std::regex_...ch_flag_type(3)

std::regex_...ch_flag_type(3) 💖

okay so this is the C++ Standard Libary page for std::regex_...ch_flag_type(3) — yes, the manual name spells “Libary” like that, and we are respecting the canon. Bestie, we’re about to get into regex match flags, and honestly it’s giving bitmask royalty. 💅

🌸 NAME 🌸

std::regex_constants::match_flag_type — std::regex_constants::match_flag_type.

That’s it. That’s the name. The repetition is iconic, no notes. ✨

✨ Synopsis ✨

First up, the (until C++17) version:

Defined in header <regex>
using match_flag_type = /* implementation-defined */;  (1) (since C++11)

constexpr match_flag_type match_default =     {};
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 */;  (since C++11)
constexpr match_flag_type match_continuous =  /* unspecified */;
constexpr match_flag_type match_prev_avail =  /* unspecified */;
constexpr match_flag_type format_default =    {};
constexpr match_flag_type format_sed =        /* unspecified */;
constexpr match_flag_type format_no_copy =    /* unspecified */;

constexpr match_flag_type format_first_only = /* unspecified */;

Then (since C++17) rolls in with inline constexpr and a (2) marker on match_default:

inline constexpr match_flag_type match_default =     {};  (2)
inline constexpr match_flag_type match_not_bol = /* unspecified */;
inline constexpr match_flag_type match_not_eol = /* unspecified */;
inline constexpr match_flag_type match_not_bow = /* unspecified */;
inline constexpr match_flag_type match_not_eow = /* unspecified */;
inline constexpr match_flag_type match_any = /* unspecified */;
inline constexpr match_flag_type match_not_null = /* unspecified */;
inline constexpr match_flag_type match_continuous = /* unspecified */;
inline constexpr match_flag_type match_prev_avail = /* unspecified */;
inline constexpr match_flag_type format_default = {};
inline constexpr match_flag_type format_sed = /* unspecified */;
inline constexpr match_flag_type format_no_copy = /* unspecified */;

inline constexpr match_flag_type format_first_only = /* unspecified */;

(1) match_flag_type is a BitmaskType that specifies additional regular expression matching options. 🫶

💅 Constants 💅

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

• 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. 🌈

🫶 Defect reports 🫶

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

• DR LWG 2053, applied to C++11
  • Behavior as published:
    1. the constants were declared static
    2. match_default and format_default were initialized from 0
  • Correct behavior:
    1. removed the static specifier
    2. initialized from {}

👑 See also 👑

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

xoxo, your regex bestie 💜 — source: http://cppreference.com, version/date: 2024.06.10, page: std::regex_...ch_flag_type(3). Slay. ✨