Struct

GLibRegex

since: 2.14

Description [src]

struct GRegex {
  /* No available fields */
}

A GRegex is a compiled form of a regular expression.

After instantiating a GRegex, you can use its methods to find matches in a string, replace matches within a string, or split the string at matches.

GRegex implements regular expression pattern matching using syntax and semantics (such as character classes, quantifiers, and capture groups) similar to Perl regular expression. See the PCRE documentation for details.

A typical scenario for regex pattern matching is to check if a string matches a pattern. The following statements implement this scenario.

const char *regex_pattern = ".*GLib.*";
const char *string_to_search = "You will love the GLib implementation of regex";
g_autoptr(GMatchInfo) match_info = NULL;
g_autoptr(GRegex) regex = NULL;

regex = g_regex_new (regex_pattern, G_REGEX_DEFAULT, G_REGEX_MATCH_DEFAULT, NULL);
g_assert (regex != NULL);

if (g_regex_match (regex, string_to_search, G_REGEX_MATCH_DEFAULT, &match_info))
  {
    int start_pos, end_pos;
    g_match_info_fetch_pos (match_info, 0, &start_pos, &end_pos);
    g_print ("Match successful! Overall pattern matches bytes %d to %d\n", start_pos, end_pos);
  }
else
  {
    g_print ("No match!\n");
  }

The constructor for GRegex includes two sets of bitmapped flags:

GRegexCompileFlags—These flags control how GLib compiles the regex. There are options for case sensitivity, multiline, ignoring whitespace, etc.
GRegexMatchFlags—These flags control GRegex’s matching behavior, such as anchoring and customizing definitions for newline characters.

Some regex patterns include backslash assertions, such as \d (digit) or \D (non-digit). The regex pattern must escape those backslashes. For example, the pattern "\\d\\D" matches a digit followed by a non-digit.

GLib’s implementation of pattern matching includes a start_position argument for some of the match, replace, and split methods. Specifying a start position provides flexibility when you want to ignore the first n characters of a string, but want to incorporate backslash assertions at character n - 1. For example, a database field contains inconsistent spelling for a job title: healthcare provider and health-care provider. The database manager wants to make the spelling consistent by adding a hyphen when it is missing. The following regex pattern tests for the string care preceded by a non-word boundary character (instead of a hyphen) and followed by a space.

const char *regex_pattern = "\\Bcare\\s";

An efficient way to match with this pattern is to start examining at start_position 6 in the string healthcare or health-care.

const char *regex_pattern = "\\Bcare\\s";
const char *string_to_search = "healthcare provider";
g_autoptr(GMatchInfo) match_info = NULL;
g_autoptr(GRegex) regex = NULL;

regex = g_regex_new (
  regex_pattern,
  G_REGEX_DEFAULT,
  G_REGEX_MATCH_DEFAULT,
  NULL);
g_assert (regex != NULL);

g_regex_match_full (
  regex,
  string_to_search,
  -1,
  6, // position of 'c' in the test string.
  G_REGEX_MATCH_DEFAULT,
  &match_info,
  NULL);

The method g_regex_match_full() (and other methods implementing start_pos) allow for lookback before the start position to determine if the previous character satisfies an assertion.

Unless you set the G_REGEX_RAW as one of the GRegexCompileFlags, all the strings passed to GRegex methods 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 G_REGEX_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.

Regarding line endings, \n matches a \n character, and \r matches a \r character. More generally, \R matches all typical line endings: CR + LF (\r\n), 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), and PS (paragraph separator, U+2029).

The behaviour of the dot, circumflex, and dollar metacharacters are affected by newline characters. By default, GRegex matches any newline character matched by \R. You can limit the matched newline characters by specifying the G_REGEX_MATCH_NEWLINE_CR, G_REGEX_MATCH_NEWLINE_LF, and G_REGEX_MATCH_NEWLINE_CRLF compile options, and with G_REGEX_MATCH_NEWLINE_ANY, G_REGEX_MATCH_NEWLINE_CR, G_REGEX_MATCH_NEWLINE_LF and G_REGEX_MATCH_NEWLINE_CRLF match options. These settings are also relevant when compiling a pattern if G_REGEX_EXTENDED is set and an unescaped # outside a character class is encountered. This indicates a comment that lasts until after the next newline.

Because GRegex does not modify its internal state between creation and destruction, you can create and modify the same GRegex instance from different threads. In contrast, GMatchInfo is not thread safe.

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

Available since: 2.14

Constructors

g_regex_new

Compiles the regular expression to an internal form, and does the initial setup of the GRegex structure.

since: 2.14

Functions

g_regex_check_replacement

Checks whether replacement is a valid replacement string (see g_regex_replace()), i.e. that all escape sequences in it are valid.

since: 2.14

g_regex_error_quark

No description available.

g_regex_escape_nul

Escapes the nul characters in string to “\x00”. It can be used to compile a regex with embedded nul characters.

since: 2.30

g_regex_escape_string

Escapes the special characters used for regular expressions in string, for instance “a.b*c” becomes “a.b*c”. This function is useful to dynamically generate regular expressions.

since: 2.14

g_regex_match_simple

Scans for a match in string for pattern.

since: 2.14

g_regex_split_simple

Breaks the string on the pattern, and returns an array of the tokens. If the pattern contains capturing parentheses, then the text for each of the substrings will also be returned. If the pattern does not match anywhere in the string, then the whole string is returned as the first token.

since: 2.14

Instance methods

g_regex_get_capture_count

Returns the number of capturing subpatterns in the pattern.

since: 2.14

g_regex_get_compile_flags

Returns the compile options that regex was created with.

since: 2.26

g_regex_get_has_cr_or_lf

Checks whether the pattern contains explicit CR or LF references.

since: 2.34

g_regex_get_match_flags

Returns the match options that regex was created with.

since: 2.26

g_regex_get_max_backref

Returns the number of the highest back reference in the pattern, or 0 if the pattern does not contain back references.

since: 2.14

g_regex_get_max_lookbehind

Gets the number of characters in the longest lookbehind assertion in the pattern. This information is useful when doing multi-segment matching using the partial matching facilities.

since: 2.38

g_regex_get_pattern

Gets the pattern string associated with regex, i.e. a copy of the string passed to g_regex_new().

since: 2.14

g_regex_get_string_number

Retrieves the number of the subexpression named name.

since: 2.14

g_regex_match

Scans for a match in string for the pattern in regex. The match_options are combined with the match options specified when the regex structure was created, letting you have more flexibility in reusing GRegex structures.

since: 2.14

g_regex_match_all

Using the standard algorithm for regular expression matching only the longest match in the string is retrieved. This function uses a different algorithm so it can retrieve all the possible matches. For more documentation see g_regex_match_all_full().

since: 2.14

g_regex_match_all_full

Using the standard algorithm for regular expression matching only the longest match in the string is retrieved, it is not possible to obtain all the available matches. For instance matching "<a> <b> <c>" against the pattern "<.*>" you get "<a> <b> <c>".

since: 2.14

g_regex_match_full

Scans for a match in string for the pattern in regex. The match_options are combined with the match options specified when the regex structure was created, letting you have more flexibility in reusing GRegex structures.

since: 2.14

g_regex_ref

Increases reference count of regex by 1.

since: 2.14

g_regex_replace

Replaces all occurrences of the pattern in regex with the replacement text. Backreferences of the form \number or \g<number> in the replacement text are interpolated by the number-th captured subexpression of the match, \g<name> refers to the captured subexpression with the given name. \0 refers to the complete match, but \0 followed by a number is the octal representation of a character. To include a literal \ in the replacement, write \\\\.

since: 2.14

g_regex_replace_eval

Replaces occurrences of the pattern in regex with the output of eval for that occurrence.

since: 2.14

g_regex_replace_literal

Replaces all occurrences of the pattern in regex with the replacement text. replacement is replaced literally, to include backreferences use g_regex_replace().

since: 2.14

g_regex_split

Breaks the string on the pattern, and returns an array of the tokens. If the pattern contains capturing parentheses, then the text for each of the substrings will also be returned. If the pattern does not match anywhere in the string, then the whole string is returned as the first token.

since: 2.14

g_regex_split_full

Breaks the string on the pattern, and returns an array of the tokens. If the pattern contains capturing parentheses, then the text for each of the substrings will also be returned. If the pattern does not match anywhere in the string, then the whole string is returned as the first token.

since: 2.14

g_regex_unref

Decreases reference count of regex by 1. When reference count drops to zero, it frees all the memory associated with the regex structure.

since: 2.14