Writing a vector to a binary file, in a loop - C++?

Question

C++ / C#

There is an input.txt file with the following content:
1 2 3 4 5 6
7 8 9 10 11 12
13 14 15 16 17 18
19 20 21 22 23 24
25 26 27 28 29 30
.dat is only element-wise with the line index. The file must have the structure: index (4 bytes) + 6 values ​​from a vector of 2 bytes.
01 00 00 00 01 00 02 00 03 00 04 00 05 00 06 00 02 00 00 00 07 00 08 00 etc.
Here is my code but it is wrong

#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <vector>
#include <iterator>
#include <algorithm>

using namespace std;

int main()
{
    std::fstream input("input.txt");
    std::vector<short> vec; // значения из файла
    std::copy(std::istream_iterator<int>(input), std::istream_iterator<int>(), std::back_inserter(vec));
    std::copy(vec.begin(), vec.end(), std::ostream_iterator<int>(std::cout, " "));

    ofstream fout("data.dat", std::ios::out | ios::binary);
    int countstring = 5;
    int index = 0;
    int row = 6;
    for (int i = 0; i <= countstring; i++) {
        index = i + 1;
        fout.write((char *)&index, sizeof index);
        for (size_t j = 0; j < row; ++j)
        {
            fout.write((char*)&vec[i * 6], row * sizeof(short));
        }
    }
    fout.close();
    return 0;

Tell me how to fix the second loop to write element by element

Answer 1

#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <vector>
#include <iterator>
#include <algorithm>


int main()
{
  std::fstream input("input.txt");
  std::vector<short> vec; // значения из файла
  std::copy(std::istream_iterator<int>(input), std::istream_iterator<int>(), std::back_inserter(vec));
  std::copy(vec.begin(), vec.end(), std::ostream_iterator<int>(std::cout, " "));

  std::ofstream fout("data.dat", std::ios::out | std::ios::binary);		
  const size_t columnCount = 6;
  for (size_t i = 0; i < vec.size(); i+= columnCount)
  {
    int index = i / columnCount + 1;
    fout.write((char *)&index, sizeof(int));
    for (size_t j = 0; j < columnCount; j++)
    {
      fout.write((char*)&vec[i + j], sizeof(short));
    }
  }
  
  fout.close();
  return 0;
}

Answer 2

index (4 bytes) + 6 values ​​from vector of 2 bytes

So choose the right data size. int, in general, can have a size of 16, 32 or 64 bits, depending on the system and compiler, short - from 8 to 64 bits.
Use int32_t for 4-byte numbers and int16_t for 2-byte numbers (__int32 and __int16 in older versions of Visual C++).
The vector structure does not contain the values ​​written to the vector, but pointers to the beginning and end of the memory block allocated to store these values ​​( https://stackoverflow.com/questions/27466373/memor... The implementation of this structure depends on the compiler. Therefore, in line
you don't get data, but bytes from a vector structure.