http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47305
Summary: std::vector::erase() destroys the wrong element!
Product: gcc
Version: 4.2.1
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: libstdc++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: shock...@gmail.com
In the C++ stdlib distribution included with Mac OS X (Darwin 10.5.0 i386), the
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. 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
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!!
