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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
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;
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]));
>>}
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
#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?
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) );
> }
--
Markus Schoder
On May 29, 3:03 am, Markus Schoder <a3vr6dsg-use@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.
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.-Cyr-l'cole, France, +33 (0)1 30 23 00 34
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