Emacs regexp groups in regex-replace

Question

I have a bunch of C macros in files, stuff like NEXT( pL ) which is expanded to ( ( pL ) -> next )

I want to remove most of them because they're unnecessary.

What I would like to do, is get the text inside the parentheses in the macro, pL. I want the replacing regexp to use that text for the rewriting. For example, in Perl I could do something like /NEXT\(\s*(.+)\s*) (may be a little incorrect) and then output something like $1->next, which should turn a line

if ( NEXT( pL ) != NULL ) {

into

if ( pL->next != NULL ) {

In Emacs, I would like to use match groups in an emacs replace-regexp on a file by file basis. I'm not entirely sure how to do this in Emacs.

M-x c-macro-expansion or M-x c-macro-expand could be used. But what you ask for looks like it will need a new function around the M-x c-macro-expansion to work on a whole file or buffer. — vpit3833
– vpit3833, Commented Dec 1, 2010 at 21:32
c-macro-expand doesn't know the macros though? They are located in a separate file/buffer. — Kizaru
– Kizaru, Commented Dec 1, 2010 at 21:37

Trey Jackson · Accepted Answer · 2010-12-01 22:02:31Z

23

M-x query-replace-regexp NEXT(\([^)]+\)) RET \1->next RET

Which can be done inside a function like so (to apply to an entire buffer)

(defun expand-next ()
  "interactive"
  (goto-char (point-min))
  (while (re-search-forward "\\<NEXT(\\([^\)]+\\))" nil t)
    (replace-match "\\1->next")))

And, to apply this to multiple files, you can mark the files in Dired and type Q to do a query-replace-regexp on all the marked files (use the regexp/replacement in the first line of this answer).

edited Dec 1, 2010 at 22:02

answered Dec 1, 2010 at 21:52

Trey Jackson

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1 Comment

Daniel Over a year ago

I'm dredging up some old muck here rather than submit a new question since this is the correct topic ... I'm using Emacs 23.1. When I use \1 as the replacement, I get "No matches found." I use the same regexp built from regexp-builder which matches the found text correctly. Any Ideas??

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