MatchInfo

class MatchInfo(*args, **kwargs)

A GMatchInfo is an opaque struct used to return information about matches.

Methods

class MatchInfo

expand_references(string_to_expand: str) → str | None

Returns a new string containing the text in string_to_expand with references and escape sequences expanded. References refer to the last match done with string against regex and have the same syntax used by replace().

The string_to_expand must be UTF-8 encoded even if RAW was passed to new().

The backreferences are extracted from the string passed to the match function, so you cannot call this function after freeing the string.

match_info may be None in which case string_to_expand must not contain references. For instance “foon” does not refer to an actual pattern and ‘n’ merely will be replaced with n character, while to expand “0” (whole match) one needs the result of a match. Use check_replacement() to find out whether string_to_expand contains references.

Added in version 2.14.

Parameters:

string_to_expand – the string to expand

fetch(match_num: int) → str | None

Retrieves the text matching the match_num'th capturing parentheses. 0 is the full text of the match, 1 is the first paren set, 2 the second, and so on.

If match_num is a valid sub pattern but it didn’t match anything (e.g. sub pattern 1, matching “b” against “(a)?b”) then an empty string is returned.

If the match was obtained using the DFA algorithm, that is using match_all() or match_all_full(), the retrieved string is not that of a set of parentheses but that of a matched substring. Substrings are matched in reverse order of length, so 0 is the longest match.

The string is fetched from the string passed to the match function, so you cannot call this function after freeing the string.

Added in version 2.14.

Parameters:

match_num – number of the sub expression

fetch_all() → list[str]

Bundles up pointers to each of the matching substrings from a match and stores them in an array of gchar pointers. The first element in the returned array is the match number 0, i.e. the entire matched text.

If a sub pattern didn’t match anything (e.g. sub pattern 1, matching “b” against “(a)?b”) then an empty string is inserted.

If the last match was obtained using the DFA algorithm, that is using match_all() or match_all_full(), the retrieved strings are not that matched by sets of parentheses but that of the matched substring. Substrings are matched in reverse order of length, so the first one is the longest match.

The strings are fetched from the string passed to the match function, so you cannot call this function after freeing the string.

Added in version 2.14.

fetch_named(name: str) → str | None

Retrieves the text matching the capturing parentheses named name.

If name is a valid sub pattern name but it didn’t match anything (e.g. sub pattern "X", matching "b" against "(?P<X>a)?b") then an empty string is returned.

The string is fetched from the string passed to the match function, so you cannot call this function after freeing the string.

Added in version 2.14.

Parameters:

name – name of the subexpression

fetch_named_pos(name: str) → tuple[bool, int, int]

Retrieves the position in bytes of the capturing parentheses named name.

If name is a valid sub pattern name but it didn’t match anything (e.g. sub pattern "X", matching "b" against "(?P<X>a)?b") then start_pos and end_pos are set to -1 and True is returned.

As end_pos is set to the byte after the final byte of the match (on success), the length of the match can be calculated as end_pos - start_pos.

Added in version 2.14.

Parameters:

name – name of the subexpression

fetch_pos(match_num: int) → tuple[bool, int, int]

Returns the start and end positions (in bytes) of a successfully matching capture parenthesis.

Valid values for match_num are 0 for the full text of the match, 1 for the first paren set, 2 for the second, and so on.

As end_pos is set to the byte after the final byte of the match (on success), the length of the match can be calculated as end_pos - start_pos.

As a best practice, initialize start_pos and end_pos to identifiable values, such as G_MAXINT, so that you can test if g_match_info_fetch_pos() actually changed the value for a given capture parenthesis.

The parameter match_num corresponds to a matched capture parenthesis. The actual value you use for match_num depends on the method used to generate match_info. The following sections describe those methods.

Methods Using Non-deterministic Finite Automata Matching

The methods match and match_full return a MatchInfo using traditional (greedy) pattern matching, also known as Non-deterministic Finite Automaton (NFA) matching. You pass the returned GMatchInfo from these methods to g_match_info_fetch_pos() to determine the start and end positions of capture parentheses. The values for match_num correspond to the capture parentheses in order, with 0 corresponding to the entire matched string.

match_num can refer to a capture parenthesis with no match. For example, the string b matches against the pattern (a)?b, but the capture parenthesis (a) has no match. In this case, g_match_info_fetch_pos() returns true and sets start_pos and end_pos to -1 when called with match_num as 1 (for (a)).

For an expanded example, a regex pattern is (a)?(.*?)the (.*), and a candidate string is glib regexes are the best. In this scenario there are four capture parentheses numbered 0–3: an implicit one for the entire string, and three explicitly declared in the regex pattern.

Given this example, the following table describes the return values from g_match_info_fetch_pos() for various values of match_num.

match_num | Contents | Return value | Returned start_pos | Returned end_pos ———– | ——– | ———— | ——————– | —————— 0 | Matches entire string | True | 0 | 25 1 | Does not match first character | True | -1 | -1 2 | All text before the | True | 0 | 17 3 | All text after the | True | 21 | 25 4 | Capture paren out of range | False | Unchanged | Unchanged

The following code sample and output implements this example.

match_num Contents                  Return value returned start_pos returned end_pos
0         glib regexes are the best 1            0                  25
1         N/A                       1            -1                 -1
2         glib regexes are          1            0                  17
3         best                      1            21                 25
4         N/A                       0            2147483647         2147483647

```
## Methods Using Deterministic Finite Automata Matching

The methods [method@GLib.Regex.match_all] and
[method@GLib.Regex.match_all_full]
return a `GMatchInfo` using
[Deterministic Finite Automaton](https://en.wikipedia.org/wiki/Deterministic_finite_automaton)
(DFA) pattern matching. This algorithm detects overlapping matches. You pass
the returned `GMatchInfo` from these methods to `g_match_info_fetch_pos()`
to determine the start and end positions of each overlapping match. Use the
method [method@GLib.MatchInfo.get_match_count] to determine the number
of overlapping matches.

For example, a regex pattern is `<.*>`, and a candidate string is
`<a> <b> <c>`. In this scenario there are three implicit capture
parentheses: one for the entire string, one for `<a> <b>`, and one for `<a>`.

Given this example, the following table describes the return values from
`g_match_info_fetch_pos()` for various values of @match_num.

`match_num` | Contents | Return value | Returned `start_pos` | Returned `end_pos`
----------- | -------- | ------------ | -------------------- | ------------------
0 | Matches entire string | True | 0 | 11
1 | Matches `<a> <b>` | True | 0 | 7
2 | Matches `<a>` | True | 0 | 3
3 | Capture paren out of range | False | Unchanged | Unchanged

The following code sample and output implements this example.


``` { .c }
#include <glib.h>

int
main (int argc, char *argv[])
{
  g_autoptr(GError) local_error = NULL;
  const char *regex_pattern = "<.*>";
  const char *test_string = "<a> <b> <c>";
  g_autoptr(GRegex) regex = NULL;

  regex = g_regex_new (regex_pattern,
                       G_REGEX_DEFAULT,
                       G_REGEX_MATCH_DEFAULT,
                       &local_error);
  if (regex == NULL)
    {
      g_printerr ("Error creating regex: %s\n", local_error->message);
      return -1;
    }

  g_autoptr(GMatchInfo) match_info = NULL;
  g_regex_match_all (regex, test_string, G_REGEX_MATCH_DEFAULT, &match_info);

  int n_matched_strings = g_match_info_get_match_count (match_info);

  // Print header line
  g_print ("match_num Contents                  Return value returned start_pos returned end_pos\n");

  // Iterate over each capture paren, including one that is out of range as a demonstration.
  for (int match_num = 0; match_num <= n_matched_strings; match_num++)
    {
      gboolean found_match;
      g_autofree char *paren_string = NULL;
      int start_pos = G_MAXINT;
      int end_pos = G_MAXINT;

      found_match = g_match_info_fetch_pos (match_info, match_num, &start_pos, &end_pos);

      // If no match, display N/A as the found string.
      if (start_pos == G_MAXINT || start_pos == -1)
        paren_string = g_strdup ("N/A");
      else
        paren_string = g_strndup (test_string + start_pos, end_pos - start_pos);

      g_print ("%-9d %-25s %-12d %-18d %d\n", match_num, paren_string, found_match, start_pos, end_pos);
    }

  return 0;
}

match_num Contents                  Return value returned start_pos returned end_pos
0         <a> <b> <c>               1            0                  11
1         <a> <b>                   1            0                  7
2         <a>                       1            0                  3
3         N/A                       0            2147483647         2147483647

Added in version 2.14.

param match_num:

number of the capture parenthesis

free() → None

If match_info is not None, calls unref(); otherwise does nothing.

Added in version 2.14.

get_match_count() → int

Retrieves the number of matched substrings (including substring 0, that is the whole matched text), so 1 is returned if the pattern has no substrings in it and 0 is returned if the match failed.

If the last match was obtained using the DFA algorithm, that is using match_all() or match_all_full(), the retrieved count is not that of the number of capturing parentheses but that of the number of matched substrings.

Added in version 2.14.

get_regex() → Regex

Returns Regex object used in match_info. It belongs to Glib and must not be freed. Use ref() if you need to keep it after you free match_info object.

Added in version 2.14.

get_string() → str

Returns the string searched with match_info. This is the string passed to match() or replace() so you may not free it before calling this function.

Added in version 2.14.

is_partial_match() → bool

Usually if the string passed to g_regex_match*() matches as far as it goes, but is too short to match the entire pattern, False is returned. There are circumstances where it might be helpful to distinguish this case from other cases in which there is no match.

Consider, for example, an application where a human is required to type in data for a field with specific formatting requirements. An example might be a date in the form ddmmmyy, defined by the pattern “^d?d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)dd$”. If the application sees the user’s keystrokes one by one, and can check that what has been typed so far is potentially valid, it is able to raise an error as soon as a mistake is made.

GRegex supports the concept of partial matching by means of the PARTIAL_SOFT and PARTIAL_HARD flags. When they are used, the return code for match() or match_full() is, as usual, True for a complete match, False otherwise. But, when these functions return False, you can check if the match was partial calling is_partial_match().

The difference between PARTIAL_SOFT and PARTIAL_HARD is that when a partial match is encountered with PARTIAL_SOFT, matching continues to search for a possible complete match, while with PARTIAL_HARD matching stops at the partial match. When both PARTIAL_SOFT and PARTIAL_HARD are set, the latter takes precedence.

There were formerly some restrictions on the pattern for partial matching. The restrictions no longer apply.

See pcrepartial(3) for more information on partial matching.

Added in version 2.14.

matches() → bool

Returns whether the previous match operation succeeded.

Added in version 2.14.

next() → bool

Scans for the next match using the same parameters of the previous call to match_full() or match() that returned match_info.

The match is done on the string passed to the match function, so you cannot free it before calling this function.

Added in version 2.14.