regex_constants Class

 

The latest version of this topic can be found at regex_constants Class.

Namespace for regular expression flags.

Syntax

namespace regex_constants {  
    typedef T1 syntax_option_type;  
    typedef T2 match_flag_type;  
    typedef T3 error_type;  
 }  

Remarks

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

Requirements

Header: <regex>

Namespace: std

regex_constants::error_type

Flags for reporting regular expression syntax errors.

typedef T3 error_type;  
static const error_type error_badbrace,
    error_badrepeat,
    error_brace,  
    error_brack,
    error_collate,
    error_complexity,
    error_ctype,  
    error_escape,
    error_paren,
    error_range,
    error_space,  
    error_stack,
    error_backref;  

Remarks

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

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_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_backref -- the expression contained an invalid back reference

regex_constants::match_flag_type

Flags for regular expression matching options.

typedef T2 match_flag_type;  
static const match_flag_type match_any,
    match_default,
    match_not_bol,  
    match_not_bow,
    match_continuous,
    match_not_eol,
    match_not_eow,  
    match_not_null,
    match_partial,
    match_prev_avail;  

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.

typedef T1 syntax_option_type;  
static const syntax_option_type awk,
    basic,
    collate,
    ECMAScript,  
    egrep,
    extended,
    grep,
    icase,
    nosubs,
    optimize;  

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:

basic -- compile as BRE

extended -- compile as ERE

ECMAScript -- compile as ECMAScript

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_constants