Regex


Object Hierarchy:

Object hierarchy for Regex

Description:

[ Compact ]
[ Version ( since = "2.14" ) ]
[ CCode ( ref_function = "g_regex_ref" , type_id = "G_TYPE_REGEX" , unref_function = "g_regex_unref" ) ]
public class Regex

The g_regex_*() functions implement regular expression pattern matching using syntax and semantics similar to Perl regular expression.

Some functions accept a start_position argument, setting it differs from just passing over a shortened string and setting NOTBOL in the case of a pattern that begins with any kind of lookbehind assertion. For example, consider the pattern "\Biss\B" which finds occurrences of "iss" in the middle of words. ("\B" matches only if the current position in the subject is not a word boundary.) When applied to the string "Mississipi" from the fourth byte, namely "issipi", it does not match, because "\B" is always false at the start of the subject, which is deemed to be a word boundary. However, if the entire string is passed , but with start_position set to 4, it finds the second occurrence of "iss" because it is able to look behind the starting point to discover that it is preceded by a letter.

Note that, unless you set the RAW flag, all the strings passed to these functions must be encoded in UTF-8. The lengths and the positions inside the strings are in bytes and not in characters, so, for instance, "\xc3\xa0" (i.e. "à") is two bytes long but it is treated as a single character. If you set RAW the strings can be non-valid UTF-8 strings and a byte is treated as a character, so "\xc3\xa0" is two bytes and two characters long.

When matching a pattern, "\n" matches only against a "\n" character in the string, and "\r" matches only a "\r" character. To match any newline sequence use "\R". This particular group matches either the two-character sequence CR + LF ("\r\n"), or one of the single characters LF ( linefeed, U+000A, "\n"), VT vertical tab, U+000B, "\v"), FF (formfeed, U+000C, "\f"), CR (carriage return, U+000D, "\r"), NEL (next line, U+0085 ), LS (line separator, U+2028), or PS (paragraph separator, U+2029).

The behaviour of the dot, circumflex, and dollar metacharacters are affected by newline characters, the default is to recognize any newline character (the same characters recognized by "\R"). This can be changed with NEWLINE_CR, NEWLINE_LF and NEWLINE_CRLF compile options, and with NEWLINE_ANY, NEWLINE_CR, NEWLINE_LF and NEWLINE_CRLF match options. These settings are also relevant when compiling a pattern if EXTENDED is set, and an unescaped "#" outside a character class is encountered. This indicates a comment that lasts until after the next newline.

When setting the g_regex_javascript_compat flag, pattern syntax and pattern matching is changed to be compatible with the way that regular expressions work in JavaScript. More precisely, a lonely ']' character in the pattern is a syntax error; the '\x' escape only allows 0 to 2 hexadecimal digits, and you must use the '\u' escape sequence with 4 hex digits to specify a unicode codepoint instead of '\x' or 'x{....}'. If '\x' or '\u' are not followed by the specified number of hex digits, they match 'x' and 'u' literally; also '\U' always matches 'U' instead of being an error in the pattern. Finally, pattern matching is modified so that back references to an unset subpattern group produces a match with the empty string instead of an error. See pcreapi(3) for more information.

Creating and manipulating the same Regex structure from different threads is not a problem as Regex does not modify its internal state between creation and destruction, on the other hand MatchInfo is not threadsafe.

The regular expressions low-level functionalities are obtained through the excellent PCRE library written by Philip Hazel.


Namespace: GLib
Package: glib-2.0

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