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From "Martin Sebor (JIRA)" <j...@apache.org>
Subject [jira] Created: (STDCXX-690) [LWG #198] std::reverse_iterator::operator*() invalidates cached values
Date Tue, 08 Jan 2008 21:24:34 GMT
[LWG #198] std::reverse_iterator::operator*() invalidates cached values
-----------------------------------------------------------------------

                 Key: STDCXX-690
                 URL: https://issues.apache.org/jira/browse/STDCXX-690
             Project: C++ Standard Library
          Issue Type: Bug
          Components: 24. Iterators
    Affects Versions: 4.2.0, 4.1.4, 4.1.3, 4.1.2
            Reporter: Martin Sebor


According to LWG issue 198 (http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#198),
the implementation of reverse_iterator::operator*() should cache the "base" iterator to prevent
dangling references to values cached by it. The test case below demonstrates the problem caused
by not doing so:

$ cat t.cpp && make t && ./t
#include <cassert>
#include <iterator>

struct Iterator: std::iterator<std::random_access_iterator_tag, int>
{
    int *cur;
    int cache;

    Iterator (int *p = 0): cur (p) { }
    ~Iterator () { cache = ~cache; }

    reference operator*() { return cache; }

    Iterator& operator++() { cache = *++cur; return *this; }
    Iterator& operator--() { cache = *--cur; return *this; }
};


int main ()
{
    int a[] = { 1, 2, 3 };
    Iterator it (a + sizeof a / sizeof *a);
    std::reverse_iterator<Iterator> rit (it);

    const int &ref = *rit;
    const int val = ref;

    ++rit;
    assert (val == ref);
}
gcc -c -I/home/sebor/stdcxx/include/ansi -D_RWSTDDEBUG   -pthread -I/home/sebor/stdcxx/include
-I/build/sebor/stdcxx-gcc-4.1.2-15D/include -I/home/sebor/stdcxx/examples/include  -pedantic
-nostdinc++ -g   -W -Wall -Wcast-qual -Winline -Wshadow -Wwrite-strings -Wno-long-long -Wcast-align
  t.cpp
gcc t.o -o t -pthread  -L/build/sebor/stdcxx-gcc-4.1.2-15D/lib  -Wl,-R/build/sebor/stdcxx-gcc-4.1.2-15D/lib
-lstd15D -lsupc++ -lm 
t: t.cpp:29: int main(): Assertion `val == ref' failed.
Aborted


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