#include <iostream>

static int index()
{
    static int idx = std::ios_base::xalloc();
    return idx;
}

void callback(std::ios_base::event evt, std::ios_base& str, int index)
{
    (void)str;
    (void)index;
    if (evt == std::ios_base::erase_event)
    {
        std::cout << "Erase event" << std::endl;
    }
}

int main()
{
    std::cout.register_callback(callback, index());
}