The following code is unsafe, and I think it's not my fault.
$ g++ -Wall -g testIterSwap.cc ; valgrind -q ./a.out
==1674== Source and destination overlap in memcpy(0x7FF000500, 0x7FF000500, 20)
==1674== at 0x4C2508B: memcpy (mc_replace_strmem.c:402)
==1674== by 0x4008D2: void swap_from_glibcxx<HarrisPoint<float, int>
>(HarrisPoint<float, int>&, HarrisPoint<float, int>&) (testIterSwap.cc:22)
==1674== by 0x400793: main (testIterSwap.cc:68)
It would appear that the auto-generated operator=() uses a memcpy() which is
not safe. The operator=() that is provided below solves the problem.
-------- cut here ------------
#include <tr1/array>
// #include <algorithm>
/**
* @brief Swaps two values.
* @param a A thing of arbitrary type.
* @param b Another thing of arbitrary type.
* @return Nothing.
*
* This is the simple classic generic implementation. It will work on
* any type which has a copy constructor and an assignment operator.
*/
template<typename _Tp>
inline void
swap_from_glibcxx(_Tp& __a, _Tp& __b)
{
// concept requirements
// __glibcxx_function_requires(_SGIAssignableConcept<_Tp>)
_Tp __tmp = __a;
__a = __b;
__b = __tmp;
}
template <typename T>
struct Point2D : public std::tr1::array<T, 2>
{
template <typename U, typename V>
Point2D(const U x, const V y)
{
(*this)[0] = x;
(*this)[1] = y;
}
};
template <typename T, typename U>
class FeaturePoint : public Point2D<U>
{
public:
typedef T data_type;
FeaturePoint(const U h, const U w) : Point2D<U>(h,w) {}
};
template <typename T, typename U>
class HarrisPoint : public FeaturePoint<T, U>
{
public:
typedef T data_type;
HarrisPoint(const U h, const U w, const T value) :
FeaturePoint<T, U>(h, w), value_(value) { }
/*
// THIS FIXES IT.
HarrisPoint &operator=(const HarrisPoint &rhs)
{
std::memmove(this, &rhs, sizeof(HarrisPoint));
return *this;
}
*/
private:
T value_;
};
int main()
{
HarrisPoint<float, int> a(1, 2, 3.0f);
// std::tr1::array<int, 2> a; a[0] = 3; a[1] = 5; // fine
a = a; // fine
// std::swap(a, a);
swap_from_glibcxx(a, a);
return 0;
}
--
Summary: generated memcpy causes trouble in assignment
Product: gcc
Version: 4.2.4
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: fpbeekhof at gmail dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39480
