Convert container of pointers to smart pointers?

Question

Is there a concise, generic way to convert a std container (such as vector) of regular/dumb pointers:

vector< T* >

to, for instance, boost::shared_ptr?:

vector< boost::shared_ptr<T> >

I thought I could pull it off using vector's range constructor:

vector< T* > vec_a;
...
vector< boost::shared_ptr<T> > vec_b( vec_a.begin(), vec_a.end() );

but that refused to compile (Visual Studio 2008).

EDIT: Test code:

void test()
{
    vector< int* > vec_a;
    vector< boost::shared_ptr<int> > vec_b( vec_a.begin(), vec_a.end() );
}

Compilation errors:

1>c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\include\memory(131) : error C2664: 'std::allocator<_Ty>::construct' : cannot convert parameter 2 from 'int *' to 'const boost::shared_ptr<T> &'
1>        with
1>        [
1>            _Ty=boost::shared_ptr<int>
1>        ]
1>        and
1>        [
1>            T=int
1>        ]
1>        Reason: cannot convert from 'int *' to 'const boost::shared_ptr<T>'
1>        with
1>        [
1>            T=int
1>        ]
1>        Constructor for class 'boost::shared_ptr<T>' is declared 'explicit'
1>        with
1>        [
1>            T=int
1>        ]
1>        c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\include\memory(822) : see reference to function template instantiation '_FwdIt std::_Uninit_copy<int**,_FwdIt,_Alloc>(_InIt,_InIt,_FwdIt,_Alloc &,std::_Nonscalar_ptr_iterator_tag,std::_Range_checked_iterator_tag)' being compiled
1>        with
1>        [
1>            _FwdIt=boost::shared_ptr<int> *,
1>            _Alloc=std::allocator<boost::shared_ptr<int>>,
1>            _InIt=int **
1>        ]
1>        c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\include\vector(1141) : see reference to function template instantiation '_FwdIt stdext::unchecked_uninitialized_copy<_Iter,boost::shared_ptr<T>*,std::allocator<_Ty>>(_InIt,_InIt,_FwdIt,_Alloc &)' being compiled
1>        with
1>        [
1>            _FwdIt=boost::shared_ptr<int> *,
1>            _Iter=std::_Vector_iterator<int *,std::allocator<int *>>,
1>            T=int,
1>            _Ty=boost::shared_ptr<int>,
1>            _InIt=std::_Vector_iterator<int *,std::allocator<int *>>,
1>            _Alloc=std::allocator<boost::shared_ptr<int>>
1>        ]
1>        c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\include\vector(956) : see reference to function template instantiation 'boost::shared_ptr<T> *std::vector<_Ty>::_Ucopy<_Iter>(_Iter,_Iter,boost::shared_ptr<T> *)' being compiled
1>        with
1>        [
1>            T=int,
1>            _Ty=boost::shared_ptr<int>,
1>            _Iter=std::_Vector_iterator<int *,std::allocator<int *>>
1>        ]
1>        c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\include\vector(889) : see reference to function template instantiation 'void std::vector<_Ty>::_Insert<_Iter>(std::_Vector_const_iterator<_Ty,_Alloc>,_Iter,_Iter,std::forward_iterator_tag)' being compiled
1>        with
1>        [
1>            _Ty=boost::shared_ptr<int>,
1>            _Iter=std::_Vector_iterator<int *,std::allocator<int *>>,
1>            _Alloc=std::allocator<boost::shared_ptr<int>>
1>        ]
1>        c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\include\vector(537) : see reference to function template instantiation 'void std::vector<_Ty>::insert<_Iter>(std::_Vector_const_iterator<_Ty,_Alloc>,_Iter,_Iter)' being compiled
1>        with
1>        [
1>            _Ty=boost::shared_ptr<int>,
1>            _Iter=std::_Vector_iterator<int *,std::allocator<int *>>,
1>            _Alloc=std::allocator<boost::shared_ptr<int>>
1>        ]
1>        c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\include\vector(514) : see reference to function template instantiation 'void std::vector<_Ty>::_Construct<_Iter>(_Iter,_Iter,std::input_iterator_tag)' being compiled
1>        with
1>        [
1>            _Ty=boost::shared_ptr<int>,
1>            _Iter=std::_Vector_iterator<int *,std::allocator<int *>>
1>        ]
1>        .\test.cpp(8364) : see reference to function template instantiation 'std::vector<_Ty>::vector<std::_Vector_iterator<int,_Alloc>>(_Iter,_Iter)' being compiled
1>        with
1>        [
1>            _Ty=boost::shared_ptr<int>,
1>            _Alloc=std::allocator<int *>,
1>            _Iter=std::_Vector_iterator<int *,std::allocator<int *>>
1>        ]

Answer 1

Combine ::std::back_inserter with ::std::transform and a little function that will perform the conversion. If you also use reserve, this should be reasonably efficient. Once all the templates are expanded you will essentially get this code:

template <class T>
static inline ::std::tr1::shared_ptr<T> to_shared_ptr(T *val)
{
   return ::std::tr1::shared_ptr<T>(val);
}

void test()
{
   ::std::vector< int* > vec_a;
   ::std::vector< ::std::tr1::shared_ptr<int> > vec_b;
   vec_b.reserve(vec_a.size());
   ::std::transform(vec_a.begin(), vec_a.end(), ::std::back_inserter(vec_b),
                    to_shared_ptr<int>);
   vec_a.clear();
}