#include <cstddef>
#include <iostream>
#include <memory>
#include <vector>
 
struct X
{
    X() { ++count; std::cout << "Constructing, count = " << count << "\n"; }
    ~X() { --count; std::cout << "Destructing, count = " << count << "\n"; }
 
    static std::size_t count;
};
std::size_t X::count = 0;
 
int main()
{
    std::vector<std::unique_ptr<X>> vec;
    vec.reserve(2);
 
    // one way
    vec.push_back(std::unique_ptr<X>(new X));
 
    // another way
    vec.emplace_back(new X);
 
    return 0;
}
 

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