Matches one or more occurrences of the preceding item, except in a bracket expression. For example, a+ matches a, aa, aaa, and so on.

Matches zero or more occurrences of the preceding item, except in a bracket expression. For example, a* matches the empty string, a, aa, and so on.

Matches zero or one occurrence(s) of the preceding item, except in a bracket expression. For example, a? matches the empty string and a.

{ and }

Specify a cardinality range, formed as follows: {m,n}. This construct matches between m and n occurrences of the preceding item. For example, a{2,3} matches aa and aaa.

This construct can also be formed using {m,} and {m}. The first matches m or more occurrences of the preceding item. For example, a{2,} matches aa, aaa, aaaa, and so on. The second matches exactly m occurrences of the preceding item. For example, a{2} matches aa.

Note: { is treated differently in a bracket expression. In this context, { denotes the beginning of a Unicode character category, as described in Unicode Regular Expressions.

[ and ]

Create a bracket expression. Bracket expressions create a set of items, any of which may be matched. For example, [abc] matches a, or b, or c.

Within a bracket expression all regular expression special characters are treated as normal, non-special characters, except::

- specifies a range of character values, based on their bit pattern. For example, [A-Za-z] matches all uppercase and lowercase English characters. To indicate - as a character in the bracket expression, it must be the first or last character in the set; for example, [-a-z] or [A-Z-].

^ is special only when placed in the first character position within the bracket set. Using ^ in the first position complements the set of items to be matched. For example, [^a-z] matches all characters except for lowercase English letters.

{ denotes the beginning of a Unicode character category (see Unicode Regular Expressions). To use { in a bracket expression, escape it by preceding it with the \ character as follows: [\{].

Finally, in order to include a ] as a character in the bracket set, you must include it as the first character in the set, as in []abc] or [^]abc].

( and )

Group regular expression items into subexpressions, which are treated as a single unit. For example, whereas ab* matches a, ab, abb, and so on, (ab)* matches the empty string, ab, abab, and so on. ( and ) are not treated as special characters inside a bracket expression.

Escapes a regular expression character, causing it to be treated as a regular character. For example, whereas (ab) indicates a subexpression consisting of ab, \(ab\) denotes the sequence of characters (, a, b, and ).

Note: To specify the \ character in C++ source code, you must specify \\, as the C++ compiler treats the \ character as special, denoting the beginning of an escape sequence embedded in the C++ source code. In data files, or text controls in dialog boxes, however, the double backslash is not necessary.

Indicates that a regular expression or subexpression is anchored at the beginning of the input string. For example, ^ab matches ab and abc, but not cab. Recall that ^ is treated differently in bracket expressions.

Indicates that a regular expression or subexpression is anchored at the end of the input string. For example, ab$ matches ab and cab, but not abc.

Denotes alternation, or the creation of a set of equally valid, alternate expressions or subexpressions, each of which can be matched. For example, ab|cd matches ab or cd.

Matches any code unit, except for those which indicate the logical end of a line, as outlined in Unicode Technical Report #18: \u2028, \u2029, \u000A, \u000B, \u000C, \u000D, \u0085.