non_default_constructor_allocator.cpp

// Allocating memory for non-default constructible objects
// This is how probably std::vector works

#include <iostream>

class Foo {
    int _m;

  public:
    Foo(int m) : _m(m) {}
    int get_m() const { return _m; }
};

int main() {
    // allocate memory even if the object is non-default constructible
    Foo* storage = static_cast<Foo*>(static_cast<void*>(new char[sizeof(Foo)]));

    // we can now place our object
    new (storage) Foo(42);

    // display
    std::cout << storage->get_m() << std::endl;
}