Using unformatted binary files under windows.

This describes the areas in which windows is different from
the usual standard.

#include <io.h>
#include <fcntl.h>

Under most versions of visual studio, nothing else needs to be
changed, but you may get the occasional meaningless warning.
Below is what windows officially expects.

open should be spelled _open

all the O_ flags should be spelled with _O_

protection when creating file may be one of

          _S_IREAD
          _S_IWRITE   (which means read and write)

example

   int f1 = _open("input.dat", _O_RDONLY | _O_BINARY);

   int f2 = _open("output.dat",
                  _O_WRONLY | _O_CREAT | _O_TRUNC | _O_BINARY,
                  _S_IWRITE);

close should be spelled _close

example

   _close(f2);

read and write should also be spelled _read and _write