Re: [boost] regex lib: bug with sets and back ref

From: John Maddock (john_at_[hidden])
Date: 2004-04-25 05:29:39

> Sorry if I wasn't clear enough.  All tests use regex_grep.  In the last
example, however, regex_grep _doesn't_ find "bcbc", even though >it should.
I would assume it's an issue with regex_compile, as the only difference
between (2) and (3) is the way the set is defined.

Got it, yes it's a bug: the backreference was interacting badly with the
heuristics regex uses to optimise some searches, there's a patch going into
cvs now (see below).  Rather than applying the patch though, I would suggest
that you get hold of a copy of the RC_1_31_0 cvs branch, as that contains
all the accumulated regex bug-fixes since the last release.

John.

$ cvs diff -u boost/regex/v4
johnmaddock_at_[hidden]'s password:
cvs diff: Diffing boost/regex/v4
Index: boost/regex/v4/regex_compile.hpp
===================================================================
RCS file: /cvsroot/boost/boost/boost/regex/v4/regex_compile.hpp,v
retrieving revision 1.11
diff -u -r1.11 regex_compile.hpp
--- boost/regex/v4/regex_compile.hpp    19 Nov 2003 12:57:17 -0000      1.11
+++ boost/regex/v4/regex_compile.hpp    25 Apr 2004 10:25:41 -0000
@@ -1350,6 +1350,7 @@
    data.clear();
    _flags = f;
    fail(REG_NOERROR);  // clear any error
+   _leading_len = 0; // set this to non-zero if there are any backrefs,
we'll r
efer to it later...

    if(arg_first >= arg_last)
    {
@@ -1600,6 +1601,7 @@
                dat = add_simple(dat, re_detail::syntax_element_backref,
sizeof(
re_detail::re_brace));
                static_cast<re_detail::re_brace*>(dat)->index = i;
                ++ptr;
+               _leading_len = 1;
                continue;
             }
             break;
@@ -2141,7 +2143,7 @@
       case re_detail::syntax_element_char_rep:
       case re_detail::syntax_element_short_set_rep:
       case re_detail::syntax_element_long_set_rep:
-         if((len == 0) && (1 == fixup_leading_rep(dat->next.p,
static_cast<re_d
etail::re_repeat*>(dat)->alt.p) ))
+         if((len == 0) && (_leading_len == 0) && (1 ==
fixup_leading_rep(dat->n
ext.p, static_cast<re_detail::re_repeat*>(dat)->alt.p) ))
          {
             static_cast<re_detail::re_repeat*>(dat)->leading = leading_lit;
             return len;