Systems & production C++

#include <cstddef>
#include <cstdlib>
#include <new>
#include <print>
#include <vector>

template <class T>
struct Mallocator {
    using value_type = T;

    Mallocator() = default;
    template <class U>
    Mallocator(const Mallocator<U>&) noexcept {}  // "rebind" conversion

    T* allocate(std::size_t n) {
        if (void* p = std::malloc(n * sizeof(T))) return static_cast<T*>(p);
        throw std::bad_alloc{};
    }
    void deallocate(T* p, std::size_t) noexcept { std::free(p); }

    // Stateless: any two Mallocators can free each other's memory.
    friend bool operator==(const Mallocator&, const Mallocator&) = default;
};

int main() {
    std::vector<int, Mallocator<int>> v{1, 2, 3};
    v.push_back(4);
    std::println("{}", v);
}