The usual suggestion to use shallow array adaptor seems kind of sarcastic to me - to be able to simply access an array through a pointer you're supposed to put it into a shared_array with all the reference counting shebang (that comes to nothing, since you don't own the array) and what's more with a nightmare of data-aliasing.
Actually, uBLAS has a fully-fledged implementation of storage (array_adaptor) which allows to use vectors with external c arrays. The only catch is vector constructor which makes a copy. Why this nice feature is not used in the library is quite beyond me, but anyway, we can use a little extension (it's actually 2 lines of code surrounded with usual c++ bloat)
template<class T>
class extarray_vector :
public vector<T, array_adaptor<T> >
{
typedef vector<T, array_adaptor<T> > vector_type;
public:
BOOST_UBLAS_INLINE
extarray_vector(size_type size, pointer p)
{ data().resize(size, p); }
template <size_type N>
BOOST_UBLAS_INLINE
extarray_vector(T (&a)[N])
{ data().resize(N, a); }
template<class V>
BOOST_UBLAS_INLINE
extarray_vector& operator = (const vector<T, V>& v)
{
vector_type::operator = (v);
return *this;
}
template<class VC>
BOOST_UBLAS_INLINE
extarray_vector& operator = (const vector_container<VC>& v)
{
vector_type::operator = (v);
return *this;
}
template<class VE>
BOOST_UBLAS_INLINE
extarray_vector& operator = (const vector_expression<VE>& ae)
{
vector_type::operator = (ae);
return *this;
}
};
you can use it like this:
int i[] = {1, 4, 9, 16, 25, 36, 49};
extarray_vector<int> iv(i);
BOOST_ASSERT_MSG(i == &iv[0], "Vector should attach to external array\n");
iv[3] = 100;
BOOST_ASSERT(i[3] == 100);
iv.resize(iv.size() + 1, true);
BOOST_ASSERT_MSG(i != &iv[0], "And detach from the array on resize\n");
iv[3] = 200;
BOOST_ASSERT(i[3] == 100);
iv.data().resize(7, i, 0);
BOOST_ASSERT_MSG(i == &iv[0], "And attach back to the array\n");
BOOST_ASSERT(i[3] == 200);
You can dynamically attach and detach vector to external storage via array_adaptor's resize method (keeping or discarding data). On resize it detaches from storage automatically and becomes regular vector. Assignment from containers goes directly into storage, but assignment from expression is done via a temporary and vector is detached from storage, use noalias() to prevent that. There's a small overhead in constructor since data_ is private member and we have to default initialize it with new T[0], then reassign to external array. You may change it to protected and assign to storage directly in the constructor.
