Showing content from https://cplusplus.com/regex_constants below:
namespace
<regex>
std::regex_constants
regex constants
This namespace declares three bitmask types used with elements of the regex library along with constant values of these types:
Each of these
bitmask types
may have been implemented in your library either as an enumerated type, an integer type, or a
bitset
. In any case, it can take one or more flags of that same type as value by combining them using the
bitwise OR
operator (
|
):
1
bitmask_type object = flag1 | flag2 | flag3;
By providing these values under a specific namespace, you have the option to include this namespace (with
using namespace std::regex_constants
) directly in your code in order to refer to these values more easily independently on whether you include the more generic namespace
std
or not.
Bitmask type syntax_option_type Aliased as member type flag_type in regex (and basic_regex), it is used in the construction or assignment of regex objects to specify the syntax used by the object. The possible values it can take are:
flag effects on syntax notes icase Case insensitive Regular expressions match without regard to case. nosubs No sub-expressions The match_results structure will not contain sub-expression matches. optimize Optimize matching Matching efficiency is preferred over efficiency constructing regex objects. collate Locale sensitiveness Character ranges, like "[a-b]", are affected by locale. ECMAScript ECMAScript grammar The regular expression follows one of these grammars.
One (and only one) of these six grammar flags needs to be set for the bitmask to have a valid value. basic Basic POSIX grammar extended Extended POSIX grammar awk Awk POSIX grammar grep Grep POSIX grammar egrep Egrep POSIX grammar flag effects on syntax notes icase Case insensitive Regular expressions match without regard to case. nosubs No sub-expressions Sub-expressions are not considered to be marked.
The match_results structure will not contain sub-expression matches. optimize Optimize matching Matching efficiency is preferred over efficiency constructing regex objects. collate Locale sensitiveness Character ranges, like "[a-b]", are affected by locale. ECMAScript ECMAScript grammar The regular expression follows one of these grammars.
At most one of these six grammar flags can be set for the bitmask to have a valid value. If none is set, ECMAScript is assumed. basic Basic POSIX grammar extended Extended POSIX grammar awk Awk POSIX grammar grep Grep POSIX grammar egrep Egrep POSIX grammar
Bitmask type match_flag_type
Used as a parameter to functions
regex_match
,
regex_search
and
regex_replace
and also as a parameter to the constructors of
regex_iterator
and
regex_token_iterator
.
flag effects notes match_default Default Default matching behavior.**. match_not_bol Not Beginning-Of-Line The first character is not considered a beginning of line ("^" does not match). match_not_eol Not End-Of-Line The last character is not considered an end of line ("$" does not match). match_not_bow Not Beginning-Of-Word The escape sequence "\b" does not match as a beginning-of-word. match_not_eow Not End-Of-Word The escape sequence "\b" does not match as an end-of-word. match_any Any match Any match is acceptable if more than one match is possible. match_not_null Not null Empty sequences do not match. match_continuous Continuous The expression must match a sub-sequence that begins at the first character.
Sub-sequences must begin at the first character to match. match_prev_avail Previous Available One or more characters exist before the first one. (match_not_bol and match_not_bow are ignored) format_default Default formatting Uses the standard formatting rules to replace matches (those used by ECMAScript's replace method).**. format_sed sed formatting Uses the same rules as the sed utility in POSIX to replace matches. format_no_copy No copy The sections in the target sequence that do not match the regular expression are not copied when replacing matches. format_first_only First only Only the first occurrence of a regular expression is replaced. ** These constants have an empty bitmask value and are ignored when combined with some other flag value.
Bitmask type error_type Used as by the regex_error to identify the kind of error that threw the exception:
flag error error_collate The expression contained an invalid collating element name. error_ctype The expression contained an invalid character class name. error_escape The expression contained an invalid escaped character, or a trailing escape. error_backref The expression contained an invalid back reference. error_brack The expression contained mismatched brackets ([ and ]). error_paren The expression contained mismatched parentheses (( and )). error_brace The expression contained mismatched braces ({ and }). error_badbrace The expression contained an invalid range between braces ({ and }). error_range The expression contained an invalid character range. error_space There was insufficient memory to convert the expression info a finite state machine. error_badrepeat The expression contained a repeat specifier (one of *?+{) that was not preceded by a valid regular expression. error_complexity The complexity of an attempted match against a regular expression exceeded a pre-set level. error_stack There was insufficient memory to determine whether the regular expression could match the specified character sequence.
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