28 Text processing library [text]

28.6 Regular expressions library [re]

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

28.6.4.3 Bitmask type match_flag_type [re.matchflag]

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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; }
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The type match_flag_type is an implementation-defined bitmask type ([bitmask.types]).
The constants of that type, except for match_default and format_default, are bitmask elements.
The match_default and format_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 114 for any bitmask elements set.
Table 114: 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 at first.
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.