Read m elements from a binary file with offset of n elements and return C++ std::vector

read_binary.h

#include <iostream>
#include <fstream>
#include <vector>

template <typename T>
std::vector<T> read_binary(std::string fname, size_t n, size_t m, bool reverse = false, bool verbose = false)
{
  union u
  {
    char c[sizeof(T)];
    T r;
  };
  union u buf;
  std::vector<T> data;

  std::ifstream ifs (fname, std::ios::binary);
  ifs.seekg(n * m * sizeof(T));
  if (verbose)
  {
    std::cout << "pos = " << ifs.tellg() << std::endl;
  }
  if (ifs.is_open())
  {
    for (int j = 0; j < m; j++)
    {
      ifs.read(&(buf.c[0]), sizeof(T));
      if (reverse)
      {
        for (int i = sizeof(T) - 1; i >= 0; i--)
        {
          ifs.read(&(buf.c[i]), sizeof(char));
        }
      }
      else {
        for (int i = 0;  i < sizeof(T); i++)
        {
          ifs.read(&(buf.c[i]), sizeof(char));
        }
      }
      data.push_back(buf.r);
      if (verbose)
      {
        std::cout << "data(" << j << ") = " << data[j] << std::endl;
      }
    }
  }
  ifs.close();
  return data;
}