C++: a binary Fortran file

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Reading an 'unformatted' Fortran file in C++

Fortran has a rather peculiar method of writing binary files; files that are created with the form='unformatted' attribute have an internal structure which distinguishes them from the raw sequences of bytes that you can create in C/C++. With the Fortran compilers installed at Calcul Québec, each write operation saves the data along with two identical boundary fields of four bytes (eight bytes when using the PGI compiler). These boundary fields indicate the total length of the data being saved. While this format is specific to Fortran, it doesn't prevent the resulting files from being portable; the following example shows how to read binary data from a Fortran-created file in a C++ program.

Here is a snippet of Fortran code which writes a binary file:

File : unformatted.f90
parameter (length = 10)
type point
   double precision x, y, z
type(point) list(length)
open(80, file='test_output', form='unformatted')
write(80) length
do i=1, length
   write(80) list(i)%x, list(i)%y, list(i)%z

Here is the C++ code which allows you to read this binary file:

File : readftn.cpp
#include <fstream>
#include <vector>
#include <string>
using namespace std;
struct Point
   double x, y, z;
bool ReadPoints(const string& fileName, vector& points)
   int nbPoints;
   // clear the points
   // open file in binary mode
   ifstream input(fileName.c_str(), ios::binary);
   if (input.good())
      // read number of points
      input.seekg(RECORD_DELIMITER_LENGTH, ios::cur);
      input.read((char*) &nbPoints, sizeof(nbPoints));
      input.seekg(RECORD_DELIMITER_LENGTH, ios::cur);
      // set vector size
      // read each point
      for (int i = 0; i < nbPoints; ++i)
         input.seekg(RECORD_DELIMITER_LENGTH, ios::cur);
         input.read((char*) &points[i].x, sizeof(points[i].x));
         input.read((char*) &points[i].y, sizeof(points[i].y));
         input.read((char*) &points[i].z, sizeof(points[i].z));
         input.seekg(RECORD_DELIMITER_LENGTH, ios::cur);
      return true;
      return false;

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