[LLVMbugs] [Bug 18786] New: Iterator overrun in std::unique

bugzilla-daemon at llvm.org bugzilla-daemon at llvm.org
Sun Feb 9 08:52:25 PST 2014


            Bug ID: 18786
           Summary: Iterator overrun in std::unique
           Product: libc++
           Version: unspecified
          Hardware: PC
                OS: Windows NT
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
          Assignee: hhinnant at apple.com
          Reporter: eric at boostpro.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

Hi Howard. Forgive me, maybe this is just because I haven't had my morning
coffee yet, but I'm looking at the implementation of std::unique, and I see

    if (__first != __last)
        // ...  a  a  ?  ...
        //      f     i
        _ForwardIterator __i = __first;
        for (++__i; ++__i != __last;)
            if (!__pred(*__first, *__i))
                *++__first = _VSTD::move(*__i);

Now image __first and __last delimit a sequence of exactly one element. __first
!= __last is true, __i is assigned begin, is incremented once (so now it equals
__last), and is then incremented *again* before comparing it to last. This
looks like a bug to me.

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