std::basic_string_view<CharT,Traits>::substr

#include <cstddef>
#include <iostream>
#include <stdexcept>
#include <string_view>
 
int main()
{
    typedef std::size_t count_t, pos_t;
 
    constexpr std::string_view data{"ABCDEF"};
 
    std::cout << data.substr() << '\n'; // ABCDEF, 即 data[0, 5]，为 [0, 6)
    std::cout << data.substr(pos_t(1)) << '\n'; // BCDEF, i.e. [1, 6)
    std::cout << data.substr(pos_t(2), count_t(3)) << '\n'; // CDE, 即 [2, 2 + 3)
    std::cout << data.substr(pos_t(4), count_t(42)) << '\n'; // EF, 即 [4, 6)
 
    try
    {
        [[maybe_unused]]
        auto sub = data.substr(pos_t(666), count_t(1)); // 抛出: pos > size()
    }
    catch (std::out_of_range const& ex)
    {
        std::cout << ex.what() << '\n';
    }
}