Fortran

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Code: octave_file_io.cc: C++ function to load a matrix from an ASCII file in Octave native format
#include <octave_file_io.h>


#include <octave/oct.h>
#include <octave/ov.h>
#include <fstream>
#include <ls-oct-ascii.h>
#include <octave/octave.h>
#include <octave/parse.h>
#include <octave/toplev.h>
#include <octave/load-save.h>
#include <octave/oct-map.h>
#include <cstring>

int octave_load (const char* filename, const char* varname, double** data, int* numel)
{
  
  string_vector argv (1);
  load_save_format format = LS_ASCII;

  install_types ();  
  argv(0) = varname;
  
  std::ios::openmode mode = std::ios::in | std::ios::binary;
  std::string fname (filename);

  std::ifstream file (fname.c_str (), mode);
  
  octave_scalar_map m = do_load (file, fname, format, oct_mach_info::flt_fmt_unknown,
                                 false, false, true, argv, 0, 1, 1).scalar_map_value ();

  file.close ();  

  Array<double> M = m.contents (varname).array_value ();
  if (error_state)
    return -1;

  *data = (double*) malloc (M.numel () * sizeof (double));
  *numel = M.numel ();

  memcpy (*data, M.fortran_vec (), *numel * sizeof (double));

  return 0;  
}


Code: octave_file_io.h: header file with C interface to octave_file_io.cc
#ifndef OCTAVE_FILE_IO_H
#define OCTAVE_FILE_IO_H

#ifdef __cplusplus
extern "C" {
#endif
  
  int octave_load (const char* filename, const char* varname, double** data, int* numel);

#ifdef __cplusplus
}
#endif

#endif


Compile the function

 mkoctfile -I. octave_file_io.cc 
Code: octave_file_io.cc: C++ function to load a matrix from an ASCII file in Octave native format

<syntaxhighlight lang="C" program octave_file_io_example

 use iso_c_binding
   
 implicit none
 interface 
    function octave_load (filename, varname, data, numel) bind(c, name="octave_load")
      
      use iso_c_binding
      implicit none
      integer(c_int) :: octave_load
      
      character(kind=c_char), intent(in) :: filename(*)
      character(kind=c_char), intent(in) :: varname(*)
      
      type(c_ptr), intent(out) :: data
      integer(c_int), intent(out) :: numel
      
    end function octave_load
 end interface
 
 integer(c_int) :: res 
 type(c_ptr) :: data
 real(c_double), pointer :: fdata(:)
 integer(c_int) :: numel
 res = octave_load (c_char_'pippo.octxt' // c_null_char, c_char_'A' // c_null_char, data, numel)
 
 call c_f_pointer (data, fdata, (/numel/))
 
 write (*,*) fdata

end program octave_file_io_example </syntaxhighlight>