ReadBigFile

#include <iostream>
#include <fstream>
#include <filesystem>
#include <chrono>
#include <string>
namespace fs = std::filesystem;


std::string readFile(fs::path path)
{
    // Open the stream to 'lock' the file.
    std::ifstream f{ path };

    // Obtain the size of the file.
    const auto sz = fs::file_size(path);

    // Create a buffer.
    std::string result(sz, ' ');

    // Read the whole file into the buffer.
    f.read(result.data(), sz);

    return result;
}

int main(int argc, char * argv[])
{

     auto  filename = argv[0];


     std::ifstream bigFile(filename);
     const auto MB = 1024 * 1024;
     constexpr size_t bufferSize = 100 * MB;
     std::unique_ptr<char[]> buffer(new char[bufferSize]);

     fs::path p = "traj.xml";
     std::cout << "File size = " << fs::file_size(p)/MB << " MB" << '\n';

     auto start = std::chrono::high_resolution_clock::now();
     std::string str;

     while (bigFile)
     {
          bigFile.read(buffer.get(), bufferSize);
          str = buffer.get();
          // process data in buffer
//    std::cout << buffer << "\n---\n"
     }
     auto end = std::chrono::high_resolution_clock::now();
     std::chrono::duration<double> diff = end-start;
     std::cout << "Time to read in chunks: "
               << diff.count() << " s\n";

     start = std::chrono::high_resolution_clock::now();
     readFile(p);
     end = std::chrono::high_resolution_clock::now();
     auto diff1 = end-start;
     std::cout << "Time to read in whole: "
               << diff1.count() << " s\n";

     std::cout << "diff1/diff: " << diff1 / diff << "\n";


     return 0;

}