Re: copying a vector of objects at runtime

Joe Greer <>
Thu, 10 Jul 2008 15:02:11 +0000 (UTC)
"Julian" <> wrote in

I have a vector defined like this:
std::vector<Load*> LoadList;
which is populated with different objects of classes that are derived
from 'Load'.
I need to make a copy of this list during runtime.
I imagine I'd have to loop through the list, make a copy of each of
the objects in the vector using the copy constructor... but I don't
know the class name during run time so that I can call the appropriate
copy constructor.

Hmmm, if copying the objects in the vector is the answer, then I have to
wonder why there are pointers in the vector to begin with. That is,
wouldn't vector<Load> have been a better place to start? Then copying
would be as simple as LoadList2 = LoadList. IME the only time you
really want a vector of pointers is if the objects have identity
(can't/shouldn't be copied at all) or are horrendously expensive to

If you still want to copy the vector of pointers (after considering
making them value types instead), you can do something like:

#include <iostream>
#include <sstream>
#include <vector>

template <typename T>
T * clone(T * a)
     return new T(*a); //assuming copy constructor

template <typename T>
class clone_insert_iterator : public std::iterator
<std::output_iterator_tag, typename T::value_type>
   T& m_Container;
   explicit clone_insert_iterator(T & container) : m_Container
(container) {}
   clone_insert_iterator<T> & operator=(typename T::value_type const &
      return *this;
   clone_insert_iterator<T> & operator*()
    return *this;
   clone_insert_iterator<T> & operator++()
    return *this;
   clone_insert_iterator<T> operator++(int)
    return *this;

int main()
    std::vector<int *> v;
    std::vector<int *> v1;

    v.push_back(new int(5));
    v.push_back(new int(1));
    v.push_back(new int(10));
    v.push_back(new int(7));

    clone_insert_iterator<std::vector<int *> > cii(v1);
    std::copy(v.begin(), v.end(), cii);

    for (int ix = 0; ix < v1.size(); ++ix)
        std::cout << *v[ix] << std::endl;
    std::cout << std::endl;
    std::cout << std::endl;
    for (int ix = 0; ix < v1.size(); ++ix)
        std::cout << *v1[ix] << std::endl;

Which seems to work, but I made no attempt at robustness nor
completeness for any particular use.


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