitions and Headers, Section 9, Regular Expressions.

💖 match_flag_type std::regex_constants::format_default [inline], [constexpr]

When a regular expression match is to be replaced by a new string, the new string is constructed using the rules used by the ECMAScript replace function in ECMA-262 [Ecma International, ECMAScript Language Specification, Standard Ecma-262, third edition, 1999], part 15.5.4.11 String.prototype.replace. In addition, during search and replace operations all non-overlapping occurrences of the regular expression are located and replaced, and sections of the input that did not match the expression are copied unchanged to the output string.

Format strings (from ECMA-262 [15.5.4.11]):

• $$ — The dollar-sign itself ($)
• $& — The matched substring.
• $` — The portion of the string that precedes the matched substring. This would be match_results::prefix().
• $' — The portion of the string that follows the matched substring. This would be match_results::suffix().
• $n — The nth capture, where n is a positive integer less than 100. If n <= match_results::size() and the nth capture is undefined, use the empty string instead. If n > match_results::size(), the result is implementation-defined.

Referenced by (all four, no cap):

std::match_results< _BidirectionalIterator, polymorphic_allocator< sub_match< _BidirectionalIterator > > >< const char * >::format(),
std::match_results< _BidirectionalIterator, polymorphic_allocator< sub_match< _BidirectionalIterator > > >< const char * >::format(),
std::match_results< _BidirectionalIterator, polymorphic_allocator< sub_match< _BidirectionalIterator > > >< const char * >::format(),
std::match_results< _BidirectionalIterator, polymorphic_allocator< sub_match< _BidirectionalIterator > > >< const char * >::format()

💖 match_flag_type std::regex_constants::format_first_only [inline], [constexpr]

When specified during a search and replace operation, only the first occurrence of the regular expression shall be replaced. First one only, bestie. ✋

💖 match_flag_type std::regex_constants::format_no_copy [inline], [constexpr]

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. So the non-matching bits get left behind. 🫥

💖 match_flag_type std::regex_constants::format_sed [inline], [constexpr]

When a regular expression match is to be replaced by a new string, the new string is constructed using the rules used by the POSIX sed utility in IEEE Std 1003.1-2001 [IEEE, Information Technology -- Portable Operating System Interface (POSIX), IEEE Standard 1003.1-2001].

💖 syntax_option_type std::regex_constants::grep [inline], [constexpr]

Specifies that the grammar recognized by the regular expression engine is the one used by POSIX utility grep in IEEE Std 1003.1-2001. This option is identical to syntax_option_type basic, except that newlines are treated as whitespace.

💖 syntax_option_type std::regex_constants::icase [inline], [constexpr]

Specifies that the matching of regular expressions against a character sequence shall be performed without regard to case. Upper, lower, she doesn't care. 👑

💖 match_flag_type std::regex_constants::match_any [inline], [constexpr]

If more than one match is possible then any match is an acceptable result. She's not picky, she's flexible. 💅

💖 match_flag_type std::regex_constants::match_continuous [inline], [constexpr]

The expression only matches a sub-sequence that begins at first. Referenced by std::regex_iterator< _Bi_iter, _Ch_type, _Rx_traits >::operator++().

💖 match_flag_type std::regex_constants::match_default [inline], [constexpr]

The default matching rules.

Referenced by:

std::regex_iterator< const char * >::regex_iterator(),
std::regex_token_iterator< const char * >::regex_token_iterator(),
std::regex_token_iterator< const char * >::regex_token_iterator(),
std::regex_token_iterator< const char * >::regex_token_iterator(),
std::regex_token_iterator< const char * >::regex_token_iterator(),
std::regex_match(),
std::regex_match(),
std::regex_match(),
std::regex_match(),
std::regex_match(),
std::regex_match(),
std::regex_match(),
std::regex_match(),
std::regex_replace(),
std::regex_replace(),
std::regex_replace(),
std::regex_replace(),
std::regex_replace(),
std::regex_replace(),
std::regex_search(),
std::regex_search(),
std::regex_search(),
std::regex_search(),
std::regex_search(),
std::regex_search(),
std::regex_search()

💖 match_flag_type std::regex_constants::match_not_bol [inline], [constexpr]

The first character in the sequence [first, last) is 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_flag_type std::regex_constants::match_not_bow [inline], [constexpr]

The expression \b is not matched against the sub-sequence [first,first).

💖 match_flag_type std::regex_constants::match_not_eol [inline], [constexpr]

The last character in the sequence [first, last) is 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_flag_type std::regex_constants::match_not_eow [inline], [constexpr]

The expression \b should not be matched against the sub-sequence [last,last).

💖 match_flag_type std::regex_constants::match_not_null [inline], [constexpr]

The expression does not match an empty sequence. Referenced by std::regex_iterator< _Bi_iter, _Ch_type, _Rx_traits >::operator++().

💖 match_flag_type std::regex_constants::match_prev_avail [inline], [constexpr]

--first is a valid iterator position. When this flag is set then the flags match_not_bol and match_not_bow are ignored by the algorithms regex_match, regex_search, and regex_replace, and by the iterators regex_iterator and regex_token_iterator. Referenced by std::regex_iterator< _Bi_iter, _Ch_type, _Rx_traits >::operator++().

💖 syntax_option_type std::regex_constants::multiline [inline], [constexpr]

Specifies that the ^ anchor matches at the beginning of a line, and the $ anchor matches at the end of a line, not only at the beginning/end of the input. Valid for the ECMAScript syntax, ignored otherwise.

Since: C++17. ✨

💖 syntax_option_type std::regex_constants::nosubs [inline], [constexpr]

Specifies that when a regular expression is matched against a character container sequence, no sub-expression matches are to be stored in the supplied match_results structure. No subs, no notes. 🙈

💖 syntax_option_type std::regex_constants::optimize [inline], [constexpr]

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. Speed of matching > speed of construction, but only when you ask. 🏎️

📝 Author

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