std:: basic_regex constants

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std::basic_regex
Defined in header <regex>
static constexpr std:: regex_constants :: syntax_option_type icase =

std:: regex_constants :: icase ;
static constexpr std:: regex_constants :: syntax_option_type nosubs =
std:: regex_constants :: nosubs ;
static constexpr std:: regex_constants :: syntax_option_type optimize =
std:: regex_constants :: optimize ;
static constexpr std:: regex_constants :: syntax_option_type collate =
std:: regex_constants :: collate ;
static constexpr std:: regex_constants :: syntax_option_type ECMAScript =
std:: regex_constants :: ECMAScript ;
static constexpr std:: regex_constants :: syntax_option_type basic =
std:: regex_constants :: basic ;
static constexpr std:: regex_constants :: syntax_option_type extended =
std:: regex_constants :: extended ;
static constexpr std:: regex_constants :: syntax_option_type awk =
std:: regex_constants :: awk ;
static constexpr std:: regex_constants :: syntax_option_type grep =
std:: regex_constants :: grep ;
static constexpr std:: regex_constants :: syntax_option_type egrep =

std:: regex_constants :: egrep ;
(since C++17)

std::basic_regex defines several constants that govern general regex matching syntax.

These constants are duplicated from std :: regex_constants :

Grammar option Effect(s)
ECMAScript Use the Modified ECMAScript regular expression grammar .
basic Use the basic POSIX regular expression grammar ( grammar documentation ).
extended Use the extended POSIX regular expression grammar ( grammar documentation ).
awk Use the regular expression grammar used by the awk utility in POSIX ( grammar documentation ).
grep Use the regular expression grammar used by the grep utility in POSIX. This is effectively the same as the basic option with the addition of newline ' \n ' as an alternation separator.
egrep Use the regular expression grammar used by the grep utility, with the -E option, in POSIX. This is effectively the same as the extended option with the addition of newline ' \n ' as an alternation separator in addition to '|' .
Grammar variation Effect(s)
icase Character matching should be performed without regard to case.
nosubs When performing matches, all marked sub-expressions ( expr ) are treated as non-marking sub-expressions (?: expr ) . No matches are stored in the supplied std::regex_match structure and mark_count() is zero.
optimize Instructs the regular expression engine to make matching faster, with the potential cost of making construction slower. For example, this might mean converting a non-deterministic FSA to a deterministic FSA.
collate Character ranges of the form "[a-b]" will be locale sensitive.
multiline (C++17) Specifies that ^ shall match the beginning of a line and $ shall match the end of a line, if the ECMAScript engine is selected.

At most one grammar option can be chosen out of ECMAScript , basic , extended , awk , grep , egrep . If no grammar is chosen, ECMAScript is assumed to be selected. The other options serve as variations, such that std:: regex ( "meow" , std :: regex :: icase ) is equivalent to std:: regex ( "meow" , std :: regex :: ECMAScript | std :: regex :: icase ) .

See also

(C++11)
general options controlling regex behavior
(typedef)
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