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# std::regex_constants::match_flag_type

From cppreference.com
< cpp‎ | regex

Defined in header `<regex>` |  |
typedef /*unspecified*/ match_flag_type; constexpr match_flag_type match_default = 0; 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 = 0; constexpr match_flag_type format_sed = /*unspecified*/; constexpr match_flag_type format_no_copy = /*unspecified*/; constexpr match_flag_type format_first_only = /*unspecified*/; |  |

`match_flag_type` is a `BitmaskType` that specifies additional regular expression matching options.

### [edit] Constants

Note: `[first, last)` refers to the character sequence being matched.

Constant | Explanation
`match_not_bol` | The first character in [first,last) will be treated as if it is not at the beginning of a line (i.e. ^ will not match [first,first)
`match_not_eol` | The last character in [first,last) will be treated as if it is not at the end of a line (i.e. $ will not match [last,last)
`match_not_bow` | "\b" will not match [first,first)
`match_not_eow` | "\b" will not match [last,last)
`match_any` | If more than one match is possible, then any match is an acceptable result
`match_not_null` | Do not match empty sequences
`match_continuous` | Only match a sub-sequence that begins at first
`match_prev_avail` | --first is a valid iterator position. When set, causes match_not_bol and match_not_bow to be ignored
`format_default` | Use ECMAScript rules to construct strings in std::regex_replace (syntax documentation)
`format_sed` | Use POSIX sed utility rules in std::regex_replace. (syntax documentation)
`format_no_copy` | Do not copy un-matched strings to the output in std::regex_replace
`format_first_only` | Only replace the first match in std::regex_replace

All constants, except for `match_default` and `format_default`, are bitmask elements. The `match_default` and `format_default` constants are empty bitmasks

### [edit] Notes

In C++11, these constants were specified with redundant keyword `static`, which was removed by C++14 via LWG issue 2053

### [edit] See also

regex_match (C++11) | attempts to match a regular expression to an entire character sequence (function template) [edit]
syntax_option_type (C++11) | general options controlling regex behavior (typedef) [edit]
error_type (C++11) | describes different types of matching errors (typedef) [edit]

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