




Using one vector to construct another
I am constructing a vector of objects of class A. The constructor for class A takes an instance of class B in its constructor. I have a vector of B objects and would like to construct a vector of A objects so that each is constructed using the corresponding B object. Is this possible or do I need to use pointers along with new and delete? Thanks
On May 28, 4:28 pm, Chris Roth <czr@mail.usask.ca> wrote: > I am constructing a vector of objects of class A. The constructor for > class A takes an instance of class B in its constructor. I have a vector > of B objects and would like to construct a vector of A objects so that > each is constructed using the corresponding B object. > Is this possible or do I need to use pointers along with new and delete? > Thanks
vector vect_of_A; for (size_t i = 0; i < vect_of_B.size();i++) { vect_of_a.push_back(A(vect_of_B[i]));
}
On Mon, 28 May 2007 14:59:19 0700, darrylsh at hotmail wrote: > On May 28, 4:28 pm, Chris Roth <czr @mail.usask.ca> wrote: >> I am constructing a vector of objects of class A. The constructor for >> class A takes an instance of class B in its constructor. I have a >> vector of B objects and would like to construct a vector of A objects >> so that each is constructed using the corresponding B object. >> Is this possible or do I need to use pointers along with new and >> delete? >> Thanks > vector vect_of_A;
Adding vect_of_A.reserve(vect_of_B.size()); here will avoid reallocations. > for (size_t i = 0; i < vect_of_B.size();i++) { > vect_of_a.push_back(A(vect_of_B[i])); > }
 Markus Schoder
Markus Schoder wrote: > On Mon, 28 May 2007 14:59:19 0700, darrylsh at hotmail wrote: >>On May 28, 4:28 pm, Chris Roth <czr@mail.usask.ca> wrote: >>>I am constructing a vector of objects of class A. The constructor for >>>class A takes an instance of class B in its constructor. I have a >>>vector of B objects and would like to construct a vector of A objects >>>so that each is constructed using the corresponding B object. >>>Is this possible or do I need to use pointers along with new and >>>delete? >>>Thanks >>vector vect_of_A; > Adding > vect_of_A.reserve(vect_of_B.size()); > here will avoid reallocations. >>for (size_t i = 0; i < vect_of_B.size();i++) { >> vect_of_a.push_back(A(vect_of_B[i])); >>}
Thanks to both.
On May 28, 5:28 pm, Chris Roth <czr@mail.usask.ca> wrote: > I am constructing a vector of objects of class A. The constructor for > class A takes an instance of class B in its constructor. I have a vector > of B objects and would like to construct a vector of A objects so that > each is constructed using the corresponding B object. > Is this possible or do I need to use pointers along with new and delete? > Thanks
With std::back_inserter... #include <iostream> #include <vector> #include <algorithm> #include <iterator> class B { }; class A { B m_b; public: A(const B& b) : m_b( b ) { } };
int main() { std::vector< B > vb(10); std::vector< A > va; std::copy( vb.begin(), vb.end(), std::back_inserter(va) );
}
Chris Roth wrote: > I am constructing a vector of objects of class A. The constructor for > class A takes an instance of class B in its constructor. I have a vector > of B objects and would like to construct a vector of A objects so that > each is constructed using the corresponding B object. > Is this possible or do I need to use pointers along with new and delete?
Any iterator whose dereferenced type can be assigned to the type in the vector can use this format: std::vector<B> b; ... std::vector<A> a( b.begin(), b.end() ); or a.assign( b.begin(), b.end() );
On Mon, 28 May 2007 15:46:01 0700, Salt_Peter wrote: > On May 28, 5:28 pm, Chris Roth <czr @mail.usask.ca> wrote: >> I am constructing a vector of objects of class A. The constructor for >> class A takes an instance of class B in its constructor. I have a >> vector of B objects and would like to construct a vector of A objects >> so that each is constructed using the corresponding B object. >> Is this possible or do I need to use pointers along with new and >> delete? >> Thanks > With std::back_inserter... > #include <iostream> > #include <vector> > #include <algorithm> > #include <iterator> > class B { }; > class A { > B m_b; > public: > A(const B& b) : m_b( b ) { } > }; > int main() > { > std::vector< B > vb(10); > std::vector< A > va; > std::copy( vb.begin(), vb.end(), std::back_inserter(va) ); > }
This of course works only if A's constructor is not explicit.  Markus Schoder
On May 29, 3:03 am, Markus Schoder <a3vr6dsguse@yahoo.de> wrote:
> On Mon, 28 May 2007 15:46:01 0700, Salt_Peter wrote: > > On May 28, 5:28 pm, Chris Roth <czr @mail.usask.ca> wrote: > >> I am constructing a vector of objects of class A. The constructor for > >> class A takes an instance of class B in its constructor. I have a > >> vector of B objects and would like to construct a vector of A objects > >> so that each is constructed using the corresponding B object. > >> Is this possible or do I need to use pointers along with new and > >> delete? > > With std::back_inserter... > > #include <iostream> > > #include <vector> > > #include <algorithm> > > #include <iterator> > > class B { }; > > class A { > > B m_b; > > public: > > A(const B& b) : m_b( b ) { } > > }; > > int main() > > { > > std::vector< B > vb(10); > > std::vector< A > va; > > std::copy( vb.begin(), vb.end(), std::back_inserter(va) ); > > } > This of course works only if A's constructor is not explicit. If A's constructor is not explicit, then: std::vector< A > va( vb.begin(), vb.end() ) ; is all that is needed. If A's constructor is explicit, then you probably need transform and a transforming object, or some sort of transforming iterator. With transform: struct XForm { A operator()( B const& b ) const { return static_cast< A >( b ) ; } } ; std::transform( vb.begin(), vb.end(), XForm(), std::back_inserter( va ) ) ;  James Kanze (GABI Software) email:james.ka@gmail.com Conseils en informatique oriente objet/ Beratung in objektorientierter Datenverarbeitung 9 place Smard, 78210 St.Cyrl'cole, France, +33 (0)1 30 23 00 34





