Re: Reassigning references (to std::map in this case)...

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Thu, 6 Sep 2007 13:51:32 -0400

Message-ID:

<fbpen4$ofc$1@news.datemas.de>

Tobe wrote:

Here's an example of something that feels like it should be OK but
does in fact produce a segfault on every compiler I've tried (VC2005,
g ++ 4.1.2/Linux, g++ 3.4.4/Cygwin). The line marked // KABOOM is the
one that segfaults. If I change the references to pointers (and make
the appropriate dereferences) everything works just fine so is this
some finer point of references I'm not grasping or an issue with the
STL ?

Answers gratefully received..

NEVER put anything beside your signature after the "-- " (the signature
separator). Now I have to manually drag your source code in here...

EntryMap &entriesRef1 = entries["1"].iEntries;
EntryMap &entriesRef2 = entries["1"].iEntries["2"].iEntries;

So, 'entriesRef2' is a reference to an entry in a member of the
'entriesRef1's referred object.

entriesRef1 = entriesRef2; // KABOOM

What happens? You start overriding 'entries["1"].iEntries' value by
means of assigning to a reference to it. And at the same time you
probably want to continue using it (since the right-hand side still
refers to it). It's not going to work. 'entriesRef2' becomes invalid
as soon as the assignment to 'entriesRef1' begins because assignment
cleans out the contents of 'entries["1"].iEntries' thus deleting what
is behind the 'entriesRef2' along with it.

V
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