Re: [Boost-users] multi_array and variants

Subject: Re: [Boost-users] multi_array and variants
From: Alle Meije Wink (a.m.wink_at_[hidden])
Date: 2010-11-09 03:41:39

Dear Kris, thanks for your reply.

> > What I now have is a class bisArray:
> > ...
> > template<typename T>
> > class bisArray: public bisObject {
> > typedef boost::variant
> > < boost::multi_array_ref<T, 1>,
> > boost::multi_array_ref<T, 2>,
> > boost::multi_array_ref<T, 3>,
> > boost::multi_array_ref<T, 4>,
> > boost::multi_array_ref<T, 5>,
> > boost::multi_array_ref<T, 6>,
> > boost::multi_array_ref<T, 7>,
> > boost::multi_array_ref<T, 8>,
> > boost::multi_array_ref<T, 9>
> > > bisArray_t;
> > bisArray_t _bisArray;
> > ...
> >
> > and a class bisImage, which has a bisArray as well as a pointer to the
> > data as read from file (1-dimensional structure):
> > ...
> >
> > template<typename T>
> >
> > class bisImage: public bisObject {
> >
> > public:
> >
> > /** Constructor using existing array data
> > Reformats array as bisImage
> > */
> > bisImage ( T* _data, size_t _dimensions, std::vector<size_t> _sizes
> > ):
> > data(_data), dimensions(_dimensions) {
> >
>
> This code (or You) comes from java or C#, doesn't it? ;-) In C++ it is
> supposed to be this->[...] instead of this.[...]

No, it's C (which doesn't use any of this -not properly at least). The
whole this[...] business was not supposed to be there anyway I
realised.
The reason that I went to boost:: is that I was hoping to get one
class for all data types (using T) and dimensionalities (using
multi_array)

> Second thing: the member storage is initialized with the default constructor
> (which in this case does not exist => error ), and then assigned (below).
>
> I suggest a change to:
> bisImage([...]) : [...], storage( _data, _dimensions, _size ) { [...]
> and remove the assignment from the body of the constructor
>
> Note also: I have read in many places, that you should not use names
> beginning with an underscore (_), because they are reserved for
> compiler/library implementation. One of those places was Herb Sutter's gotw
> series.

Ah! The underscore names come from a library that I tried to imitate
which has successfully incorporated some aspects of boost(it is called
MIMAS). Have not reached the stage of 'nicifying' the code yet...

I moved the storage thing to where you suggested (1 line up) and that
does get rid of lots of errors.
However what I am stuck with seems to be, in essence, still the same thing:

>>> /home/amwink/programs/cpp/bis/src/bisniftiimage.cpp||In function ‘void bis::bisReadNifti(std::string)’:|
>>> /home/amwink/programs/cpp/bis/src/bisniftiimage.cpp|102|warning: unused variable ‘testimage’|
>>> /usr/include/boost/variant/variant.hpp||In constructor ‘boost::variant<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16, T17, T18, T19>::variant() [with T0_ = boost::multi_array_ref<unsigned char, 1ul>, T1 = boost::multi_array_ref<unsigned char, 2ul>, T2 = boost::multi_array_ref<unsigned char, 3ul>, T3 = boost::multi_array_ref<unsigned char, 4ul>, T4 = boost::multi_array_ref<unsigned char, 5ul>, T5 = boost::multi_array_ref<unsigned char, 6ul>, T6 = boost::multi_array_ref<unsigned char, 7ul>, T7 = boost::multi_array_ref<unsigned char, 8ul>, T8 = boost::multi_array_ref<unsigned char, 9ul>, T9 = boost::detail::variant::void_, T10 = boost::detail::variant::void_, T11 = boost::detail::variant::void_, T12 = boost::detail::variant::void_, T13 = boost::detail::variant::void_, T14 = boost::detail::variant::void_, T15 = boost::detail::variant::void_, T16 = boost::detail::variant::void_, T17 = boost::detail::variant::void_, T18 = boost::detail::variant::void_, T19 = boost::detail::variant::void_]’:|
>>> /home/amwink/programs/cpp/bis/src/bisarray.hpp|52|instantiated from ‘bis::bisArray<T>::bisArray(T*, size_t, std::vector<long unsigned int, std::allocator<long unsigned int> >) [with T = unsigned char]’|
>>> /home/amwink/programs/cpp/bis/src/bisimage.hpp|33|instantiated from ‘bis::bisImage<T>::bisImage(T*, size_t, std::vector<long unsigned int, std::allocator<long unsigned int> >) [with T = unsigned char]’|
>>> /home/amwink/programs/cpp/bis/src/bisniftiimage.cpp|126|instantiated from here|
>>> /usr/include/boost/variant/variant.hpp|1198|error: no matching function for call to ‘boost::multi_array_ref<unsigned char, 1ul>::multi_array_ref()’|
>>> /usr/include/boost/multi_array/multi_array_ref.hpp|623|note: candidates are: boost::multi_array_ref<T, NumDims>::multi_array_ref(T*, const typename boost::const_multi_array_ref<T, NumDims, T*>::storage_order_type&, const typename boost::const_multi_array_ref<T, NumDims, T*>::index*, const typename boost::const_multi_array_ref<T, NumDims, T*>::size_type*) [with T = unsigned char, long unsigned int NumDims = 1ul]|
>>> /usr/include/boost/multi_array/multi_array_ref.hpp|469|note:                 boost::multi_array_ref<T, NumDims>::multi_array_ref(T*, const boost::detail::multi_array::extent_gen<NumDims>&, const boost::general_storage_order<NumDims>&) [with T = unsigned char, long unsigned int NumDims = 1ul]|
>>> /usr/include/boost/multi_array/multi_array_ref.hpp|463|note:                 boost::multi_array_ref<T, NumDims>::multi_array_ref(T*, const boost::detail::multi_array::extent_gen<NumDims>&) [with T = unsigned char, long unsigned int NumDims = 1ul]|
>>> /usr/include/boost/multi_array/multi_array_ref.hpp|417|note:                 boost::multi_array_ref<unsigned char, 1ul>::multi_array_ref(const boost::multi_array_ref<unsigned char, 1ul>&)|
>>> ||=== Build finished: 1 errors, 1 warnings ===|

So boost.variant now sugegsts that multi_array_ref() is called, a
constructor with no arguments! I don't use that, and I don't even
think it exists (because it produces a multi_array view of an
*existing* C-style array!

The only way I knew to initialise a bisArray was with using a switch
statement -proper C:

switch dims{
      case 1: _bisarray=multi_array_ref<T,1> (data, sizes); break;
      case 2: _bisarray=multi_array_ref<T,2> (data, sizes); break;
      ...
}

That is the only way multi_array_ref is called!
Any idea why a problem with the *default* constructor would turn up?

Thanks for your suggestions! My error list already fits on one screen :)

Alle Meije