http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47305
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution| |INVALID
--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-01-15
11:08:06 UTC ---
(In reply to comment #0)
> In the C++ stdlib distribution included with Mac OS X (Darwin 10.5.0 i386),
> the
GCC 4.2 is no longer maintained, you should either try a current release or
report bugs to Apple.
> implementation of std::vector::erase() from vector.tcc lines 106-116 is shown
> here:
>
> template<typename _Tp, typename _Alloc>
> typename vector<_Tp, _Alloc>::iterator
> vector<_Tp, _Alloc>::
> erase(iterator __position)
> {
> if (__position + 1 != end())
> std::copy(__position + 1, end(), __position);
> --this->_M_impl._M_finish;
> this->_M_impl.destroy(this->_M_impl._M_finish);
> return __position;
> }
>
>
> Note that "destroy()" will be called for the element that is *last* in the
> vector prior to the call to this erase(), instead of being called for the
> element pointed to by __position. I believe this is incorrect -- I think it
> should instead call destroy() for the element pointed to by __position.
No, the element at position is overwritten by the call to std::copy()
> For
> simple POD types, this isn't that big of a deal, but for classes where the
> destructors have side effects (such as smart pointers), it can be critical.
>
> The following code illustrates the problem:
>
>
> #include <vector>
> #include <iostream>
>
> class MyClass
> {
> int m_x;
> public:
> MyClass(int x) : m_x(x) { }
> ~MyClass()
> {
> std::cerr << "Destroying with m_x=" << m_x << std::endl;
> }
> };
>
> int main(void)
> {
> std::vector<MyClass> testvect;
> testvect.reserve(8);
> testvect.push_back(MyClass(1));
> testvect.push_back(MyClass(2));
> testvect.push_back(MyClass(3));
> testvect.push_back(MyClass(4));
> testvect.push_back(MyClass(5));
>
> std::cerr << "ABOUT TO DELETE #3:" << std::endl;
>
> testvect.erase(testvect.begin() + 2);
>
> std::cerr << "DONE WITH DELETE." << std::endl;
>
> return 0;
> }
>
>
> When I compile this with g++ version 4.2.1 (no command line arguments) on my
> Mac, it produces the following when I run it:
>
> Destroying with m_x=1
> Destroying with m_x=2
> Destroying with m_x=3
> Destroying with m_x=4
> Destroying with m_x=5
> ABOUT TO DELETE #3:
> Destroying with m_x=5
> DONE WITH DELETE.
> Destroying with m_x=1
> Destroying with m_x=2
> Destroying with m_x=4
> Destroying with m_x=5
As you can see, the results are correct, the vector contains {1,2,4,5}
> Note that the key line after the "ABOUT TO DELETE #3" message shows that the
> destructor was actually called for the fifth thing I added. Importantly, the
> destructor for #3 is never called!!
Doesn't matter, the requirements of std::vector do not say that must happen
