{

using namespace std::literals::string_view_literals;

constexpr auto fmt_str { "Hubble's H{0} {1} {2:*^4} miles/sec/mpc."sv };

constexpr auto sub_zero { "₀"sv }; // { "\u2080"sv } => { 0xe2, 0x82, 0x80 };

constexpr auto aprox_equ { "≅"sv }; // { "\u2245"sv } => { 0xe2, 0x89, 0x85 };

constexpr int Ho { 42 }; // H₀

const auto min_buffer_size = std::formatted_size(fmt_str, sub_zero, aprox_equ, Ho);

std::cout << "Min buffer size = " << min_buffer_size << '\n';

// Use std::vector as dynamic buffer. Note: buffer does not include the trailing '\0'.

std::vector<char> buffer(min_buffer_size);

std::format_to_n(buffer.data(), buffer.size(), fmt_str, sub_zero, aprox_equ, Ho);

std::cout << "Buffer: \"" << std::string_view{buffer.data(), min_buffer_size} << "\"\n";

// Or we can print the buffer directly by adding the trailing '\0'.

buffer.push_back('\0');

std::cout << "Buffer: \"" << buffer.data() << "\"\n";