#include <iostream>
#include <qrinvoice/util/iban_util.hpp>
// ...
std::cout << qrinvoice::iban_util::format_iban("CH3908704016075473007") << std::endl;
std::cout << qrinvoice::iban_util::format_iban("CH39 0870 4016 0754 7300 7") << std::endl;
// prints "CH39 0870 4016 0754 7300 7"