The C Standard Library

C++ Regex Library - regex_constants

Quiz

Description

It is a regex constants.

The types of regex constants should be as shown below −

Bitmask type error_type

It is used in the regex_error to identify the kind of error that threw the exception.

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

Bitmask type syntax_option_type

it is used in the construction or assignment of regex objects to specify the syntax used by the object.

C++11

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

C++14

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

It is 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.

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