Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!tds.kth.se!juha
From: juha@tds.kth.se (Juha Sarlin)
Newsgroups: gnu.emacs.bug
Subject: match data cannot always be restored
Message-ID: <8910201435.AA02459@ttds.tds.kth.se>
Date: 20 Oct 89 16:35:27 GMT
Sender: daemon@tut.cis.ohio-state.edu
Distribution: gnu
Organization: GNUs Not Usenet
Lines: 18

After a string-match the value of (match-beginning 0) can be zero.
The zero is changed into one by:
    (store-match-data (match-data))

The function below demonstrates the error. In emacs 18.55 on a Sun 3/60
running SunOS 4.0.1 it returns (0 1), which means that match-beginning
has changed from 0 to 1.

(defun bug ()
  (string-match "foo" "foobar")
  (let ((before (match-beginning 0)))
    (store-match-data (match-data))
    (list before (match-beginning 0))))

This error makes the debugging of some functions that use string-match
difficult, because the debugger uses match-data and store-match-data.
--
Juha Sarlin	juha@tds.kth.se