31 Regular expressions library [re]

31.5 Namespace std​::​regex_­constants [re.const]

31.5.1 Bitmask type syntax_­option_­type [re.synopt]

namespace std::regex_constants {
  using syntax_option_type = T1;
  inline constexpr syntax_option_type icase = unspecified;
  inline constexpr syntax_option_type nosubs = unspecified;
  inline constexpr syntax_option_type optimize = unspecified;
  inline constexpr syntax_option_type collate = unspecified;
  inline constexpr syntax_option_type ECMAScript = unspecified;
  inline constexpr syntax_option_type basic = unspecified;
  inline constexpr syntax_option_type extended = unspecified;
  inline constexpr syntax_option_type awk = unspecified;
  inline constexpr syntax_option_type grep = unspecified;
  inline constexpr syntax_option_type egrep = unspecified;
  inline constexpr syntax_option_type multiline = unspecified;
}
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The type syntax_­option_­type is an implementation-defined bitmask type. Setting its elements has the effects listed in Table 130. A valid value of type syntax_­option_­type shall have at most one of the grammar elements ECMAScript, basic, extended, awk, grep, egrep, set. If no grammar element is set, the default grammar is ECMAScript.

Table 130 — syntax_­option_­type effects
ElementEffect(s) if set
icase Specifies that matching of regular expressions against a character container sequence shall be performed without regard to case.
nosubs Specifies that no sub-expressions shall be considered to be marked, so that when a regular expression is matched against a character container sequence, no sub-expression matches shall be stored in the supplied match_­results structure.
optimize Specifies that the regular expression engine should pay more attention to the speed with which regular expressions are matched, and less to the speed with which regular expression objects are constructed. Otherwise it has no detectable effect on the program output.
collate Specifies that character ranges of the form "[a-b]" shall be locale sensitive.
ECMAScript Specifies that the grammar recognized by the regular expression engine shall be that used by ECMAScript in ECMA-262, as modified in [re.grammar].
basic Specifies that the grammar recognized by the regular expression engine shall be that used by basic regular expressions in POSIX, Base Definitions and Headers, Section 9, Regular Expressions.
extended Specifies that the grammar recognized by the regular expression engine shall be that used by extended regular expressions in POSIX, Base Definitions and Headers, Section 9, Regular Expressions.
awk Specifies that the grammar recognized by the regular expression engine shall be that used by the utility awk in POSIX.
grep Specifies that the grammar recognized by the regular expression engine shall be that used by the utility grep in POSIX.
egrep Specifies that the grammar recognized by the regular expression engine shall be that used by the utility grep when given the -E option in POSIX.
multiline Specifies that ^ shall match the beginning of a line and $ shall match the end of a line, if the ECMAScript engine is selected.