Copy/wrap vector<Class*> to vector<Class> - c++

Question

Is there an std function to easily copy a vector of pointers to classes into a vector of classes or do I have to manually iterate over them?
Looking for the solution with the fastest/fewer lines of code :).
A solution that avoids copying without leaking memory is also welcomed!

Answer 1

I doubt there is such, below is one liner with for:
std::vector<X*> vec1 = { new X, new X };
std::vector<X> vec2;
vec2.reserve(vec1.size());
for (auto p : vec1) vec2.push_back(*p);
if you want to make sure no copies are made then you can use std::reference_wrapper<>:
std::vector<std::reference_wrapper<X>> vec2;
for (auto p : vec1) vec2.push_back(*p);
but then you have to make sure no element of vec2 is accessed after vec1 elements were deallocated.
Another aproach is to use unique_ptr like that:
std::vector<std::unique_ptr<X>> vec2;
for (auto p : vec1) vec2.emplace_back(p);
now you can ditch vec1, but then why not make vec1 of type std::vector<std::unique_ptr<X>>?

Answer 2

A one-liner with no manual iteration at all:
std::for_each(vec1.begin(), vec1.end(), [&](auto x) { vec2.push_back(*x); });
(Disclaimer: I'm not 100% sure about the reference-capturing lambda syntax.)

Answer 3

You have to do it yourself. std:transform or std::for_each will help you:
#include <algorithm>
#include <vector>
#include <functional>
using namespace std::placeholders;
class Myclass{};
Myclass deref(const Myclass *mc) { return *mc;}
void append(std::vector<Myclass> &v, Myclass *mc) {v.push_back(*mc);}
int main(){
std::vector<Myclass*> foo;
std::vector<Myclass> bar;
/* foo is initialised somehow */
/* bar is initialised somehow to hold the same amount of dummy elements */
//solution with transform
std::transform (foo.begin(), foo.end(), bar.begin(), deref);
bar={};
// solution with for_each
auto bound_append = std::bind(append, bar, _1);
std::for_each(foo.begin(), foo.end(), bound_append);
}
Compile wit -std=c++11 (gcc).