c++ 文件

读文件

#include <fstream>
#include <iostream>
#include <random>
#include <sstream>
#include <string>

  std::ifstream inFile("d:\bigfile.txt");

  std::stringstream strStream;
  strStream << inFile.rdbuf();
  std::string grimmsTales = strStream.str();

  size_t size = grimmsTales.size();

读取目录和层次

#include <fstream>
#include <iostream>
#include <string>
#include <filesystem>
namespace fs = std::filesystem;
 
int main()
{
    fs::current_path(fs::temp_directory_path());
    fs::create_directories("sandbox/a/b/c");
    fs::create_directories("sandbox/a/b/d/e");
    std::ofstream("sandbox/a/b/file1.txt");
    fs::create_symlink("a", "sandbox/syma");
    for(auto i = fs::recursive_directory_iterator("sandbox");
             i != fs::recursive_directory_iterator();
           ++i ) {
        std::cout << std::string(i.depth(), ' ') << *i;
        if(fs::is_symlink(i->symlink_status()))
            std::cout << " -> " << fs::read_symlink(*i);
        std::cout << '
';
    }
    fs::remove_all("sandbox");
}

随机数：

#include <random>
#include <string>
#include <vector>


  // random values
  std::random_device seed;
  std::mt19937 engine(seed());
  std::uniform_int_distribution<> uniformDist(0, 100);
  std::vector<int> randValues;
  for (auto i = 0; i < access; ++i)
    randValues.push_back(uniformDist(engine));

算耗时：

#include <chrono>

  auto start = std::chrono::steady_clock::now();
  
//do some thing time-consuming

  std::chrono::duration<double> durString =
      std::chrono::steady_clock::now() - start;
  std::cout << "duration:      " << durString.count() << " seconds"
            << std::endl;