C++ ofstream write does not work under Windows. Works fine under Linux

Question

The code below does not work under Windows and GNU C++, VS10,VS12, Intel C++ 14.0. The code below does work under Linux and GNU C++ 4.7, 4.8, Intel C++ 14, Open64 5.0.Replacing DIMEN with DIMEN-256 in the inner test for-loop ... works!? Any idea?

//============================//
// Read and Write binary file //
// using buffers              //
//============================//

#include <iostream>
#include <fstream>
#include <string>
#include <cmath>

using namespace std;

int main()
{
  // 1. variables and parameters

  const long int DIMEN = static_cast<long int>(pow(10.0,8.0));
  const long int I_DO_MAX = 100;
  const string fileName = "my_file.bin";
  ofstream fileOUT;
  ifstream fileIN;
  double* myArrayAlpha = new double [DIMEN];
  double* myArrayBeta = new double [DIMEN];
  long int i;
  long int j;

  // 2. build the array with some data

  cout << " 1 --> Build the array with some data" << endl;

  for (i = 0; i < DIMEN; i++)
  { myArrayAlpha[i] = static_cast<double>(i); }

  for (i = 0; i < I_DO_MAX; i++)
  {
    // 3. open the file stream

    cout << "-------------->>> " << i << endl;
    cout << " 2 --> Open the file stream" << endl;

    fileOUT.open(fileName.c_str(), ios::out | ios::binary | ios::trunc);
    fileIN.open(fileName.c_str(), ios::in | ios::binary); 

    // 4. test if the file stream is opened 

    cout << " 3 --> Test if the file stream is opened with success" << endl;

    if (!fileOUT.is_open())
    { cout << "Error! The output file stream is not opened. Exit." 
           << endl; return -1; }

    if (!fileIN.is_open())
    { cout << "Error! The input file stream is not opened. Exit." 
           << endl; return -1; }

    // 5. write the contents of myArrayAlpha[] to a file

    cout << " 4 --> Write and then Read to the file" << endl;

    fileIN.seekg(0, fileIN.beg);
    fileOUT.seekp(0);

    fileOUT.write(reinterpret_cast<char*>(&myArrayAlpha[0]), 
                  DIMEN * sizeof(double));
    fileIN.read(reinterpret_cast<char*>(&myArrayBeta[0]), 
                DIMEN * sizeof(double));

    // 6. test that I am writting and reading correctly

    for (j = 0; j < DIMEN; j++) // replace DIMEN 
    {                           // with DIMEN-256 to work under Windows
      if (myArrayAlpha[j] != myArrayBeta[j])
      { cout << myArrayAlpha[j] << endl;
        cout << myArrayBeta[j] << endl;
        cout << "j = " << j << endl;
        cout << "Error!"; return -1; }
    }

    cout << " 5 --> Read and Write with success" << endl;
    cout << " 6 --> Close the I/O streams" << endl;

    // 7. close the file stream

    fileIN.close();
    fileOUT.close();
  }

  // 8. free up the RAM

  delete [] myArrayAlpha;
  delete [] myArrayBeta;

  return 0;
}

Answer 1

The problem is that your data is not being flushed to the external sequence after the write call, so it is still positioned in the internal buffer. Add this line after write():

fileOUT << std::flush;