34.6.3 Accessing the Entire Match Data

The functions match-data and set-match-data read or write the entire match data, all at once.

function match-data \&optional integers reuse reseat

This function returns a list of positions (markers or integers) that record all the information on the text that the last search matched. Element zero is the position of the beginning of the match for the whole expression; element one is the position of the end of the match for the expression. The next two elements are the positions of the beginning and end of the match for the first subexpression, and so on. In general, element number 2n corresponds to (match-beginning n); and element number 2n + 1 corresponds to (match-end n).

Normally all the elements are markers or nil, but if integers is non-nil, that means to use integers instead of markers. (In that case, the buffer itself is appended as an additional element at the end of the list, to facilitate complete restoration of the match data.) If the last match was done on a string with string-match, then integers are always used, since markers can’t point into a string.

If reuse is non-nil, it should be a list. In that case, match-data stores the match data in reuse. That is, reuse is destructively modified. reuse does not need to have the right length. If it is not long enough to contain the match data, it is extended. If it is too long, the length of reuse stays the same, but the elements that were not used are set to nil. The purpose of this feature is to reduce the need for garbage collection.

If reseat is non-nil, all markers on the reuse list are reseated to point to nowhere.

As always, there must be no possibility of intervening searches between the call to a search function and the call to match-data that is intended to access the match data for that search.

(match-data)
     ⇒  (#<marker at 9 in foo>
          #<marker at 17 in foo>
          #<marker at 13 in foo>
          #<marker at 17 in foo>)

function set-match-data match-list \&optional reseat

This function sets the match data from the elements of match-list, which should be a list that was the value of a previous call to match-data. (More precisely, anything that has the same format will work.)

If match-list refers to a buffer that doesn’t exist, you don’t get an error; that sets the match data in a meaningless but harmless way.

If reseat is non-nil, all markers on the match-list list are reseated to point to nowhere.

store-match-data is a semi-obsolete alias for set-match-data.