C++ File Handling and Formatting: Open, Read, Check Existence, and Format File Size

#include <fstream>

int main() {
  std::ofstream out_file("D:/out.txt");
  // ...
  return 0;
}

#include <fstream>

int main() {
  std::ifstream in_file;
  in_file.open("x.json");
  if (!in_file.is_open()) {
    std::cout << "x.json does not exist" << std::endl;
    return 1;
  }
  // ...
  return 0;
}

#include <iostream>
#include <filesystem>

int main() {
  std::filesystem::path file_path("x.json");
  if (!std::filesystem::exists(file_path)) {
    std::cout << "x.json does not exist" << std::endl;
    return 1;
  }
  // ...
  return 0;
}

#include <iostream>
#include <fstream>
#include <filesystem>
#include <iomanip>

int main() {
  std::filesystem::path file_path("x.json");
  
  if (!std::filesystem::exists(file_path)) {
    std::cout << "x.json does not exist" << std::endl;
    return 1;
  }
  
  std::uintmax_t file_size = std::filesystem::file_size(file_path);
  
  std::ofstream out_file("D:/out.txt");
  
  out_file << std::fixed << std::setprecision(1) << std::setw(5) << std::setfill('*') << static_cast<double>(file_size) / 1e9 << std::endl;
  out_file << std::fixed << std::setprecision(2) << std::setw(6) << std::setfill('*') << static_cast<double>(file_size) / 1e9 << std::endl;
  out_file << std::fixed << std::setprecision(3) << std::setw(7) << std::setfill('*') << static_cast<double>(file_size) / 1e9 << std::endl;
  out_file << std::fixed << std::setprecision(4) << std::setw(8) << std::setfill('*') << static_cast<double>(file_size) / 1e9 << std::endl;
  out_file << std::fixed << std::setprecision(5) << std::setw(9) << std::setfill('*') << static_cast<double>(file_size) / 1e9 << std::endl;
  
  return 0;
}