namespace std::regex_constants {
using match_flag_type = T2;
constexpr match_flag_type match_default = {};
constexpr match_flag_type match_not_bol = unspecified;
constexpr match_flag_type match_not_eol = unspecified;
constexpr match_flag_type match_not_bow = unspecified;
constexpr match_flag_type match_not_eow = unspecified;
constexpr match_flag_type match_any = unspecified;
constexpr match_flag_type match_not_null = unspecified;
constexpr match_flag_type match_continuous = unspecified;
constexpr match_flag_type match_prev_avail = unspecified;
constexpr match_flag_type format_default = {};
constexpr match_flag_type format_sed = unspecified;
constexpr match_flag_type format_no_copy = unspecified;
constexpr match_flag_type format_first_only = unspecified;
}
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 [tab:re:matchflag] for any bitmask elements set.
| 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. |