Are std::list iterators broken in VC++2008?
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Thread: Are std::list iterators broken in VC++2008?

  1. #1
    Join Date
    Feb 2010
    Posts
    2

    Are std::list iterators broken in VC++2008?

    From my understanding of STL, list iterators are supposed to remain valid after a splice operation, however I seem to be getting a problem when I use an iterator to splice one object from list A to list B. The iterator seems to have been invalidated by the STL implementation. If I then try to use the same iterator to splice the object back from list B to list A, "bad things" happen (assertion fail on a debug build, worse on a release build). Here is a simple test case:

    #include <list>
    #include <assert.h>

    typedef std::list<int> IntList;

    extern "C" int main(int argc, char *argv[])
    {
    IntList list1, list2;

    IntList::iterator iter = list1.insert(list1.end(), 42);
    list2.splice(list2.end(), list1, iter);
    list1.splice(list1.end(), list2, iter);
    assert(list1.size() == 1);
    assert(list2.empty());
    assert(*(list1.begin()) == 42);

    return 0;
    }


    This code builds and appears to run fine using GCC, but not with Visual Studio 2008 (the second splice operation fails an internal assertion). Am I missing something fundamental here or is this a problem with VC++?

    Peter

  2. #2
    Join Date
    Aug 2000
    Location
    West Virginia
    Posts
    7,646

    Re: Are std::list iterators broken in VC++2008?

    I am not sure, but I think the result of the second splice operation
    is undefined. According to the standard, the splice operation:

    Invalidates only the iterators and references to the spliced element
    So, I read that to mean that the first splice operation would invalidate
    the iterator (iter) , which you use in the second splice operation.

    I could be wrong ... I am not a language expert on these types
    of matters.

  3. #3
    Join Date
    Feb 2010
    Posts
    2

    Re: Are std::list iterators broken in VC++2008?

    I suspect you are correct, at least from what I can tell tracing through VC++'s STL list source. The problem is relatively easily fixed/worked around by reassigning the iterator to list2.end() and decrementing it after the first splice, but one line of code is usually preferable to three

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