BadCats

#include <iostream>
#include <fstream>
#include <vector>
#include <cstring>
#include <random>
#include <iterator>
#include <experimental/filesystem>
using namespace std;
namespace fs = experimental::filesystem;

void fill_random(vector<char>& data)
{
  std::random_device rd;
  std::mt19937 gen(rd());
  std::uniform_int_distribution<> dis(0, 255);
  generate(data.begin(), data.end(), [&]{ return dis(gen); });
}

int main()
{
  vector<char> content(318);

  fill_random(content); // для чистоты эксперимента

  vector<char> content_copy;

  if(fs::exists("temp"))
  {
    cout << "delete temp dir\n";
    fs::remove_all("temp");
  }

  fs::create_directory("temp");
  cout << "create temp dir\n";

  if(auto file = ofstream("temp/file", ios_base::binary); file)
  {
    file.write(content.data(), content.size());
    cout << "write " << content.size() << " bytes\n";
  }

  if(fs::exists("temp/file"))
  {
    cout << "create copy..." << "\n";
    fs::copy_file("temp/file", "temp/file_copy");
  }
 
  if(fs::file_size("temp/file") == fs::file_size("temp/file_copy"))
  {
    auto file = ifstream("temp/file_copy", ios_base::binary);
    content_copy.resize(fs::file_size("temp/file_copy"));
    file.read(content_copy.data(), content_copy.size());
  }

  auto eq = memcmp(content.data(), content_copy.data(), content.size());

  if(eq == 0)
  {
    cout << "temp/file eq temp/file_copy\n"
         << "file size      == " << fs::file_size("temp/file") << "\n"
         << "file_copy size == " << fs::file_size("temp/file_copy") << endl;
  }

  if(auto text_file = ofstream("temp/text_file"); text_file)
  {
    copy(content.begin(), content.end(), ostream_iterator<char>(text_file));
  }
  
  if(fs::file_size("temp/file") == fs::file_size("temp/text_file"))
  {
    cout << "temp/file eq temp/text_file\n";
  }
  else
  {
    cout << "Surprise\n"
         << R"(fs::file_size("temp/file") == )" << fs::file_size("temp/file") << "\n"
         << R"(fs::file_size("temp/text_file") == )" << fs::file_size("temp/text_file") << endl;
  }

  cin.get();
}