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Ublas : |
From: Nico Galoppo (nico_at_[hidden])
Date: 2007-10-06 01:32:19
Thanks. Unfortunately, my code is sprinkled with these calls. I may
want to write a specialization of assign() for vector_range<>.
--nico
On 10/6/07, Vardan Akopian <vakopian_at_[hidden]> wrote:
> On 10/5/07, Nico Galoppo <nico_at_[hidden]> wrote:
> > Hi,
> >
> > I have the snippet of code below that compiles OK with MSVC 8.0, but
> > fails with gcc 4.0.1 (OSX). I guess my question is whether my
> > templated helper function is actually valid, or violating the C++
> > spec.
> >
> > template <typename V, typename T>
> > inline void assign(ublas::vector_expression<V>& bv, const vector3<T>&
> > {
> > for (unsigned int i = 0; i < 3; ++i)
> > bv () (i) = v(i);
> > }
> >
> > int main()
> > {
> > ublas::vector<float> v(100);
> > vec3<float> tuple;
> >
> > assign(subrange(v, 3,6), tuple);
> > }
> >
> > vec3<T> is a specialized (non-ublas) 3-vector class. gcc gives an
> > error at the 'assign' line in main():
> >
> > error: invalid initialization of non-const reference of type
> > 'boost::numeric::ublas::vector_expression<boost::numeric::ublas::vector_range<boost::numeric::ublas::vector<float,
> > boost::numeric::ublas::unbounded_array<float, std::allocator<float> >
> > > > >&' from a temporary of type
> > 'boost::numeric::ublas::vector_range<boost::numeric::ublas::vector<float,
> > boost::numeric::ublas::unbounded_array<float, std::allocator<float> >
> > > >'
>
> gcc is correct, but the problem is not the templates. The call to
> subrange(v, 3,6) creates a temporary, and you're not allowed to pass a
> temporary as a non constant reference.
> One easy way to fix this is to do:
> subrange sr(v, 3,6); // or sr = subrange(v, 3,6), if subrange() is a
> function, not a class.
> assign(sr, tuple);
>
> -Vardan
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>
-- Nico Galoppo :: http://www.ngaloppo.org