std::regex_constants Namespace Reference
Regular Expressions

## 5.1 Regular Expression Syntax Options

enum | __syntax_option { _S_icase, _S_nosubs, _S_optimize, _S_collate, _S_ECMAScript, _S_basic, _S_extended, _S_awk, _S_grep, _S_egrep, _S_syntax_last }
typedef unsigned int | syntax_option_type
constexpr syntax_option_type | icase
constexpr syntax_option_type | nosubs
constexpr syntax_option_type | optimize
constexpr syntax_option_type | collate
constexpr syntax_option_type | ECMAScript
constexpr syntax_option_type | basic
constexpr syntax_option_type | extended
constexpr syntax_option_type | awk
constexpr syntax_option_type | grep
constexpr syntax_option_type | egrep

## 5.2 Matching Rules

Matching a regular expression against a sequence of characters [first, last) proceeds according to the rules of the grammar specified for the regular expression object, modified according to the effects listed below for any bitmask elements set.
enum | __match_flag { _S_not_bol, _S_not_eol, _S_not_bow, _S_not_eow, _S_any, _S_not_null, _S_continuous, _S_prev_avail, _S_sed, _S_no_copy, _S_first_only, _S_match_flag_last }
typedef std::bitset < _S_match_flag_last > | match_flag_type
constexpr match_flag_type | match_default
constexpr match_flag_type | match_not_bol
constexpr match_flag_type | match_not_eol
constexpr match_flag_type | match_not_bow
constexpr match_flag_type | match_not_eow
constexpr match_flag_type | match_any
constexpr match_flag_type | match_not_null
constexpr match_flag_type | match_continuous
constexpr match_flag_type | match_prev_avail
constexpr match_flag_type | format_default
constexpr match_flag_type | format_sed
constexpr match_flag_type | format_no_copy
constexpr match_flag_type | format_first_only

## 5.3 Error Types

enum | error_type { _S_error_collate, _S_error_ctype, _S_error_escape, _S_error_backref, _S_error_brack, _S_error_paren, _S_error_brace, _S_error_badbrace, _S_error_range, _S_error_space, _S_error_badrepeat, _S_error_complexity, _S_error_stack, _S_error_last }
constexpr error_type | error_collate (_S_error_collate)
constexpr error_type | error_ctype (_S_error_ctype)
constexpr error_type | error_escape (_S_error_escape)
constexpr error_type | error_backref (_S_error_backref)
constexpr error_type | error_brack (_S_error_brack)
constexpr error_type | error_paren (_S_error_paren)
constexpr error_type | error_brace (_S_error_brace)
constexpr error_type | error_badbrace (_S_error_badbrace)
constexpr error_type | error_range (_S_error_range)
constexpr error_type | error_space (_S_error_space)
constexpr error_type | error_badrepeat (_S_error_badrepeat)
constexpr error_type | error_complexity (_S_error_complexity)
constexpr error_type | error_stack (_S_error_stack)

## Detailed Description

ISO C++-0x entities sub namespace for regex.

## Typedef Documentation

typedef std::bitset<_S_match_flag_last> std::regex_constants::match_flag_type

This is a bitmask type indicating regex matching rules.

The `match_flag_type` is implementation defined but it is valid to perform bitwise operations on these values and expect the right thing to happen.

Definition at line 198 of file regex_constants.h.

typedef unsigned int std::regex_constants::syntax_option_type

This is a bitmask type indicating how to interpret the regex.

The `syntax_option_type` is implementation defined but it is valid to perform bitwise operations on these values and expect the right thing to happen.

A valid value of type syntax_option_type shall have exactly one of the elements `ECMAScript`, `basic`, `extended`, `awk`, `grep`, `egrep` set.

Definition at line 80 of file regex_constants.h.

## Enumeration Type Documentation

enum std::regex_constants::__match_flag

This is a bitmask type indicating regex matching rules.

The `match_flag_type` is implementation defined but it is valid to perform bitwise operations on these values and expect the right thing to happen.

Definition at line 175 of file regex_constants.h.

enum std::regex_constants::__syntax_option

This is a bitmask type indicating how to interpret the regex.

The `syntax_option_type` is implementation defined but it is valid to perform bitwise operations on these values and expect the right thing to happen.

A valid value of type syntax_option_type shall have exactly one of the elements `ECMAScript`, `basic`, `extended`, `awk`, `grep`, `egrep` set.

Definition at line 54 of file regex_constants.h.

enum std::regex_constants::error_type

The expression contained an invalid collating element name.

Definition at line 49 of file regex_error.h.

## Function Documentation

constexpr error_type std::regex_constants::error_backref | ( | _S_error_backref |  | ) |

The expression contained an invalid back reference.

constexpr error_type std::regex_constants::error_badbrace | ( | _S_error_badbrace |  | ) |

The expression contained an invalid range in a {} expression.

constexpr error_type std::regex_constants::error_badrepeat | ( | _S_error_badrepeat |  | ) |

One of *?+{ was not preceded by a valid regular expression.

constexpr error_type std::regex_constants::error_brace | ( | _S_error_brace |  | ) |

The expression contained mismatched { and }

constexpr error_type std::regex_constants::error_brack | ( | _S_error_brack |  | ) |

The expression contained mismatched [ and ].

constexpr error_type std::regex_constants::error_collate | ( | _S_error_collate |  | ) |

The expression contained an invalid collating element name.

constexpr error_type std::regex_constants::error_complexity | ( | _S_error_complexity |  | ) |

The complexity of an attempted match against a regular expression exceeded a pre-set level.

constexpr error_type std::regex_constants::error_ctype | ( | _S_error_ctype |  | ) |

The expression contained an invalid character class name.

constexpr error_type std::regex_constants::error_escape | ( | _S_error_escape |  | ) |

The expression contained an invalid escaped character, or a trailing escape.

constexpr error_type std::regex_constants::error_paren | ( | _S_error_paren |  | ) |

The expression contained mismatched ( and ).

constexpr error_type std::regex_constants::error_range | ( | _S_error_range |  | ) |

The expression contained an invalid character range, such as [b-a] in most encodings.

constexpr error_type std::regex_constants::error_space | ( | _S_error_space |  | ) |

There was insufficient memory to convert the expression into a finite state machine.

constexpr error_type std::regex_constants::error_stack | ( | _S_error_stack |  | ) |

There was insufficient memory to determine whether the regular expression could match the specified character sequence.

## Variable Documentation

constexpr syntax_option_type std::regex_constants::awk

Specifies that the grammar recognized by the regular expression engine is that used by POSIX utility awk in IEEE Std 1003.1-2001. This option is identical to syntax_option_type extended, except that C-style escape sequences are supported. These sequences are: \\, \a, \b, \f, \n, \r, \t , \v, \', ', and \ddd (where ddd is one, two, or three octal digits).

Definition at line 144 of file regex_constants.h.

constexpr syntax_option_type std::regex_constants::basic

Specifies that the grammar recognized by the regular expression engine is that used by POSIX basic regular expressions in IEEE Std 1003.1-2001, Portable Operating System Interface (POSIX), Base Definitions and Headers, Section 9, Regular Expressions [IEEE, Information Technology – Portable Operating System Interface (POSIX), IEEE Standard 1003.1-2001].

Definition at line 126 of file regex_constants.h.

constexpr syntax_option_type std::regex_constants::collate

Specifies that character ranges of the form [a-b] should be locale sensitive.

Definition at line 107 of file regex_constants.h.

constexpr syntax_option_type std::regex_constants::ECMAScript

Specifies that the grammar recognized by the regular expression engine is that used by ECMAScript in ECMA-262 [Ecma International, ECMAScript Language Specification, Standard Ecma-262, third edition, 1999], as modified in section [28.13]. This grammar is similar to that defined in the PERL scripting language but extended with elements found in the POSIX regular expression grammar.

Definition at line 117 of file regex_constants.h.

constexpr syntax_option_type std::regex_constants::egrep

Specifies that the grammar recognized by the regular expression engine is that used by POSIX utility grep when given the -E option in IEEE Std 1003.1-2001. This option is identical to syntax_option_type extended, except that newlines are treated as whitespace.

Definition at line 160 of file regex_constants.h.

constexpr syntax_option_type std::regex_constants::extended

Specifies that the grammar recognized by the regular expression engine is that used by POSIX extended regular expressions in IEEE Std 1003.1-2001, Portable Operating System Interface (POSIX), Base Definitions and Headers, Section 9, Regular Expressions.

Definition at line 134 of file regex_constants.h.

constexpr match_flag_type std::regex_constants::format_default

When a regular expression match is to be replaced by a new string, the new string is constructed using the rules used by the ECMAScript replace function in ECMA- 262 [Ecma International, ECMAScript Language Specification, Standard Ecma-262, third edition, 1999], part 15.5.4.11 String.prototype.replace. In addition, during search and replace operations all non-overlapping occurrences of the regular expression are located and replaced, and sections of the input that did not match the expression are copied unchanged to the output string.

Format strings (from ECMA-262 [15.5.4.11]):

- $$ The dollar-sign itself ($)
- $& The matched substring.
- $` The portion of string that precedes the matched substring. This would be match_results::prefix().
- $' The portion of string that follows the matched substring. This would be match_results::suffix().
- $n The nth capture, where n is in [1,9] and $n is not followed by a decimal digit. If n <= match_results::size() and the nth capture is undefined, use the empty string instead. If n > match_results::size(), the result is implementation-defined.
- $nn The nnth capture, where nn is a two-digit decimal number on [01, 99]. If nn <= match_results::size() and the nth capture is undefined, use the empty string instead. If nn > match_results::size(), the result is implementation-defined.

Definition at line 280 of file regex_constants.h.

constexpr match_flag_type std::regex_constants::format_first_only

When specified during a search and replace operation, only the first occurrence of the regular expression shall be replaced.

Definition at line 301 of file regex_constants.h.

constexpr match_flag_type std::regex_constants::format_no_copy

During a search and replace operation, sections of the character container sequence being searched that do not match the regular expression shall not be copied to the output string.

Definition at line 295 of file regex_constants.h.

constexpr match_flag_type std::regex_constants::format_sed

When a regular expression match is to be replaced by a new string, the new string is constructed using the rules used by the POSIX sed utility in IEEE Std 1003.1- 2001 [IEEE, Information Technology – Portable Operating System Interface (POSIX), IEEE Standard 1003.1-2001].

Definition at line 288 of file regex_constants.h.

constexpr syntax_option_type std::regex_constants::grep

Specifies that the grammar recognized by the regular expression engine is that used by POSIX utility grep in IEEE Std 1003.1-2001. This option is identical to syntax_option_type basic, except that newlines are treated as whitespace.

Definition at line 152 of file regex_constants.h.

constexpr syntax_option_type std::regex_constants::icase

Specifies that the matching of regular expressions against a character sequence shall be performed without regard to case.

Definition at line 86 of file regex_constants.h.

constexpr match_flag_type std::regex_constants::match_any

If more than one match is possible then any match is an acceptable result.

Definition at line 235 of file regex_constants.h.

constexpr match_flag_type std::regex_constants::match_continuous

The expression only matches a sub-sequence that begins at first .

Definition at line 245 of file regex_constants.h.

Referenced by std::regex_iterator< _Bi_iter, _Ch_type, _Rx_traits >::operator++().

constexpr match_flag_type std::regex_constants::match_default

The default matching rules.

Definition at line 203 of file regex_constants.h.

constexpr match_flag_type std::regex_constants::match_not_bol

The first character in the sequence [first, last) is treated as though it is not at the beginning of a line, so the character (^) in the regular expression shall not match [first, first).

Definition at line 210 of file regex_constants.h.

constexpr match_flag_type std::regex_constants::match_not_bow

The expression \b is not matched against the sub-sequence [first,first).

Definition at line 223 of file regex_constants.h.

constexpr match_flag_type std::regex_constants::match_not_eol

The last character in the sequence [first, last) is treated as though it is not at the end of a line, so the character ($) in the regular expression shall not match [last, last).

Definition at line 217 of file regex_constants.h.

constexpr match_flag_type std::regex_constants::match_not_eow

The expression \b should not be matched against the sub-sequence [last,last).

Definition at line 229 of file regex_constants.h.

constexpr match_flag_type std::regex_constants::match_not_null

The expression does not match an empty sequence.

Definition at line 240 of file regex_constants.h.

Referenced by std::regex_iterator< _Bi_iter, _Ch_type, _Rx_traits >::operator++().

constexpr match_flag_type std::regex_constants::match_prev_avail

–first is a valid iterator position. When this flag is set then the flags match_not_bol and match_not_bow are ignored by the regular expression algorithms 28.11 and iterators 28.12.

Definition at line 252 of file regex_constants.h.

Referenced by std::regex_iterator< _Bi_iter, _Ch_type, _Rx_traits >::operator++().

constexpr syntax_option_type std::regex_constants::nosubs

Specifies that when a regular expression is matched against a character container sequence, no sub-expression matches are to be stored in the supplied match_results structure.

Definition at line 93 of file regex_constants.h.

constexpr syntax_option_type std::regex_constants::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.

Definition at line 101 of file regex_constants.h.