regex_constants namespace

Namespace for regular expression flags.

Syntax

namespace regex_constants {
    enum syntax_option_type;
    enum match_flag_type;
    enum error_type;
}

Remarks

The namespace regex_constants encapsulates several flag types and their associated flag values.

Name	Description
error_type	Flags for reporting regular expression syntax errors.
match_flag_type	Flags for regular expression matching options.
syntax_option_type	Flags for selecting syntax options.

Requirements

Header: <regex>

Namespace: std

regex_constants::error_type

Flags for reporting regular expression syntax errors.

enum error_type
    {    // identify error
    error_collate,
    error_ctype,
    error_escape,
    error_backref,
    error_brack,
    error_paren,
    error_brace,
    error_badbrace,
    error_range,
    error_space,
    error_badrepeat,
    error_complexity,
    error_stack,
    error_parse,
    error_syntax
    };

Remarks

The type is an enumerated type that describes an object that can hold error flags. The distinct flag values are:

error_backref -- the expression contained an invalid back reference

error_badbrace -- the expression contained an invalid count in a { } expression

error_badrepeat -- a repeat expression (one of '*', '', '+', '{' in most contexts) was not preceded by an expression

error_brace -- the expression contained an unmatched '{' or '}'

error_brack -- the expression contained an unmatched '[' or ']'

error_collate -- the expression contained an invalid collating element name

error_complexity -- an attempted match failed because it was too complex

error_ctype -- the expression contained an invalid character class name

error_escape -- the expression contained an invalid escape sequence

error_paren -- the expression contained an unmatched '(' or ')'

error_parse -- the expression failed to parse

error_range -- the expression contained an invalid character range specifier

error_space -- parsing a regular expression failed because there were not enough resources available

error_stack -- an attempted match failed because there was not enough memory available

error_syntax -- parsing failed on a syntax error

error_backref -- the expression contained an invalid back reference

regex_constants::match_flag_type

Flags for regular expression matching options.

enum match_flag_type
    {    // specify matching and formatting rules
    match_default = 0x0000,
    match_not_bol = 0x0001,
    match_not_eol = 0x0002,
    match_not_bow = 0x0004,
    match_not_eow = 0x0008,
    match_any = 0x0010,
    match_not_null = 0x0020,
    match_continuous = 0x0040,
    match_prev_avail = 0x0100,
    format_default = 0x0000,
    format_sed = 0x0400,
    format_no_copy = 0x0800,
    format_first_only = 0x1000,
    _Match_not_null = 0x2000
    };

Remarks

The type is a bitmask type that describes options to be used when matching a text sequence against a regular expression and format flags to be used when replacing text. Options can be combined with |.

The match options are:

match_default

match_not_bol -- do not treat the first position in the target sequence as the beginning of a line

match_not_eol -- do not treat the past-the-end position in the target sequence as the end of a line

match_not_bow -- do not treat the first position in the target sequence as the beginning of a word

match_not_eow -- do not treat the past-the-end position in the target sequence as the end of a word

match_any -- if more than one match is possible any match is acceptable

match_not_null -- do not treat an empty subsequence as a match

match_continuous -- do not search for matches other than at the beginning of the target sequence

match_prev_avail -- --first is a valid iterator; ignore match_not_bol and match_not_bow if set

The format flags are:

format_default -- use ECMAScript format rules

format_sed -- use sed format rules

format_no_copy -- do not copy text that does not match the regular expression

format_first_only -- do not search for matches after the first one

regex_constants::syntax_option_type

Flags for selecting syntax options.

enum syntax_option_type
    {    // specify RE syntax rules
    ECMAScript = 0x01,
    basic = 0x02,
    extended = 0x04,
    awk = 0x08,
    grep = 0x10,
    egrep = 0x20,
    _Gmask = 0x3F,

    icase = 0x0100,
    nosubs = 0x0200,
    optimize = 0x0400,
    collate = 0x0800
    };

Remarks

The type is a bitmask type that describes language specifiers and syntax modifiers to be used when compiling a regular expression. Options can be combined with |. No more than one language specifier should be used at a time.

The language specifiers are:

ECMAScript -- compile as ECMAScript

basic -- compile as BRE

extended -- compile as ERE

awk -- compile as awk

grep -- compile as grep

egrep -- compile as egrep

The syntax modifiers are:

icase -- make matches case-insensitive

nosubs -- the implementaton need not keep track of the contents of capture groups

optimize -- the implementation should emphasize speed of matching rather than speed of regular expression compilation

collate -- make matches locale-sensitive

See also

<regex>
regex_error Class
<regex> functions
regex_iterator Class
<regex> operators
regex_token_iterator Class
regex_traits Class
<regex> typedefs