Re: libstdc++/4354

Re: libstdc++/4354

[Paolo Carlini]

The following reply was made to PR libstdc++/4354; it has been noted by GNATS.

From: Paolo Carlini <pcarlini@unitus.it>
To: bagnara@cs.unipr.it, gcc-gnats@gcc.gnu.org,
 	gcc-prs@gcc.gnu.org, ncm@cantrip.org, pcarlini@unitus.it,
 	gcc-bugs@gcc.gnu.org, nobody@gcc.gnu.org
Cc:  
Subject: Re: libstdc++/4354
Date: Fri, 28 Sep 2001 12:57:39 +0200

 In the meanwhile I cross checked on the comp.std.c++ list that indeed we are
 dealing with a regression wrt libstdc++-v2
 
 But reference counting issues (basic_string class is COW) prevents from working
 a solution involving the swap of the aforementioned calls whenever *this is
 shared.
 
 On the other hand, the following simple patch seems to robustly solve the
 problem with basic_string::assign (and its siblings involving overlapping ranges
 for basic_string::replace), at the cost of an additional temporary string.
 
 The patch has been tested with no regressions on x86, deals correctly with
 Roberto's testcase and variants of it and moreover basic_string::replace now
 does the right thing in case of overlapping ranges:
 
 
 --- basic_string.tcc.orig       Sun Sep 23 16:56:21 2001
 +++ basic_string.tcc    Sun Sep 23 17:00:11 2001
 @@ -453,10 +453,14 @@
         if (__dmax <= __dnew)
           __throw_length_error("basic_string::_M_replace");
         size_type __off = __i1 - _M_ibegin();
 +       // Save concerned source string data in a temporary
 +       const basic_string __temp = basic_string(__k1, __k2);
         _M_mutate(__off, __dold, __dnew);
 -       // Invalidated __i1, __i2
 +       // Invalidated __i1, __i2 (and clobbered original source string
 +       // data when destination string == source string and the string
 +       // is unshared)
         if (__dnew)
 -         _S_copy_chars(_M_data() + __off, __k1, __k2);
 +         _S_copy_chars(_M_data() + __off, __temp.begin(), __temp.end());
 
         return *this;
        }
 
 
 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view&pr=4354&database=gcc