#include <cmath>
#include <filesystem>
#include <fstream>
#include <iostream>
namespace fs = std::filesystem;
 
struct HumanReadable {
    std::uintmax_t size{};
  private: friend
    std::ostream& operator<<(std::ostream& os, HumanReadable hr) {
        int i{};
        double mantissa = hr.size;
        for (; mantissa >= 1024.; mantissa /= 1024., ++i) { }
        mantissa = std::ceil(mantissa * 10.) / 10.;
        os << mantissa << "BKMGTPE"[i];
        return i == 0 ? os : os << "B (" << hr.size << ')';
    }
};
 
int main(int, char const* argv[])
{
    fs::path example = "example.bin";
    fs::path p = fs::current_path() / example;
    std::ofstream(p).put('a'); // create file of size 1
    std::cout << example << " size = " << fs::file_size(p) << '\n';
    fs::remove(p);
 
    p = argv[0];
    std::cout << p << " size = " << HumanReadable{fs::file_size(p)} << '\n';
 
    try {
        std::cout << "Attempt to get size of a directory:\n";
        fs::file_size("/dev");
    } catch(fs::filesystem_error& e) {
        std::cout << e.what() << '\n';
    }
 
    std::error_code ec;
    for (fs::path bin: {"cat", "mouse"}) {
        bin = "/bin"/bin;
        std::uintmax_t size = fs::file_size(bin, ec);
        if (ec) {
            std::cout << bin << " : " << ec.message() << '\n';
        } else {
            std::cout << bin << " size = " << HumanReadable{size} << '\n';
        }
    }
}